September 22, 2020
Welcome and Opening Remarks 8:15 AM – 8:30 AM
Oral Presentations & Poster Session
ORAL PRESENTATIONS SESSION I: BIOTECHNOLOGY
8:30 AM – 10:00 AM
Background: Genome editing has become an essential capability in bacteria to probe important phenotypes, study microbe-host interactions, and enhance beneficial properties. Currently, the most effective means of genome editing in bacteria combines low-efficiency recombineering with high-efficiency counter selection by nucleases from CRISPR-Cas systems, where the Cas9 nuclease from Streptococcus pyogenes (SpyCas9) has been the most studied and utilized Cas nuclease. However, differences among bacterial strains have limited success of SpyCas9-based genome editing, where some strains require trying multiple strategies for editing and others fail completely due either to cytotoxicity of SpyCas9 or poor genetic tools [1-3] .
Results: Here, we highlight insights gained from directly comparing two commonly deployed methods of SpyCas9-based genome editing in different strains of the putative probiotic Lactobacillus plantarum. We found instances where either method outperformed the other, and the success of each method varied with both the L. plantarum strain and designed edit. We also revealed several unique failure modes of SpyCas9-based genome editing, including an unintended genomic deletion and one instance where the recombineering template reverted to the wild-type sequence, and suggest workarounds to circumvent these failure modes. Finally, we discuss collaborative work where SpyCas9-genome editing is utilized to elucidate beneficial properties of the probiotic L. plantarum and an industrial strain of L. paracasei.
Conclusions: Currently, genome editing with SpyCas9 in bacteria is inconsistent and can be difficult to implement in new strains. Furthermore, most developed methods of SpyCas9-based genome editing only test a single method in a single strain of bacteria, thus when attempting editing in a new strain it’s often difficult to predict the best strategy for editing. By comparing two methods of SpyCas9-based genome editing in multiple Lactobacilli strains, we provide insights into the advantages of each method and failure modes that are strain or method dependent. Together, this work highlights the importance of CRISPR-based genome editing in bacteria and should help others improve genome editing across Lactobacilli and other industrially relevant bacteria.
- Jiang Y, Qian F, Yang J, et al (2017) CRISPR-Cpf1 assisted genome editing of Corynebacterium glutamicum. Nat Commun 8:15179
- Cho S, Choe D, Lee E, et al (2018) High-level dCas9 expression induces abnormal cell morphology in Escherichia coli. ACS Synth Biol 7:1085–1094
- Song X, Huang H, Xiong Z, et al (2017) CRISPR-Cas9 nickase-assisted genome editing in Lactobacillus casei. Appl Environ Microbiol 83:e01259–17
Background: Orchestration of cell migration, directed by soluble and extracellular matrix (ECM)-associated factors, is essential for wound healing, cancer metastasis, and the immune response. This dynamic process involves the coupling of adhesion, signaling, and cytoskeletal subprocesses, integrated across spatial and temporal scales. In mesenchymal cells integrins engage the ECM proteins and cluster to form adhesion complexes, which mediate both biochemical signal transduction and physical interaction with the F-actin cytoskeleton , .
Results: This is the first model to combine the mechanical and signaling aspects of motility at the leading edge that allows the lamellipodium, guided by the mechanosensitive nascent adhesions, to function as a versatile sensor of the cell’s environment. This integrative model considers spatiotemporal dynamics of all of the following: nascent adhesion density, active signaling molecules, F-actin density, and mechanical stress within the F-actin network. The model predicts an optimal ECM density for maximal protrusion velocity. At lower ECM densities, the abundance of nascent adhesions is too low to support effective signal transduction and to resist retrograde flow. With increasing ECM density, substantial gains in membrane protrusion rely on a positive feedback loop, in which adhesion-mediated activation of Rac fosters increased formation of barbed ends and F-actin, enhancing membrane protrusion, formation of new adhesions, and stabilization of existing ones. Mitigating or opposing membrane protrusion at high ECM density are the competition among barbed ends for G-actin and myosin contractility, which manifest as reduced F-actin polymerization and increased F-actin retrograde flow, respectively. By applying stress on the F-actin network, myosin II mechanically destabilizes nascent adhesions, weakening the positive feedback between nascent adhesions and F-actin. Increased F-actin turnover, mediated by ADF/cofilin, offsets the influence of myosin II. Finally, we examined the influence of adhesion/F-actin bond stiffness, which is expected to reflect the stiffness of the underlying substratum.
Conclusions: Our model predicts an optimal adhesion density for maximal protrusion velocity due to positive feedback between nascent adhesions and F-actin. At near optimal ECM density increased myosin contractility can significantly reduce protrusion velocity by mechanically destabilizing the adhesion-based clutch.
- J. T. Parsons, A. R. Horwitz, and M. a Schwartz, “Cell adhesion: integrating cytoskeletal dynamics and cellular tension,” Nat. Rev. Mol. Cell Biol., vol. 11, no. 9, pp. 633–643, 2010.
- C. K. Choi, M. Vicente-Manzanares, J. Zareno, L. A. Whitmore, A. Mogilner, and A. R. Horwitz, “Actin and alpha-actinin orchestrate the assembly and maturation of nascent adhesions in a myosin II motor-independent manner.,” Nat. Cell Biol., vol. 10, no. 9, pp. 1039–50, 2008.
Background: Several environmental factors affect longevity in C. elegans. Most of these function through the DAF-16/FOXO transcription factor, which regulates expression of genes involved in aging and stress response . We aim to elucidate how the lifelong molecular activity of daf-16, driven by environmental interventions, determines lifespan in C. elegans. Current methods to track DAF-16 activity have a destructive nature (microarrays, RT-PCR), and utilized strains with multiple copies of daf-16. Thus, we created a single copy GFT-tagged strain at the endogenous locus of daf-16. This strain, along with quantitative analysis of fluorescence imaging enables lifelong tracking of DAF-16 activity in response to environmental perturbations in vivo. Thus, the relationships between environmental perturbations, longitudinal gene activity, and lifespan can be explored. This will enable elucidating how the lifelong history of these perturbations determines lifespan in C. elegans.
Results: Using a custom image-processing algorithm, we tracked DAF-16 activity under various dietary restriction regimes. In particular, the image processing approach enabled evaluation of complex patterns of DAF-16 nuclear migration, a hallmark of active DAF-16, at the tissue and cellular levels. To characterize DAF-16 activity, we developed a strain that labels the endogenous DAF-16 protein with GFP using the CRISPR/Cas9 system . We observed increased migration of DAF-16 to cell nuclei in tissues (intestine, hypodermis, muscles, and neurons) of nematodes under conditions of reduced food intake. This pattern increased the longer the animals were under this condition, reaching a peak after approximately 12 hours of dietary restriction and decreasing thereafter. Moreover, under repeated and intermittent exposure of the same C. elegans population to dietary restriction, we identified a decreasing activity of DAF-16 in subsequent days. Additionally, we have observed migration of DAF-16 to nucleoli, a phenomena not described previously, and an increased response of DAF-16 in neurons when compared to other tissues. We aim to quantify how tissue specific activity of DAF-16 contributes to longevity in this nematode. Lifespan measurements were performed for animals under the same dietary restriction regimes, obtaining a correlation between DAF-16 levels of expression, measured as cumulative intensity at the cellular level, and average lifespan.
Conclusions: We have developed an experimental platform for the characterization of lifespan in C. elegans, while correlating this metric to quantifiable endogenous activity of DAF-16 under various dietary restriction regimes. Furthermore, our findings show that DAF-16 activity is tissue specific and its life-long activity is correlated with longevity. These results will help understand the fundamental mechanisms by which this transcription factor regulates the aging process.
- K. Lin, H. Hsin, N. Libina, and C. Kenyon, “Regulation of the Caenorhabditis elegans longevity protein DAF-16 by insulin/IGF-1 and germline signaling,” Nature Genetics, vol. 28, no. 2. pp. 139–145, 2001.
- D. J. Dickinson, A. M. Pani, J. K. Heppert, C. D. Higgins, and B. Goldstein, “Streamlined genome engineering with a self-excising drug selection cassette,” Genetics, vol. 200, no. 4, pp. 1035–1049, 2015.
- Schneider, I. C. & Haugh, J. M. J. Cell Biol. (2005)
- Welf, E, J. Cell Biol. (2012)
Background: Plant diseases caused by pathogens (e.g., fungi, viruses, and bacteria) significantly impact the agricultural yield worldwide. According to the Food and Agriculture Organization (FAO) of the United Nations, more than 30% of global crop production is lost annually due to plant pathogens and pests. Nucleic acid based molecular diagnosis reveals valuable information at the genomic level about the identity of the disease-causing pathogens and their pathogenesis, which help farmers to detect the presence of pathogens, track the spread of disease, and guide treatment more efficiently. However, the current methods for molecular diagnosis of plant diseases are constrained to the laboratory settings due to the cumbersome assay procedures and requirement of bulky equipment . For rapid plant disease detection directly in the field, an integrated microneedle-smartphone nucleic acid amplification platform has been developed.
Results: This handheld diagnostic platform consists of a disposable microneedle (MN) patch for nucleic acid extraction and a smartphone device for loop-mediated isothermal amplification (LAMP) and detection. The MN patch effectively extracts both DNA and RNA from plant tissues in a nondestructive fashion, which reduces sample preparation time from hours of a conventional extraction method to ∼1 min [2,3]. The MN-extracted DNA/RNA is purification-free and directly applicable for amplification assays such as PCR and LAMP . On the other side, the smartphone device consists of an electric resistor heater integrated sample cartridge to receive the microneedles and a fluorescent imaging system to quantify the assay signals. This integrated diagnostic platform successfully detects both DNA-based (Phytophthora infestans) [2,3] and RNA-based (tomato spotted wilt virus (TSWV) pathogens from infected tomato leaves with minimum operational steps. Moreover, this platform is capable of simultaneously detecting multi-infections through a single extraction and amplification on the smartphone.
Conclusions: A novel MN-based plant nucleic acid extraction method was developed, which isolates DNA or RNA from plant leaves by simple compression and retraction. The rapid extraction method was further combined with a handheld smartphone device for plant pathogen detection directly in the field. The integrated platform has been successfully used to detect P. infestans DNA and TSWV RNA in infected plant leaves.
- Li, Zheng, Tao Yu, Rajesh Paul et al. (2020). Agricultural Nanodiagnostics for Plant Diseases: Recent Advances and Challenges. Nanoscale Adv. 2, 3083-3094.
- Paul, Rajesh, Amanda C. Saville, Jeana C. Hansel et al. (2019). Extraction of Plant DNA by Microneedle Patch for Rapid Detection of Plant Diseases. ACS nano, 13: 6540-6549.
- Paul, Rajesh, Emily Ostermann, Zhen Gu et al. (2020). DNA Extraction from Plant Leaves Using a Microneedle Patch. Current Curr. Protoc. Plant Biol., 5, e20104.
- Ristaino, Jean B., Amanda C. Saville, Rajesh Paul et al. (2019). Detection of Phytophthora infestans by LAMP, real-time LAMP and droplet digital PCR. Plant Disease, 104: 708-716.
Background: Fibroblasts migrate directionally in response to numerous cues. For instance, in chemotaxis, cells migrate in response to gradients of soluble chemoattractants, while in haptotaxis, cells migrate in response to gradients of surface-bound extracellular matrix (ECM). The directed migration of fibroblasts supports critical biological events such as wound healing and tissue development, while errant migration exacerbates cancer metastasis. The current literature exploring these processes relies heavily on population based, endpoint assays, such as the Boyden Chamber. However, Boyden Chamber assays suffer from transient gradients, confound numerous modes of invasion, and do not provide taxis information at the individual cell level. Furthermore, fibroblast haptotaxis may be understudied given that chemotaxis publications outnumber haptotaxis publications approximately 30:1.
Results: We tackle these issues using a novel combination of microfluidic gradient generating devices and evaporative paper pumps [1, 2] in an assay that is compatible with total internal reflection fluorescence microscopy (TIRF-M). Our microfluidic design generates stable, bubble-free flow with soluble gradients of various steepnesses for over ten hours. Additionally, each experiment produces hundreds of cell trajectories, which is an order of magnitude increase over competing technologies. We analyze the high throughput data using in-house automated cell motility and cell signaling tracking software. Our results reveal that NIH/3T3 fibroblasts chemotax in a preferred platelet derived growth factor (PDGF) gradient regime that aligns with a previous model of NIH/3T3 PI3K signaling responses [3, 4]. In addition to soluble chemotactic cues, we produce surface bound haptotactic cues using a similar microfluidic approach. Our preliminary haptotaxis data shows that the IA32 fibroblast cell line haptotaxes robustly, while simultaneously disrupting and consuming fibronectin as it migrates.
Conclusions: We have developed a workflow that can produce response maps of fibroblast chemotaxis and haptotaxis over a comprehensive gradient landscape. Key to our workflow is a bubble-mitigating microfluidic device enabled by a passive pumping system that maintains stable gradients. Our high-throughput chemotactic data leads us to suggest that chemotaxing fibroblasts may be particularly adept at converting PI3K signaling into forward motility specifically in a preferred gradient regime. Furthermore, our preliminary haptotactic data leads us to hypothesize a potentially novel directed migration mechanism that we call phagotaxis, whereby cells self-generate local, steepened haptotactic gradients via endocytosis of ECM.
- Cummins, Brian M., et al. Technology (2017)
- Shay, Tim, et al. NCSU Thesis (2017)
- Schneider, I. C. & Haugh, J. M. J. Cell Biol. (2005)
- Welf, E, J. Cell Biol. (2012)
Break I 09:45 AM- 10:00 AM
10:00 AM – 12:00 PM
Background: The structure and composition of the colloidal components within dispersions, gels, and composites critically determine the properties of many products such as paints, pharmaceuticals, nonwovens, and food products. We discuss here results based on our method for nanofabrication of a new class of materials called soft dendritic colloids (SDCs). By constraining and templating polymer precipitation phenomena within a turbulent liquid flow, we produce highly branched and nanofibrous SDC particles with unique properties. SDCs have extraordinary adhesion and networking properties due to the formation of a physical, colloidal network of fibers mimicking the contact splitting mechanism that gives geckos their remarkable adhesion. This inter-particle fiber entanglement allows SDCs to form surface coatings and nonwoven materials.
Results: Different precipitation methods can be utilized to make SDCs. Here, we describe the production of SDCs using nonsolvent-induced phase separation, ionic hydrogel cross-linking, and polyelectrolyte complexation as precipitation mechanisms to produce pure polymer SDCs, hydrogel SDCs, and composite SDCs, respectively. We report how synthetic polymer SDCs can be used to make porous superhydrophobic coatings and nonwoven cell scaffolds with multi-scaled, hierarchical features. The networking effect of SDCs is also apparent in suspension, where they impart a yield stress at extremely low concentrations making them efficient rheological modifiers. We show how these properties can be used to make “homocomposite” hydrogel materials for 3D printing.
Conclusions: Polymer precipitation within a turbulent flow provides an entire platform to scalably produce nanostructured materials with control over the resulting morphology. The versatility of the platform enables nearly any polymer to be used including both synthetic and bioderived polymers. Moreover, SDCs are inherently produced in suspension rather than confined to a 2D mat, allowing their facile dispersion in other liquid media and composite materials. Specific applications of SDCs as hydrophobic coatings, nonwoven bioscaffolds, and 3D printing composites are presented as leading examples how this fabrication technique enables a toolbox of colloidal materials for wide-ranging soft materials with applications in biomedical, pharmaceutical, coating, packaging and food products.
- S. Roh, A.H. Williams, R.S. Bang, S.D. Stoyanov, and O.D. Velev. Soft dendritic microparticles with unusual adhesion and structuring properties, Nat. Mater. 18 (2019) 1315–1320. https://doi.org/10.1038/s41563-019-0508-z.
- A.H. Williams, S. Roh, A.R. Jacob, S.D. Stoyanov, L. Hsiao, and O.D. Velev. Printable self-reinforced homocomposite hydrogels with a molecular-colloidal double network. Manuscript in Preparation.
- A.H. Williams, A.M. Hebert, R.C. Boehm, O.D. Velev, and M.T. Nelson. Impact of bioscaffold stiffness on nanoparticle aerosol exposure mediated toxicity of lung epithelial cells. Manuscript in Preparation.
Background: To transfer heat from high-intensity solar-energy collectors, a eutectic mixture of diphenyl ether and biphenyl (71.5 and 28.5 mol %) is used. This compound mixture does not crystallize at 400°C and is more stable compared to paraffin-based heat transfer fluids. However, the mixture degrades gradually when used for a long period of time. The present study employs experiments, machine learning, and theory to probe the degradation process.
Results: Fresh samples of heat transfer fluids are degraded at 370°C temperature for 1000 hours in closed ampoules under N2 atmosphere. At the end of the experiments, the samples are dropped in a dry-ice/acetone bath, and subsequently are analyzed with two-dimensional gas chromatography coupled with electron-ionization time-of-flight mass spectrometry (GCxGC/EI-ToFMS) after 5 μl injections. In the fresh sample, 72±7 mol% diphenyl ether and 27±3 mol% biphenyl is observed. Degradation generates a 23 mol % drop of diphenyl ether and 2% drop of biphenyl. There are multiple compounds identified that indicate the degradation chemistry of diphenyl ether, such as benzene (1.3 %), phenol (7%), and dibenzofuran (15%). Higher molecular-weight compounds are also identified, such as phenoxybiphenyls (<1%), terphenyls (1.5%), phenyl dibenzofurans (<1%), quaterphenyls (<1%), and larger poly-phenoxyphenyls (<1%). For the quantification, calibration factors of the available compounds such as benzene, biphenyl, terphenyls, and phenol are measured directly from calibration experiments. However, as the other compounds are not available commercially, a machine-learning-based approach is adopted to obtain their electron ionization cross sections (EI-CS), used to compute EI-MS calibration factors and then their yields in the degraded samples. Developing this approach involved building a database of experimental EI-CS of 396 compounds and a neural net model using atom and group descriptors for each compound. A good match in the experimental and predicted yields is found for the fresh samples.
Conclusions: The initial reaction mechanism is developed using Reaction Mechanism Generator (RMG) for the high-pressure gas-phase fluids and liquid-phase fluids. Longer-residence time calculations in a constant-volume batch reactor are performed in Chemkin and MATLAB. These calculations reveal that the decomposition of the ether bond in diphenyl ether to form phenyl and phenoxyl radicals is the rate limiting step. Once the phenyl radical is formed, it either abstracts an H atom, forming benzene, or it adds to an aromatic molecule , forming a radical and a weakly held tertiary H that can be abstracted by phenoxyl radicals to form phenol. If it abstracts an ortho H from diphenyl ether, that radical can add to its other phenyl ring, creating a tertiary H. Then dibenzofuran is formed when the tertiary H is abstracted by phenoxyl radical or some other radical. Good agreement is observed between the measured yields from the experiments and yields predicted with the reaction mechanism.
Background: Tuning rheological properties in suspensions has gained interest in recent years . Increase of viscosity at higher stress, known as shear-thickening, is one of the phenomena relevant in everyday industrial suspension processing. To explore the effect of surface roughness on shear-thickening, we use spherically-symmetric and surface anisotropic poly(hydroxystearic acid)-grafted-poly(methyl methacrylate) (PHSA-g-PMMA) colloids. We combine the traditional rheometry techniques and microstructural parameters obtained using confocal microscopy to generate flow curves and form universal correlations in colloidal suspension flow.
Results: We synthesize smooth and rough colloids of particle diameters 2a in range of 0.99 μm – 1.82 μm using dispersion polymerization route from PHSA brushes prepared in-house. Controlled addition of crosslinker, ethylene glycol dimethacrylate, durog polymerization produces polymer microspheres with rough surface textures . We disperse them in index-match solvent squalene to miminize van der Waals forces and mimic hard-sphere behavior. We generate steady shear flow curves for particles of various roughness using rheological measurements. Furthermore, we predict flow curves in smooth and rough colloids by incorporating experimentally obtained contact scalings through micromechanical model developed in literature . Average contact numbers , an experimental parameter that goes into the model, are estimated by combining the particle locations obtained from image-processing routines of three-dimensional stacks and arguments of mechanical isostaticity from granular physics. We obtain ~ 6 for smooth and 4 < < 4.5 for rough particles . Contact scaling factor (α) in smooth suspensions is close to unity while α<1 for rough particles suggesting that rough suspensions requires less contacts to jam compared to their smooth counterparts. We find a universal correlation in shear-thickening strength and scaled distance from jamming in spherically-symmetric colloidal suspensions .
Conclusions: Mechanical isostatic considerations suggest that particle-particle contact distance can be estimated if relevant lengthscales such as average diameter, surface roughness, and polymer brush length are taken into account. Furthermore, we observe a universal behavior of strong shear-thickening characteristic below scaled distance of 0.1 for colloidal suspensions from our experiments and from literature (experiments and simulations) which suggests distance from jamming as a critical tuning parameter while preparing suspensions for industrial processing.
- L C Hsiao, S Jamali, E Glynos, P F Green, R G Larson, and M J Solomon (2017), Rheological state diagrams for rough colloids in shear flow, Phy Rev Lett, 1119: 158001.
- L C Hsiao and S Pradeep (2019), Experimental synthesis and characterization of rough particles for colloidal and granular systems, Curr Opin Colloid Interface Sci, 43: 94-112.
- M Wyart and M E Cates (2014), Discontinuous shear-thickening without inertia in dense non-Brownian suspensions, Phy Rev Lett, 112: 098302.
- S Pradeep and L C Hsiao (2020), Contact criterion in suspensions of smooth and rough colloids, Soft Matter, 16:4980-4989.
- S Pradeep, A R Jacob, and L C Hsiao (2020), Jamming distance dictates shear-thickening strength, arXiv preprint, arXiv:2007.01825.
Background: Among all types of Li-ion battery (LIB) separators, fibrous mats have the advantage of low cost, low mass, and high porosity. Fibrous Poly(Vinylidene difluoride) (PVDF) shows promising results because of its stability and affinity for electrolytes commonly employed in Li-ion cells. Despite numerous studies published on fibrous LIB separators, none reports structure-property relationships for the identification of an ideal structure. We investigated the properties of a melt-blowable PVDF and produced meltblown PVDF mats in scale-up equipment with the objective of elucidating its performance as a LIB separator. We also present a new class of LIB separators, PVDF-based highly branched, colloidal polymer particulates called soft dendritic colloids that are produced by shear-driven polymer precipitation within a highly turbulent nonsolvent flow, followed by filtration. We show that the morphology of the resulting PVDF particulates can be modulated from fibrous soft dendritic colloids (SDC) to thin and highly porous sheet-like particles.
Results: Through a scale-up system, we obtained high-quality meltblown PVDF with high homogeneity, low number of defects, an average fiber diameter of 1.4 μm, and pore size as low as 0.9 μm. Small fiber diameter provides high-surface area and high electrolyte uptake. We show interactions of the meltblown PVDF with the electrolyte lead to a morphology change in the fibers. The highest ionic conductivity was ~ 9.6 mS/cm, and the first-cycle capacity was 140 mAh/g (Li/LiCoO2). After melt-pressing, the thickness and pore size decrease, but the mats electrolyte absorbency and conductivity decrease commensurately. PVDF SDC separators show high porosity (up to 80%) and high particle surface area, which results in high conductivity (1.2 mS/cm), high-electrolyte uptake (325%), and high-cell capacity (112 mAh/g in Li/LiCoO2 cell) with <10% loss after 50 cycles. Both processes yield separators with low thermal shrinkage (<5% at 90 oC) and high tensile strength (<0.5% offset at 1000 psi), with the highest-performing separator possessing low average fiber diameter with a wide diameter distribution.
Conclusions: Both meltblowing and shear-driven precipitation are facile and versatile processes for high volume fabrication of LIB separators with one single polymer without necessarily requiring post-processing and with characteristics similar to commercially available battery separators. Fibrous LIB should be fabricated with a low fiber diameter (<1 μm) but also with a wide diameter distribution. When the strength and openness of the microfiber support is coupled with the highly permeable nanofibers for a low average pore size, an ideal fibrous Li ion battery separator is obtained.
- Luiso, S., Henry, J. J., Pourdeyhimi, B. & Fedkiw, P. S. (2020). Fabrication and Characterization of Meltblown Poly(vinylidene difluoride) Membranes. ACS Appl. Polym. Mater., 2, 2849 2857
- S. Roh, A. H. Williams, R. S. Bang, S. D. Stoyanov, and O. D. Velev (2019). Soft dendritic microparticles with unusual adhesion and structuring properties. Nature Materials, vol. 18, no. 12. pp. 1315–1320.
Break II 11:00 AM- 11:15 AM
Background: Highly selective and light-weight protective suits featuring excellent breathability, mechanical robustness and catalytic degradation performance towards chemical warfare agents (CWAs) are highly desirable for first responders and the military. However, current multilayered chemical/biological (CB) protective textiles containing activated carbon and separate aerosol protective layers exhibit several drawbacks including high thermal burden and secondary contamination. Recently, Polymers of Intrinsic Microporosity (PIMs) have attracted attention as a novel class of high free-volume polymers with highly rigid and contorted molecular structure. Most research on PIMs has focused on fundamental membrane properties, with only a few studies on the fiber form.
Results: Herein, we present, a highly sorptive, breathable, mechanically strong aerosol-protective layered fabric with prominent catalytic degradation capability of CWAs. Electrospun PIM-1 fiber web with hierarchical porosity is utilized as a matrix material, preventing toxic gas penetration while providing pathways for air and water vapor molecules. Polyacrylonitrile (PAN) nanofibers assembled with PIM-1 fibers via a layer-by-layer electrospun-deposition approach are shown to achieve significantly enhanced mechanical integrity and filtration efficiency, due to the high polar chemical structure and small fiber diameter of PAN. Subsequent incorporation of UiO-66-NH2 particles, a Zr-based metal organic framework (MOF) also endows the fiber web with remarkable catalytic degradation towards CWA simulants. The resulting PIM/PAN/MOF composite fiber mat demonstrates unprecedented integrated properties with water vapor transmission rate of 1013 g/m2/24hrs, surface area of 574 m2/g, increased tensile strength (over 70 times compared to neat PIM-1 fiber web), and PM2.5 and PM10 filtration efficiency of 99.88%
Conclusions: This facile and effective fabrication of such multifunctional composite fiber mat is valuable for the design of protective garments in health care, personal protective gear, law enforcement and military uniforms.
- Wang, S., Pomerantz N.L., Dai Z., Xie W., Anderson E.E., Miller T., Khan, S.A. and Parsons, G.N., 2020. “Polymer of intrinsic microporosity (PIM) based fibrous mat: combining particle filtration and rapid catalytic hydrolysis of chemical warfare agent simulants into a highly sorptive, breathable, and mechanically robust fiber matrix.” Materials Today Advances, 8, p.100085.
- Wang, S., Shi K., Tripathi A., Chakraborty U., Khan, S.A. and Parsons, G.N., 2020. “Designing PIM-1 microfibers with tunable morphology and porosity via controlling polymer/solvent/nonsolvent interactions.” ACS Applied Polymer Materials. 2020, 2, 6, 2434–2443.
Background: Stimuli responsive surface coatings get deployed in numerous applications, including water repellency, biosensing, regenerative medicine, and advanced filtration. Central to the performance of these technologies is the use of hydrogel microparticles (microgels) that are amenable to either physical or chemical conjugation and respond to external stimuli with reversible changes in their physicochemical properties. Several research groups have developed and characterized a variety of microgels at the microscopic level. However, few have investigated the effects of surface patterning beyond areal density and thickness.
Results: This work presents a toolbox to derive quantitative correlations connecting microgel composition, deposition method, and environment, to the resulting morphology and stimuli- responsiveness of NIPAM co-Acrylic Acid microgel coatings. The characterization of microgel- coated silicon wafers led to the identification of three metrics describing microgel arrangement: density (ρ); heterogeneity (H), which correlates strongly with ρ and depends on deposition temperature and pH; and packing efficiency (PE), which portrays the regularity of microgel arrangement and exhibits no correlation with ρ nor H. The values of ρ, H, and PE calculated for in silico models of microgel coatings confirmed that these three metrics portray distinct characteristics of surface topology. From these results, we designed a novel “grafting through” surface coating mechanism, growing microgels directly onto the surface of polypropylene nonwoven fiber mats (NWFs) to create novel membranes with thermoresponsive permeability. These “smart” NWFs were evaluated using different model solutes: sodium chloride, citric acid, and Doxorubicin. These tests consistently showed that (1) the flux (φ) of the solute is higher at temperatures above the LCST of NIPAM, where the hydrogel layer collapses, thus opening the pore space, and decreases at temperatures below the LCST (2) the change in flux (φ) from high to low temperature depends upon the chemical composition of the gel (larger φ for hydrogels with higher AA content); and (3) the thermoresponsive change in permeability is fully reversible. Finally, we engineered an array of photothermal surfaces that leverage localized heating to rapidly activate free radical polymerization while maintaining the bulk of the solution at room temperature, resulting in polymer-coated/patterned macro and micro surfaces.
Conclusions: This project developed a toolkit for analyzing the morphological structure of surface coated microgel networks. Correlating the results of these analyses with well-understood deposition techniques led to the development of a novel surface coating procedure that was implemented on NWFs to create self regulating environmentally adaptive membranes. Studying the mechanisms for microgel surface attachment and growth also led us to discover a novel “grafting from” polymerization technology to quickly functionalize graphitic surfaces with thermoresponsive polymer under mild reaction conditions.
Background: Stimuli responsive materials have been a topic of intensive scientific interest due to their perspective applications in engineered materials response to stimuli such as optical, mechanical, and magnetic fields. This ability to tune the material properties could be very valuable in numerous fields such as biomedicine, soft robotics, coatings, catalysts, filtration membranes, and 3D printed materials . Magnetic-field-directed assembly of superparamagnetic nanoparticles, for example, allows for the remote control of the particles’ organization as well as the generation of anisotropic nanostructured materials .
Results: Magnetic interactions can be used to form smart gel systems. We present here a system composed of soft micromagnets of polydimethylsiloxane (PDMS) beads that have internally embedded magnetic nanoparticles (MNPs). The organization of the internalized magnetic nanoparticles can be controlled via magnetic-field directed assembly, allowing for the generation of permanent, anisotropic, chained nanoparticle structures in PDMS beads. Once magnetized, the beads’ magnetic interactions result in the formation of linear and branched networks. The chain-containing microspheres could have a permanently embedded dipole moment and hence, residual polar magnetization. We also present two types of magneto-capillary gels that differ in the location of the MNPs. The capillary bridges are composed of a fatty acid that wets and brings together the PDMS beads, thus forming the gels. The first magnetically responsive capillary gel (MRCG1) has the MNPs in the PDMS beads and MRCG2 has the MNPs in the capillary bridges. We evaluate the differences in rheological properties of the gels and compare their magnetic properties. We also discuss their self-repairing abilities.
Conclusions: We proved the tunability of the new chained soft bead systems by conducting magnetization, demagnetization, and re-magnetization experiments that show evidence of the successful reformation of percolating networks. We are currently using magnetic interaction templating to study and manipulate the magnetic response of our systems. The direct structure templating could potentially improve the precision of rheological measurements by anchoring the gels to 3D printed patterns We will discuss how the control of the capillary forces and magnetic interactions can be used to form new smart multiphasic gel systems. Overall, we have constructed and are developing further a rich toolbox of structures and interactions for making novel magneto-responsive gel networks.
- Schneider, Monica, Koos, Erin, and Willenbacher, Norbert (2016). Highly conductive, printable pastes from capillary suspensions. Sci. Rep., 6:1-10.
- Fameau, Anne-Laure, Lam, Stephanie, and Velev, Orlin D. (2013). Multi-stimuli responsive foams combining particles and self-assembling fatty acids. Chem. Sci., 4: 3874-3881.
Lunch 12:00 PM- 01:15 PM
Background: Cells sense and respond to multiple extracellular cues that results in directed migration, which is a critical process for cancer metastasis, embryonic development, and wound repair. The wound healing response requires the coordinated migration of several cell types such as immune cells to ingest bacteria and fibroblasts to remodel the extracellular matrix. Fibroblasts migrate up a gradient of soluble growth factors (chemotaxis) such as platelet-derived growth factor (PDGF) or immobilized cues (haptotaxis) like fibronectin, and the impairment of directed motility in fibroblasts can lead to the formation of chronic wounds. Elucidating the mechanism of chemotaxis and haptotaxis in fibroblasts will be critical for understanding the nature of wound repair. In mesenchymal cell migration, the direction of migration is often determined by the winner of multiple competing protrusions called lamellipodia. The protrusion dynamics of lamellipodia are regulated by actin polymerization as well as myosin contractility. The primary mechanism of fibroblast chemotaxis is the local inhibition of myosin contractility at the region exposed to a higher PDGF concentration that allows these protrusions to persist . However, less is known about fibroblast haptotaxis. To better understand this mode of directed motility, the dynamics of lamellipodial protrusions will be measured with respect to their position along the gradient. In addition, filopodia, or the finger-like protrusions that can promote the formation of lamellipodia will also be examined . Elucidation of these morphodynamics permits the development of molecular models to predict these behaviors, and the molecular models can then be tested experimentally.
Results: To create and visualize a gradient of fibronectin, the extracellular matrix protein was labeled with a fluorescent dye, “printed” on a glass slide using Y-junction microfluidic devices, and image using epifluorescence microscopy. The Y-junction device produces fibronectin gradients of various steepness to study fibroblast behavior. In initial studies, fibroblasts have not migrated up the gradient of fibronectin in a statistically significant manner as expected, precluding any analysis of their morphodynamics. Current research efforts are aimed at overcoming these technical challenges.
- Asokan, S.B., Johnson, H.E., Rahman, A., King, S.J., Rotty, J.D., Lebedeva, I.P., Haugh, J.M., and Bear, J.E. (2014) Mesenchymal Chemotaxis Requires Selective Inactivation of Myosin II at the Leading Edge via a Noncanonical PLCγ/PKCα Pathway. Dev. Cell, 31: 747-760.
- Johnson, H.E., King, S.J., Asokan, S.B., Rotty, J.D., Bear, J.E, and Haugh, J.M. (2015) F-actin bundles direct the initiation and orientation of lamellipodia through adhesion-based signaling. J. Cell Biol., 208(4): 443-455.
Background: The disease progression of Alzheimer’s Disease (AD) is hallmarked by two major protein interactions: the formation of amyloid-beta (Aβ) aggregates and microtubule associated protein tau (MAPT) tangles . While consistently present within AD cases, treatments focusing on the removal of these proteins have largely failed . Other hallmarks of the disease, such as oxidative stress, inflammation, and neurodegeneration, indicate that alternatively to being a disease of protein dysfunction, AD is caused by an infection [1,2]. Several pathogens have been implicated in AD, through their presence in AD patients and their interactions with Aβ and MAPT. One such pathogen, P. gingivalis, has been found in the brain of AD patients and possess the ability to produce toxic gingipains capable of degrading MAPT, allowing it to aggregate into the characteristic tangles . To examine this interaction, we rely on the organism C. elegans, a small nematode that has been used to study this disease previously. Current models of AD in C. elegans only express and aggregate Aβ intracellularly, whereas in humans, the protein largely aggregates extracellularly . By improving the C. elegans model of AD through expressing A extracellularly and infecting it with AD pathogens, such as P. gingivalis, we will be able to elucidate key steps in AD progression.
Results: We have generated a C. elegans strain that is capable of pan-neuronally expressing the human C99 fragment of amyloid precursor protein (APP), the progenitor of Aβ. The fragment is cleaved by an endogenous γ-secretase, releasing Aβ extracellularly. We have shown the presence of Aβ through PCR, RT-qPCR, and staining with a dye specific to Aβ aggregates. Once we have confirmed extracellular expression, we will infect the worms with the pathogen P. gingivalis. We can then begin examining them for various characteristics of AD, such as locomotive decline and neurodegeneration, comparing those results to the intracellular Aβ model.
Conclusions: This improved model of AD in C. elegans will give insights into the disease not possible with higher organisms. One of the main benefits is that C. elegans is transparent, which allows for us to image and track disease progression in individual worms throughout their lifespan. Specifically, this organism enables the observation of the production and aggregation of extracellular Aβ and its interactions with AD pathogens in vivo. In future work, we hope to include MAPT and more pathogens into the model so that we may improve it further.
- Chen, G. F., Xu, T. H., Yan, Y., Zhou, Y. R., Jiang, Y., Melcher, K., & Xu, H. E. (2017). Amyloid beta: Structure, biology and structure-based therapeutic development. In Acta Pharmacologica Sinica (Vol. 38, Issue 9, pp. 1205 1235). Nature Publishing Group. https://doi.org/10.1038/aps.2017.28
- Dominy, S. S., et. al ins: Evidence for disease causation and treatment with small-molecule inhibitors. Science Advances, 5(1), eaau3333. https://doi.org/10.1126/sciadv.aau3333
- Teo, E., Ravi, S., Barardo, D., Kim, H. S., Fong, S., Gassiot, A. C., Tan, T. Y., Ching, J., Kovalik, J. P., Wenk, M. R., Gunawan, R., Moore, P. K., Halliwell, B., Tolwinski, N., & Gruber, J. (2019). Metabolic stress is a primary pathogenic event in transgenic Caenorhabditis elegans expressing pan-neuronal human amyloid beta. ELife, 8. hhtps://doi.org/10.7554/eLife.50069
Background: Pregnancy disorders are typically the result of improper placentation and trophoblast differentiation. We aim to investigate key molecular mechanisms involved in placental development using human trophoblast stem cell models in order to better understand how pregnancy disorders arise in vivo. Previous work resulted in the discovery of two human trophoblast stem cell states, a more primitive, trophectoderm cell type (TEs) and a state that closer resembles cells from later stage-placental villi deemed villous cytotrophoblast cells (CTBs) [1,2]. CTBs could then further differentiate into the two terminal trophoblast subtypes, extravillous trophoblasts (EVTs) or syncytiotrophoblast (STB). Current CTB, EVT and STB in vitro media are chemically undefined, rendering investigation into molecular mechanisms difficult. Additionally, protocols used for EVT and STB differentiation are not representative of in vivo human development.
Results: We have proposed new EVT and STB conditions that better represent in vivo cell environments and are fully defined. The only variance between STB and EVT culture conditions is the addition of a basement extracellular matrix protein, laminin-111, in EVT differentiation. This signifies that the extracellular matrix acts as a switch in determining terminal trophoblast fate. Similar to laminin-111, S1P signaling also initiates EVT differentiation. Both S1P and laminin-111 act through the Protein Kinase C (PKC) signaling pathway leading to EVT differentiation.
Conclusions: This novel in vitro technique shed light on key mechanisms involved in differentiation to the extravillous trophoblast lineage. Further investigation is needed to understand what pathways downstream of PKC are involved in EVT differentiation.
- Mischler, A., Karakis, V., Mahinthakumar, J., Carberry, C., San Miguel, A., Rager, J., … & Rao, B. M. (2019). Two distinct trophectoderm lineage stem cells from human pluripotent stem cells. bioRxiv, 762542.
- Okae, H., Toh, H., Sato, T., Hiura, H., Takahashi, S., Shirane, K., … & Arima, T. (2018). Derivation of human trophoblast stem cells. Cell stem cell, 22(1), 50-63.
Background: Saccharomyces boulardii is a widely used yeast probiotic which can counteract various gastrointestinal disorders . A relative of Saccharomyces cerevisiae, S. boulardii exhibits rapid growth at 37°C, able to resist low pH [2,3] and is easy to transform , and thus represents a promising chassis for delivery of biomolecules to the gut.
Results: We first demonstrated tunability of gene expression over 2 orders of magnitude using plasmid-based constructs derived from S. cerevisiae. We next established >95% efficient genome editing using LbCas12a and revealed up to 3.4-fold variation in gene expression depending on the genomic integration site. We further harnessed S. boulardii’s high rates of homologous recombination to combinatorially assemble pathways for vitamin (β-carotene) and drug (violacein) production, revealing non-intuitive designs enabling up to 7.27 mg/L β-carotene in shake-flask culture. We next established S. boulardii’s ability to colonize germ-free and antibiotic-treated mice and found that microbial competitors significantly reduce S. boulardii’s gut residence time. Finally, we established that β-carotene-producing yeast can colonize germ-free mice over 14 days and continuously produce significant levels (up to 0.37 mg/g) of β-carotene.
Conclusions: The gut and the microbes that live within it play a major role in health, and as such are promising targets for small molecule or biologic drugs. Unfortunately, delivering drugs to the gut remains challenging due to the digestive action of the host, especially for protein-based therapies. Due to its probiotic properties and similarity to the biomanufacturing workhorse S. cerevisiae, we characterized the ability of S. boulardii to produce biomolecules in the mammalian gut. Taken together, our results establish S. boulardii as the first non-bacterial chassis for biomolecule production in the gut and provide a quantitative framework for continued engineering.
- Tiago, F. C. P. et al. Adhesion to the yeast cell surface as a mechanism for trapping pathogenic bacteria by Saccharomyces probiotics. J. Med. Microbiol. 61, 1194–1207 (2012).
- Khatri, I., Tomar, R., Ganesan, K., Prasad, G. S. & Subramanian, S. Complete genome sequence and comparative genomics of the probiotic yeast Saccharomyces boulardii. Sci. Rep. 7, 371 (2017).
- Hudson, L. E. et al. Characterization of the Probiotic Yeast Saccharomyces boulardii in the Healthy Mucosal Immune System. PLoS One 11, e0153351 (2016).
- Fietto, J. L. R. et al. Molecular and physiological comparisons between Saccharomyces cerevisiae and Saccharomyces boulardii. Can. J. Microbiol. 50, 615–621 (2004).
Background: In wound healing, directed migration of fibroblasts to the wound is essential for wound closure and insufficient migration is associated with chronic wounds . Directed migration prompted by physio-chemical cues include gradients of soluble growth factors (chemotaxis) and surface-bound extracellular matrix proteins (haptotaxis). The development of in vitro single-cue directed migration assays has shed light on the molecular underpinnings of fibroblast chemotaxis and haptotaxis  but directed migration in multi-cue environments consisting of both chemotactic and haptotactic gradients remains understudied. To this end, we are developing novel microfluidic migration assays to study integrated cell migration in parallel, anti-parallel, and orthogonal chemotactic/haptotactic gradients.
Results: Herein, we present a prototype multi-gradient chemotactic/haptotactic assay compatible with Total Internal Reflection Fluorescence (TIRF) microscopy, thereby allowing simultaneous tracking of cell motility as well as cell signaling. Importantly, our assay approach quantifies the gradient stimuli for single-cells and therefore connects quantitative chemotactic/haptotactic inputs to quantitative cellular behavior such as cell speed, directional fidelity, and directional persistence.
Conclusions: The assay we have developed, in conjunction with signaling pathway perturbation techniques (e.g., small molecule inhibitors, genetic knockdown, etc.), establishes an avenue to elucidate mechanisms associated with integration of multiple migration cues.
- Eming, S. A., Martin, P. & Tomic-Canic, M (2014). Wound repair and regeneration: Mechanisms, signaling, and translation. Sci. Transl. Med., 6: 265sr6.
- Bear, J. E. & Haugh, J. M. (2014). Directed migration of mesenchymal cells: where signaling and the cytoskeleton meet. Curr. Opin. Cell Biol., 30: 74–82.
Background: As the predominant form of biomass on Earth, lignocellulose is a prime candidate for conversion into renewably sourced chemicals and fuels. The extremely thermophilic bacterium, Caldicellulosiruptor bescii (Topt=78oC), natively has the ability to metabolize the cellulose and hemicellulose contained in lignocellulose . C. bescii can be genetically engineered to produce valuable chemicals such as ethanol and acetone [2,3]. Additionally, C. bescii can solubilize recalcitrant biomass, including switchgrass and poplar [1,4]. Populus trichocarpa provides a potential lignocellulose feedstock . The Forest Biotechnology program at NCSU has the ability to genetically alter the monolignol synthesis pathway in the trees, allowing for feedstock improvements . C. bescii grown on transgenic poplar biomass had improved fermentation characteristics and the microbe-feedstock pair showed potential for further optimization . C. bescii also demonstrated an ability to ferment poplar stem sections nearly as well as milled poplar, potentially eliminating the need for pretreatment milling . Both volatile production by C. bescii and the feed stock propertied of P. trichocarpa need to be improved for potential industrial impact.
Results: Efforts to create an optimal transgenic poplar line with good growth and fermentation characteristics is underway. C. bescii fermentations are used to quantify the recalcitrance of poplar lines. Highlights from these results are presented. Additional efforts are underway to produce acetone at industrially relevant levels through targeted protein and metabolic engineering. Progress toward this goal is presented.
Conclusions: The available genetic tools for both P. trichocarpa and C. bescii provide potential to optimize this microbe-feedstock pairing to become industrially relevant. Here we aim to produce high amounts of acetone from the fermentation of transgenic poplar biomass.
- Straub, C.T., Khatibi, P.A., Wang, J.P. et al., Quantitative Fermentation of Unpretreated Transgenic Poplar by Caldicellulosiruptor bescii. Nat. Commun. 10 (2019)
- Williams-Rhaesa, A.M., Rubinstein, G.M., Scott, I.M. et al., Engineering redox-balanced ethanol production in the cellulolytic and extremely thermophilic bacterium, Caldicellulosiruptor bescii, Metab. Eng. Commun. 7 (2018) 1–9.
- Straub, C.T., Bing, R.G., Otten, J.K. et al., Metabolically engineered Caldicellulosiruptor bescii as a platform for producing acetone and hydrogen from lignocellulose, Biotechnol. Bioeng. (2020).
- Sannigrahi, P., Ragauskas, A.J., Tuskan, G.A., Poplar as a feedstock for biofuels: A review of compositional characteristics, Biofuels, Bioprod. Biorefining. 4 (2010) 209–226.
- Wang, J.P., Matthews, M.L., Williams, C.M. et al., Improving wood properties for wood utilization through multi-omics integration in lignin biosynthesis, Nat. Commun. 9 (2018).
- Straub, C.T., Bing, R.G., Wang, J.P. et al., Use of the lignocellulose-degrading bacterium Caldicellulosiruptor bescii to assess recalcitrance and conversion of wild-type and transgenic poplar. Biotechnol. Biofuels. 13, 43 (2020)
Background: The genus Caldicellulosiruptor consists of extremely thermophilic, Gram- positive, fermentative anaerobic bacteria (Topt > 70oC), typically isolated from terrestrial thermal features. All species with available genome sequence information to date degrade hemicellulose, whereas only a subset degrade microcrystalline cellulose. Caldicellulosiruptor species physically associate with the substrate during growth on the plant biomass. One mechanism for this association is through multi-domain hemicellulases, which are anchored to the cell surface through S-layer homology (SLH) domains .
Results: Engineered strains of Caldicellulosiruptor bescii in which an SLH-domain hemicellulose from Caldicellulosiruptor kronotskyensis was inserted bound more tightly to certain xylans. These bacteria also deploy novel binding proteins, called tāpirins , which are encoded in proximity to the region of the genome referred to the Glucan Degradation Locus (GDL), which contains up to six multi-domain cellulases. Tāpirins specifically interact with microcrystalline cellulose to various extents . For example, the tāpirin (Calkro_0844) from Caldicellulosiruptor kronotskyensis has a cellulose binding affinity comparable to family 3 carbohydrate binding modules (CBM3). The tāpirins from Caldicellulosiruptor hydrothermalis (Calhy_0908) and Caldicellulosiruptor kristjianssonii (Calkr_0826) bind to cellulose to a greater extent compared to other tāpirins, although these species are not prolific cellulose degraders. Furthermore, Caldicellulosiruptor bescii mutants lacking the tāpirin genes did not bind to the cellulose.
Conclusions: Discussed here are current efforts to engineer the surface of C. bescii to improve its capacity for biomass degradation. This includes inserting genes for non-native SLH-domain hemicellulases from other Caldicellulosiruptor species into the C. bescii genome. Furthermore, we are investigating the tāpirin cellulose binding mechanism through site- directed mutations in Calhy_0908, Calkr_0826, and Calkro_0844 in which cysteine residues are being inserted to strategically enable disulfide bridges within the protein to form. Our goal is to assess the significance of flexibility in hydrophobic binding pocket in the tāpirins as this relates to cellulose affinity.
- Conway, J.M.; et al (2016), Multidomain, surface layer-associated glycoside hydrolases contribute to plant polysaccharide degradation by Caldicellulosiruptor species. J of Biol Chem, 291(13): p. 6732-6747.
- Blumer-Schuette, S.E.; et al (2015), Discrete and structurally unique proteins (tāpirins) mediate attachment of extremely thermophilic Caldicellulosiruptor species to cellulose. J of Biol Chem, 290(17): p. 10645-10656.
- Lee, L.L.; et al (2019), Comparative Biochemical and Structural Analysis of Novel Cellulose Binding Proteins (Tāpirins) from Extremely Thermophilic Caldicellulosiruptor Species. J Appl Environ Microbiol, 85(3): p. 01983-18.
Background: When invading a wound, skin cells called fibroblasts are presented with an array of different directional cues. Among the directional cues, gradients of immobilized ligands found in the extracellular matrix are understudied yet thought to be critical for invasion. Recent publications show an importance of lamellipodia and integrin-actin machinery in migration toward these surface bound ligands, called haptotaxis . Considering the initial literature on the haptotactic response of fibroblasts a 2-D haptotactic migration model was developed to mimic fibroblast migration with integrin signaling.
Results: The multiphysics simulation software COMSOL has been used to simulate the building of a surface bound gradient of a haptotactic cue. This adsorption-diffusion model simulates the binding of fibronectin in the microfluidic devices used for experimental work in our lab. Cells, modeled according to the phase field formalism, are superimposed on the gradient. Initial iterations of the model the cell simply responded to the magnitude of the gradient, while the current model includes signal transduction that locally influences membrane protrusion.
Conclusions: Preliminary results of the model show that in high gradients cells behave similarly to what is seen in experimental fibroblasts on fibronectin gradients. These results are promising as these initial iterations are toy models that at their basic level still grasp some biological relevance. In later model iterations, it would be desired to find a signaling network that mimics cells in vitro where cells are able to integrate lower signaling gradients less readily than steeper ones.
- King SJ, Asokan SB, Haynes EM, et al. Lamellipodia are crucial for haptotactic sensing and response. J Cell Sci. 2016;129(12):2329-2342. doi:10.1242/jcs.184507
Background: The order Sulfolobales is comprised of thermoacidophilic archaea (Topt > 65°C, pHopt < 3.5) . The order contains a diverse metabolic landscape, including chemolithoautotrophic growth on iron and sulfur . These organisms already have application in the biomining for solubilizing precious metals, and their novel growth modes have potential for biosynthesis of industrial chemicals . Sulfolobus acidocaldarius (Saci) serves as a model organism in this order and has an established genetic system which enables metabolic engineering for chemical biosynthesis . However, Saci is an obligate heterotroph and must be engineered to fix CO2 by oxidation of reduced inorganic sulfur compounds (RISCs). The mechanism of sulfur oxidation in the Sulfolobales is only somewhat understood, and is complicated by myriad abiotic RISC reactions . Comparative genomics of newly sequenced Sulfolobales, coupled with select transcriptomic data, has provided insight into these mechanisms and offers targets for engineering Saci to enable the organism to oxidize elemental sulfur [5-6].
Results: Utilization of sulfur substrates was assessed in select Sulfolobales through growth curves and dissolved oxygen consumption. A database of homologous protein clusters within the Sulfolobales was mined to identify highly conserved proteins in sulfur-oxidizing species, and these targets were used to evaluate the transcriptomic response to elemental sulfur in the strong sulfur- oxidizer Acidianus brierleyi (Abri) versus Saci. Thermodynamic free energy calculations were used to evaluate equilibrium behavior of a network of abiotic sulfur reactions. Select enzymes implicated in sulfur oxidation were inserted into the Saci genome, and the resulting mutant was evaluated for sulfur oxidation and chemolithoautotrophic growth.
Conclusions: A set of sulfur oxidation proteins were identified in the Sulfolobales, including components of the electron transport chain (ETC). Transcriptomic analysis emphasizes key regulation of ETC components in response to sulfur presence in Abri. Thermodynamic calculations indicate key changes in reaction favorability between the acidic extracellular environment and the near-neutral cytoplasm. The mutant Saci demonstrates the ability to oxidize sulfur.
- Wheaton, G. H., et al. (2015). The confluence of heavy metal biooxidation and heavy metal resistance: implications for bioleaching by extreme thermoacidophiles. Minerals-Basel 5: 397-451.
- Auernik, K. S., et al. (2008). Life in hot acid: Pathway analyses in extremely thermoacidophilic archaea. Current Opinion in Biotechnology 19(5): 445-453.
- Wagner, M., et al. (2012). Versatile genetic tool box for the Crenarchaeote Sulfolobus acidocaldarius. Front. Microbiol. 3: e214.
- Suzuki, I. (1999). Oxidation of inorganic sulfur compounds: Chemical and enzymatic reactions. Canadian Journal of Microbiology 45(2): 97-105.
- Zeldes, B. M., et al. (2019). Determinants of sulphur chemolithoautotrophy in the extremely thermoacidophilic Sulfolobales. Environmental Microbiology 21(10): 3696-3710.
- Counts, J.A., et al. (Accepted 2020). Life in Hot Acid: A Genome-based Reassessment of the Archaeal Order Sulfolobales. Environ. Microbiol.
CATALYSIS, COMPUTATION, AND KINETICS POSTERS
Background: Clostridium difficile infection is the leading cause of diarrhea and colitis (inflammation of the colon) in North America and Europe. There is a growing concern about the failure of the first line of treatment for C. diff infection (metronidazole and vancomycin), and thus current attention is focused on the search for alternative treatment options like biologic drugs that might be safer or more efficacious . A viable strategy is the development of targeted peptide-based therapeutics that prevent and treat C. diff infections by deactivating the pathogen while leaving the resident gut microbiota unharmed. During infection, the C. diff pathogen produces two large virulent toxins (Toxin A and B) that share 71% sequence homology. The glucosyltransferase domain (GTD) of these toxins acts by binding UDP (Uridine diphosphate)-glucose, hydrolyzing it into glucose and UDP, and attaching the glucose monomer to the human Rho family of GTPases. Glycosylation of the GTPases by TcdA and TcdB GTDs leads to disruption of the cytoskeleton of the host cells, apoptosis, and cell death . The objective of this project is to computationally design peptide inhibitors that bind with high affinity and specificity to the glucosyltransferase domain of C. diff toxins A and B to inhibit their activity. We have developed a computational approach to discover peptide sequences that bind to a biomolecular target with high affinity. Our peptide search algorithm employs Monte Carlo methods, self-consistent mean-field theory, and the concerted rotation (CONROT) technique . The algorithm requires a reference ligand, an experimentally determined peptide sequence that has a good binding affinity to the target protein, to start the search.
Results: We have discovered two peptides, NPA and NPB, that can inhibit the glucosyltransferase activity of Toxin A GTD using EGWHAHTGGG (Kd 100 nM) as the reference ligand, a peptide previously identified by the Feig lab using phage display. Simulations of NPA and NPB at the binding site of Toxin A showed that they have a high affinity for Toxin A. Calculations of the binding free energy for these peptides based on atomistic molecular dynamics simulations suggest that the computationally discovered peptides are better binders than the reference ligand. Experimental results demonstrate highly effective neutralization of TcdA toxicity for NPA in jejunum cells (human small intestine) but no efficacy when tested in human colonic epithelial cells (large intestine).
Conclusions: Current work is focused on furthering our understanding of the interaction of these peptides with the toxins, redesigning shorter peptide inhibitors for Toxin A, and discovering peptides that can bind to Toxin B.
- Ananthakrishnan, AN (2011). Clostridium difficile infection: epidemiology, risk factors and management. Nat.
Rev. Gastroenterol. Hepatol., 8(1): 17-26.
- Alvin, J.W. and Lacy, D.B (2017). Clostridium difficile toxin glucosyltransferase domains in complex with a non-hydrolyzable UDP-glucose analogue. J. Struct. Biol., 198(3): 203-209
- Xiao, X., Agris, P.F and Hall, C.K (2017). Extended Concerted Rotation Technique Enhances the Sampling Efficiency of the Computational Peptide-Design Algorithm. J. Chem. Theory. Comput. 13, 5709-5720.
Background: Reactive inorganic nanolaminates contain metastable interfaces, such as those between metals and metal oxides, that when disturbed by heat or shock undergo highly exothermic reactions. Largely due to the potential complexity of the system dynamics and the challenges associated with experimental probes of the dynamics at buried interfaces, the mechanisms that initiate this chemistry are unknown. We use atomistic molecular dynamics simulations of nanolaminates to investigate the mechanisms by which the energy of a shock pulse – delivered by a simulated flyer plate – can initiate chemical mixing at a buried metal-metal interface.
Results: Our simulations show dislocations initiated at the edges of the flyer plate and propagating downward along slip planes. This damage at the plate perimeter is consistent with recent experiments by Dlott and co-workers in which the initiation of buried exothermic reactivity in a reactive nanolaminate is observed in a ring pattern matching the geometry of the flyer plate. We further investigated the simulated shock-induced damage using common neighbor analysis and dislocation extraction algorithms to calculate and determine specific types of line defects. In a single layer FCC structure, we predominantly observe Shockley partial dislocations originating on the impact surface at the plate edge. These partial dislocations surround regions of atoms with a local HCP structure, indicating the possible presence of stacking faults. Our multilayer systems show the simulated dislocations can reach a buried interface. In the case of a Cu-Zr nanolaminate simulation, the dislocations appear to be terminated at the first interface but transferred an elastic energy pulse into subsequent layers.
Conclusions: The presence of the observed defects appears to relieve the shock-induced stresses. The crystal orientation and the energy delivered by the flyer plate affect the depth of damage observed and its transfer across interfaces. Our simulations indicate the mechanisms by which energy is delivered across a series of buried interfaces may differ depending on the interface location with respect to the shock pulse.
This work was supported by the U.S. Department of Defense, Multidisciplinary University Research Initiative through the Army Research Office, Grant No. W911NF-16-1-0406.
Background: The perovskite structured calcium manganite family (CaxA1-xMnyB1-yO3-δ) has been demonstrated as one of the promising materials in chemical looping applications, such as chemical looping combustion (CLC) and chemical looping oxidative dehydrogenation (CL-ODH) -. The complex redox behaviors of the CaMnO3 family offer significant versatility and thus understanding the effect of dopants on the redox thermodynamics and kinetics of CaMnO3 family oxygen carriers are important from both scientific and practical standpoints. In this work, both the thermodynamic properties and reduction kinetics of selected A-site and B-site doped CaMnO3 materials were investigated to improve oxides and optimize the redox processes.
Results: The thermochemical properties of two oxygen-deficient B-site ordered perovskite oxides, Ca2MnAlO5+δ (CAM) and Ca2-xSrxMnAlO5+δ, have been systematically investigated. The undoped and 5% doped CAM are able to release approximately 2.80 wt% oxygen. Further doping the material limits the amount of oxygen released to only 2.40 wt%. The reaction enthalpy and entropy of CAM and 5% Sr doped CAM were predicted by van’t Hoff equation, indicating that 5% Sr CAM has higher enthalpy value (166.2 ± 3.2 kJ/mol O2) than that of undoped CAM (146.5 ± 4.7 kJ/mol O2) and thus expands the operating conditions to a lower temperature range. Next, the reduction kinetics of CaMn0.9Fe0.1O3 redox catalyst under H2 and C2H4 were examined. The reduction of CaMn0.9Fe0.1O3 under H2 and C2H4 is well-described by reaction-order models. The activation energy for the reduction of unpromoted-CaMn0.9Fe0.1O3 under H2 is 44.3 kJ/mol, and the corresponding value is 122.2 kJ/mol under C2H4. The reduction models predict greater dependence on oxygen site density for CaMn0.9Fe0.1O3 reduction under C2H4 as compared with H2.
Conclusions: Several CaMnO3 based materials have been investigated and found to exhibit varying redox properties. 5% dopants on CAM show little effects on the oxygen uncoupling properties (~2.80 wt%), which are significantly suppressed at 12.5% dopant level. Across the vacancy range studied, the molar enthalpy ∆H° and entropy ∆S° of Sr-doped Ca1.95Sr0.05MnAlO5+δ are greater than those of CAM, indicating the doped material is more sensitive to small variations in temperature. It proves that a small portion of dopant is able to functionally tune the studied material to a wider operating window while still maintaining desired oxygen-storage capacity. The rate parameters obtained for CaMn0.9Fe0.1O3 reduction by H2 and C2H4 also provide insights to optimize the redox processes that employ these materials, such as the ethane CL-ODH process.
- Moldenhauer, P., Rydén, M., Mattisson, T., Hoteit, A., Jamal, A., & Lyngfelt, A. (2014). Chemical- Looping Combustion with Fuel Oil in a 10 kW Pilot Plant. Energy & Fuels, 28(9), 5978-5987.
- Galinsky, N., Mishra, A., Zhang, J., Li, F. (2015). Ca1−xAxMnO3− δ (A = Sr and Ba) perovskite based oxygen carriers for chemical looping with oxygen uncoupling (CLOU). Applied Energy, 157, 358–367.
- Dudek, R. B., Gao, Y., Zhang, J., Li, F. (2018). Manganese-containing redox catalysts for selective hydrogen combustion under a cyclic redox scheme. AIChE Journal, 64(8), 3141–3150.
Background: With a pressing need to reduce CO2 emissions to decrease the effects of global warming, it is essential to increase the efficiency for air separation. Previous thermochemical air separation process modeling has shown the potential for it to replace cryogenic air separation units. A realistic scale up of the process is needed to understand the practicality of the process. Researchers have studied perovskite materials for this process as they exhibit flexibility in reversibly creating oxygen vacancies under low temperature (>650 °C)) [1–3] which can potentially reduce cost and improve efficiency. These low temperature sorbents have unique thermodynamic properties, such as vacancy concentration that’s a continuous function of temperature and oxygen partial pressure with no phase change
Results: Experimental data obtained from the perovskite Sr0.8Ca0.2Fe0.4Co0.6O3 oxygen sorbent is used in the simulation to compare to the state-of-the-art cryogenic air separation method. Using ASPEN Plus®, the effects of the reactor and process conditions were investigated. Parameters such as heat loss, steam requirements, coefficient of lost work, kinetics, and pressure drop were all investigated to effectively determine the energy cost of CLAS. Potential advantages of the CLAS process were validated in comparison to cryogenic separation when considering these parameters using a detailed process analysis
Conclusions: When compared to cryogenic air separation, the net energy requirement was lowered from 0.781 MJ/ kg O2 to between 0.359 to 0.752 MJ/ kg O2, an 8% reduction in energy consumption, using SCFC at 600 °C and based on a 1000 MW IGCC plant. Primary thermodynamic irreversibility stems from the steam condensation and regeneration for the removal of oxygen from the oxide. This reduction in energy allows for carbon capture to be more easily integrated into a gasifier unit and therefore cause a reduction in anthropomorphic CO2 release.
- B. Bulfin, J. Lapp, S. Richter, D. Gubàn, J. Vieten, S. Brendelberger, M. Roeb and C. Sattler, Chemical Engineering Science, 2019, 203, 68–75.
- J. Dou, E. Krzystowczyk, A. Mishra, X. Liu and F. Li, ACS Sustainable Chem. Eng., 2018, 6, 15528–15540.
- E. Krzystowczyk, X. Wang, J. Dou, V. Haribal and F. Li, Physical Chemistry Chemical Physics, 2020, 22, 8924–8932.
- A. Darde, R. Prabhakar, J.-P. Tranier and N. Perrin, Energy Procedia, 2009, 1, 527–534.
Background: Utilizing CO2 for chemical production can be an economically attractive option for carbon emission reduction. Among the various CO2 utilization approaches, oxidative dehydrogenation (ODH) with CO2 as a soft oxidant offers the potential to produce value-added CO while upgrading light alkanes, such as ethane to ethylene[1,2]. However, CO2-assisted ethane ODH is nevertheless an energy intensive process largely due to the limited ethane and CO2 conversions and hence a high energy cost for product separations. Currently, the highest reported CO2 conversion in CO2-ODH of ethane is only 50% at 800 °C. Meanwhile, ethylene yield is generally limited to <20% at lower temperature. Aside from these challenges, CO2-ODH requires a concentrated CO2 stream. This adds another energy-consuming step since CO2 capture from emission sources such as fossil-based power plants are highly energy intensive[1,2]
Conclusions: To address the challenges from both CO2 separation and CO2-ODH, we propose to utilize tailored molten salts as a reaction medium for simultaneous CO2 capture and utilization. In this scheme, we demonstrate that CO2 can be captured from a (simulated) power plant flue gas and subsequently utilized via a modified reverse water gas shift reaction with a high CO2 conversion. Results from temperature programmed reaction (TPR) and in-situ Diffuse Reflectance Infrared Spectroscopy (DRIFTS) suggest that the coupled radical reactions and reverse water gas shift reaction in the molten salt medium was responsible for the high CO2 to CO conversion and ethylene yield.
- Vitillo, J. G.; Smit, B.; Gagliardi, L. Introduction: Carbon Capture and Separation. Chem. Rev. 2017, 117 (14), 9521–9523. https://doi.org/10.1021/acs.chemrev.7b00403.
- Gomez, E.; Yan, B.; Kattel, S.; Chen, J. G. Carbon Dioxide Reduction in Tandem with Light-Alkane Dehydrogenation. Nat Rev Chem 2019, 3 (11), 638–649.
Background: Next generation technology such as batteries,  catalysts,  semiconductor devices, and solar cells  benefit from protective coatings that improve performance and extend lifetime. These organic or hybrid organic/inorganic coatings are formed via molecular layer deposition (MLD), a thin film deposition technique that enables sub-nanometer, uniform thickness control and conformality on complex 3D substrates. Different precursors precisely tune film properties, for example to improve electrical conductivity, facilitate electrode volume expansion, or increase density. Therefore, understanding MLD growth with new precursors and advanced analysis is a key enabler to improving performance of the aforementioned technologies. We gain insight on underlying growth mechanisms during polyurea MLD using novel film structures and analysis techniques to facilitate MLD incorporation into these commercial applications.
Results: Polyurea is deposited with traditional ethylenediamine and p-phenylene diisocyanate precursors between 30-90°C. Highly flexible 1,6-hexanediamine (HD) and 1,6 hexamethylene diisocyanate (HDIC) are introduced to polyurea MLD for the first time to systematically alter film structure. The growth rate decreases with increasing film flexibility due to double reactions from the long carbon chain HD and HDIC monomers, which terminate growth sites. These flexible films reveal a transition from initial, accelerated growth on SiO2 to steady growth on the polymer surface, as observed by in situ ellipsometry and quartz crystal microbalance. Picosecond acoustics measurements analyze MLD films for the first time, confirming physical changes in polymer modulus during the growth transition.  This is attributed to increased monomer diffusion/adsorption on polymer surfaces, which causes increased chain entanglement/cross-linking. These growth regimes must be considered to fulfill precise film thicknesses and properties requirements.
Conclusions: Two new precursors, HD and HDIC, are utilized to deposit polyurea via MLD for the first time. These new, highly flexible films along with a new MLD analysis technique, picosecond acoustics, reveal a transition in growth rate and physical properties around ~30 cycles, which is dependent on monomer structure. Understanding this transition is key to enhancing control over organic coating quality for next generation energy storage and microelectronics.
- Li, X.; Lushington, A.; Sun, Q.; Xiao, W.; Liu, J.; Wang, B.; Ye, Y.; Nie, K.; Hu, Y.; Xiao, Q.; et al. Safe and Durable High-Temperature Lithium–Sulfur Batteries via Molecular Layer Deposited Coating. Nano Lett. 2016, 16 (6), 3545–3549.
- MacIsaac, C.; Schneider, J. R.; Closser, R. G.; Hellstern, T. R.; Bergsman, D. S.; Park, J.; Liu, Y.; Sinclair, R.; Bent, S. F. Atomic and Molecular Layer Deposition of Hybrid Mo-Thiolate Thin Films with Enhanced Catalytic Activity. Adv. Funct. Mater. 2018, 28 (26), 1800852.
- Kim, D. H.; Atanasov, S. E.; Lemaire, P.; Lee, K.; Parsons, G. N. Platinum-Free Cathode for Dye- Sensitized Solar Cells Using Poly(3,4-Ethylenedioxythiophene) (PEDOT) Formed via Oxidative Molecular Layer Deposition. ACS Appl. Mater. Interfaces 2015, 7 (7), 3866–3870.
- Nye, Rachel A., Kelliher, Andrew P., Gaskins, John T., Hopkins, Patrick P., Gregory N. Parsons (2020). “Understanding Molecular Layer Deposition Growth Mechanisms in Polyurea via Picosecond Acoustics Analysis.” Chem. Mater., 32, 4, 1553–1563
Background: Sweat is an important biofluid for monitoring individuals’ health as it contains a number of essential biomarkers. However, sampling sweat for analysis still remains challenging as most of the commercially available sweat sensing devices are either invasive in nature or work only under active perspiration . These devices fail to function under low-sweating conditions and are incapable of deriving sweat measurements from subjects at rest. We demonstrate a new principle for the design of flexible and wearable devices, which are capable of extracting sweat under both sedentary and actively perspiring conditions using osmotic pressure difference for pumping, and evaporation for liquid disposal . The device is constructed of silicone, polyacrylamide hydrogel patch, and paper microfluidic conduit with a site of evaporation at the end (evaporation pad). The hydrogel is equilibrated with glycerin, glucose, or NaCl solution to build up the desired osmotic strength.
Results: In-vitro testing with gelatin-based model skin platform has initially revealed that both glucose and glycerin treated hydrogels facilitate high dye (model biomarker in model skin) accumulation on the evaporation pad, with glucose being the highest. Human trials with devices embedded with a glucose hydrogel have shown the potential of the prototype to extract sweat containing lactate under both resting and non-resting (during exercise) conditions within a period 2 hours. Results reveal the following two observations: (1) sweat lactate increases with exercise and (2) there is no direct correlation between the blood and sweat lactate. Integration of a “glycerogel” (hydrogel treated with pure glycerin) hosted patch with microneedles have shown the potential of this combined system to sample model biomarker from model skin. Such an arrangement is essential for long-term interstitial fluid (ISF) sampling since ISF glucose levels are similar to that in blood. A continuous sweat lactate sensing platform is also currently being established on the prototype by using enzymatic electrochemical sensors on a polyimide film, which is adhered directly onto the paper microfluidic channel. Initial testing with this integrated platform has shown that this wearable prototype can be easily tuned for continuous sweat lactate monitoring.
Conclusions: The novel simple, low cost, continuous sweat sampling platform with specific sensors can either be worn directly onto the skin or be used as a wearable, that can reveal a throve of health information. We are presently expanding our prototype to a lateral flow assay (LFA) platform and working towards utilizing it for early disease diagnosis from sweat.
- Min S, Balooch G, Kang D, Koh A, Kim J, Pielak RM, et al. (2016). A soft, wearable microfluidic device for the capture, storage, and colorimetric sensing of sweat. Sci Transl Med., 8(366), 366ra165-366ra165.
- Shay, T., Saha, T., Dickey, M. D. & Velev, O. D. Principles of long-term fluids handling in paper-based wearables with capillary-evaporative transport (2020). Biomicrofluidics 14(034112), 1-9.
Background: The synthesis of metal oxide particles has attracted substantial attention due to the variety of unique optoelectronic and physicochemical characteristics, as well as the breadth of available applications, ranging from drug delivery to catalysis.  Many synthetic techniques have been utilized to fabricate metal oxide microspheres, including sol-gel, hydrolysis, emulsion, and deposition. However, these techniques are often conducted in batch, reducing control over many particle characteristics, including size, surface area, and crystallinity. By comparison, continuous microfluidic synthesis techniques benefit from enhanced heat and mass transfer rates, allowing precise control over the particle characteristics. This precise parametric control enables synthesis of microparticles with properties tailored to specific applications.
Results: Using an intensified capillary microfluidic reactor, we demonstrate the synthesis of titania (TiO2) microspheres ranging from 10 μm -250 μm in size via flow-focusing. To prevent premature (i.e., on-chip) hydrolysis, a polar, aprotic solvent (i.e., formamide) is used as the continuous phase, and the dispersed phase is composed of the metal precursor, a photocurable polymer, and toluene. The microdroplets formed by the flow-focusing microreactor are photo-crosslinked in flow, thus intensifying the overall synthesis process. Finally, the formed microparticles are annealed at high temperature (500 °C), forming the desired oxides via the oxidative route. [2, 3] These microspheres possess intriguing characteristics, including high specific surface areas (up to 360 m2g-1), resistance to phase transition, and highly tunable morphologies.
Conclusions: The developed intensified microfluidic technique offers a generalizable synthetic approach for the production of a wide variety of metal oxide microspheres which may be effectively implemented as heterogenous catalysts.
- Campbell, Zachary S. and Milad Abolhasani (2020). Facile synthesis of anhydrous microparticles using plug-and-play microfluidic reactors. React. Chem. Eng., 5: 1198-1211.
- Campbell, Zachary S., Matthew Parker, Jeffrey A. Bennett, Seif Yusuf, Amur K. Al-Rashdi, Jacob Lustik, Fanxing Li, and Milad Abolhasani (2018). Continuous Synthesis of Monodisperse Yolk – Shell Titania Microspheres. Chem. Mater. 30: 8948-8958.
- Campbell, Zachary S., Daniel Jackson, Jacob Lustik, Amur K. Al-Rashdi, Jeffrey A. Bennett, Fanxing Li, and Milad Abolhasani (2020). Continuous flow synthesis of phase transition-resistant titania microparticles with tunable morphologies. RSC Adv. 10: 8340-8347.
Background: Surface-anchored polymer coatings with controllable surface properties have drawn attention due to its broad applicability in various fields, including soft electronics, drug delivery, microfluidics, and biotechnology. UV- or thermally-active cross-linkable groups are incorporated into the precursor polymer to trigger the crosslinking and surface attachment reaction. However, the conventional method has some limitations, which require specific functional groups inside the polymers and multiple fabrication steps to generate surface- anchored polymer networks. Here we use a versatile and straightforward one-pot synthesis method to make surface-anchored polymer networks by using thermally active functional small molecular gelators (FSMGs). The sulfonyl azide (SAz) tail group and triethoxysilane headgroup group in 6-azidosulfonylhexyltriethoxysilane (6-ASHTES) generate a simultaneous crosslinking and a surface attachment of the polymer network to the substrate.
Results: We studied the formation of surface-anchored polymer network by using poly(vinyl pyrrolidone) (PVP) with various molecular weights and 6-ASHTES amounts. We deposited thin films (thickness d) of PVP/6-ASHTES mixture onto a silicon substrate by dip-coating and annealed them at 120, 130, and 140°C for the desired time. The films were extracted in methanol, and ellipsometry measured the film thickness d0. The gel fraction (Pgel), which is the insoluble fraction of polymer in the network, was determined as Pgel=d/d0. Pgel increased with increasing the concentration of 6-ASHTES (x), annealing temperature (T), and annealing time (t). We have demonstrated that Pgel can be controlled independently by varying x, T, and t. We have produced master plots for Pgel that confirm the x-T-t superposition. Also, we studied the swelling behavior of polymer gel with various molecular weights of PVP and concentrations of 6-ASHTES. The swelling ratio increased with an increased average molecular weight between crosslinks (i.e., decreased crosslink density).
Conclusions: In this study, we investigated a one-pot synthesis to generate the surface-anchored polymer network using 6-ASHTES gelator. We studied gel fraction and swelling ratio to determine the effects of the molecular weight of PVP, annealing time, and temperature on the reaction kinetics of the surface-anchored polymer network. Further development on the surface-anchored polymer network would result in successful adaptation in the biomedical industry.
- Pandiyarajan, C. K.; Rubinstein, M.; Genzer, J. (2016). Surface-Anchored Poly(N -Isopropylacrylamide) Orthogonal Gradient Networks. Macromolecules, 49: 5076−5083.
- Pandiyarajan, C. K., & Genzer, J. (2019). Thermally Activated One-Pot, Simultaneous Radical and Condensation Reactions Generate Surface-Anchored Network Layers from Common Polymers. Macromolecules, 52(2): 700-707.
Background: Volatile organic solvents are widely used in a variety of physical and chemical processes across various fields. Due to the absence of viable alternative solvent removal and recovery strategies, energy-intensive distillation processes are increasingly being used worldwide with volatile toxic and flammable solvents. Recently, switchable hydrophilicity solvents (SHSs) have emerged as a promising green class of solvents for energy-efficient solvent removal and recovery, offering a facile reversible tuning of hydrophilicity triggered by carbon dioxide (CO2) under ambient conditions. Despite intriguing characteristics of switchable solvents, the time-intensive nature of conventional flask-based screening methods have inhibited further development and industrial adoption of this class of green solvents. In this work, we develop and utilize a microscale flow chemistry strategy utilizing a highly gas-permeable Teflon AF-2400 tubular membrane in a tube-in-tube flow reactor configuration,  for accelerated development of SHSs.
Results: We developed and utilized a reconfigurable, intensified microreactor for accelerated screening and continuous extraction of SHSs in the presence of CO2 and water. The role of the molecular structure (e.g., alkyl chain length and bulky functional groups) of SHSs (e.g., secondary and tertiary amines) as well as varying range of operation parameters (e.g., CO2 pressure, organic to aqueous phase volume ratio, concentration, flow velocity) were studied systematically utilizing a material-efficient, single-droplet flow reactor.  Then, utilizing a flow reactor geometry similar to the single-droplet flow reactor, we demonstrated direct adaptation of the optimized SHS extraction process conditions to a continuous flow reactor. Furthermore, utilizing a membrane- based liquid-liquid phase separation module, we demonstrated continuous in-line separation and recovery of the extracted SHS.
Conclusions: The reconfigurable flow chemistry platform resulted in process intensification for both process development (i.e., accelerated R&D with in-situ characterization) and continuous extraction of SHSs. Single-droplet screening resulted full SHS recovery in 3~8 min (~25 times faster than a batch reactor) with consuming only 4~8 μL of SHS mixture (~500 times less chemical consumption than a batch reactor). Utilizing optimized process conditions in continuous flow reactor, continuous extraction of SHS at the recover rate of 20 mmol/h was achieved (~10 times higher than a batch reactor) in a single-channel flow reactor. Further implications of the developed flow chemistry strategy (e.g., scaling out) may accelerate adoption of SHSs in chemical industries.
- P.G. Jessop, S. M. Mercer, and D. J. Heldebrant, CO2-Triggered Switchable Solvents, Surfactants, and Other Materials, Energy Environ. Sci., 2012, 5 (6), 7240-7253.
- S. Han, M. A. Kashfipour, M. Ramezani, and M. Abolhasani. Accelerating Gas-Liquid Chemical Reactions In Flow, Chem. Commun., DOI: 10.1039/d0cc03511d
- S. Han, K. Raghuvanshi, and M. Abolhasani, Accelerated Material-Efficient Investigation of Switchable Hydrophilicity Solvents for Energy-Efficient Solvent Recovery, ACS Sustainable Chem. Eng., 2020, 8, 3347-3356.
Background: We will discuss the principles and applications of a new class of highly flexible and versatile silicone elastomeric materials for 3D printing that can also undergo complex shape-morphing reconfiguration in external magnetic fields. These magneto-active soft actuators are fabricated by 3D printing with a new class of polydimethylsiloxane (PDMS) homocomposite capillary pastes (HCP-3DP), developed in our group . Instead of carbonyl iron , neodymium-iron-boron (NdFeB) particles are now embedded into silicone microbeads to render the resulting ink magnetically responsive as well as enhance residual magnetization without compromising its mechanical properties due to an additional phase.
Results: This new ultrasoft multiphasic material is biocompatible and has tunable mechanical characteristics, which make it suitable for biomedical and soft robotics applications. One of our goals has been to build responsive structures to be used as new bioscaffolds, biosensors and diagnostic tools. The results establish the good mechanical stability of the printed and cured structures. Optimal volume of the capillary bridging PDMS liquid that results in soft yet stretchable material capable of elongations of up to 300 % the original length has been formulated. Maximum possible actuation distance has been achieved by optimizing the HCP material moduli as well as the volume fraction of the magnetic material present in the ink. Spatial anisotropy in the architectures can be tuned to guide the direction of actuation.
Conclusions: We will show that we can fabricate 3D printed structures which are very soft, yet strong enough to withstand multiple cycles of expansion and contraction when actuated by external magnetic fields. This is achieved by optimal NdFeB particle loading into the silicone microbeads, optimal volume of liquid polymer precursor used for bridging the microbeads, and controlled degree of polymer crosslinking. The cyclic actuation of these objects can be modulated to mimic the pumping mechanism such as the one seen in heart and lung muscles, while their moduli can be tuned by design to match that of live tissues. The ink’s biocompatibility as well as tunable response to magnetic field actuation makes it suitable for building bioscaffolds with enhanced and controllable properties. Its ability to retain residual magnetization is a feature that makes it ideal for soft robotics applications.
- S. Roh, D. P. Parekh, B. Bharti, S. D. Stoyanov, O. D. Velev. 3-D Printing by Multiphase Silicone/Water Capillary Inks. Adv. Mater. 29:1701554, (2017).
- S. Roh, L.B. Okello, N. Golbasi, J. P. Hankwitz J. A.‐C. Liu, J. B. Tracy, O. D. Velev. 3D‐Printed Silicone Soft Architectures with Programmed Magneto‐Capillary Reconfiguration. Adv. Mater. Technol. 4:1800528, (2019).
Background: Conventional flask-based experimentation, while being easy to set up and convenient for multistep chemistries, pales in comparison with microscale flow synthesis strategies with regards to heat and mass transfer efficiency, real-time data acquisition throughput, and reproducibility. The performance disparity between the two modes of experimentation gets amplified with reactions of multivariable complex nature, such as that of the nascent inorganic lead halide perovskite quantum dots (LHP QDs). In this work, we develop an artificial intelligence (AI)- integrated microscale flow reactor for the characterization and optimization of the two-step synthesis and halide exchange of CsPbBr3 without an intermediate washing step. The modular microscale flow reactor utilizes a three-phase (gas-liquid-liquid) flow format coupled with passive self-synchronizing inline injection.
Results: The developed autonomous microscale flow reactor facilitated the exploration of the vast “chemical reaction universe” of the end-to-end manufacturing of inorganic LHP QDs consisting of 10 input and 2 output parameters. Furthermore, utilizing an AI-guided decision making algorithm, we demonstrate self-driven formulation discovery of high-quality CsPbX3 QDs for any desired peak emission energy.
Conclusions: The developed smart (i.e., AI-guided) LHP QD synthesizer in this work will accelerate adoption of the emerging concept of smart modular manufacturing in energy and chemical industries through seamless integration of discovery, synthesis optimization, and end-to-end material manufacturing stages. The autonomous QD synthesis strategy integrated with the modular microfluidic reactors provides an “all-in-one” platform capable of autonomous learning, optimization, and on-demand manufacturing of LHP QDs with optoelectronic properties precisely tuned for targeted applications in photonic devices, lighting/displays, organic synthesis (photocatalysis), and bioimaging. The autonomous modular QD manufacturing strategy can result in a paradigm shift in development and manufacturing of colloidal nanomaterials, while promoting energy and environmental sustainability.
- Abdel-‐Latif, K., Epps, R. W., Kerr, C. B., Papa, C. M., Castellano, F. N., & Abolhasani, M. (2019). Facile Room‐Temperature Anion Exchange Reactions of Inorganic Perovskite Quantum Dots Enabled by a Modular Microfluidic Platform. Advanced functional materials, 29(23), 1900712.
- Epps, R. W., Bowen, M. S., Volk, A. A., Abdel‐Latif, K., Han, S., Reyes, K. G., … & Abolhasani, M. (2020). Artificial Chemist: An Autonomous Quantum Dot Synthesis Bot. Advanced Materials, 2001626.
Background: Capacitive stress sensors have attracted significant interest due to their high sensitivity and low energy consumption and have been used in a variety of applications, including healthcare monitoring, human-machine interfaces, and electronic textiles. Capacitive stress sensors consist of a dielectric layer sandwiched between electrodes. Sensitivity and measurement range of capacitive sensors can be increased by decreasing or increasing the elastic modulus of the dielectric layer, which leads to a contradiction with each other. To solve this problem, a capacitive stress sensor based on dual-structure liquid metal elastomer foam (DSLMEF) is proposed. Inclusion of liquid metal in elastomer is used to tune the dielectric constant of the mixed material, which was shown to give the higher stress sensitivity.
Results: The DSLMEF is composed of a stiff elastomer slab (elastic modulus: ~655 kPa) and a soft liquid metal elastomer foam (LMEF, elastic modulus: ~7 kPa). Small stress ( 10 kPa) deforms the soft LMEF and the stiff elastomer slab at the same time. Using the DSLMEF as the dielectric layer, a capacitive stress sensor with high sensitivity (0.073 kPa-1), and large stress measurement range (200 kPa) is demonstrated.
Conclusions: We report a bioinspired soft multi-scale capacitive stress sensor based on dual structure liquid metal elastomer foam. The fabrication process of the sensor is easy to implement, low cost, and environment friendly. Compared with other capacitive soft stress sensors, this work achieves a better combination of sensitivity and measurement range. In addition, the high elastic modulus and high energy loss coefficient of DSLMEF also mimic the dermis of human skin, which can cushion objects from stress and strain. The development of the bioinspired soft multi-scale capacitive stress sensor based on DSLMEF has important scientific value and practical significance.
- Gao, Y.; Yu, L.; Yeo, J. C.; Lim, C. T. Flexible Hybrid Sensors for Health Monitoring: Materials and Mechanisms to Render Wearability. Adv. Mater. 2020, 32 (15), e1902133, DOI: 10.1002/adma.201902133.
- Hammock, M. L.; Chortos, A.; Tee, B. C.; Tok, J. B.; Bao, Z. 25th anniversary article: The evolution of electronic skin (e-skin): a brief history, design considerations, and recent progress. Adv. Mater. 2013, 25 (42), 5997-6038, DOI: 10.1002/adma.201302240.
- Kim, D. C.; Shim, H. J.; Lee, W.; Koo, J. H.; Kim, D. H. Material-Based Approaches for the Fabrication of Stretchable Electronics. Adv. Mater. 2020, 32 (15), e1902743, DOI: 10.1002/adma.201902743.
- Yang, J. Y.; Tang, D.; Ao, J. P.; Ghosh, T.; Neumann, T. V.; Zhang, D. G.; Piskarev, E.; Yu, T. T.; Truong, V. K.; Xie, K.; Lai, Y. C.; Li, Y.; Dickey, M. D. Ultrasoft Liquid Metal Elastomer Foams with Positive and Negative Piezopermittivity for Tactile Sensing. Adv. Funct. Mater. 2020, DOI: ARTN 2002611 10.1002/adfm.202002611.
Background: Microplastic and oil droplet contamination in freshwater and marine environments has increased dramatically with the boom of plastic and oil industries. Their accumulation in these environments has increased at a startling rate, and studies have shown their detrimental effects to these ecosystems [1, 2]. Current methods of removal such as filtration or centrifugation may be resource-heavy, time-consuming, and cost-prohibitive [2, 3]. We present a novel solution of using soft dendritic microparticles, or dendricolloids, as a physical method for adsorption and removal of particulates and droplets. With their spread-out nanofibrils and large surface area to volume ratio , dendricolloids can physically capture enormous amounts of contaminants from heavily polluted water. When fabricated from biodegradable polymers, they will further reduce the amount of post-processing pollution after waste collection as the dendricolloids themselves can degrade into more natural byproducts than non-biodegradable ones.
Results: Soft dendritic microparticles are formed through a liquid nanofabrication process in which polymer is precipitated and/or cross-linked in highly turbulent flow . This results in a hierarchical nanofibrous morphology, which endows the dendricolloids with large excluded volume and unusual networking capabilities. Our focus is on microplastic removal by using latex microbeads as a model system. In both pure and salt water conditions, we observe significantly larger latex bead adsorption with dendricolloids (~ 50× dendricolloids weight) when compared against amorphous chunks fabricated from the same polymer. After bead capture, the dendricolloid-microbead aggregates sediment rapidly. Preliminary work with oil emulsions shows significant oil adsorption using poly(lactic acid) dendricolloids, which can capture and remove both droplets and polymer beads.
Conclusions: This project will develop the foundational basis for understanding dendricolloids’ capture mechanisms with regards to their morphology and surface charge as well as their colloidal behavior before/after adsorption. On a practical level, the development of environmentally-benign microcleaners can be an effective solution for microplastics and oil pollutant cleanup while reducing resource consumption and limiting residual impact on the environment.
- J.R. Jambeck et al. “Plastic waste inputs from land into the ocean,” Science, 347, 768-771 (2015).
- P. Cherukupally et al. “Surface-engineered sponges for recovery of crude oil microdroplets from wastewater,” Nat. Sustain., 3, 136-143 (2020).
- R.L. Coppock et al. “A small-scale, portable method for extracting microplastics from marine sediments,” Environ. Pollut., 230, 829-837 (2017).
- Roh, S., Williams, A.H., Bang, R.S., Stoyanov, S.D., Velev, O.D. “Soft dendritic microparticles with unusual adhesion and structuring properties,” Nat. Mater., 18, 1315-1320 (2019).
Background: The packaging industry accounts for more than 26% of the total plastics produced worldwide, from which a staggering 90% is discarded as non-degradable waste after a single use . To limit such environmental damage, there is a rapidly growing industrial and scientific interest for alternatives of the petroleum based plastic packaging. In this work, biocomposite films based on an agarose (AG) polysaccharide matrix, robustly reinforced with soft dendrimeric microparticles (SDM), have been developed. The filler particles endow superior properties to the sustainable films such as mechanical toughness and hydrophobicity, which represent the most common challenges for biodegradable packaging materials. The reinforcing microparticles are made from biocompatible chitosan (CS) through a shear induced polymer precipitation technique.
Results: We found that the presence of a high interfacial area, due to the nanofiber coronas around the microparticles, makes significant improvements in the films’ properties even at low microparticles loading. These biopolymer films mechanically outperform most of the common present bio-based packaging materials that face major problems due to fragility and increased water uptake. Due to a dense network formation and potential intermolecular interactions between the SDM and the matrix, the films become hydrophobic upon the incorporation of SDM in the matrix. Other pivotal films properties, including swelling characteristics, oxygen and water vapor permeability were characterized. They all showed the presence of synergistic effects due to the SDM inclusion.
Conclusions: We have introduced a new class of sustainable films made from all-natural components that have superior or competing properties compared to the conventional petroleum-based packaging materials. The efficient and continuous fabrication process, the completely natural, sustainable, and biodegradable components as well as the excellent mechanical and optical properties of these films can easily lead to their use as single use packaging alternatives. We are currently investigating the fundamentals governing the components interactions and reinforcement mechanism.
- V. Talashuk, “Closing the loop on single-use food packaging.” [Online]. Available: https://www.ellenmacarthurfoundation.org/case-studies/closing-the-loop-on-single-use-food-packaging. [Accessed: 21-Apr-2020].
- S. Roh, A. H. Williams, R. S. Bang, S. D. Stoyanov, and O. D. Velev, “Soft dendritic microparticles with unusual adhesion and structuring properties,” Nature Materials, 2019.
Background: Wearable electronics have attracted great attention over the past decade due to their potential applications in health care and human-machine interfaces. Next generation wearable technology demands compatible energy sources that are soft, stretchable, and sustainable. Efforts have been made to develop energy harvesters that can convert human motion/ambient mechanical energy to electrical energy.[1-4] Triboelectric and piezoelectric harvesters are prominently used to convert mechanical energy to electrical energy.[1-4] Triboelectric harvesters have gained great popularity due to their relatively straightforward fabrication. They induce electrical current based on contact electrification (rubbing two surfaces) and electrostatic induction (oscillating the distance between charged surfaces).[1,3-5] Triboelectric harvesters generate high voltages and low currents. They require moisture free environments to enable contact electrification.[1,3-5] Piezoelectric harvesters, in contrast, require extensive fabrication techniques and loss in energy conversion when converted to flexible devices, as their fundamental materials are intrinsically hard and brittle.[1-3]
Results: We report a new approach to energy harvesting that utilizes liquid metals. These devices generate around 1mW/m2 by harnessing energy from mechanical motion. We have characterized the behavior of these devices as a function of a variety of parameters including material properties and physical deformation. The devices behave as expected and the response of the devices to deformation match a physics-based model.
Conclusions: The liquid metal based soft device generate electrical signal when deformed, which may be useful for energy harvesting as well as self-powered sensors. These devices can be used to monitor human activities thereby find many applications in wearable electronics, dynamic tactile surfaces, healthcare systems like rehabilitation and prosthetics.
- Zhou, M. et al. A review on heat and mechanical energy harvesting from human – Principles, prototypes and perspectives. Renewable and Sustainable Energy Reviews 82, 3582–3609 (2018).
- Sim, H. J. et al. Flexible, stretchable and weavable piezoelectric fiber: Flexible, Stretchable and Weavable Piezoelectric. Advanced Engineering Materials 17, 1270–1275 (2015).
- Yang, Y. et al. Liquid-Metal-Based SuperStretchable and Structure-Designable Triboelectric Nanogenerator for Wearable Electronics. ACS Nano 12, 2027–2034 (2018).
- Gao, S. et al. Wearable high-dielectric constant polymers with core–shell liquid metal inclusions for biomechanical energy harvesting and a self-powered user interface. Journal of Materials Chemistry A 7, 7109–7117 (2019).
- Wang, Z. L., Jiang, T. & Xu, L. Toward the blue energy dream by triboelectric nanogenerator networks. Nano Energy 39, 9–23 (2017).
Background: Ultralow density, high porosity, and high specific surface area of aerogels make them ideal candidates for diverse applications such as liquid and gas separation, acoustic shielding, tissue scaffold, fire retardancy and thermal
insulation1,2. Conventional aerogels are fabricated via solvent removal from a gelatinous network which is typically a time-consuming process involving multiple solvent exchanges1,3. Recently, nanofiber-based aerogels (NFAs) have started getting attention because of their straightforward and robust method of preparation. NFAs are prepared by freeze drying a dispersion of short nanofiber pieces (⁓40 μm) in a non-solvent4,5. Since the properties of aerogels can be further enhanced by combining the functionality of polymers with sol-gel processed materials, we present a sustainable approach to fabricate a mechanically robust aerogel from sol-gel electrospun Titania (TiO2) – Polyvinylpyrrolidone (PVP) nanofibers.
Results: Scanning electron microscopy (SEM) images of the electrospun TiO2-PVP nanofibers demonstrate the fiber diameters ranging from 100-250 nm, while energy dispersive X-ray (EDX) studies show that we have a homogeneous distribution of Titania in the structure of the electrospun nanofibers. Fourier-transform infrared spectroscopy (FTIR) analysis confirms the presence of Ti-O-Ti and Ti-OH bonds in the nanofibers. Finally, we prepared NFA from the TiO2-PVP electrospun nanofibers which has a low bulk density (⁓ 9 mg cm-1) and high porosity(>99%).
Conclusions: We have successfully fabricated a 3D, self-supportive aerogel structure from sol-gel electrospun TiO2-PVP nanofibers. Results from SEM, EDX, and FTIR demonstrates that we have a homogeneous distribution of TiO2 into the electrospun nanofibers. TiO2-PVP NFA can be used as a substrate for incorporation of different types of materials and making advanced hybrid aerogel with multiple applications. Moreover, it can be used as an antibacterial material and photocatalysis substrate.
- Soleimani Dorcheh, A. & Abbasi, M. H. Silica aerogel; synthesis, properties and characterization. J. Mater. Process. Technol. 199, 10–26 (2008).
- Pirzada, T., Ashrafi, Z., Xie, W. & Khan, S. A. Cellulose Silica Hybrid Nanofiber Aerogels: From Sol–Gel Electrospun Nanofibers to Multifunctional Aerogels. Adv. Funct. Mater. 30, 1907359 (2020).
- Lavoine, N. & Bergström, L. Nanocellulose-based foams and aerogels: Processing, properties, and applications. J. Mater. Chem. A 5, 16105–16117 (2017).
- Deuber, F. & Adlhart, C. From Short Electrospun Nanofibers to Ultralight Aerogels with Tunable Pore Structure. Chim. Int. J. Chem. 71, 236–240 (2017).
- Macwan, D. P., Dave, P. N. & Chaturvedi, S. A review on nano-TiO2 sol–gel type syntheses and its applications. J. Mater. Sci. 46, 3669–3686 (2011).
Background: As a new type of luminescent materials, fully-inorganic lead halide perovskite quantum dots (QDs) (CsPbX3; X=Cl,Br,I) have gained significant attention due to their outstanding optoelectronic properties, including near-unity photoluminescence quantum yield (PLQY), high color purity, narrow luminescence linewidth, and high mobility and diffusion of charge carriers. [1,2] However, one of the main barriers for industrial adoption of CsPbX3 QDs in next-generation, solution-processed photonic devices is the high content of lead (Pb2+) ions in their crystalline structure. To reduce the lead toxicity of QDs, while preserving the crystalline structure and stability, one synthetic approach is partial replacement of Pb2+ ions with a dopant impurity, resulting in less toxic perovskite QD with similar superior optoelectronic properties. Several studies have considered Mn2+ ions as the choice of the dopant impurity, since it has similar ionic radius and electron configuration to Pb2+ ions. Moreover, it has been demonstrated that with the doping of Mn2+ ions into the host colloidal nanocrystals, extra optical, electronic, and magnetic properties can be introduced. [3,4] Among all available fully-inorganic lead halide perovskite QDs, CsPbCl3 QDs is the most desirable host for Mn doping, as it possesses the highest bandgap energy. Thus, it has more favorable crystalline structure for efficient energy transfer from band-edge excitons to Mn internal d-d states. [3,4] The main common method for the doping of Mn2+ ions into the CsPbCl3 QDs is reported as one-pot, hot-injection method. [3,4] However, the flask-based, one-pot synthesis technique suffers from several major limitations, including batch-to-batch variability, uncontrolled and irreproducible heat and mass transfer rates, and prolonged experimental times. [5,6] Microfluidic material synthesis strategy can provide a facile approach for the accelerated and controlled synthesis, screening, in-situ characterization, and optimization of the Mn-doped CsPbCl3 QDs as well as fundamental studies of the doping mechanism of Mn2+ ions into the CsPbCl3 QDs. In this study, we employ the previously developed fully-automated modular microfluidic platform  to: (i) accurately control the Mn-doping incorporation ratio in the host QDs, thereby tuning the emission color of the doped perovskite QDs from blue-violet to red-orange region, and (ii) understand the fundamental doping mechanism of the Mn2+ ions into the CsPbCl3 QDs.
Results: A modular flow chemistry platform was developed and utilized for accelerated in-flow studies of Mn doping of CsPbCl3 QDs. The transient process of doping the Mn2+ ions into the host CsPbCl3 QDs was monitored through a temporal in-situ spectral characterization enabled by a fully automated modular microfluidic platform. The Mn2+ incorporation ratio and the emission color were tuned in-flow through a continuous flow dilution strategy. Different inflow-adjusted concentrations of Mn precursor enabled precisely controlled double emission color tunability. The kinetics of the Mn doping process was obtained at different Mn:Pb ratios. Furthermore, we systematically studied the effect of reaction solvent and ligand concentration on the extent and kinetics of the cation doping process.
Conclusions: The developed microscale flow synthesis platform enabled precise, on-demand tuning of the Mn doping and thereby the emission color of fully inorganic lead halide perovskite QDs from blue-violet to red-orange. The in-situ obtained photoluminescence and absorption spectra of Mn-doped CsPbCl3 QDs indicate a fast kinetics for the doping of Mn2+ ions into the lattice of the host QDs.
- Loredana Protesescu, Sergii Yakunin, Maryna I. Bodnarchuk, Franziska Krieg, Riccarda Caputo, Christopher H. Hendon, Ruo Xi Yang, Aron Walsh, and Maksym V. Kovalenko (2015). Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, and I): Novel Optoelectronic Materials Showing Bright Emission with Wide Color Gamut. Nano Letter, 6: 3692–3696.
- Georgian Nedelcu, Loredana Protesescu, Sergii Yakunin, Maryna I. Bodnarchuk, Matthias J. Grotevent, and Maksym V. Kovalenko (2015). Fast Anion-Exchange in Highly Luminescent Nanocrystals of Cesium Lead Halide Perovskites (CsPbX3, X = Cl, Br, I). Nano Letter, 8: 5635–5640.
- David Parobek, Benjamin J. Roman, Yitong Dong, Ho Jin, Elbert Lee, Matthew Sheldon, and Dong Hee Son (2016). Exciton to-Dopant Energy Transfer in Mn-Doped Cesium Lead Halide Perovskite Nanocrystals. Nano Letter, 16: 7376−7380.
- Wenyong Liu, Qianglu Lin, Hongbo Li, Kaifeng Wu, István Robel, Jeffrey M. Pietryga, and Victor I. Klimov (2016). Mn2+ -Doped Lead Halide Perovskite Nanocrystals with Dual-Color Emission Controlled by Halide Content Journal of the American Chemical Society (JACS), 138: 14954−14961.
- Robert W. Epps, Kobi C. Felton, Connor W. Coley, and Milad Abolhasani (2017). Automated microfluidic platform for systematic studies of colloidal perovskite nanocrystals: towards continuous nano-manufacturing. Lab on a Chip, 17: 4040–4047.
- Kameel Abdel-Latif, Robert W. Epps, Corwin B. Kerr, Christopher M. Papa, Felix N. Castellano, and Milad Abolhasani (2019). Facile Room-Temperature Anion Exchange Reactions of Inorganic Perovskite Quantum Dots Enabled by a Modular Microfluidic Platform. Advanced Functional Materials, 29: 1900712.
Background: Metal-mediated chemical reactions have been a vital area of research for over a century due to their utility in pharmaceutical and organic synthesis. Poly(methylhydrosiloxane) (PMHS) has been demonstrated to efficiently reduce palladium (Pd), anchor reduced Pd to the polymer backbone, and act as an active volumetric Pd catalyst for cross-coupling reactions such as Suzuki Miyaura. Current methods of performing cross-coupling reactions in flow generally involve either homogeneous or heterogeneous catalysis; homogeneous catalysis primarily uses expensive air-sensitive ligands that require a catalyst recovery step, whereas conventional heterogeneous catalysis utilizes complex, multi-step catalyst immobilization on a solid substrate (e.g., silica particles). [REF] Heterogeneous catalysis does not require recovery, but it notoriously has lower reproducibility, accessibility, and selectivity than homogeneous catalysis. Ideally, a hybrid catalyst would be tunable (chemical affinity, temperature, catalytic metal, etc.) with no need for recovery but also have high selectivity and accessibility.
Results: In this work, we used a tri(ethylene glycol) divinyl ether (VTEG) moiety as a hydrophilic crosslinker to make PMHS/VTEG elastomeric particles for utilization in a packed bed reactor for continuous flow, carbon-carbon cross-coupling reactions. In order to systematically study the performance and activity of the gel-supported catalysts under different process conditions, we developed and utilized an automated flow chemistry platform integrated with an in-line high performance liquid chromatography coupled with an automatic sampling and injection module. At 10-min residence times, 40% yield was obtained for an exemplary Suzuki-Miyaura cross-coupling reaction. Furthermore, we observed a 50% yield increase and improved start-up times with VTEG cross-linker compared to a nonpolar hexadiene crosslinker.
Conclusions: The developed flow chemistry platform can be readily adapted for accelerated screening and process optimization of polymer-based catalysts. The PMHS/VTEG polymer network was demonstrated to improve catalytic performance and activity as a continuous, ligand-free C-C cross-coupling low-leaching catalyst.
- Chen, Xiao, Keary M. Engle, Dong-Hui Wang, and Jin-Quan Yu (2009). Palladium(II)-Catalyzed C-H Activation/C-C Cross Coupling Reactions: Versatility and Practicality. J. Am. Chem. Soc., 48, 5094-5115.
- Stibingerova, Iva, Svatava Voltrova, Sarka Kocava, Matthew Lindale, and Jiri Srogl (2016). Modular Approach to Heterogeneous Catalysis. Manipulation of Cross-Coupling Catalyst Activity. Org. Lett., 18: 312-315.
Background: Hydrogels are hydrophilic polymer networks, which contain water and electrolytes. However, single network hydrogels have weak mechanical strength. Double network hydrogels can overcome this limitation . By adding another natural polymer network (such as alginate), when the hydrogel stretches, the secondary polymer network dissipates energy through sacrificial bonds that fracture during elongation. In contrast, the first polymer network remains intact. The double network hydrogel can be toughened further by crosslinking between carboxylic groups in alginate and di- or trivalent metal ions. With this interaction, hydrogel stiffness can be tuned locally. Previously, ionoprinting with Cu2+ was employed to increase stiffness locally to actuate the hydrogels . However, this method can increase stiffness only at the surface of the gel. Here, we used metal redox reactions between Bi particles and Ag+ to tune hydrogel stiffness locally. By controlling particle distribution and reaction time, we produce various types of locally tuned
Results: We fabricated polyacrylamide/alginate double network hydrogels embedded with Bi particles. The hydrogels were dipped into AgNO3 solution to initiate a reaction between Bi and Ag+. Bi particles are ionized into Bi3+, which crosslinks with carboxylic groups (COO–) of the alginate. The crosslinking bonds stiffen the hydrogels, leading to an increase of the dynamic modulus by two-fold. The local strain level within the hydrogel was mapped using digital image correlation (DIC). By correlating the particle distribution with the local strain level, we confirmed that Bi3+ produced on the Bi particle surfaces caused a heterogenous local strain level in the gel. Tuning the dipping time in AgNO3 solution leads to the gradient of modulus in the hydrogels. We mapped dynamic gradient modulus by cutting the hydrogels into different parts, which were measured separately. Modulus gradient hydrogels from the reactions can act as a bridge between soft and hard materials. This modulus gradient was similar to that of cartilage. With Bi particles settling in pre-gel solution, the hydrogel was found to bend toward the side with high particle density due to the difference in modulus within the hydrogels. As an application, we confirmed Ag particles generated by the redox reaction could be used as antibacterial agents. Bacterial
inhibition zone increased with increasing concentration of AgNO3.
Conclusions: Double network hydrogel with Bi particles was designed to locally tune its stiffness by a redox reaction between Bi and Ag+. Our research expands the understanding of how metal redox reaction happens in hydrogels.
- Sun, Jeong-Yun, Xuanhe Zhao, Widusha R. K. Illeperuma, Ovijit Chaudhuri, Kyu Hwan Oh, David J. Mooney, Joost J. Vlassak, and Zhigang Suo (2012). Highly Stretchable and Tough Hydrogels. Nature, 489: 133–136.
- Palleau, Etienne, Daniel Morales, Michael D. Dickey, and Orlin D. Velev (2013). Reversible Patterning and Actuation of Hydrogels by Electrically Assisted Ionoprinting. Nat. Commun., 4: 2257.