2019 Schoenborn Graduate Research Symposium

Sponsored by Praxair, Inc.

January 28, 2019

Continental Breakfast 8:15 – 8:45 AM

Opening Remarks 8:45 AM

Oral Presentations & Poster Session

MATERIALS ORAL PRESENTATIONS

8:50-10:30 AM

8:50 AM
Amber Hubbard
Background: Folding and bending are common phenomena found in nature, prominent in the formation of structures ranging from plants to proteins. In addition, research has shown that materials can be made to autonomously change their shape from planar materials into functional, three-dimensional objects. [1] By harnessing this potential of man-made materials, self-folding structures have applications in everything from biomedical to aerospace engineering. Different materials are chosen for these applications based on their mechanical properties and the variety of external stimuli with which they can be activated. The work presented here implements both rigid and soft polymer materials to generate devices ranging from microgrippers to artificial muscles.

Results: A variety of polymers including thermoplastics, hydrogels, and elastomers are presented here as viable materials for stimuli-responsive devices. Thermoplastics implemented herein are strained polystyrene and poly(methyl methacrylate). Material strain is locally released by exposure to an infrared light or heat gun for controlled heating above the glass transition temperature (Tg), resulting in controlled out-of-plane folding and bending of the sheets. [2-4] Similar out-of-plane movement is realized with flexible materials by generating polyampholyte hydrogel/elastomer composites. The composites are bound to a fabric interphase of glass fiber fabric acting as an interfacial compatibilizer between the gels. [5-6] By exposing the laminate composites to organic solvents and salt solutions, the gels selectively swell or de-swell resulting in controlled curvature.

Conclusions: Thermoplastics, rigid polymer materials, are shown transforming from planar sheets into complex geometries such as spheres or microgrippers; these microgrippers demonstrate the ability to withstand loads >24,000 times their own mass. Hydrogel and elastomeric composites, flexible polymer materials, are shown transforming from planar laminates into curved structures for applications such as actuators or artificial muscles. These composites demonstrate a synergistic increase in Young’s modulus of the composite (~1.2 GPa) as compared to the individual gels (~0.1-1.3 MPa). Meanwhile, the composites exhibit a low bending modulus (~7 MPa), prompting its application as an artificial muscle with an actuation stress ~20% that of human skeletal muscle.

References:

  1. Liu, Ying, Jan Genzer, and Michael D. Dickey (2015). 2D or not 2D: Shape Programming polymer sheets. Prog. Polym. Sci., 52: 79-106.
  2. Liu, Ying, Julie K. Boyles, Jan Genzer, and Michael D. Dickey (2012). Self-folding of polymer sheets using local light absorption. Soft Matter, 8: 1-6.
  3. Hubbard, Amber M., Russell W. Mailen, Mohammed A. Zikry, Michael D. Dickey, and Jan Genzer (2017). Controllable Curvature from planar polymer sheets in response to light. Soft Matter, 13: 2281-2412.
  4. Hubbard, Amber M., Duncan S. Davis, Michael D. Dickey, and Jan Genzer (2018). Shape memory polymers for self-folding via compression of thermoplastic sheets. J. Appl. Polym. Sci., 135: 46889.
  5. Huang, Yiwan, Daniel R. King, Tao Lin Sun, Takayuki Nonoyama, Takayuki Kurokawa, Tasuku Nakajima, and Jian Ping Gong (2017). Energy-dissipative matrices enable synergistic toughening in fiber reinforced soft composites. Adv. Funct. Mater., 27: 1605350.
  6. King, Daniel R., Tao Lin Sun, Yiwan Huang, Takayuki Kurokawa, Takayuki Nonoyama, Alfred J. Crosby, and Jian Ping Gong (2015). Extremely tough composites from fabric reinforced polyampholyte hydrogels. Mater. Horiz., 2: 584-591.

9:10 AM
Yeongun Ko
Background: Polymer brushes comprise densely grafted polymer chains on surfaces, which possess high stability and high concentration of reactive centers per unit area compared to physisorbed polymer film. Polymer brushes are employed in many applications, including anti-fouling surfaces, cell adhesive surfaces, responsive surfaces, low-friction surfaces, etc. Recently, researchers reported that charged (or chargeable) polymer brushes can be degrafted from substrate while incubated in buffer solutions. [1]

Results: Based on previous experiments conducted in our group [2,3] and by others [4], we assume that chain degrafting results from the hydrolysis of Si-O groups in head-group of the initiator and/or the ester groups in main body of the initiator. We study the stability of strongly and weakly charged polymeric grafts derived from poly(2-dimethyl aminoethyl methacrylate) (PDMAEMA). We employ surface-initiated atom transfer radical polymerization to prepare polymer assemblies featuring gradients of grafting density and molecular weight. The degree of permanent charge in strong electrolytes is adjusted by reacting PDMAEMA with methyl iodide to a given extent. We interrogate the stability of those surface-grafted polymers under various pH at ionic strength values in solution. Swelling of the brush due to electrostatic charging in aqueous media (adjusted by varying pH and degree of quaternization) generates tension along the grafted macromolecular backbone. Such tension focuses at the bottom-most section of the polymer brush close to the substrate. This lowers the activation energy for breaking labile chemical bonds either in the initiator itself or the head-group chemistry of the initiator that links the initiator to the underlying substrate. Weak polyelectrolyte brushes are more stable than strong polyelectrolyte grafts. The stability of brushes decreases with increasing pH and decreasing ionic strength of surrounding solution.

Conclusions: The degrafting kinetics is largely affected by mechanical forces acting on the initiators. The force depends on the grafting densities of the brush and the degree of charges along the macromolecule.

References:

  1. Tugulu, Stefano and Klok, harm-Anton (2008). Stability and Nonfouling Properties of Poly(poly(ethylene Glycol) Methacrylate) Brushes under Cell Culture Conditions. Biomacromolecules, 9: 906–912.
  2. Bain, Erich D., Dawes, Keith, Özçam A. Evren, Hu, Xinfang, Gorman, Christopher B., Šrogl, Jiří and Genzer, Jan (2012). Surface-Initiated Polymerization by Means of Novel, Stable, Non-Ester-Based Radical Initiator. Macromolecules, 45: 3802-3815.
  3. Galvin, Casey J., Bain, Erich D., Henke Adam and Genzer Jan (2015). Instability of Surface-Grafted Weak Polyacid Brushes on Flat Substrates. Macromolecules, 48: 5677-5687.
  4. Melzak, Kathryn A., Yu, Kai, Bo Deng, Kizhakkedathu, Jayachandran N. and Toca-Herrera, José L (2015). Chain Length and Grafting Density Dependent Enhancement in the Hydrolysis of Ester-Linked Polymer Brushes. Langmuir, 31: 6463-6470.

9:30 AM
Sabina Islam
Background: Waterborne polymers have enormous potential as an environment-friendly substitute of organic solvent-borne polymers, which are one of the major sources of harmful VOC volatile organic compound) emission. Aromatic polyesters are one of the most widely used classes of coating polymers with superior mechanical, optical, and processing properties. Driven by environmental and legislative pressures, the specialty polyesters were rendered water-dispersible by functionalizing the polymer backbone with ionic monomers. Since these polyesters are designed to be used as waterborne dispersions, understanding their colloidal interactions in dispersions is critical for their application.

Results: By using a range of commercially available water-dispersible sulfopolyesters as a model system, we investigated the relationship between their molecular composition, colloidal interactions, and phase equilibria. As a result of being partially water-soluble, these polyesters form self-assembled nanoaggregates (20 ~ 50 nm) in water without the need for additional stabilizer(s). These nanoaggregates are composed of hundreds of polymer molecules, where their aggregation number is determined by the composition, ionic groups and molecular weight of the polymers. [1] By using static, dynamic, and electrophoretic light scattering, we present a model for nanoaggregate formation in water based on the critical surface charge density of these nanoparticles. Since the ultimate goal of developing such waterborne system is to apply them in films and coatings, we also explored how these films interact with water by forming nanofilms of brilliant structural colors. To test the structure and properties of the dried films, we deposited sessile water drops on the films which lead to partial dispersion and evaporation-induced “coffee ring” formation. We further characterized this new class of coffee ring phenomena as “coffee ring erosion” and demonstrated that such water-damage property is governed by the ionic composition of the polyesters. Additionally, we showed that the water resistivity and integrity of the coatings can be significantly improved by incorporating rapid thermal-curing polymer components of these films.

Conclusions: This research enabled better understanding of the fundamental mechanism of film formation by waterborne polymer nanoparticles. Such fundamental understanding of colloidal interactions could be used to efficiently control and improve the colloidal stability and film-formation ability of these polyesters. Therefore, this study may enable the design of novel high-performance volatile solvents-free and surfactant-free waterborne dispersion systems.

References:

  1. Islam, S., Inglefield, D. L. & Velev, O. D. (2018). Revisiting the colloidal fundamentals of water-dispersible polyesters: Interactions and self-assembly of polymer nanoaggregates in water. Soft Matter, 14: 2118–2130.

9:50 AM
Jason Miles
Background: Many chemical and biological processes rely strongly on surface interactions, such as wettability and adhesion. The use of chemical and surface energy gradients allows for a wide range of parameters to be evaluated on a single substrate. This high-throughput approach facilitates faster screening and discovery of materials and surface phenomena. Surface-bound gradients can be used to direct dynamic phenomena on surfaces, such as the motion of water droplets [1] or locomotion of cells [2]. The gradient surfaces are most commonly formed using self-assembled monolayers (SAMs) or grafted polymer assemblies [3]. A successful method for this application must result in a gradient, which is easy to fabricate, should provide sufficient control over the profile of the gradient, and should allow for specific chemistries to be placed on the surface to be used for the appropriate application [4].

Results: We have fabricated wettability gradients on hard substrates by a simple, two-step procedure that permits precise tuning of the gradient profile. This process involves the deposition of homogeneous silane SAMs followed by the formation of a surface coverage gradient through the selective removal of silanes from the substrate. Removal of silanes from surfaces is achieved by using tetrabutylammonium fluoride (TBAF) which cleaves selectively the Si-O bond that holds the silane to the surface. The kinetic of degrafting have been modeled by using a series of first order rate equations, based on the number of attachment points broken to remove a silane from the surface. Degrafting of mono-functional silanes exhibits a single exponential decay in surface coverage; however, there is a delay in degrafting of tri-functional silanes due to the presence of multiple attachment points. Uniformity in the initial silane SAMs has a large effect on the rate of degrafting, with ordered SAMs following the first order rate equations and SAMs featuring aggregate structures deviating from this behavior.

Conclusions: Wettability and chemical gradients can be achieved by selectively degrafting homogeneous silane SAMs from the substrate. The gradient profile can be tuned by varying the degrafting temperature and time. We observe a relatively homogenous coverage of silane throughout the process (i.e. without the presence of islands or holes), providing a more uniform surface compared to additive approaches of gradient formation. We design and form linear gradients in silane coverage to demonstrate the reproducibility and tuneability of this approach.

References:

  1. Chaudhury, M. K. & Whitesides, G. M. How to make water run uphill. Science 20, 38–59 (2013).
  2. Lee, E. J., Chan, E. W. L., Luo, W. & Yousaf, M. N. Ligand slope, density and affinity direct cell polarity and migration on molecular gradient surfaces. Rsc Adv. 4, 31581–31588 (2014).
  3. Genzer, J. & Bhat, R. R. Surface-bound soft matter gradients. Langmuir 24, 2294–2317 (2008).
  4. Bhat, R. R., Fischer, D. A. & Genzer, J. Fabricating planar nanoparticle assemblies with number density gradients. Langmuir 18, 5640–5643 (2002).

MATERIALS, CATALYSIS, AND KINETICS ORAL PRESENTATIONS

10:50 AM-12:30 PM

10:50 AM
Dennis Lee
Background: It has been about a century since the first large scale production of sulfur mustard (HD) as a chemical warfare agent appeared during World War I in 1917. Unfortunately, more variety of chemical weapons are still posing an increasing threat not only to military population but also to civilian. Activated carbon, for instance, is one of the commercially available adsorbents to physically remove such toxic chemicals. However, degrading adsorptive performance as used and concentrated hazards within the carbon filter limit the use of the activated carbon-based materials for long-lasting chemical protection. Therefore, developing novel materials, which are capable of selectively accumulating and destructing the hazardous chemicals, and integrating them into functional systems are highly required to resolve the problems present in the current technology [1-3].

Results: In this study, we fabricate non-woven textiles functionalized with highly porous metal-organic frameworks (MOFs), composed of Al(OH)(CO2)2 metal clusters interconnected with porphyrin linkers, and primarily investigate their adsorptive and catalytic performance for removing 2-chloroethyl ethyl sulfide (CEES), a simulant of HD. More specifically, we found an optimized co-solvent system facilitating a lower temperature conversion process from Al2O3 thin film deposited via atomic layer deposition (ALD) on fibers into Al-PMOF film. An optimized ratio of DMF and water solvent system not only enables a MOF film formation with good quality, but also remains the integrity of polymeric fibers during the MOF synthesis, which cannot be facilitated by the conventional MOF growth approach. We also observed substantially enhanced adsorptive capacity (14.2 vs 6 mmol/gMOF) and faster photo-catalytic degradation performance (t1/2=6 min by 0.26 mgMOF on fiber vs t1/2=16 min by 1.2 mgMOF) for CEES using MOF on fibers compared to MOF powder.

Conclusions: We for the first time demonstrated a water-stable 2D Al-PMOF integration into polymeric fiber systems, identified the MOF growth mechanism, and confirmed remarkably improved sequestration performance of MOF/fiber composites for CEES, a vesicant simulant, in comparison with that of MOF powder on a per gram of MOF basis. In addition, we found the Al-PMOF/fiber textiles can be characterized as a reversible colorimetric pH sensor and an adsorbent for a selective removal of chloroform contaminant over water.

References:

  1. Lee, Dennis, et al (2017) Catalytic “MOF-Cloth” Formed via Directed Supramolecular Assembly of UiO-66-NH2 Crystals on Atomic Layer Deposition-Coated Textiles for Rapid Degradation of Chemical Warfare Agent Simulants. Chemistry of Materials, 29: 4894-4903.
  2. Lee, Dennis, et al (2017) UiO-66-NH2 Metal–Organic Framework (MOF) Nucleation on TiO2, ZnO, and Al2O3 Atomic Layer Deposition-Treated Polymer Fibers: Role of Metal Oxide on MOF Growth and Catalytic Hydrolysis of Chemical Warfare Agent Simulants. ACS Applied Materials & Interfaces, 9: 44847-44855.
  3. Lee, Dennis, et al (2018) Toxic Organophosphate Hydrolysis Using Nanofiber-Templated UiO-66-NH2 Metal–Organic Framework Polycrystalline Cylinders. ACS Applied Materials & Interfaces, 10: 25794-25803.

11:10 AM
Seif Yusuf
Background: Oxidative dehydrogenation (ODH) of ethane represents a promising alternative to steam cracking for the production of ethylene that can result in a higher ethane conversion, lower energy consumption and lower CO2/NOx emissions. Conventional ODH, however, suffers from challenges in process safety, controllability, and high capital cost due to the needs to co-feed gaseous oxygen with ethane. In chemical looping ODH (CL-ODH), ethane is partially oxidized by active lattice oxygen in a redox catalyst, producing ethylene and water. The reduced redox catalyst is subsequently re-oxidized with air in a separate reactor prior to the initiation of another redox cycle. Such a cyclic redox scheme eliminates the needs for cryogenic air separation as well as O2 co-feeding. Previous studies have shown that Na2WO4 promoted Mg6MnO8 was an effective catalyst for the CL-ODH of ethane1,2. This study focuses on the nature of the Na-W promoters and its effect on the Mg6MnO8 based redox catalysts for the CL-ODH of ethane.

Results: Na-W promoted Mg6MnO8 redox catalysts with various Na:W molar ratios were able to improve ethylene yield as compared to thermal cracking. In order to optimize the ethylene yield, a balance between Na and W was needed. Na is needed to increase ethylene yields but is only retained when W is present but an excess of W leads to a decrease in ethylene yield. X-ray Photoelectron Spectroscopy (XPS) and Low Energy Ion Scattering (LEIS) analyses indicate that the sodium tungstate promoter suppresses the amount of surface manganese and reduces the average manganese oxidation state. In-Situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and Methanol Temperature Programmed Surface Reaction (TPSR) studies indicated that the NaW promoter inhibits the activation of reactant molecules on the surface of the redox catalyst. 18O-16O exchange experiments indicate that the NaW promoter reduces the rate of oxygen exchange in the Mg6MnO8 redox catalyst.

Conclusions: Design and optimization of effective redox catalysts are crucial for successful development of CL-ODH. A previous study indicates that CL-ODH can reduce the CO2 and NOx emissions for ethylene production by as high as 82%3. The current study reports on the nature and effect of a promoter that results in a highly effective redox catalyst for the ODH of ethane. The findings are useful to guide the design of novel redox catalysts for CL-ODH.

References:

  1. Neal, L. M.; Yusuf, S.; Sofranko, J. A.; Li, F.(2016) Oxidative Dehydrogenation of Ethane: A Chemical Looping Approach Energy Technology 4 (10), 1200–1208.
  2. Yusuf, S.; Neal, L. M.; Li, F. (2017) Effect of Promoters on Manganese-Containing Mixed Metal Oxides for Oxidative Dehydrogenation of Ethane via a Cyclic Redox Scheme.
  3. Haribal, V. P.; Neal, L. M.; Li, F. (2017) Oxidative Dehydrogenation of Ethane Under a Cyclic Redox Scheme – Process Simulations and Analysis Energy, 119, 1024–1035.

11:30 AM
Charles McGill
Background: A mechanism of pericyclic reactions involving metaphosphoric acid has been developed for the dehydration of acetic acid to form ketene using an organophosphate catalyst. Ketene is an important and highly reactive chemical precursor, including for the production of acetic anhydride. Dehydration of acetic acid with organophosphate catalysts has been studied and documented in patents.1,2 The only elementary reaction mechanism of this sort that has been published was a study of catalysis by P2O3/P2O5 was published by Sebbar et al.3, addressing the reaction as a primarily radical reaction mechanism. This current work approaches the dehydration of acetic acid using triethylphosphate as the catalyst and considering only pericyclic reactions and demonstrates that the reaction proceeds through formation of the reactive intermediate metaphosphoric acid (HPO3).

Results: Stable intermediate species and transition-state structures included in the proposed mechanism were simulated using computational quantum chemistry software (Gaussian). Initial structure exploration and optimization were carried out using DFT methods at a B3LYP/6-31G(d,p) level of theory. Refined structures and their thermochemical properties were calculated with the composite method CBS-QB3. Rates of reaction were calculated using the Mesmer master equation code. Experimental testing of kinetics was carried out using a flow reactor, sampled by molecular-beam mass-spectrometry. Reaction conversions were predicted from the proposed reaction pathways using Chemkin Pro and compared against the experimental conversions. Eight potential pathways were considered, but only one pathway demonstrated conversions of the magnitude observed in experiment. The significant pathway involved a catalytic cycle with a rate-limiting-step of dehydrating phosphoric acid into HPO3.

Conclusions: The model-predicted conversion agreed with experimental data within an order of magnitude over a range of reaction conditions without requiring any parameter fitting. This validates the proposed elementary reaction mechanism involving only pericyclic reactions.

References:

  1. Padmanabhan, N.; Deshpande, P. K.; Kuloor, N. R. Catalytic Cracking of Acetic Acid to Acetic Anhydride. Ind. Eng. Chem. Process Des. Dev. 1968, 7 (4), 511–516.
  2. Arnold, D.; Bartels, J.; Lenzmann, H.; Jacobsen, G.; Wendt, H.; Stoltenberg, M. Process for the Preparation of Ketene. U.S. Patent No. 4455439, 1984.
  3. Sebbar, N.; Appel, J.; Bockhorn, H. Ketene Formation Through Interaction Reactions During P2O3/P2O5/CH3C(=O)OH Pyrolysis. Combust. Sci. Technol. 2016, 188 (4–5), 745–758.

11:50 AM
Yunfei Gao
Background: Chemical looping oxidative dehydrogenation (CL-ODH) of ethane utilizes a transition metal oxide based oxygen carrier, also known as redox catalyst, to convert ethane into ethylene under an autothermal cyclic redox scheme. Unlike conventional ODH, CL-ODH eliminates the needs for gaseous oxygen, rendering a potentially more efficient process. We reported Li-promoted La0.6Sr1.4FeO4 (LaSrFe) as an effective redox catalyst for CL-ODH. However, its oxygen capacity is relatively low (<0.3 wt%) [1].

Results: The current study investigates Na or K as a promoter and finds similar promotional effects: alkali promoter notably increases the selectivity of the pristine LaSrFe but suppresses its oxygen carrying capacity. The K-promoted LaSrFe was further characterized with Low Energy Ion Scattering (LEIS) and 18O2-exchange experiments. LEIS analysis indicates that the surface layer contained exclusively of K2O whereas 18O2-exchange experiments confirm that the oxygen surface exchange and incorporation rates are significantly lower for K-promoted LaSrFe. Meanwhile, co-promotion of Li and K achieved up to 86% ethylene selectivity and 60% ethane conversion while maintaining an oxygen capacity of 0.65 wt%. This enhanced performance was ascribed to the higher oxygen capacity of K substituted LaSrFe and the higher selectivity induced with Li promotion. In addition to LaSrFe, other oxide substrates within the same Ruddlesden- Popper structure family were also investigated to determine the general effects of A-site and B-site compositions of the oxide substrate on the ODH performance of the alkali promoted redox catalysts.

Conclusions: Li and K co-promoted LaSrFe resulted in 86% ethylene selectivity and 60% ethane conversion while maintaining an oxygen capacity of ca. 0.65 wt%. These findings not only offer mechanistic insights on alkali metal promoted LaSrFe for CL-ODH of ethane but also resulted in promising redox catalysts for this novel process scheme.

References:

  1. Yunfei Gao, Luke M. Neal and Fanxing Li (2016). Li-Promoted LaxSr2–xFeO4−δ Core–Shell Redox Catalysts for Oxidative Dehydrogenation of Ethane under a Cyclic Redox Scheme. ACS Catalysis. 6, 7293–7302.

12:10 PM
Vasudev Pralhad Haribal
Background: Among the various processes for sustainable hydrogen generation, solar thermochemical water-splitting based on redox cycles of metal oxides represents an attractive approach. This can be extended to CO production using CO2. A key challenge for these processes is the high temperature needed for thermal decomposition of the metal oxide (›1200 °C) [1]. In addition, the need to balance the oxygen release and H2O/CO2 splitting properties of metal oxides often leads to low conversions. A hybrid solar-redox redox process for cogeneration of hydrogen/CO and liquid fuels using methane and solar energy operates at lower temperatures and higher H2O/CO2 conversions [2]. In such a process, a reduced metal-oxide based redox catalyst is used to split water/CO2, producing concentrated hydrogen/CO. The resulting (oxidized) redox catalyst is subsequently used to partially oxidize methane (POx step), forming syngas for Fischer-Tropsch synthesis. Over 58% syngas yield in the POx step and 77% steam to hydrogen conversion in the water-splitting step are achieved in a layered reverse-flow reactor configuration using La0.8Sr0.2FeO3-δ (LSF) supported Fe3O4 as the redox catalyst [2]. Further improvements in syngas yield and steam-to-hydrogen/CO2-to-CO conversion at reduced temperatures are desirable to improve the overall process efficiency.

Results: Density Functional Theory (DFT) calculations reveal that the equilibrium oxygen partial pressure (PO2) and oxygen vacancy formation energy (ΔEvacancy) of perovskite-structured BaMnxFe1-xO3-δ are significantly different from those of FeO and MnO, and can be manipulated by varying the Fe:Mn ratios in the B-sites. These studies indicate that BaMn0.5Fe0.5O3-δ possesses desirable properties for the hybrid solar-redox scheme. Fluidized bed experiments demonstrate over 90% steam conversion in the water-splitting step and higher than 90% syngas yield in the methane POx step [3]. Further, low temperature operation is possible using modified ceria, which allows for integration of the industrial waste heat. Efficient CO production is an attractive route to CO2-utilization and can boost sustainable downstream chemical production via carbonylation [4]. ASPEN Plus® simulations indicate the potential to obtain higher efficiencies than the state-of-the-art hydrogen/CO and liquid fuel production processes with lower CO2 emissions.

Conclusions: We proposed and validated a rational strategy to optimize transition metal oxide based redox catalysts for water/CO2 and syngas generation via a hybrid solar redox scheme.

References:

  1. W. C. Chueh et al. (2010), High-Flux Solar-Driven Thermochemical Dissociation of CO2 and H2O Using Nonstoichiometric Ceria, Science, 330:1797–1801.
  2. F. He and F. Li (2015), Perovskite promoted iron oxide for hybrid water-splitting and syngas generation with exceptional conversion, Energy Env. Sci, 8:535–539.
  3. Haribal, V. P., He, F., Mishra, A., & Li, F. (2017). Iron‐Doped BaMnO3 for Hybrid Water Splitting and Syngas Generation. ChemSusChem, 10(17), 3402-3408.
  4. Haribal, V.P., Paulus, C, Shafiefarhood, A., & Li, F (2018). Modified Ceria for Low-Temperature Methane Partial Oxidation and Water/CO2 splitting, AIChE Annual Meeting 2018, Pittsburgh, PA

 

Lunch 12:30-2:20 PM

 

1:10 PM
Announcement of Vivian T. Stannett Fellow Award
1:20 PM
Announcement of Praxair Exceptional Teaching Assistant Award
1:35 PM
Keynote Address: Dr. David Sehgal, FujiFilm Diosynth Biotechnologies

 

COMPUTATION AND BIOTECHNOLOGY ORAL PRESENTATIONS

2:20-4:20 PM

2:40 PM
Ryan Maloney
Background: Self-assembly of binary mixtures that contain anisotropic, interacting colloidal particles have been proposed as a way to create new, multi-functional materials. We simulate binary mixtures of dipolar rods and dipolar discs in two-dimensions using discontinuous molecular dynamics to determine how the assembled structures of these mixtures differs from those seen in single component systems. Two different binary mixtures are investigated: a mixture of an equal number of dipolar rods and dipolar discs, and a mixture where the area fraction of dipolar rods is equal to the area fraction of dipolar discs.

Results: Phase boundaries between fluid, string-fluid, and “gel” phases are calculated and compared to the phase boundaries of the pure components. Looking deeper at the underlying structure of the mixture reveals complex interplay between the rods and discs and the formation of states where the two components are in different phases. The mixtures exhibit phases where both rods and discs are in the fluid phase, where rods form a string fluid while discs remain in the fluid phase, a rod string-fluid coexisting with a disc string-fluid, a “gel” that consists primarily of rods while the discs form either a fluid or string-fluid phase, and a “gel” that contains both rods and discs.

Conclusions: Our results give insight into the general assembly pathway of binary mixtures, and how complex aggregates can be created by varying the mixture composition, strength of interaction between the two components, and the temperature. By manipulating the properties of one of the components it should be possible to fabricate bifunctional, thermally responsive self-assembled materials.

References:

  1. Maloney, Ryan C., Hall, Carol K (2018). Phase diagrams of mixtures of dipolar rods and discs. Soft Matter 14: 7894-7905.

3:00 PM
Jennifer Clark
Background: In order to reduce the computational cost of molecular dynamics simulations, atoms are often grouped into coarse-grained beads. The short-range, nonbonded parameters for these groups of atoms must represent all nonbonded interactions, excluding the long-range coulombic potential. Top-down methods are an attractive option to define these interactions, as they use experimental data to build coarse-grained models. For example, the interaction parameters used for the SAFT-y-Mie force field are fit to phase-equilibrium data [1,2]. All parameters then require experimental data for each bead-bead interaction and an iterative fitting routine. However, suitable experimental data is not always available for all different bead pairs. By expanding the Berthelot combining rules to include all nonbonded interactions, we derive a bottom-up parameterization method where coarse-grained parameters are directly obtained from ab initio calculations, greatly reducing parameterization effort. Our combining rules will predict Mie potential cross-interaction parameters of the SAFT-y-Mie to compare to experimental data.

Results: We derived mixing rules for the SAFT-y-Mie force field to include multipole interactions. In the resulting model, the unlike-pair interactions account for the effect of charges, dipole moments, and quadrupole moments. We developed a procedure to calculate the multipole moments of molecular fragments from ab initio simulations, and showed that their use in our new combining rules produced favorable results. We observed a notable improvement when compared to the values predicted from the usual SAFT combining rules, and found our results are comparable to those parameters fit to experimental data.

Conclusions: By estimating multipole moments for coarse-grained molecular fragments using ab initio calculations, it is possible to obtain realistic cross-interaction energies without the need for extensive experimental data.

References:

  1. Dufal, S. et al. (2014). Prediction of Thermodynamic Properties and Phase Behavior of Fluids and Mixtures with the SAFT-y Mie Group-Contribution Equation of State. J. Chem. Eng. Data, 59. 3272–3288.
  2. Papaioannou, V. et al. (2014). Group contribution methodology based on the statistical associating fluid theory for heteronuclear molecules formed from Mie segments. J. Chem. Phys., 140. 054107.

 

Coffee Break 3:20 PM- 3:40 PM

 

3:40 PM
R. Ashton Lavoie
Background: The removal of host cell proteins (HCPs) represents a significant challenge in biomanufacturing, given their diversity in composition, structure, and abundance, and their potential homology with the target product [1]. Traditional approaches to HCP clearance rely on affinity-based product capture in “bind-and-elute” mode and adsorption of HCPs in “flow-through” polishing steps [2,3]. This approach has been extensively utilized in the manufacturing of monoclonal antibodies (mAb) for decades, relying on Protein A, and ion exchange or mixed-mode chromatography for product capture and polishing, respectively. Recent studies, however, have highlighted the presence of HCP species that can degrade the mAb product or produce toxic metabolites, or are immunogenic; most importantly, these “problematic HCPs” co-elute with the mAb product from Protein A and are not efficiently removed by commercial polishing media [4]. Improving removal of these impurities will improve the robustness of traditional platform processes or enable continuous processing that relies on end-to-end flow-through operations. To ensure the clearance of these “problematic HCPs”, we have developed an ensemble of synthetic peptides as next-generation mixed-mode ligands to ensure higher HCP removal in mAb purification processes.

Results: The identified HCP-binding lead peptides were grouped into two categories, based on sequence homology detected after screening, and conjugated on chromatographic resins to be evaluated in terms of HCP clearance and mAb yield using an industrial IgG-producing CHO harvest as model fluid. To gather detailed knowledge on the %-removal of individual HCPs, the flow through fractions were subjected to proteomic analysis by mass spectrometry. In terms of global HCP removal, we observed equivalent or higher binding of HCPs with minimal IgG binding, compared to commercial polishing media. Notably, the proteomic analysis showed effective capture of “problematic HCPs”, including those that are not effectively captured by commercial media, particularly under high salt conditions.

Conclusions: We have identified synthetic peptide ligands for selective removal of HCPs for use in flow-through purification processes. We have further demonstrated enhanced salt-tolerance for these ligands in removal of problematic HCPs.

References:

  1. Wang, X.; Hunter, A. K.; Mozier, N. M. (2009). Host cell proteins in biologics development: Identification, Quantification and Risk Assessment. Biotech. Bioeng., 103: 446-458.
  2. Shukla, A. A.; Hubbard, B.; Tressel, T.; Guhan, S.; Low, D. (2007). Downstream processing of monoclonal antibodies-Application of platform approaches. J. Chromatogr. B, 848: 28–39.
  3. Shukla, A. A.; Thömmes, J. (2010). Recent Advances in large-scale production of monoclonal antibodies and related proteins. Trends in Biotechnology, 28: 253-261.
  4. Goey, C.; Alhuthali, S.; Kontoravdi, C. Host cell protein removal from biopharmaceutical preparations: Towards the implementation of quality by design. Biotechnol. Adv., 36: 1223-1237.

4:00 PM
Christopher Straub
Background: The primary challenge of generating renewable fuels from plant based feedstocks is the ability of the microorganism to access the abundant carbohydrate content of the complex biomass. The other critical metrics, including low cost feedstock, high titer, high volumetric productivity, and low cost separations have largely been demonstrated economically at industrial scale, at least for ethanol. Even with thermal, chemical, and enzymatic treatments that can account for more than 25% of the process costs, carbohydrate conversion to product has remained at around only 50%.

Results: This barrier has been overcome by pairing a transgenic line of poplar trees1 to a natural lignocellulose degrading extreme thermophile, Caldicellulosiruptor bescii (Topt = 78°C). The transgenic poplar trees have been engineered to not only contain lower lignin content but modifications to lignin structure and monomer ratio. With untreated poplar trees as the sole carbon source, C. bescii was able to improve carbohydrate conversion from 15% with the wild type poplar to 80% with the transgenic poplar lines. In addition to high conversion of these transgenic plants, C. bescii must be engineered to produce a valuable fermentation metabolite. Its native products, acetate and lactate, are of low value and difficult to separate from water. C. bescii has been previously engineered to produce ethanol at 60-65°C, a growth range which severely inhibits its biomass degrading capabilities.2 Here we develop a pathway to produce acetone3 at 70°C and an ethanol pathway with more thermally stable enzymes to allow ethanol production at 70°C. We further demonstrate a method to separate acetone (Tb = 56°C) and ethanol (Tb = 78°C) in situ during active fermentation via distillation at 70°C under moderate vacuum.

Conclusions: The ability to of a microorganism, C. bescii, to convert untreated lignocellulosic biomass to industrially useful biofuels and chemicals has been demonstrated at high conversion. Ongoing improvements in titer and product selectivity are pushing this promising technology toward viability on a commercial scale.

References:

  1. Wang, Jack P.; Matthews, Megan L.; Williams, Cranos M.; et al (2018). Improving wood properties for wood utilization through multi-omics integration in lignin biosynthesis. Nat Comm, 9:1-16.
  2. Williams-Rhaesa, Amanda M.; Rubinstein, Gabriel M.; Scott, Israel M.; et al (2018). Engineering redox-balanced ethanol production in the cellulolytic and extremely thermophilic bacterium Caldicellulosiruptor bescii. Metabolic Engineering Communications, 7:1-9.
  3. Zeldes, Benjamin M.; Straub, Christopher T.; Otten, Jonathan K.; et al (2018). A synthetic enzymatic pathway for extremely thermophilic acetone production based on the unexpectedly thermostable acetoacetate decarboxylase from Clostridium acetobutylicum. Biotechnology and Bioengineering, 115:1-11.

Poster Session 4:30-6:00 PM

BIOTECHNOLOGY

Kaitlyn Bacon
Background: Genomic advances have accelerated the discovery of biomarkers that can be targeted for bioseparation, diagnostic, and therapeutic applications increasing the need for improved technologies to identify affinity ligands specific to these targets. Many of these targets are cell surface proteins that are difficult to recombinantly express. As an alternative, combinatorial ligand libraries are biopanned against adherent whole cells because it allows targeting of the protein in its native confirmation and with appropriate posttranslational modifications. However, low target receptor density and high levels of other proteins on native mammalian cell surface may lead to significant non-specific binding. Yeast display has emerged as an alternative eukaryotic display platform for expressing membrane proteins, as proteins can be highly expressed with a relatively clean background. Phage display libraries have been successfully screened against membrane proteins displayed on yeast cells, using centrifugation to isolate positive binders. Yet, for some scaffolds, it may be advantageous to express the scaffold library using yeast display. However, a critical challenge in screening yeast display libraries using yeast displayed targets is the separation of binder cells from non-binders as centrifugation cannot be used.

Results: To achieve this separation, we investigated a strategy wherein target proteins are expressed as cell surface fusions on magnetized yeast cells. The target protein is co-expressed on the yeast cell surface with an iron oxide binding protein. These yeast cells are then magnetized through incubations with iron oxide nanoparticles. Afterwards, the magnetized target yeast cells are incubated with a yeast display library, and binder cells that complex with the target-displaying yeast are separated using a magnet. We analyzed our strategy by quantitatively assessing the enrichment of yeast displaying a moderate affinity binder (KD ~ 450 nM) using magnetic target yeast. The binder cell population was enriched >100 fold in a single round of screening, even when it was present at low frequency (1 in 105), suggesting feasibility of this method to screen combinatorial libraries. Subsequently, we screened a yeast display library of Sso7d protein mutants and successfully isolated binders specific to the cytosolic domain of the mitochondrial membrane protein TOM22 and the extracellular domain of the c-KIT receptor. Notably, an Sso7d variant with a KD ~ 400 nM for TOM22 was used to enrich mitochondria from cell lysates, confirming the identified ligand could bind the native mitochondrial protein.

Conclusions: In contrast to recombinant protein expression, yeast display of a membrane domain or protein is simplistic. Therefore, the use of yeast displayed targets in combinatorial library screens is likely to increase the efficiency of identifying ligands for membrane proteins of interest.

Scott Baldwin
Background: In a 1978 Croonian Lecture, Abercrombie remarked “although it is something that everybody has longed to find […] there are as yet little more than hints that fibroblasts have […] a chemotactic response.” By chemotaxis, he means the directed migration of cells toward chemoattractants, which underlies critical biological events such as embryogenesis, wound healing, and cancer metastasis. In what could be interpreted as a challenge, he went on to say “…of course, it may merely be that [the fibroblasts] have not yet been exposed to the appropriate experimental conditions.” [1] In the decades that followed, some groups reported that fibroblasts do indeed chemotax, but the generality and robustness of these assays has been constantly questioned [2].

Results: To this end, we have developed a live-cell imaging compatible microfluidic device that hosts up to 1000 viable cells subjected to stable and tunable chemoattractant gradients for over twenty hours. Furthermore, we use a machine-trained algorithm to automatedly acquire cell trajectories from the microscopy images.

Conclusions: As such, we are able to reproducibly explore a comprehensive fibroblast response landscape with higher throughput than other current assays. Our early results suggest that fibroblasts only sense a narrow chemoattractant regime, but the response could support physiologically significant directed migration.

References:

  1. Abercrombie, Michael. “The Croonian Lecture, 1978-The crawling movement of metazoan cells.” Proc. R. Soc. Lond. B 207.1167 (1980): 129-147.
  2. Kim, Beum Jun, and Mingming Wu. “Microfluidics for mammalian cell chemotaxis.” Annals of biomedical engineering 40.6 (2012): 1316-1327.

John Bowen
Background: Peptide and protein engineering via directed evolution are important tools to allow for de novo design of new diagnostic or therapeutic molecules; however, these tools such as yeast surface display, phage display, and mRNA display are limited due to their inability to introduce post translational modifications such as glycosylation, phosphorylation, or cyclization. These modifications are ideal as they increase specificity or stability of the engineered molecule. We are developing a system to introduce intracellular endogenous post translational modifications to a peptide library within the context of the yeast surface display protein engineering platform.

Results: Specifically, we are using the yeast surface display platform to enzymatically cyclize peptides within the host cell and display them as a cell surface protein fusion. This demonstrates the use of a biological system to create synthetic peptides which can be screened to select for cyclic peptide binders to specific antigens. In addition to confirmation of the correct post translational modification via mass spectrometry, we are developing a flow cytometry based assay in which peptide cyclization can be detected via the expression and ratio of specific fluorescent tags which are incorporated at precise locations in the peptide fusion construct.

Conclusions: Lastly, this library is currently being screened for binding affinity to specific protein targets. This proof of concept demonstration will show that synthetic peptides manufactured through a biological system are discoverable using yeast surface display.

James Crosby
Background: Lignocellulose is the most abundant organic carbon source and its effective utilization can potentially replace petroleum in traditional chemical processing. Caldicellulosiruptor is a genus of Gram-positive, extremely thermophilic bacteria (Topt = 70-78 °C) that deconstructs plant biomass through secreted multi-catalytic domain glycoside hydrolases (GHs) and ferment both C5 and C6 sugars with high efficiency. Of the Caldicellulosiruptor species, only C. bescii is genetically tractable. Advances in genetic tools have allowed for heterologous expression of enzymes and iterative genomic modifications in stable parental strains [1]. To date, only ethanol production in C. bescii has been reported, albeit at low productivities [2, 3]. However, more valuable chemicals, such as butanol and succinic acid, for use as fuels or chemical building blocks have the potential to be produced via consolidated bioprocessing of lignocellulose. Enhancing titer and productivity of these two heterologous products requires the combination of pathway optimization, analysis of sugar uptake and biomass deconstruction mechanisms, metabolic modeling, and transcriptomic response [4].

Results: We overexpressed and purified 10 GHs from 3 Caldicellulosiruptor species and investigated the hydrolysis on crystalline cellulose using a mixture design of experiments. The 6 primary GHs from C. bescii were synergistic with each other, with the optimal in vitro mixture matching the predicted composition of the secreted in vivo GH mixture. Mixtures of GHs from 3 Caldicellulosiruptor species were also synergistic with each other, suggesting the combination of catalytic domains is important for cellulose hydrolysis. In parallel, continuous culturing of C. bescii has been performed. At a dilution rate of 25 mL/hr, yields of lactate and acetate in the wild-type strain were 0.175 and 0.395 g/g glucose, respectively. Total sugar consumption was 0.041g/hr. Further studies will look at physiological and transcriptomic differences between relevant sugars for lignocellulose processing to validate a genome reconstruction of metabolism.

Future Work: Continuous culturing and transcriptomic data collection will be collected for 4 important sugars in lignocellulose processing; cellobiose, xylose, glucose, and arabinose. In conjunction with enzymatic hydrolysis of polysaccharides, this will produce a metabolic reconstruction that can predict deconstruction of lignocellulose. In parallel, transformation and optimization of the butanol and succinic acid pathways in C. bescii will occur by using the metabolic reconstruction to predict the important pathways to either delete or modify regulation.

References:

  1. Williams-Rhaesa, A.M., et al., Genome stability in engineered strains of the extremely thermophilic lignocellulose-degrading bacterium Caldicellulosiruptor bescii. Appl Environ Microbiol, 2017
  2. Williams-Rhaesa, A.M., et al., Engineering redox-balanced ethanol production in the cellulolytic and extremely thermophilic bacterium, Caldicellulosiruptor bescii. Metab Eng Commun, 2018
  3. Chung, D., et al., Direct conversion of plant biomass to ethanol by engineered Caldicellulosiruptor bescii. Proc Natl Acad Sci U S A, 2014.
  4. Crosby, J., et al., Extreme Thermophiles as Emerging Metabolic Engineering Platforms. Curr. Opin. Biotechnol. (submitted)
  5. Conway, J., Crosby, J., et al., Parsing in vivo and in vitro contributions to microcrystalline cellulose hydrolysis by multi-domain glycoside hydrolases in the Caldicellulosiruptor bescii secretome. Biotech. Bioengineering, 2018
  6. Conway, J., Crosby, J., et al., Novel Multi-domain, Multi-functional Glycoside Hydrolases from Lignocellulolytic Caldicellulosiruptor species. AIChE Journal

Javier Huayta
Background: Several environmental factors affect longevity in C. elegans, and most of these stressors function through the DAF-16/FOXO transcription factor, which regulates expression of genes involved in aging and stress response. In turn, spatiotemporal activity of these genes alters lifespan and healthspan of C. elegans [1]. Tracking longitudinal activity of these aging-related genes is challenging due to the destructive nature of most quantitative gene expression assays. Moreover, microfluidic platforms allow for easy animal handling and immobilization without need of anesthetics and time-consuming manual manipulation [2]. By this means, longitudinal in vivo tracking of gene activity in response to environmental perturbations can be achieved through quantitative analysis of gene expression by fluorescence imaging. The data sets thus acquired can be used to relate environmental perturbations, longitudinal gene activity, and healthspan and lifespan. Quantitative mathematical models derived with these data will enable elucidating how this lifelong background determines lifespan and healthspan in C. elegans.

Results: We developed a microfluidics platform for lifespan and healthspan characterization for age-synchronized C. elegans populations. This device was fabricated through standard PDMS molding, and designed with chambers and adjacent channels for feeding, immobilization, and imaging. We applied differential pressure to the chamber containing C. elegans, with a fluorescent-tagged gene, to force the animals into the imaging channels. After imaging was completed, the animals were taken back to their original chamber by applying pressure in the opposing direction. A synchronized MAH97 C. elegans population expressing GFP-tagged DAF-16 under dietary restriction exhibited an increased migration of DAF-16 to the nuclei of the cells with an increasing trend from the time 0 hours until 6 hours. In repeated experiments, this trend was observed at days 3, 6, and 9; but with a maximum nuclear to cytoplasmic DAF-16 ratio after 6 hours showing a decreasing trend.

Conclusions: The microfluidic platform enables the immobilization and imaging of C. elegans under controlled environmental stimuli. These stimuli affect the localization of DAF-16 in a spatiotemporal basis that can be measured through our MATLAB algorithm. In further studies, we will explore the effects of other lifespan-altering environmental conditions, and additional key aging pathways affecting C. elegans.

References:

  1. M. Uno and E. Nishida, “Lifespan-regulating genes in C. elegans,” Aging Mech. Dis., vol. 2, no. 1, p. 16010, 2016.
  2. A. San-Miguel and H. Lu, “Microfluidics as a tool for C. elegans research,” WormBook, pp. 1–19, 2013

Victoria Karakis
Background: TBA

Results: TBA

Conclusions: TBA

Jenna Meanor
Background: Post-translational chromatin modifications play key roles in gene expression and consequently, in almost all cellular functions. Importantly, chromatin modifications can be highly dynamic, for instance, throughout the cell cycle, during development and differentiation, in pathogenesis, and in response to external stimuli. These dynamic properties of chromatin have been hypothesized to underlie key cellular properties and processes, from control over gene expression noise to facilitating persistent gene expression changes. The ability to track temporal changes of chromatin modifications would unlock access to a previously hidden dynamic realm of cell biology.

Results: Here we describe our progress in creating genetically encoded, fluorescently labeled binders to specific histone modifications. We employed yeast surface display to engineer binders with enhanced affinity and specificity towards chromatin modifications. We derived these binders from a naturally occurring chromatin binding protein as well as an unrelated protein scaffold derived from archaea. The advantages of these binders include their ability to simultaneously track temporal changes in chromatin modifications and conformations in live cells, their ability to bind and label endogenous chromatin epitopes without the need for cell fixation, and their potential utility in engineering synthetic circuits at the chromatin level rather than the genetic level. Their small size also allows for their stable expression in cells for long-term longitudinal studies and may promote their nuclear localization.

Conclusions: We anticipate this work will enable a new range of studies into the importance of dynamics in chromatin biology.

Jamie Nosbisch
Background: In fibroblasts responding to gradients of platelet-derived growth factor (PDGF), signaling through the phospholipase C (PLC)/protein kinase C (PKC) pathway proved necessary for chemotaxis [1]. PKC is activated through its binding to the lipid second messenger diacylglycerol (DAG), which is formed from hydrolysis of phosphatidylinositol (4,5)-
bisphosphate (PIP2) by PLC. Strikingly, in fibroblasts exposed to a shallow PDGF gradient, the density of DAG in the plasma membrane is focally enriched at the up-gradient leading edge, characteristic of an internal amplification mechanism [1]. In previous work, we developed a reaction-diffusion model of the PLC/PKC signaling pathway and implicated phosphorylation of myristoylated alanine-rich C kinase substrate (MARCKS) by membrane-localized PKC as a positive feedback mechanism sufficient for local amplification of DAG and active PKC [2]. However, the MARCKS feedback only weakly amplifies the signal in shallow PDGF gradients.

Results: The new model includes phosphatidic acid (PA), a lipid intermediate in the metabolism of DAG. Feedback loops incorporating PA were added to the model based on evidence that PA increases the rate of PIP2 hydrolysis by stabilizing the recruitment of PLC [3] and that active PKC can enhance the activity of phospholipase D, an enzyme that produces PA [4]. Simulations show that the MARCKS feedback mechanism synergizes with these new feedback loops for increased amplification even at shallow PDGF gradients and over an appreciable range of midpoint PDGF concentrations. Simulations with variations of parameter values or cell geometry further indicate that this signaling network is a sensitive and robust gradient sensing circuit.

Conclusions: Experiments will need to be performed, in concert with refinement of our modeling framework, to validate the source(s) of nonlinearity in this signaling pathway. In the future, this model will be linked to models describing the organization of the actin cytoskeleton and directionality of cell migration for a more comprehensive understanding of how fibroblast chemotaxis proceeds during physiological processes such as wound healing.

References:

  1. Asokan SB, Johnson HE, Rahman A, King SJ, Rotty JD, Lebedeva IP, Haugh JM, Bear JE (2014). Mesenchymal chemotaxis requires selective inactivation of myosin II at the leading edge via a noncanonical PLCγ/PKCα pathway. Developmental Cell, 31(6): 747-60.
  2. Mohan K, Nosbisch JL, Elston TC, Bear JE, Haugh JM (2017). A reaction diffusion model explains amplification of the PLC/PKC pathway in fibroblast chemotaxis. Biophysical Journal, 113: 185-194.
  3. Jones GA, Carpenter G (1993) The Regulation of Phospholipase C-γ1 by Phosphatidic Acid. J Biol Chem (28), 20845-20850.
  4. Balboa MA, et al. (1994) Protein Kinase Cα Mediates Phospholipase D Activation by Nucleotides and Phorbol Ester in Madin-Darby Canine Kidney Cells. J Biol Chem 269 (14), 10511-10516.

John Schneible
Background: Currently, multiple (combination) drug chemotherapy is the prescribed treatment for cancer in the clinic. It affords a much higher therapeutic outcome as compared to single-drug chemotherapy. To manipulate multi-drug pharmacokinetics in a favorable manner, nanotechnology has been employed for developing advanced combination-drug delivery strategies [1-3], and has unveiled many important phenomena that are crucial towards success in anti-cancer therapy, namely drug synergism and scheduled delivery. Currently, we have developed a hydrogel platform constituted by an FDA-approved polymer, a modified-chitosan hydrogel. Through chemical modification, we have been able to control the electrostatic and hydrophobic interactions of such systems to govern drug loading and release, insofar that scheduled delivery of our combination chemotherapy choice is delivered in a synergistic dose.

Results: To evaluate delivery, a synergistic dose of two drugs Doxorubicin (DOX) and Gemcitabine (GEM), a synergistic pair for breast cancer, was used. In single drug release studies, gels that were ~ 10% modified were prepared and distinct release kinetics of the two drugs were achieved. In the acetyl-modified gel, GEM was released more quickly than DOX, achieving 20% release in 1 hr compared to 6.5 hrs and delivering to a molar ratio dose of 6.3 of GEM/DOX, both values are conducive to an appropriate schedule and molar ratio for optimal synergism [4]. In the butanoyl-modified gel, DOX was released more quickly than GEM, achieving, 20% release instantaneously compared to 1 hr for GEM, and releasing a molar ratio of 2.6 of GEM/DOX. Furthermore, when co-loaded, acetyl-modified gels are capable of delivering a variable dose of GEM/DOX ranging from 2-14 over increasing modification level, whereas in butanoyl-modified gels deliver a dose of GEM/DOX ranging from 10-5 over increasing modification level. In dual drug systems, all molar ratios demonstrate synergism, to some degree, and release of GEM with faster kinetics that DOX, which is synergistic. To further supplement experimental work, computational coarse-grained models of chitosans modified with acetyl and butanoyl moieties have been developed and performed. Computational models demonstrated excellent agreement with single-drug release data, whereby GEM is released faster than DOX in acetyl-modified gels with increasing modification, and GEM is release slower than DOX in butanoyl-modified gels with increasing modification. This model can provide deep insight, as a predicative tool for the rational design of a chitosan hydrogel that would afford the best therapeutic outcome of a chitosan hydrogel, in terms of (i) modification type, (ii) modification level, and (iii) starting concentrations of the two drugs.

Ongoing work is being conducted to optimize the design of a tissue-on-a-chip in vitro with MDA-MB-231 (breast cancer) and MCF-10a (epithelial breast) cells. These devices will be used to test overall therapeutic outcome of the dual-drug loaded chitosan hydrogels, as they are better suited to study pharmacokinetics and pharmacodynamics and afford better reproducibility as compared to traditional mouse models.

References:

  1. Hu, Q., Sun, W., Wang, C. & Gu, Z. Recent advances of cocktail chemotherapy by combination drug delivery systems. Adv. Drug Deliv. Rev. 98, 19–34 (2016).
  2. Park, K. Drug delivery of the future: Chasing the invisible gorilla. J. Control. Release 240, 2–8 (2016).
  3. Bhattacharjee, S. Nanomedicine literature: the vicious cycle of reproducing the irreproducible. Int. J. Pharmacokinet. 2, 15–19 (2016).

Dilara Sen
Background: Epigenetic mechanisms play essential roles in mammalian neurodevelopment. Genomic imprinting is a process causing the mono-allelic expression of a gene in a parent of origin specific manner, and it is controlled by a hierarchy of epigenetic events. Although they are small in number, many imprinted genes are expressed in the human brain and hold important roles in development and disease. As a key example, the imprinted gene UBE3A is an important nexus in neurodevelopment and complex brain disorders where deletion of the maternal or paternal alleles of UBE3A differentially leads to Angelman Syndrome or Prader-Willi Syndrome, respectively. In addition, duplication of maternal UBE3A occurs in some forms of Autism Spectrum Disorder. These three diseases share some common neurological comorbidities strongly suggesting UBE3A’s role in neural function; yet, it is still unclear when, where, and how UBE3A is regulating or disrupting normal neurodevelopment or adult brain function. Therefore, mapping the spatiotemporal localization of UBE3A expression in neurons and other cell types in the brain could provide key insights into the underlying mechanisms of UBE3A-related disorders and suggest key cell types and brain regions for further study. However, due to technical and ethical limitations, such maps have yet to be generated in humans. Here we aim to map UBE3A expression throughout early prenatal brain development by using human cerebral organoids. Human cerebral organoids are model systems that exhibit most cell types of the human brain as well as polarized tissue structures, and have been temporally correlated with early fetal neurodevelopment. Through this human system, we connect molecular processes to tissue-level properties by spatiotemporally mapping UBE3A. This map suggests several specific brain regions, cell types, developmental time windows, and mechanistic hypotheses to pursue in understanding UBE3A’s role in the human brain and in neurodevelopmental disorders.

CATALYSIS, COMPUTATION, AND KINETICS

Arnab Bose
Background: Xylan pyrolysis plays a crucial role in the pre-treatment of biomass. It falls under the class of hemicellulose copolymers, which are the least thermally stable components of lignocellulosic biomass. Different lumped models are available to understand xylan’s decomposition kinetics, but little insight into various reaction pathways can be obtained from those models [1]. To obtain a detailed view of its pyrolysis kinetics, extracted xylan from beech wood and D-xylose are flash-pyrolyzed (Pyroprobe, CDS Analytical) at 200˚C – 400˚C and gas-phase products are analyzed with GC x GC/TOFMS (Pegasus 4D, Leco).

Results: Simultaneous thermogravimetric analysis and calorimetry (SDT Q600, TA Instruments) provide overall kinetics during linearly ramped temperature increases such as at 20°C/min, and pyrolysis products are analyzed using flash pyrolysis (Pyroprobe 5200, CDS Analytical) at different temperatures with product analysis performed using two-dimensional gas chromatography / time-of-flight mass spectroscopy (Pegasus 4D GCxGC-TOFMS, Leco). Various C/H/O compounds were identified from zero carbon atoms (water) to eight carbon atoms. In general, their chemical structures contain alcohol, carbonyl, ether, and, ester groups. Different saturated and unsaturated cyclopropanyl, cyclopentanyl, furyl, 1,4-dioxane and pyranyl rings were also observed. A higher number of linear compounds was identified in xylan pyrolysis. Thermogravimetric analysis of the reactions showed that there are three different stages of reaction for xylan, a primary stage peaking at roughly 250°C, a secondary one peaking at roughly 300°C and a tail starting at roughly at 350°C. The effect of water and mineral ions on the overall kinetics were also studied. Drifts of the peaks towards lower temperature were observed when water was added to xylan matrix. On the other hand, changes in the peak hights were observed on the after adding different sodium salts to the xylan matrix. In parallel, computational quantum chemistry (Gaussian 16) has been used to predict transition states for reactions involved in torrefaction. The transition states have been initially modeled at a B3LYP/6-311++G(d,p) level of theory. This modeling will be used to build reaction pathways leading to the major observed products and to describe the reaction observations made with thermal analysis.

Conclusions: Four types of possible reaction routes from xylan were identified: glycosidic bond breakage, cross-linkage of two xylopyranosyl units, methanol removal, and, ionic bond formation due to minerals present in xylan.

References:

  1. E. Ranzi, A. Cuoci, T. Faravelli, A. Frassoldati, G. Migliavacca, S. Pierucci, S. Sommariva, “Chemical kinetics of biomass pyrolysis,” Energy & Fuels, 2008, 4292–4300.

Ankit Chandra
Background: Cell migration is essential for wound healing, immune response and cancer metastasis. Amongst the different cell migration phenotypes, mesenchymal migration is characterized by slow locomotion, strong adhesions with extracellular matrix (ECM), and distinct localization of nonmuscle myosin II bound to the actin cytoskeleton [1]. Nascent adhesion complexes, composed of integrin receptors and many other proteins, orchestrate the dynamics of the actin cytoskeleton by 1) mediating activation of Rac and other signaling pathways that promote F-actin polymerization by increasing the density of barbed ends at the membrane; and by 2) interacting with F-actin and thus acting as a mechanical clutch, which allows polymerizing actin to overcome membrane stress and push the membrane forward [2], [3]. Myosin II minifilaments also associate with the F-actin network, mediating its contraction. This contractility correlates with increased retrograde flow and diminished membrane protrusion, but it is not clear how this is caused.

Results: In this study, we have constructed a PDE model that integrates and spatially resolves adhesion, cytoskeletal, and signaling dynamics at the leading edge of a mesenchymal cell. The model considers both biochemical regulation and mechanics of the F-actin network. The model predicts an optimal ECM density for maximal protrusion velocity, consistent with literature. At lower ECM densities, not enough F-actin-bound adhesions are formed, and most of the actin polymerization results in retrograde flow. At the optimum ECM density, the density of nascent adhesions is sufficient to bind F-actin and mediate activation of Rac, while membrane protrusion promotes formation of nascent adhesions; with this positive feedback loop engaged, F-actin retrograde flow is decreased, and there is an acutely sensitive increase in membrane velocity. At higher ECM densities, the density of barbed ends increases further, but competition for G-actin diminishes protrusion velocity below optimum levels. Increasing myosin contractility for nearoptimal ECM density restricts protrusion velocity. Its mechanical influence destabilizes the adhesion-based clutch, and F-actin retrograde flow increases. Thus, the positive feedback between nascent adhesions and F-actin is disrupted.

Conclusions: Our model predicts an optimal adhesion density for maximal protrusion velocity. This occurs 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.

References:

  1. J. E. Bear and J. M. Haugh, “Directed migration of mesenchymal cells: Where signaling and the cytoskeleton meet,” Curr. Opin. Cell Biol., vol. 30, no. 1, pp. 74–82, 2014.
  2. 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.
  3. 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.

Ryan Dudek
Background: Steam cracking of naphtha is a commercially proven technology for light olefin production and the primary source of ethylene in the Europe and Asia-Pacific markets. However, its significant energy consumption and high CO2 intensity (up to 2 tons CO2/ton C2H4), stemming from endothermic cracking reactions and complex product separations, make this state-of-the-art process increasingly undesirable from an environmental standpoint. We propose a redox oxidative cracking (ROC) approach as an alternative pathway for naphtha conversion. Enabled by perovskite oxide-based redox catalysts, the ROC process converts naphtha (represented by n-hexane) in an auto-thermal, cyclic redox mode.

Results: The addition of 20 wt.% Na2WO4 to SrMnO3 and CaMnO3 created highly selective redox catalysts capable of achieving enhanced olefin yields from n-hexane oxy-cracking. This was largely attributed to the redox catalysts’ high activity, selectivity, and stability towards selective hydrogen combustion (SHC) under a redox mode. Na2WO4/CaMnO3 demonstrated significantly higher olefin yield (55–58%) when compared to that from thermal cracking (34%) at 725°C and 4500 h-1. COx yield as low as 1.7% was achieved along with complete combustion of H2 over 25 cycles. Similarly, Na2WO4/SrMnO3 achieved 41% olefin yield, 0.4% COx yield, and 73% H2 combustion at this condition. Oxygen-temperature-programmed desorption (O2-TPD) indicated that Na2WO4 hindered gaseous oxygen release from CaMnO3. Low-energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS) revealed an outermost perovskite surface layer covered by Na2WO4, which suppressed near-surface Mn and alkaline earth metal cations. The formation of non-selective surface oxygen species was also inhibited. XPS analysis further confirmed that promotion of SrMnO3 with Na2WO4 suppressed surface Sr species by 90%, with a similar effect also observed on CaMnO3.

Conclusions: These findings point to the promoting effect of Na2WO4 and the potential of promoted SrMnO3 and CaMnO3 as selective redox catalysts for efficient production of light olefins from naphtha via the ROC process.

Petr Novotný
Background: Ethylene is a basic building block in the petrochemical industry; annual production of ethylene exceeds 150 million tonnes—more than any other organic compound [1]. Catalytic oxidative dehydrogenation (ODH) of ethane offers large potential reductions in energy consumption and associated greenhouse gas emissions when compared to conventional steam cracking for ethylene production [2]; however, ethane ODH using co-fed O2 requires costly air separation. As an alternative, we are investigating catalysts that operate in a cyclic redox mode and utilize lattice oxygen (O2-) as the sole oxidant [3].

Results: In this work, redox catalysts with 1 and 3 monolayer (ML) equivalents of MoO3 supported on 3 different commercial gamma-alumina (γ-Al2O3) carriers were prepared, characterized by powder x-ray diffraction (XRD), Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), and evaluated for ethane chemical looping (CL)-ODH at 500–550°C. The 1ML MoO3/Al2O3 catalysts contained primarily well-dispersed supported molybdate species, however, at higher loading (3ML) the bulk Al2(MoO4)3 phase was predominant. In cyclic redox mode at 500 and 550°C, the 1 ML catalysts exhibited high ethylene selectivity that decreased linearly from 96% at near zero conversion to 82% at 29% conversion. The 3ML catalysts generally gave higher conversions with 10–12% lower selectivity under equivalent conditions. Catalysts reduced under ethane at 550°C for varying times were analyzed via XPS in order to elucidate the dependence of CL-ODH performance on Mo oxidation state. Based on these results, the initial high selectivity toward ethylene corresponds to a reduction of Mo+VI to Mo+V. Subsequently, the presence of lower Mo oxidation states (+V, +IV) triggers production of H2 and CH4 from ethane resulting in substantial selectivity loss. Even after extended reduction in ethane at 550°C, the 1ML catalyst retained about 25% Mo+VI. In contrast, Mo+VI in the 3ML catalyst is rapidly consumed, and its concentration approaches zero eventually.

Conclusions: The 1ML catalysts contained primarily well-dispersed supported molybdate species and generally gave 10–12% higher selectivity under equivalent conditions when compared to 3ML catalysts. We suggest that enhanced interaction with the support decreases molybdate reducibility enhancing selectivity in ethane CL-ODH. High selectivity toward ethylene corresponds to a reduction of Mo+VI to Mo+V only. The presence of lower Mo oxidation states (+V, +IV) triggers production of H2 and CH4 from ethane resulting in substantial selectivity loss. Our findings illustrate that to attain high ethylene selectivity and to ensure effective usage of the catalyst; redox cycles need to be precisely executed with respect to the reduction of the catalyst.

References:

  1. H. Zimmermann, R. Walzl, in: Ullmann’s Encycl. Ind. Chem., Wiley-VCH Verlag GmbH & Co. KGaA, 2000.
  2. C.A. Gärtner, A.C. van Veen, J.A. Lercher, ChemCatChem 5 (2013) 3196–3217.
  3. S.Yusuf, L. Neal, V. Haribal, M. Baldwin, H. H. Lamb, F. Li, Applied Catalysis B: Environmental, 232, 2018, 77-85.

Amrutha Raghu
Background: Using Reactive Molecular Dynamics, elementary-reaction paths are explored and tentatively identified for pyrolysis of xylose, used because xylan is a major part of hemicellulose. Exploitation of conventional fuels for several decades and increase in demand for energy has created a pressing need for biomass to be used as a sustainable, affordable and environmentally friendly source of renewable energy. Xylan, a polymer of xylose (β-D-xylopyranose), is an essential component of lignocellulosic biomass, such as bagasse and corn stover. This study focuses on studying the kinetics of xylan pyrolysis and predicting the products at different temperatures using Reactive Molecular Dynamics simulation, to be compared to xylan pyrolysis data from our group.

Results: Reactive Molecular Dynamics (RMD) simulation is performed on systems of xylose molecules using ReaxFF [Ref. 1] as implemented in LAMMPS [Ref. 2]. This technique simulates the reaction taking place in a system of molecules by considering the energy changes happening in the system due to changes in bonded and non-bonded interactions. Hemicellulose pyrolysis is proposed to occur through pericyclic reactions, based on analyses of cellulose pyrolysis [Ref. 3], in which bond scissions and bond formations occur concertedly within cyclic transition states. RMD simulations allow moment-by-moment observations of these simulated changes. The unimolecular and bimolecular reactions of β-D-xylopyranose occurring between 600-900K are simulated with RMD to find glycolaldehyde, ethanol, formic acid, carbon monoxide, and water as major products which are consistent with results obtained from GC-MS experiments conducted by other group members in the Westmoreland lab.

Conclusions: Reactive Molecular Dynamics has proven to be a powerful tool to observe smallest nuances taking place in a reaction. The transition state of pyrolysis reactions has been quantitatively characterized to understand the various reaction paths. Furthermore, the elementary reactions among the various parallel reactions taking place during pyrolysis have been isolated and studied. Additional products, and rate kinetics of elementary reactions taking place during hemicellulose pyrolysis will be elaborated during the poster presentation.

References:

  1. C.T. van Duin, S. Dasgupta, F. Lorant, and W.A. Goddard. ReaxFF: A Reactive Force Field for Hydrocarbons. J. Phys. Chem. A 105:41 (2001) 9396-9409.
  2. M. Aktulga, J.C. Fogarty, S.A. Pandit, A.Y. Grama. Parallel reactive molecular dynamics: Numerical methods and algorithmic techniques. Parallel Computing, 38:4-5 (2012) 245-259.
  3. Seshadri, P. R. Westmoreland. Concerted reactions and mechanism of glucose pyrolysis and implications for cellulose kinetics. J. Phys. Chem. A 116:49 (2012) 11997-20013; V. Seshadri, P. R. Westmoreland. Roles of Hydroxyls in the Noncatalytic and Catalyzed Formation of Levoglucosan from Glucose. Catalysis Today 269(2016) 110-121.

J. Matthew Mansell
Background: Inclusion complexes formed when atoms of sulfur, selenium, tellurium, and other elements enter ultra-narrow single-walled carbon nanotubes (SWCNTs) exhibit interesting properties and structure. The structures of the included molecules are often unstable outside the nanotube. In some cases, the complex is significantly more conductive than the isolated CNT.[1,2] The radial breathing modes of the CNT can be substantially hardened in the complex.[1] Yet, this class of materials remains little studied. Further, there are significant advantages to the use of computational methods to study these systems (e.g., the ease of isolating a single complex in-silico versus in-vitro). Currently, we are carrying out computational studies in an attempt to reproduce the structure and properties (mechanical, thermodynamic, optical, etc.) of the “S@(5,5)SWCNT” complex formed by the inclusion of sulfur in (5,5)SWCNT using ab initio simulation methods.

Results: Our results include calculations (based on electronic density functional theory) of the ground state configuration for empty (5,5)SWCNT and S@(5,5)SWCNT; axial stress-strain curves; and analyses of the vibrational (phonon) modes. From these results, we predict the free energy of formation of the S@(5,5)SWCNT confined complex at 1 bar, over a range of temperature.

Conclusions: Preliminary conclusions suggest that the inclusion of sulfur in (5,5)SWCNT causes the CNT to stretch axially, and also causes the Young’s modulus along the axis to decrease. Our initial prediction of the free energy of inclusion is not in agreement with experiment, and we identify several sources of error which we aim to investigate and address in the future.

References:

  1. Fujimori, T. et al. Conducting linear chains of sulphur inside carbon nanotubes. Nat. Comm. 4, (2013).
  2. Medeiros, P. V. C. et al. Single-Atom Scale Structural Selectivity in Te Nanowires Encapsulated Inside Ultranarrow, Single-Walled Carbon Nanotubes. ACS Nano 11, 6178–6185 (2017).

MATERIALS

Heather Barton
Background: Metal-organic frameworks (MOFs) are highly porous, high surface area structures consisting of metal clusters connected via organic linkers. MOFs span applications in adsorption, separations, catalysis, electronics, and cancer therapeutics.[1] In particular, zirconium-based MOFs have proven effective in catalytically hydrolyzing chemical warfare agents (CWAs) at the metal sites.[2] Coupling this with photoactive porphyrin linkers, MOFs can also catalytically and selectively photo-oxidize agents in the presence of light and oxygen.[3] The dual functionality of Zr-porphyrin MOFs, such as PCN-222, makes them active against the most prominent agents used in war-stricken regions. Most MOFs, however, are synthesized in powder form, making them hard to incorporate into useful devices and materials. Our group works to synthesize MOFs on fabrics with metal oxide coatings deposited via atomic layer deposition (ALD). The metal oxide enables MOF nucleation due to increased hydroxyl density and roughness at the fabric surface.[4]

Results: Here we demonstrate PCN-222 MOF functionalized fabrics for the degradation of CWA simulants dimethyl-4-nitrophenyl phosphate (DMNP) and 2-chloroethyl ethyl sulfide (2CEES). Traditional PCN-222 crystals are 10’s of microns in length and failed to adhere to microfibers. To overcome this, we decreased synthesis concentrations and temperature and created conformal nano-scale MOF crystal films on fabrics. The nano-crystal coatings are more uniform and better adhered to the MOF fibers than the micro-crystals. Due to the inherent smaller crystal size, the MOF loading on fibers is significantly reduced on nano-crystal samples. SEM, XRD, and BET surface area analysis all reflect this MOF loading. For DMNP and 2-CEES degradation, we see the nano-crystal coated fabrics perform better on a per MOF mass basis.

Conclusions: By decreasing the crystal size, we were able to improve MOF film adhesion and uniformity on metal oxide coated fibers. While the amount of active material on the fabrics decreases with smaller crystals, the quality is not sacrificed and the nano-crystal samples degrade simulants faster on a MOF mass basis. The resulting fabrics can be incorporated into military suits to provide protection against all major CWAs without shedding MOF material with wear or adding significant weight to the uniform.

References:

  1. Yuan, Shuai, et al. (2018). Stable Metal-Organic Frameworks: Design, Synthesis, and Applications. Adv. Mater. 30: 1-35.
  2. Bai, Yan, et al. (2016). Zr-based metal-organic frameworks: design, synthesis, structure, and applications. Chem. Soc. Rev. 45: 2327–2367.
  3. Liu, Y, et al. (2015). Selective Photooxidation of a Mustard-Gas Simulant Catalyzed by a Porphyrinic Metal – Organic Framework. Angew. Chem. 127: 9129-9133.
  4. Lemaire, Paul, et al. (2016). Copper Benzenetricarboxylate Metal–Organic Framework Nucleation Mechanisms on Metal Oxide Powders and Thin Films formed by Atomic Layer Deposition. ACS Appl. Mater. Interfaces. 8: 9514–9522.

E. Daniel Cárdenas-Vásquez
Background: Hydrogels are 3-D networks of crosslinked polymers that can swell to hold vast quantities of water (up to 90% their own weight). They are widely used in many applications such as tissue engineering, drug delivery, 3D printing, food chemistry and others. However, they have many limitations such as low mechanical strength and low surface area, as well as weak responsiveness to external stimuli. We develop a novel way of manufacturing hydrogels into composite fibers, using UV light in the spinning process. We add colloidal thermoresponsive nanoparticles that self-assemble at a set temperature to tune the yielding structure, with a bridging polymer that induce colloidal gelation in which the characteristic length scale can be tuned based on the temperature. Additionally, this same polymer molecules provide photochemically crosslinked hydrogel materials on demand.

Results: We were able to produce composite hydrogel fibers with a variety of network morphologies. We used the droplet size, oil fraction, gelation temperature and precursor preparation time and flow rate as tuning parameters for the targeted structure. We used a Confocal Laser Scanning Microscope (CLSM) to analyze the characteristic length scale of the fibers. The images show a non-Newtonian flow profile.

Conclusions: The self-assembly that takes part in the precursor previous to the UV spinning process yields a wide variety of morphologies that could be used to engineer microporous materials, such as metallic bijel templates and hydrogel scaffolds that facilitate wound healing. Further experimental and simulation work to understand the flow rate-dependent phenomena of UV spinning would provide a guiding framework to design these types of multiphase materials.

Natasha Castellanos
Background: TBA

Results: TBA

Conclusions: TBA

Camden Cutright
Background: TBA

Results: TBA

Conclusions: TBA

Salvatore Luiso
Background: While significant research efforts have focused on the negative and positive electrode materials in rechargeable Lithium-ion (Li-ion) batteries, battery separators have only recently received more consideration from the scientific community. The separator plays a critical role in Li-ion batteries by preventing physical contact between the positive and negative electrodes while permitting efficient ionic transport across the separator. There are four major types of separators: microporous polyolefins membranes, nonwoven polymeric mats, gel-polymer electrolytes and composite membranes. Relative to the more conventional microporous membrane separators, nonwovens have the advantage of low cost, low mass and high porosity; in addition, the fibrous mat provides good structural cohesion due to its intertwined fibers. Although most polymers used to make nonwoven battery separators have resulted in lower cell performance (lower ionic conductivity and higher resistance) than conventional microporous separators, polyvinylidene difluoride (PVDF) shows promising results because of its stability and affinity for electrolytes commonly employed in Li-ion cells. The best manner to produce nonwoven PVDF would employ a melt-blowing process, which is a well-developed, high-volume production technology. Melt-processable PVDF has recently become commercially available and has been used only (to our knowledge) in water filter applications. Melt processing of PVDF to form a battery separator has significant advantages over electrospinning, such as greater processing speeds and solvent-free operation, and melt-blowing has the potential to fabricate unique structures, blends, and composites heretofore unobtainable.

Results: We investigated the fundamental properties and characteristics of a novel melt-blowable PVDF (from Arkema) with the objective of elucidating its structure-property-process relationships and studying its performance as separator in Li-ion batteries. High-quality melt-blown PVDF has successfully been produced and consolidated through thermal bonding. Electrolyte uptake was as high as 200%, part of which is embodied in the swollen fibers. The fiber diameter and the porosity increase, and the uptake is generally lower than at low throughputs, because of the lower surface area between the fibers and the electrolyte. Small fiber diameter provides higher surface area and higher electrolyte uptake. The best conductivity was 0.56 mS/cm, comparable to market value (0.5-0.8 mS/cm). The interactions with the electrolyte lead to a gel formation in the fiber outer layers, thus allowing a tri-phase system. The upper oxidation limit was 4 V and the interfacial resistance was relatively low. In this work, we will report on the physical, chemical, and electrochemical properties of nonwoven PVDF relevant to its use as a battery separator.

Conclusions: Melt-blown PVDF has most of the requirements to be a successful Li-ion battery separator, but some improvements need to be considered. The electrochemical data show that a smaller fiber diameter is desirable to obtain a fully charged battery and avoid micro-short circuits. A new trial has been recently performed in 1 m Reifenhauser-Reicofil Meltblown Line and preliminary data show a decrease in fiber diameter.

Taylor Neumann
Background: Additive manufacturing has received significant public interest due to its ability to manufacture unique designs not possible with traditional manufacturing techniques. For the field to make steps away from highly niche use cases, novel material designs are required. Specifically, we have focused on soft and conductive materials, for use in soft electronics and wearable devices. Typically, printing metals either requires high temperature sintering processes to achieve high conductivity. Using liquid metal alloys with low melting points allows us to direct write conductive patterns directly alongside polymers and other temperature sensitive materials. We have used this printing technique to enable soft and stretchable wearable electronic devices, including thermoelectric generators and antennas.

Results: Liquid metals have been patterned via additive processing for use in soft and stretchable electronics. Direct writing as been used to integrate flexible circuitry into wearable energy harvesters and flexible antenna systems. Stenciling techniques have been used to develop ultrathin multilayer flexible electronics. Elastomer composites with conductive liquid metal fillers have been developed for multilayer direct write processing.

Conclusions: Patterning liquid metal alongside polymer materials opens up a wide array of potential use cases, especially within the stretchable electronics field.

Lilian B. Okello
Background: Soft intelligent structures that are programmed to reshape and reconfigure under magnetic field can find applications such as in soft robotics and biomedical devices. While a number of methods for making responsive materials have been reported, 3D printing is one of the most efficient fabrication techniques, due to its inherent rapid prototyping capabilities [1].

Results: We will report a new class of smart elastomeric architectures [2,3] that undergo complex reconfiguration and shape change in applied magnetic fields, while floating on the surface of water. These magnetoactive soft actuators are fabricated by 3D printing with homocomposite silicone capillary ink. The ultrasoft actuators easily deform by the magnetic force exerted on carbonyl iron particles embedded in the silicone, as well as lateral capillary forces [3]. The tensile and compressive moduli of the actuators are determined by their topological design through 3D printing. As a result, their responses can be engineered by the interplay of the intensity of the magnetic field gradient and the programmable moduli.

Conclusions: 3D printing allows us to fabricate soft architectures with different actuation modes, such as isotropic/anisotropic contraction and multiple shape changes, as well as functional reconfiguration. Meshes that reconfigure in magnetic fields and respond to external stimuli by reshaping could serve as active tissue scaffolds for cell cultures and soft robots mimicking creatures that live on the surface of water.

References:

  1. Gladman, A.S., et al. (2016). Biomimetic 4D Printing. Nature Materials, 15: 413.
  2. Roh, S. et al. (2017). 3D Printing by Multiphase Silicone / Water Capillary Inks. Advanced Materials, 29: 1701554.
  3. Roh, S., Okello, L. B., Velev, O.D., (2018). 3D-Printed Silicone Soft Architectures with Programmed Magneto-Capillary Reconfiguration. Advanced Materials, (Submitted).

Matthew Parker
Background: Continued increase in global energy demand coupled with continued reliance on hydrocarbon fuels as well as emissions caused by other human activities necessitate development of new, environmentally-conscious sources of energy. An interesting possibility for both mitigation of emissions and as a source of fuel is the capture of CO2 and CH4 emissions from livestock farming operations and landfills. These gases can undergo dry reforming of methane (DRM)/ CO2 reforming of methane (CRM) to produce syngas, which may be used for production of carbon-neutral fuels via Fischer-Tropsch upgrading.

However, DRM processes possess a prohibitive energy barrier, often requiring temperatures ranging from 1000-1500K for the reaction to proceed (reaction enthalpy = 247 kJ/mol), even with catalysts. A solution that has been tested for the reduction of the DRM energy barrier is the implementation of dual-functionality thermo/photocatalysts by impregnation of transition metal catalysts like platinum on “black” titanium oxide (TiO2). This combination permits the reforming reaction to proceed via both the thermocatalytic and visible-light photocatalytic pathways, thus dramatically reducing the heating required for DRM. Unfortunately, implementation of these processes is affected by the undesirable polydispersity and nano-scale of the most easily available TiO2 catalyst particles, which will cause high pressure drop across flow reactors.

Results: This work explores the synthesis of porous, hollow TiO2 microspheres for use in thermo/photocatalytic DRM reactions via a microfluidic synthesis process. Using this method, TiO2 microparticles are formed via flow-focusing droplet formation in custom built glass microfluidic reactors. The inner tapered-tip capillary injects the precursor (comprised of titanium butoxide, toluene, a photocurable polymer, and a radical photoinitiator) into a constricted outlet, where precursor droplets are formed via dripping particle breakup. The continuous phase, comprised of formamide with 1 wt% Pluronic F108, is fed via independently controlled co- and counter-annular flows. The droplets then exit the reactor into a DI water bath, where the titanium butoxide undergoes rapid hydrolysis to form an amorphous titania shell. Following the hydrolysis, the collected particles are UV cured, washed, dried, and calcined in a muffle furnace to form crystalline TiO2 hollow microspheres. After calcination, the particles are impregnated with rhodium and reduced to “black” TiO2 to achieve the dual-functionality catalyst. Using these particles without illumination at 550°C, we have achieved yields approximately 3 orders of magnitude higher than those previously reported at similar temperatures[1].

Conclusions: These results suggest an exciting path by which DRM processes may be made feasible both economically and environmentally.

Srivatsan Ramesh
Background: Self-repairing nonwovens are loaded with stimuli-responsive microgels capable of restoring the mechanical integrity of a torn nonwoven to its initial structural and mechanical integrity. The objective is to replicate the bio-response of platelets to cuts in a human body on a nonwoven (NW) system. Polypropylene (PP) NW fabric is loaded with the stimuli-responsive microgels, resembling the platelets present in the blood stream. Upon damage, a magnetic field is employed to activate the microgels and guide them towards the point of rupture, imitating platelet congregation at a wound site. After accumulation of the microgels at the tear, ultraviolet light (UV) exposure is used to crosslink the microgels along and across the point of tear, similar to the formation of a blood clot to repair the wound. Such a nonwoven-hydrogel composite will lead to a new class of smart membranes, separation filters, and textiles that can be repaired in situ, without removing it from the point of application. The work comprises of two overarching objectives: design and optimization of a microgel system that responds to magnetic and UV stimulus; incorporation of these stimuli-responsive microgels in the nonwoven matrix and characterizing the composite in terms of stimuli response and mechanical behavior.

Results: Magnetically responsive hydrogels have been synthesized by grafting Nisopropylacrylamide (NIPAM) – Acrylic acid (AAc) based polymers onto iron oxide nanoparticles functionalized with different linker molecules [1]. Efforts are ongoing to optimize the magnetic response and charge of the responsive hydrogels in aqueous state.

Conclusions: In the upcoming months, the synthesized ferrogels will be characterized rheologically. Subsequent efforts include mechanical and optical characterization of the nonwoven polypropylene (PP) substrates. Further, the optimized hydrogel system will be incorporated on PP surface and the hybrid hydrogel-nonwoven system will be further tested and optimized.

References:

  1. Y. H. Ding, M. Floren, and W. Tan, “Mussel-inspired polydopamine for bio-surfacefunctionalization,” Biosurface Biotribology, vol. 2, no. 4, pp. 121–136, Dec. 2016.

Tamoghna Saha
Background: Sweat is an important source of information for monitoring individuals’ health because it contains a number of essential biomarkers. However, collecting sweat for analysis is still challenging because most of the commercially available health-monitoring devices are either invasive in nature or work only during active sweating, while patients are undergoing strenuous physical exertion [1]. These devices cannot function in low-sweating conditions.

Results: We demonstrate a new principle for the design of flexible and wearable devices, which are capable of extracting sweat under normal conditions using osmotic pressure difference for pumping, and evaporation for liquid disposal. The device is composed of silicone, polyacrylamide hydrogel patch, and paper microfluidic conduit. The hydrogel is equilibrated with glycerin, glucose, or NaCl solution to build up the desired osmotic strength. The multicomponent hydrogel device is attached onto gelatin model which mimics the properties of human skin. Due to difference in chemical potentials, water and dye move slowly from the gelatin skin model to the hydrogel pump, and then to the paper strip, where the bio-analytes can be sensed and the water evaporated. It was found out that for short time extraction and analysis, glucose and glycerin work better, while NaCl is a better osmolyte for long term extraction of analytes that are present in low concentrations and require a longer sampling time.

Conclusions: We are presently developing new devices that will extent similar principles for the long and short-term extraction and pumping of interstitial fluid by microneedles, which can constitute another rich source of health information via wearable devices.

References:

  1. Koh, A. et. al (2016). A soft, wearable microfluidic device for the capture, storage, and colorimetric sensing of sweat. Sci. Transl. Med., 8: 366ra165.

Austin Williams
Background: We report how porous, elastic, and biocompatible membranes can be made by combining nonwoven sheets from soft dendritic colloids (SDCs) with a magnetically-responsive, 3D printed silicone scaffold. The resulting multilayer structures could be used as tissue matrix surrogate scaffolds in magnetically-actuated cyclic strain bioreactors. SDCs are a new class of polymeric material characterized by a branched corona of nanofibers spread out in all directions. They are produced in a scalable polymer precipitation process under intensive shear. Their fractal, hierarchical structure enables remarkable adhesion and networking properties, mimicking the contact splitting effect seen in gecko leg adhesion. We show that SDC nonwovens composed of a thermoplastic polyurethane can be fabricated into porous, nonwoven membranes with morphological features similar to that of the branched, fibrous architectures comprising physiological tissues such as lung tissue. The SDC membranes are ultrasoft, with controllable moduli of physiological softness that can mimic both soft, healthy tissue and stiffened, diseased tissues characterized by stiffened fibers resulting from pathologies such as cystic fibrosis. These SDC membranes, combined with a new method of 3D printing of magnetically-responsive silicone mesh scaffolds, allow modulated, cyclic actuation of the material to predetermined strain values. The inclusion of these ultrasoft, porous membranes in a magnetically-actuated bioreactor setup will allow their facile, untethered, long-term actuation during cell growth to determine the effects of the scaffold’s mechanical properties on cell proliferation and viability for in vitro toxicological and human performance evaluations.

Jiaqi Yan
Background: Most polymer pairs tend to be inherently immiscible and macrophase-separate due to their low entropy of mixing and endothermic mixing, thereby resulting in poor interfacial adhesion and thus limiting the use of such materials in engineered systems [1-3]. The large domains of phase separation provide relatively little interfacial area, leading to poor entanglements between polymer chains. In often cases, the domain reduction is achieved through emulsification, this is the very same concept underlying the development of oil/water emulsions commonly encountered in food products. At its core, compatibilization is often required to improve the adhesion of highly incompatible commercial polymer pairs in blends. Hence, the mechanical properties and fracture resistance will be enhanced [4]. A more common methodology is to generate compatibilized polymer blends composed of two or more homopolymers with a block copolymer to yield desirable property combinations.

Results: The modified SIS has been successfully synthesized by grafting the ester group on parent SIS using thiol-ene click chemistry. The thermal properties were investigated by DSC studies, modified SIS dramatically decreased the glass transition temperatures due to a better compatibility between polymers. The similarity of pendant ester group of esterified SIS (eSIS) with poly(lactic acid) significantly increased the compatibility between PLA and eSIS blends. The successful compatibilization was evidenced by a measured improvement in reduction of size scale of phase separation domains between compatibilized neat PLA and eSIS. It was also evidenced by the enhanced mechanical properties. With 1 wt% incorporation of eSIS, toughness and modulus was increased to 62 MJ/m3 (~16 times than that of neat PLA) and 380 MPa, respectively. It was also found that 1 wt% of eSIS was the optimum amount addition, since higher content was not necessarily beneficial for the rubber toughening effect.

Conclusions: The study provides a novel, simple, and effective method to synthesize and incorporate thermoplastic elastomers into poly(lactic acid) for the purposes of compatibilization and rubber toughening, with significant toughness improvement over previously reported toughened materials.

References:

  1. Hamley, I. W. The Physics of Block Copolymers; Oxford University Press: New York, 1998.
  2. Matsen, M. W. Effect of Architecture on the Phase Behavior of AB-Type Block Copolymer Melts. Macromolecules 2012, 45 (4), 2161–2165.
  3. Bates, C. M.; Bates, F. S. 50th Anniversary Perspective: Block Polymers—Pure Potential. Macromolecules 2017, 50 (1), 3–22.
  4. Wang, D.; Li, Y.; Xie, X.-M.; Guo, B.-H. Compatibilization and Morphology Development of Immiscible Ternary Polymer Blends. Polymer 2011, 52 (1), 191–200.

Bharadwaja S.T.P.
Background: Adherence of pathogens such as bacteria, fungi and viruses on various surfaces leads to subsequent transmission to new hosts and significantly contributes towards their proliferation. This is seen especially in case of antibiotic-resistant pathogens, causing a major threat to human health. With only a few novel discoveries in the field of antibiotics since last two decades, often referred to as the discovery void, drug-resistance in pathogens has increased. Previously, infections that were easily treatable have now become fatal. Infections caused by antibiotic-resistant pathogens can occur anywhere, but, it is observed to take maximum effect in healthcare settings such as hospitals and nursing homes. The pathogens attach to surfaces such as counter tops, drapes, linens, door handles, monitory and sanitation equipment in health-care settings contribute to increase in HAIs [1]. According to a survey in the United Kingdom, it is estimated that more than 10 million lives could be lost to drug-resistant infections, higher than cancer related deaths [2]. As increase in microbial drug resistance causes conventional methods of treatment to fail, researchers are looking at alternative routes to tackle the infections. Instead of ex post facto medical treatment, we intend to incorporate the PS on surfaces that will result in inactivation of microbes by continuous surface disinfection and serve as a preventive measure. In this study, sulfonated block copolymers have been prepared that could be used as anti-infective materials. The mechanism of activation would be through water stimulus via a change in pH. NEXAR, a sulfonated pentablock ionomer and TsST (midblock-sulfonated p-tert-butylstyrene-b- styrene-b-p-tert-butylstyrene) were used in this work.

Results: The NEXAR films were solvent cast in tetrahydrofuran. The TST (p-tert-butylstyrene-b- styrene-b-p-tert-butylstyrene) films were sulfonated as per the protocol previously reported to produce TsST [3]. In this study, we have tested six bacterial strains that include Methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium. Two grades of NEXAR films, NEXAR 1.0 and NEXAR 2.0 were tested while three grades of TsST were tested. We found out that all the NEXAR films that were tested achieved at least 99.9555% inactivation. Time based studies were carried out on MRSA and it was revealed that after the first 5 min of contact NEXAR 1.0 and 2.0 inactivated 98.8073% and 99.9999% respectively. Three grades of other sulfonated polymer, TsST were tested against S. aureus. Higher degrees of sulfonation, 63% and 40 % inactivated 99.9999% of S. aureus in 5 min while 17% after a contact time of 60 min could inactivate 99.9555%.

Conclusions: The sulfonated polymers can inactivate bacteria and virus within the first 5 min of contact and are as fast acting as commercial antimicrobial wipes conventionally used. We achieved at least 98.8073% inactivation in all cases within the first 5 min.

References:

  1. Kramer, A., Schwebke, I., Kampf, G. (2006) How long do nosocomial pathogens persist on inanimate surfaces? A systematic review. BMC Infect. Dis., 6: 130.
  2. O’Neill, J. Tackling Drug-Resistant Infections Globally: Final Report and Recommendations; Review on Antimicrobial Resistance: London, 2016 (amr-review.org).

Sabina Islam
Background: “Coffee rings” have captured the attention of scientists for several decades, as they represent a beautiful example of colloidal self-assembly. A multitude of liquids, surfactants, and chemical modifiers have been pursued in order to guide the patterns of such coffee ring assembly. Even whiskey is not outside the realm of study; previous work has shown that uniform films are deposited in drying droplets from whiskey and correlate to its inherent chemical properties1. This poster introduces an interesting self-assembly mechanism that occurs when a drop of bourbon whiskey is evaporated on a hydrophobic surface. Evaporation of a dilute drop of bourbon at a particular range of proofs leaves a unique web formation where each web pattern is unique to a specific brand of bourbon. The fundamental mechanism of self-assembly of these bourbon webs were investigated here. Despite being so popular, to date, there is no quantitative study on whiskey colloids. Using dynamic light scattering technique, fundamental investigation on colloid occurrence as a function of (i) aging, (ii) proof, and (iii) temperature was also performed in this study.

Results: Commercial whiskey is available at alcohol-by-volumes of 40% or greater and do not inherently contain a large concentration of colloids as its components are mostly solubilized. However, we demonstrated that sub-micrometer colloidal micelles form when whiskey is diluted with water or the temperature is lowered. These colloids are electrostatically stabilized, and the particle size remained stable at low alcohol concentrations. Additionally, these whiskey colloids increased in concentration with higher barrel aging. During droplet evaporation, as alcohol evaporates at a rate much faster than water, these water-insoluble colloidal species precipitated. This results in a dynamic and complex evaporation process whose initial conditions govern the resultant pattern of assembled colloids. At low alcohol content (< 15% ABV) the pattern resembled a coffee ring and at high alcohol content (> 35% ABV) the colloids formed a thin film. However, at intermediate proofs rich variety of web-like microstructures formed. Moreover, we found that, only bourbon whiskeys formed these highly visual patterns (sample size of ten brands) whereas others did not (one Cognac, one Irish whisky, one Scotch, and one Canadian whiskey tested).

Conclusions: The web-like patterns were qualitatively different between commercial brands. Various aged samples (12 months to 71 months) were acquired from a local distillery and, for this brand, the web’s density increased with age; webs did not form with unaged whiskey (a.k.a. “white dog”). This facile technique could be used for maturation analysis or counterfeit detection based on a new class of evaporation-deposition phenomena. Additionally, the colloidal findings of this study will impact industrial filtration and tasting practices of bourbon whiskeys.

References:

  1. H. Kim, et al. PRL 116, 124501, 2016.

Symposium Reception 5:00-6:00 PM