Abstracts

Many previous studies demonstrated evidence that an enhancer and promoter should be in close proximity to recruit RNA Polymerase II (Pol II) and initiate transcription. Recent efforts to measure the distances between active enhancers and their target promoters suggest distances on the order of 200~400nm. However, the dynamics at which enhancers interact with the target promoter is still poorly understood. Specifically, is there a distance threshold for gene activation? Is sustained enhancer-promoter interaction necessary to induce transcription, or is transient interaction sufficient? We study the dynamics of enhancer-promoter communications using the phenomenon of transvection in early Drosophila embryos. In our transvection assay, the enhancer is on one allele and the promoter is on the homologous allele. The alleles are separated when they are transcriptional inactive and only come together during transvection. The difference in distance between transcriptionally active and inactive states allows easy distinction when pairing with fluorescent labeling, making the transvection assay a favorable platform to study enhancer-promoter communications. With the combination of ParS/ParB-mediated DNA labeling and MS2/MCP-mediated RNA labeling, we measured the distance between an enhancer and its target promoter across homologous chromosomes in transcriptionally active and inactive nuclei. We characterized how the trans chromatin loops formed by insulators affect enhancer-promoter communications and subsequent transcriptional activity.

Catalytic microswimmers are artificial systems that self-propel from the conversion of chemical energy into mechanical force. Despite their demonstrated application in fields such as environmental remediation or microrobotics, their implementation in biomedicine remains limited since the materials they rely on are often toxic or have limited bioavailability. Enzyme-powered micromotors have emerged as an attractive alternative since the catalysts they rely on are biocompatible. Moreover, numerous enzymes have been shown to increase the motion of micron-sized particles, including in our lab, where the activity of entrapped catalase was shown to induce large-scale random motion of surface-adherent polymersomes. Despite these exciting outcomes, the fundamental aspects underlying the motion behavior of enzyme-powered motors is still largely unknown; this is even further complicated by the heterogeneity in structure and number of catalytic elements that occurs when using conventional particle assembly approaches. In this study, we prepare uniform micron-sized particles templated from water-in-oil-in-water (W/O/W) double emulsions droplets assembled in a capillary microfluidic device. The assembled particle is a hollow microcapsule made of poly(lactic-co-glycolic acid) (PLGA), a polymer with excellent biocompatibility and tunable biodegradability. PLGA stabilized droplets rapidly assemble into shells with high mechanical rigidity due to fast evaporation of the organic solvent. Moreover, the size of PLGA-containing double emulsions and that of resulting microcapsules can be tuned by osmotic annealing, which depends on the ratio of solute in the inner and outer phases of the double emulsion. We demonstrate the use of these annealed capsules by directly attaching the enzyme urease to the shell through carbodiimide chemistry. We then examine their motion in solution in response to enzymatic turnover. Consistent with previous reports, our initial findings suggest that a high density of active enzymes is required to induce self-propulsion. Our work is the first of its kind to demonstrate motion of uniform particles prepared by double emulsion microfluidics. Moreover, it offers unique advantages to existing methods for robustly screening differences between the thermodynamic and kinetics properties of enzymes and the effects such properties have on observed particle motion.

The demand for thermal management fluids of greater efficiency is on the rise due to increased electrification across multiple industries. Conventional thermal management fluids do not possess the heat sink rates to match or exceed the heat source rates in high power applications. Adding various additives is a promising approach to engineering the properties of thermal management fluids for intended applications. The thermal conductivity of mixtures and suspensions has been extensively studied; however, there are few reports that study their convective heat transfer properties. Additionally, observation of these fluids in-situ is rarely undertaken creating a degree of separation between experimentation and characterization. This work aims to test suspensions for their convective thermal properties using a microfluidic platform comprising a microheater and a PDMS microchannel. An infrared camera is used to measure temperatures of the fluid in-situ under laminar flow conditions. The thermal conductivity can be semi-quantitatively assessed by examining the axial temperature profile, while the convective heat transfer coefficient (and by extension the Nusselt number) can be quantitatively assessed via a macroscopic energy balance between Joule heating of the microheater and convective cooling of the fluid. This work aims to aid in the rational design of thermal management fluids with enhanced cooling efficiency.

Thrombin and fibrin are crucial proteins in relation to coagulation and hemostasis. It has been shown previously that thrombin becomes trapped within fibrin fibers during this process [Zhu et al. ATVB 2018], but not much is known about thrombin activity while bound, nor have there been direct measurements of clot-bound thrombin by its enzymatic activity. A fluorogenic thrombin sensitive substrate BOC-VPR-AMC (628 Da, Km = 21 μM, kcat = 109 s-1) was perfused over whole blood and plasma clots formed in microfluidic devices and washed with buffer to remove free thrombin. The flow was repeatedly stopped and started to allow for cleavage of the substrate by bound thrombin during stopped flow cycles and washed away during start flow cycles. It was observed that bound thrombin maintains its enzymatic activity over long periods of time under flow over repeated stop-start cycles. Three stop/start cycles were averaged to approximate the substrate conversion V0 = 0.78 ± 0.03 µM/s and apparent active clot bound thrombin (IIa) concentration within the reaction volume of 9.24 ± 0.35 nM. The signal from the substrate cleavage comes from a 60 x 250 x 250 µm volume in which the clot forms upon a collagen/tissue factor patterned surface. Clot bound thrombin is confined to a thin fibrin layer ~10-20 µM in height, therefore it is expected that the actual concentration of active clot bound thrombin is up to 10-fold higher. This was further expanded to investigate the effect of clot bound thrombin of heparin/antithrombin (Hep-AT) complex perfused with substrate over fully formed clots. Hep-AT was able to penetrate fibrin structures and inhibit thrombin’s activity after a short waiting period. The activity and capabilities of clot bound thrombin to polymerize purified fibrinogen, introduced following buffer wash, to remove free thrombin was also probed. Clot bound thrombin maintains its enzymatic activity and its ability to facilitate fibrin formation for long periods of time under flow. It is important to understand the dynamics between thrombin and fibrin and the extent of anticoagulant activity of thrombin’s retention in fibrin fibers.  

Platelets have toll-like receptors (TLRs), however their function in thrombosis or hemostasis under flow conditions is not fully known. Thrombin-inhibited anticoagulated whole blood was treated with various TLR agonists and then perfused over fibrillar collagen using microfluidic assay at venous wall shear rate (100 s-1). Platelet deposition was imaged with fluorescent anti-CD61. For perfusion of whole blood without TLR agonist addition, platelets rapidly accumulated on collagen and eventually occluded the microchannels. Interestingly, most of the tested TLR agonists (Pam3CKS4, MALP-2, polyinosinic-polycytidylic acid HMW, imiquimod, and CpG oligodeoxynucleotides) strongly reduced platelet deposition on collagen, while only the TLR4 agonist endotoxin lipopolysaccharide (LPS) enhanced deposition. Following 90 sec of deposition under flow of untreated blood, the addition of various TLR-7 agonists (imiquimod, vesatolimod and GSK2245035) all caused immediate blockade of further platelet deposition. Since TLR signaling can activate nuclear factor-kappa B (NF-B), the IKK-inhibitor (IKK inhibitor VII) and NF-B inhibitor (Bay 11-7082) were tested. The IKK/NF-B inhibitors strongly inhibited platelet deposition under flow. Furthermore, addition of Pam3CSK4 (TLR1/2 ligand), MALP-2 (TLR2/6 ligand) and Imquimod (TLR7 ligand) reduced phosphotidylserine (PS) exposure. Apart from LPS, the addition of TLR agonists to whole blood reduced platelet deposition under flow on collagen, potentially revealing a platelet adjustment to reduce thrombotic clot growth during infection or tissue damage.

Characterization of polymer-solid interactions is critical for understanding the reaction of polymers on catalyst surfaces for polymer upcycling. In the present study, we measure rates for capillary infiltration of polystyrene (PS) and polyethylene (PE) into disordered packings of silica nanoparticles that had been modified by ALD with submonolayer and monolayer coverages of TiO2, WO3 and CaCO3. Infiltration times depends strongly on the size and surface composition of nanoparticles. The effective viscosities of polymers determined from the infiltration times and the Lucas-Washburn equation decrease linearly with pore size in the range from 2 to 20 nm. Infiltration rates measured as a function of surface composition are used to calculate contact angles and interfacial energies for PS and PE. To understand the effect of composition, microcalorimetry measurements with n-hexane and benzene on ALD-modified SBA-15 show a strong correlation between n-hexane adsorption and PE-solid interfacial energies and between benzene and PS-solid interfacial energies. The implications of these measurements for understanding reactions on solid surfaces will be discussed.

Modeling thrombus growth in pathological flows allows evaluation of risk under patient-specific
The excessive formation of blood clots within the circulatory system (thrombosis) is known to
initiate heart attacks and strokes. Therefore, obtaining insights into the formation and

progression of a clot (thrombus) under pathological flows allows evaluation of risk under patient-
specific pharmacological, hematological, and hemodynamical conditions. To this end, we have

developed a 3D multiscale simulation framework for the prediction of thrombus growth under
flow on a spatially resolved surface presenting collagen and tissue factor (TF). The multiscale
framework is composed of four coupled modules: a Neural Network (NN) that accounts for
platelet signaling, a Lattice Kinetic Monte Carlo (LKMC) simulation for tracking platelet positions,
a Finite Volume Method (FVM) simulator for solving convection-diffusion-reaction equations
describing agonist release and transport, and a Lattice Boltzmann (LB) flow solver for computing
the blood flow field over the growing thrombus. Computationally efficient parallel simulations
were achieved by using open-source software where applicable: Palabos (LB), OpenFOAM
(FVM), and Multiscale Universal Interface for module-coupling. Parallel versions of LKMC and
NN were achieved by employing a novel parallel platelet-decomposition approach. A reduced
model of the coagulation cascade was embedded into the framework to account for TF-driven
thrombin production. The 3D model was first tested against in vitro microfluidics experiments of
whole blood perfusion with various antiplatelet agents targeting COX-1, P2Y1, or the IP receptor.
The model was able to accurately capture the evolution and morphology of the growing
thrombus. Certain problems of 2D models for thrombus growth (artifactual dendritic growth) were
naturally avoided with realistic trajectories of platelets in 3D flow. The generalizability of the 3D
multiscale solver enabled simulations of important clinical situations, such as cylindrical blood
vessels and acute flow narrowings (stenoses). Enhanced platelet-platelet bonding at
pathologically high shear rates (e.g., von Willebrand factor unfolding) was required for accurately
describing thrombus growth in stenotic flows. Overall, the approach allows consideration of
patient-specific platelet signaling and vascular geometry for the prediction of thrombotic
episodes.

It is known that an enhancer regulates transcriptional activity of its gene through activators and repressors by establishing the spatiotemporal expression of a target gene. Since enhancers may contain multiple binding sites for the same transcription factors (TFs), it is not yet understood how each binding site affects the overall transcriptional competency of the enhancer. In this study, we have implemented the MS2-MCP live imaging technique to quantitatively analyze dynamic transcriptional activity of a region of the snail distal enhancer. Through systematically modulating 3 Dorsal (Dl) and 1 Twist (Twi) binding domains, we found that the mutations in these binding sites caused a drastic reduction in the maximum intensity, resulting in a reduction in total mRNA production. Using an equilibrium binding model, we characterized the synergistic capabilities of each binding site by quantifying the contribution of each binding site to the total transcriptional dynamics. While the timing of activation was not substantially affected in the mutated constructs, the bursting dynamics and nuclei activation were altered to varying degrees. To further investigate bursting dynamics, we implemented the Hidden Markov model and determined the time spent in the on and off states as well as other kinetic parameters. Through this we identified distinct mechanisms by which TFs regulate proper gene expression during development.

Ice formation and growth are ubiquitous and play an important role in atmospheric sciences, biology, and materials science. However, controlling the growth of ice at an interface requires a detailed understanding of the underlying interfacial thermodynamics and of how the chemical and structural features of a surface influence the favorability of its interactions with ice (or the “icephilicity” of a surface). To better understand this phenomenon, we leverage molecular simulations and novel enhanced sampling techniques to characterize the free energetics of ice nucleation and growth at an interface. By exploring a family of realistic surfaces, like AgI and BaF2, and model surfaces based on the structure of bulk ice, we provide new insights into the key molecular determinants of icephilicity.

It is shown that both epigenetic states and cell signaling pathways have significant effects on cell reprogramming efficiency. However, the kinetics at which activation of the signaling pathway or epigenetic modifications affect downstream gene expression dynamics remain unclear. Using live imaging, we characterized how upstream cell signaling pathway or epigenetic modulations affect the downstream gene expression dynamics. To visualize endogenous transcriptional activity of Sox2 and Klf4, we used CRISPR/Cas9 system to add 24 copies of the MS2 or PP7 to endogenous Sox2 and Klf4 gene loci. Upon transcription, MS2 coat protein (MCP) or PP7 coat protein (PCP) fused with fluorescent proteins would bind to MS2 or PP7 transcripts, allowing us to visualize nascent transcripts in individual cells. We modulated the LIF/STAT3 signaling pathway by adding JAK inhibitor I or by adding different amount of the LIF ligand to the Sox2/Klf4 tagged cells. Cells were imaged every 6 hours to characterize how fast the genes could respond to the cell signaling changes. To further analyze pluripotent gene expression dynamics upon epigenetic changes, we developed a reversible and inducible CRISPR/dCas9-based tool to modulate epigenetic states on a specific locus in living cells. Histone modifiers were recruited to induce histone methylation on the target locus (Sox2 and Klf4 in this project) in the presence of the ABA inducer. Histone methylation level is analyzed through ChIP-PCR using histone modification antibody. With live imaging, we can characterize the time scale of epigenetic changes and the kinetics of Sox2/Klf4 gene expression.

Creatures living in cold environment have developed unique strategies to survive. One of their tactics is to evolve antifreeze proteins (AFPs) which lower the freezing temperature by binding to ice. AFPs bind to ice through specific regions on their surface known as ice binding sites (IBS). Each AFP has its own IBS which binds to specific ice planes. Identifying IBS is crucial for understanding how AFPs bind to ice. Here, we use specialized molecular simulation wherein an external potential is used to stimulate ice formation in the AFP hydration shell. We find that the most ice-philic AFP regions, where ice nucleates most readily in response to the external potential, display a strong correspondence with the experimentally-determined IBS (using site-directed mutagenesis). In addition to identifying the IBS, our specialized simulations also shed light on ice polymorph and facet that optimally binds the AFP IBS.

The ability to modify free energy landscapes of chemical systems by introducing metastable states where systems become kinetically trapped in desired conformations has allowed for the design of far-from-equilibrium functional materials. One example is a class of soft matter known as bicontinuous interfacially jammed emulsion gels (bijels). Bijels consist of two immiscible fluid phases whose phase separation has been arrested by the energetically-favorable adsorption of a dense monolayer of nanoparticles (NPs) at the fluid-fluid interfaces and it is this unique structure that makes them ideal for applications requiring inter-phase mass transfer or NP-laden interfaces. While bijel formation has traditionally relied on thermal quenching of binary mixtures to induce phase separation, prior work by the Lee group has demonstrated bijel formation using solvent transfer-induced phase separation (STRIPS). In STRIPS a co-solvent compatibilizes two otherwise immiscible fluids to obtain a homogeneous ternary mixture and phase separation is triggered by the removal of the co-solvent via liquid phase diffusion. One of the benefits of using STRIPS to create bijels is the introduction of additional processing parameters which provide ways to exercise control over the structure of the STRIPS bijels. However, the STRIPS bijel processing-structure relationship is not well understood and constitutes the primary bottleneck to designing bijels with tailor-made properties. The goal of our research is to develop a fundamental understanding of the relationship between the STRIPS processing parameters and bijel morphology by encoding the physics of STRIPS bijels in a hybrid computational model, capturing the relationship between the high-dimensional processing parameter space and bijel morphology using machine learning, and performing the inverse design and synthesis of custom STRIPS bijels.

Atomic layer deposition (ALD) was used to prepare ZrO2 films on the surface of the mesoporous silica, SBA-15, and to modify the surface of these films with WO3 in order to form tungstated zirconia. Adsorption-desorption isotherms, pore size distributions, and transmission electron microscopy demonstrated that the ALD synthesis produced zirconia films that were conformal to the SBA-15 pores. DRIFT spectroscopy of pyridine adsorbed on the tungstated-zirconia SBA-15 samples showed adsorbed pyridinium ions, confirming the presence of Brønsted-
acid sites on this material, consistent with what has been reported for bulk tungstated zirconia. The ALD-synthesized, tungstated-zirconia SBA-15 was also shown to be active in the acid-catalyzed H-D exchange between toluene and D2O.

Thin films with a stoichiometry of CeFeOx were conformally deposited on high-surface-area γ-Al2O3 by Atomic Layer Deposition (ALD). X-ray diffraction (XRD) patterns, High-Resolution Transmission Electron Microscopy (HRTEM) images, Raman spectra, and Mӧssbauer spectra demonstrated that 2-nm-thick films exhibited a perovskite structure after reduction at 1073 K but converted to a fluorite phase upon oxidation at 1073 K. The transition between the fluorite and perovskite structures was reversible for at least five oxidation and reduction cycles. Coulometric titration at 1073 K showed that reduction of the fluorite phase occurred in two steps, one at a P(O2) of 10-15 atm and a second at a P(O2) of 10-8 atm. X-ray Photoelectron Spectra (XPS) demonstrated that Ce has +3 valence in the perovskite phase and +4 valence in the fluorite phase, while Fe is mixed +2 and +3 valence in the reduced perovskite phase and +3 valence in the fluorite phase. The CeFeOx thin films were found to retain high surface area and remain conformal to the γ-Al2O3 support upon redox cycling suggesting that they may be useful in applications ranging from catalysis to spintronics.

The biological world consists of several cells and microorganisms that contain renewable biofuels and bioproducts that can help resolve current climate and environmental waste crises. I am targeting algae in two categories for large-scale processing: biofuels and bioplastics. By using cavitation of microbubbles, the energy needed to lyse algae cells can be greatly reduced; thus, making it economically viable to produce biodegradable plastics and biofuels. Using advanced techniques in very large-scale microfluidic integration (VLSMI) we can generate production scale quantities of uniformly sized microbubbles. Using results from computational modeling, we can determine the resonant frequency of the bubbles based on size and composition, high powered ultrasound at the resonant frequency. Thus far, we have worked on a model to visualize the response of various microbubbles and their time-dependent response to high frequency ultrasound. This modeling has led us to the creation of microfluidic devices that can produce uniformly sized microbubbles. It also has led us to developing a high-power ultrasound setup to experimentally test cavitation events on microbubbles to verify computational results. In this research, the timescale of cavitation is on the order of microseconds. High speed imaging is limited when trying to measure cavitation events, thus we rely on using acoustic sensing to measure a shift in echo response to quantify cavitation. Finding the most efficient cavitation regimes and scaling them up will be a major challenge we foresee. Cavitation studies for lysis of cell walls have been shown as the most energy efficient way for extraction and recovery of bioproducts from algae; however, no studies have tried to optimize ultrasound frequency to increase the efficiency of the cavitation and minimize the energy input.

Polymer upcycling has become a major focus to tackle the global problem of plastic pollution. The goal of polymer upcycling is to make products that are much more valuable than commodity plastics. Our strategy is to convert a small fraction (< 5%) of C-C bonds into C=C bonds in the polyolefin molecules using heterogeneous catalysis and then functionalize those double bonds with various functional groups (e.g., alcohols, aldehydes, carboxylic acids, etc.). This would allow us to maintain the high degree of polymerization of the molecules. Generally, heterogeneous catalysts need to be incorporated onto a porous support to maximize the catalytically active area and facilitate intimate contact with the polymer. The typical size of these pores is of the order of a few nanometers which means that for the polymer molecules to undergo reaction, they will have to move into these nanopores which might be significantly smaller than the characteristic size of the polymer chains. Extreme nanoconfinement of polymers will lead to loss of their conformational entropy, which could significantly alter their reactivity and kinetics. Moreover, existing literature shows that confinement of high molecular weight polymers can substantially change their transport properties (e.g., diffusion limitations). Pore geometry is another important factor that could affect the transport of polymer molecules inside these nanopores. Finally, interactions between the catalyst surface and the dehydrogenated & fully hydrogenated segments of the polymers can drastically influence the reaction efficacy. For example, if the dehydrogenated segments have a higher affinity for the catalyst surface, then after the dehydrogenation of the first few polyolefin molecules, the catalytic sites will get deactivated and will no longer be available for fresh polyolefin molecules to undergo dehydrogenation. My goal is to study these phenomena and gain insights to optimize the catalytic dehydrogenation of polyolefins. I use a dense nanoparticle packing as a model porous support and study the transport of model polyolefin molecules using techniques like spectroscopic ellipsometry, IR spectroscopy and optical and electron microscopy. Preliminary results show the displacement of model partially dehydrogenated polyolefin molecules by fully hydrogenated polyolefin molecules inside the nanopores of our model porous system, which could potentially imply effective heterogeneous catalysis for dehydrogenation of polyolefin moecules.

Polymer composites have been widely studied because of their outstanding properties. Typically, polymer nanocomposites (PNC) are fabricated by adding inorganic nanofillers to a polymer matrix. In this work, a high-filler PNC is created by infiltrating polystyrene (PS) or poly(2-vinylpyridine) (P2VP) into a nanoporous gold scaffold exhibiting a bicontinuous structure and nanoscale pores. Infiltration occurs through capillary forces by heating PS (P2VP) above its glass transition temperature. PS and P2VP, having different affinities to the gold scaffold, exhibit
different segmental dynamics inside the confined pores as measured through Tg. The more attractive P2VP shows a 20°C increase in Tg while PS shows only a 6°C increase at a comparable molecular weight. The effect of molecular weight on infiltration kinetics is presented with P2VP exhibiting a longer infiltration time compared to PS having a similar molecular weight. The interconnected structure of these composites could facilitate high ion (electron) conductivity, thus enabling enhanced performance for batteries and flexible electronics.

Highly loaded polymer nanocomposite films (PNCFs) have improved physical properties due to the
synergistic combination of organic polymers with inorganic nanomaterials. The properties of a PNCF could
theoretically be further augmented by incorporating a polymer blend, which may impart the desired traits
of each polymer. However, blend-PNCFs suffer from similar compatibility issues that plague current
polymer blends, as most polymers are thermodynamically immiscible. Recent work has shown that the
confined geometry of highly loaded PNCFs strongly influence the dynamics and morphology of these
materials. What is relatively unexplored, however, is how the confinement within the interstitial pores of a
dense nanoparticle packing can affect the thermodynamics of polymers. This experimental work studies the
role of confinement and polymer-nanoparticle interactions on the phase behavior of two typically
immiscible polymers. The phase behavior is characterized by optical microscopy, scanning electron
microscopy, and measurements of the glass transition temperature. Promising initial findings suggest that
confinement suppresses macroscopic phase separation, in good agreement with recent theoretical
predictions. By understanding the role of confinement and polymer-nanoparticle interactions in these
systems, a myriad of novel applications could be unlocked for blend-PNCFs with finely tuned mechanical,
electrical, and transport properties.

Understanding nanoparticle diffusion is a vital component to polymer nanocomposite (PNC) applications including self-healing materials or drug delivery. Traditional measurement methods such as Rutherford Backscattering Spectroscopy (RBS) or dynamic light scattering (DLS)/X-ray photon correlation spectroscopy (XPCS) have limitations in diffusion model, material systems, or length scales (< 1 μm). Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) is a powerful tool for identifying the chemical composition and 3D distribution of particles in polymer nanocomposite (PNC) systems. Using ToF-SIMS, we measure nanoparticle diffusion in a poly(2-vinylpyridine) (P2VP) and silica (SiO2) system across multiple molecular weights and NP sizes in a cross-sectional sample. We construct novel polymer-PNC-polymer trilayer samples and anneal ex-situ followed by ToF-SIMS of a cross-section to detect silicon ions as the nanoparticles diffuse from the PNC into the adjacent polymer layers. We established a method to analyze 3D ToF-SIMS data that corrects for sample tilt, deconvolutes beam resolution, and produces a 1D concentration profile that we fit to extract the NP diffusion coefficient. Our results expand our current understanding of NP diffusion in polymer melts across micron length scales which were previously not possible and are supported by previous RBS results. These results also prove ToF-SIMS is a powerful tool for determining NP dynamics and can be extended to polymer dynamics in future work.

Polyolefins constitute the majority of both plastic production and waste, but less than 10% is successfully recycled. Conventional mechanical recycling degrades polyolefins, reducing the value of the reclaimed material. In addition, the stability of C-C bonds composing the backbone of polyolefins poses an obstacle to chemical recycling. To both
target polyolefin waste and create a sustainable resource for the production of specialty polymers we propose a new approach to polymer-to-polymer chemical upcycling. We propose dehydrogenating C-C into C=C then functionalizing the resulting unsaturations. This poster demonstrates progress in the latter step with well controlled functionalization of poly(cyclooctene) (PCOE)—a model dehydrogenated polyolefin—using thiolene click chemistry. This reaction proceeds under mild conditions and avoids undesired crosslink-ing or chain scission side reactions. Successful functionalization of PCOE with mercap-toethanol increases ultimate shear stress in a lap joint application to a maximum of 4.10± 0.48 MPa from 0.48 ± 0.15 for hydrogenated PCOE, demonstrating enhancement of a
property critical to commercial applications in packaging or adhesives.

Polymers are known to adopt extended solvophilic conformations in good solvents and collapse into globular solvophobic conformations in poor solvents. The ability to exercise precise control over the collapse of solvated polymers has diverse applications ranging from drug delivery to plastics recycling. The design of polymers and processes for such applications requires a comprehensive understanding of the effects of chain length, branching, temperature, and solvent composition on polymer conformation. Using specialized molecular simulations, which involve applying a tunable external potential to the solvent in the vicinity of a polymer, we can sample different conformational states of the polymer and characterize its propensity to collapse. We use such simulations to study the collapse of simple hydrophobic polymers in water. We characterize the effects of temperature, polymer chain length and polymer architecture on the collapse transition. We also show how similar specialized simulations can be used to study conformational transitions in proteins.

Liquid crystal (LC) forms long ranged orientational order that can controlled by electric/magnetic field, temperature and boundary conditions of surfaces. Because of these properties, LC molecules such as 5CB are emerging to be a desired soft template for reconfigurable self-assembly of nanocrystalline particles (NCP). However, the insertion of NCP into 5CB causes disturbance to the orientational order making NCP thermodynamically unfavorable to disperse. Coating NCP with ligands of various chemical moieties has proven to be a useful technique to help prevent phase separation of NCP. The rational design and control of self-assembly behavior of NCP in 5CB host requires a molecular understanding of the interaction between 5CB molecules and ligand chemistry. In this research, we employ all-atomistic simulation to understand the interaction of different chemical moieties with 5CB and the binding behavior of NCPs in 5CB.

Crystal nucleation is an important phenomenon in the broader field of colloidal self assembly. A defining feature of colloidal crystallization is that it takes place in a liquid (usually water) medium. Yet, most computational studies of colloidal crystallization have largely ignored the role of hydrodynamic interactions (HI) during nucleation, growth, and dissolution. Recent studies, however, have indicated that HI between particles, even in a quiescent liquid medium, may play a significant role during assembly, potentially impacting crystal growth kinetics [1] and gelation [2]. Jenkins et al. [3], and later Lee et al. [4] also showed that hydrodynamic correlations between particles mediate transformation pathways in a floppy colloidal crystal.
The primary technical challenge associated with including HI into particle simulations is the computational expense associated with the resolution of short-ranged (lubrication) interactions while also capturing Brownian fluctuations. Malevanets and Kapral [5] have constructed a “mesoscale” simulation method referred to as multiparticle collision dynamics (MPCD), which is a coarse-grained method that describes the solvent in terms of effective particles subject to “collision” and “streaming” operations. Although MPCD has been shown to appropriately capture the fluid behavior, it was not obvious how to couple the solvent to colloidal particles, especially while also resolving short-ranged hydrodynamics [6]. In this regard, Poblete et al. proposed a discrete particle model within the MPCD framework (MPCD+DP) and demonstrated accurate
reproduction of Stokes flow around a spherical colloid [7]. Wani et al. used the same model to study diffusion and sedimentation in colloidal suspensions [8].
Despite this progress, the use of MPCD+DP has not yet been quantitatively validated in the context of crystallization and gelation, where short-ranged hydrodynamic effects are likely to be critical. Here, we explore the use of MPCD+DP with the goal of quantitatively validating the method for use in crystallization settings. We first validate the method by investigating (1) the near-wall diffusion behavior and (2) the dynamics of two associated colloids. The diffusivities in both situations are quantitatively measured and compared to theoretical results. The discretization of the colloidal particles also is studied in detail. Finally, we consider a system of attractive
particles in which both the growth and dissolution of a colloidal crystallite are studied with MPCD+DP. We demonstrate that significant variations in the crystal dissolution and growth rate are found when HI is included.

The fracture of end-linked polymer networks strongly affects the performance of these widely-used materials, but a fully quantitative understanding of the fracture behavior is still lacking. In recent years, theories built on the Lake-Thomas theory have emerged to predict the fracture energy by incorporating the effect of defects in the networks.
However, experimental studies have suggested that the energy stored in each bond at the time of fracture (U) may be much smaller than the bond dissociation energy, which is a usual assumption in these theories.
In this study, we perform molecular dynamics (MD) simulations to model end-linked polymer network systems and analyze the energy dissipated during fracture. Previous studies in our group have shown that a loop-modified Lake-Thomas theory successfully predicts the fracture properties of polymer networks without any adjustable non-
physical parameters, but questions around the choice of U remain. Additionally, a dependence of the energy dissipated per bond on the polymer strand length is observed. I will describe our simulations attempting to uncover how the energy dissipated depends on the polymer strand length, the network volume fraction, and defect
concentration in the network.

Glassy materials, or disordered solids, are ubiquitous in modern life and provide a wide opportunity for applications to different engineering problems, including the design of membranes for separations. Despite their importance, the relationship between dynamic behavior and local structure remains an open scientific question. In this work we study the simple diffusion of small particles in homopolymer melts near and below the glass transition of the polymer. We use a machine-learned quantity, softness, to measure whether a local chemical environment permits high or low particle mobility. The probability of a particle’s rearrangement at temperatures near the glass transition has been previously shown to be an Arrhenius process with energy and entropy scales which are dependent on softness; we explore how changes in the size of the penetrant molecules and their interaction potential with the polymer medium impact the rearrangement behavior and examine the relationship between softness and the self-diffusion coefficient. A more comprehensive understanding of the interplay between structure and dynamics in these systems could provide an opportunity to design materials for low-energy separations processes and other applications where the use of glassy membrane materials is common.

The dynamics of systems biological processes are usually modeled by a system of ordinary differential equations (ODEs) with many unknown parameters that need to be inferred from noisy and sparse measurements. Here, we introduce systems-biology informed neural networks for parameter estimation by incorporating the system of ODEs into the neural networks. To complete the workflow of system identification, we also describe structural and practical iden tifiability analysis to analyze the identifiability of parameters. We use the ultridian endocrine model for glucose-insulin interaction as the example to demonstrate all these methods and their implementation.

Polymer nanocomposites (PNCs), a combination of inorganic and organic fillers in polymer matrices, are of considerable interest because of their versatile properties. Specifically, the wetting behavior of nanoparticles (NPs) can enhance surface properties, such as wettability, friction, and durability. In our work, we utilize time-of-flight secondary ion mass spectrometry (ToF-SIMS) to investigate the wetting of poly(methyl methacrylate) grafted silica nanoparticles (PMMA-NPs) in a poly(styrene-ran-acrylonitrile) (SAN) matrix. To utilize ToF-SIMS, experimental parameters such as incident beam energy and current as well as charge compensation are optimized to maximize secondary ion yields and minimize sample damage. From ToF-SIMS depth profiles, the PMMA-NP surface excesses (Z*) are measured as a function of time, allowing for the determination of the mutual diffusion coefficient. By varying the PMMA-NP loadings and film thicknesses, we study the diffusion behavior of PMMA-NPs in SAN and aim to elucidate a morphology map for the PNC system using ToF-SIMS, along with other characterization techniques such as atomic force microscopy and transmission electron microscope. The results will allow for greater control over NP dispersions and PNC morphologies, which are crucial in tailoring PNC properties.

Aedes aegypti is a species of mosquitoes that can spread dengue fever, Zika fever, yellow fever viruses, and other disease agents, which affect millions of people worldwide, especially in tropical and developing countries. There is an urgent need for new pesticides that specifically target mosquitoes and are safe for humans to stop further disease spread. Drug transporters, especially P-glycoprotein (P-gp), have been particularly interesting targets for understanding drug metabolism, pesticide toxicity, and designing drugs. However, their role in mosquitoes remains unexplored. This study aims to characterize the role of P-gp transporter in Aedes aegypti xenobiotic transport and explores Aedes aegypti cell line Aag2 cells as a probable model to study insect drug transporters. The multigene family of P-gp and the multi-number of paralogues make this transporter difficult to study in most insects. Almost all insects carry between two to seven paralogues that appear to be different in terms of their spatial expression. A. aegypti are almost unique in having a single paralog copy of P-glycoprotein, which facilitates the study of this gene in this organism. Analysis of RNA-seq data shows inherently low expression of P-gp in Aag2 cells. No significant differences between Aag2 wild-type and Aag2 knock-out lines (both heterogeneous and clonal) were observed in in vitro toxicology assays with paclitaxel and pyridaben. The data suggest that Aag2 is a suitable system for studying drug transporters in insects due to the low endogenous expression of P-gp in Aag2 cells.

Biofouling, the undesired formation of biofilms, can contaminate a wide variety of surfaces that operate in aqueous environments, such as medical device implants and water filtration membranes. One way to combat this issue is to increase a surface’s hydration to prevent proteins from adsorbing onto the surface, which is the first step in biofilm formation. While homogeneous surface modifications, such as polar and/or zwitterionic surface coatings employ electrostatics to enhance surface hydration, more heterogeneous surface modifications derived from proteins themselves could also provide enhanced surface hydration, since proteins surfaces have evolved to resist non-specific aggregation and fouling by other proteins in the crowded cellular environment. By identifying and characterizing the most hydrophilic regions, we aim to uncover the chemical patterns responsible for protein-protein selectivity and provide a basis for the creation of non-fouling surfaces. Using specialized molecular dynamics simulations, we have characterized the atomic-level hydrophilicity of a protein surface directly based on water affinity. Using this characterization and the DBSCAN clustering algorithm, we have identified protein surface patches of similar water affinity for various proteins, ranging from highly hydrophobic to highly hydrophilic. Our results indicate that patches of similar water affinity contain both polar and nonpolar atoms as well as amino acids of varying hydrophilicity. We have also found that proteins surface patches of similar partial charge do not have similar water affinity, indicating the importance of other factors, such as chemical patterning and surface topology on protein surface hydrophilicity.

To combat climate change and phase out fossil fuels, hydrogen has been proposed as an alternative fuel source since it release no CO2 when it burns and it 3 times more energy dense than hydrocarbons (gravimetric). One of the main hurdles to a hydrogen economy, is hydrogen storage. MXenes have been shown to be capable of some hydrogen storage. However, there is a demonstrable gap with respect to where in the MXene is hydrogen stored, how is it stored (as H or H2) and how much hydrogen can be stored in a particular MXene. To bridge this gap, we came up with a framework that systematically explores hydrogen in MXenes using Ti2C and Ti3C2 as starting models through Density Functional Theory (DFT) calculations. We look at two levels of complexity stoichiometric vs nonstoichiometric Ti2C and Ti3C2. We also look at how hydrogen storage changes with tuning the terminations. In the end we have been able to show that hydrogen storage in MXenes is possible but is highly vacancy, metal, and termination dependent.

The fabrication and production of useful polymers from renewable or sustainably derived  components represent an increasingly important societal concern. Plant-derived fatty acids are  candidates for such applications due to their unsaturated polymerizable structure and accessibility. Here,  we report on the utilization of such species to generate highly ordered nanostructured polymers.  Specifically, we examine a thermotropic hexagonal columnar liquid crystal that is formed by self-assembly  of a supramolecular complex of a ‘template’ molecule with complementary ligands. In this case, the  template is a tri-functional amine, and the ligands are based on sustainably-derived, citronellol, which is  a natural aliphatic monoterpenoid extracted from rose oil. We explore the phase behaviors of the system  as a function of the stoichiometric ratio between the template and ligand. We observe the formation of  hexagonal columnar mesophases in a relatively broad range of stoichiometries from 1:1.5 to 1:4. Chemically cross-linking the mesophase and removal of the molecular templates create nanoscale pores with diameters ranging from 1.6 to 1.0 nm respectively. Nanoporous networks made by these systems  exhibit sharp selectivity for penetrants with different charge and size, and appear also to demonstrate  shape selectivity, as investigated by adsorption experiments using dye molecules. We anticipate that  these materials can retain or further improve the performance of current state-of-the-art nanofiltration  membranes, while contributing an important sustainability aspect. 

The development of low-carbon sources of energy is critical for society, and there are myriad associated challenges for materials research. For example, alkaline fuel cells and energy harvesting from osmotic pressure gradients (so-called “blue energy”) are attractive energy technologies, but their practical implementations are stymied by critical performance shortcomings in the membranes that are integral to devices. A key requirement is the realization of highly selective ion-conducting membranes that are stable under the use conditions in the devices (e.g. high pH and elevated temperature for alkaline fuel cell membranes). The use of uniform nanostructured materials provides a route to addressing the selectivity issue. However, we face critical knowledge gaps regarding transport in nanoscale environments in the presence of charge. These knowledge gaps frustrate attempts to rationally design nanostructured membranes that are fit for purpose. Additionally, currently available membranes are based on random, disordered structures, and offer neither the selectivity needed in applications, nor the ability to conduct fundamental studies connecting structure to transport properties. Here, we present a polymerizable surfactant that self-assembles into a variety of mesophases that, upon crosslinking, yield solid polymer films featuring highly regular ordered nanostructures. We determine the structural characteristics of each of these mesophase-derived membranes via small angle x-ray scattering, and then assess how well their structure is maintained under aggressive conditions for extensive lengths of time. Electrical impedance spectroscopy is used to assess the conductivity of the films in a variety of conditions found in alkaline fuel cells. We find that the majority of these mesophases are exceptionally robust in heated basic conditions. Conductivity is competitive with other works in the field. We propose a model detailing how mesophase structure and chemical composition impact conductivity on a theoretical level, showing how the advancement of conductivity studies relies on the design of ordered, high-conductivity mesophases.

Electrowetting (EW)-based technologies inform state-of-the-art platforms for droplet wetting state modulation on surfaces. However, the requirement of direct droplet-electrode contact may pose scalability challenges as droplet sizes become smaller and the number of droplets to be actuated increases. Here we present a contactless method that is capable of modulating droplet wetting states reversibly on non-wetting substrates. The method, dubbed dielectric charge injection (DCI), involves corona discharge-based charge injection – above a critical voltage, electric field concentration around a sharp, conductive probe exceeding the surrounding medium’s dielectric strength leads to ionization of the dielectric medium. The generated ions then accelerate away from the probe due to like-polarity repulsion, leading to charge injection onto any target surface containing a reference electrode and overlaying dielectric layer. Voltage plays a central role in this multiscale transport phenomena, manifesting as discrete molecular ions and electric fields toward manipulation of macroscopic contact angles. Using DCI, we demonstrate wetting of a pure water droplet on a polydimethylsiloxane (PDMS) surface immersed in hexadecane, a low dielectric liquid. Starting from a completely non-wetting state, DCI is able to facilitate wetting of the droplet, with tunable wide-range resultant contact angles. By simple removal of the external physical stimulus, the droplet is able to dewet fully back to the non-wetted state. The nonwetting-wetting state reversible transition is capitalized in an application towards temporally controllable droplet-surface material interchange, which possesses utility in integrating droplet encapsulation-based technologies (e.g. microfluidics) to surface-based analytical technologies (e.g. MALDI-MS). DCI presents a contactless, reversible droplet wetting state modulation platform that builds upon the inspiring successes of EW-based technologies – simple yet powerful, with vast application potentials in digital fluidics, lenses/displays, and beyond.

Bicontinuous interfacially jammed emulsion gels (bijels), a unique class of particle-stabilized fluid-bicontinuous structures, are formed by arresting the spinodal decomposition process of two liquid phases via jamming of nanoparticles at interface. The unique self-assembled bicontinuous morphology and the presence of nanoparticles at the interface make bijels interesting in many applications. However, existing methods of bijels fabrication face the challenges of limitations on feature size, material selection and scalability. We have developed new pathways for triggering spinodal decomposition that enable scalable fabrication of bijels with various designed features. For instance, bijels with uniform submicron domain sizes are generated by regulating the quenching dynamics during phase separation. The resulting structure resembles the Spinodal-like structures possessing superior optical properties found in nature, therefore, greatly extending the potential of bijels in optical applications as their domain sizes match the wavelength of interest (visible and solar). Passive daytime radiative cooling (PDRC) based on bijels is demonstrated as an example to show the structure-optical property relationship of bijels. By carefully tuning the feature size and material selections, ultra-white/bright bijel film with >97% reflectance in the solar spectrum and >95% emittance in the long-wave IR window is obtained. Its cooling performance is further tested in outdoor tests with prototype devices. Furthermore, carbonized Bijel serves as template for carbon air cathode with 3D continuous tri-phasic contact, which solves the hurdle of sluggishness of ORR reaction.