Abstracts
Oral Presentations
Session I
Mechanics of polymer nanocomposites with high nanoparticle loading
Polymer nanoparticle composites (PNC) with ultra high loading of nanoparticles (>50%) have been shown to exhibit markedly improved strength, stiffness, and toughness simultaneously, compared to the neat systems, and therefore have become an interesting class of material for a wide range of applications. A recently established method, unsaturated capillary rise infiltration (UCaRI), allows for fabrication of PNC thin films with uniform or graded porosity, which have been shown to increase in hardness and modulus as fill fraction of polymer increases even at low polymer fill fraction. In our study, we aim to understand the origin of these performance enhancements by examining the dynamics of both polymer and nanoparticles under deformation. We performed molecular dynamics simulation of coarse-grained, glass forming, mono-dispersed polymers equilibrated with random-close-packed nanoparticles, and applied uniaxial tensile strain to the system. We examined the mechanical characteristics of the PNC systems with different polymer fill fractions at temperatures below the glass transition temperature. We also compared the nanoparticle rearrangement behavior in the presence of polymer to the neat nanoparticle systems.
Proton transport within acid aggregates in a hydrated precise sulfophenylated polyethylene
Hydrated acid aggregates in a precise sulfophenylated polyethylene exhibit high proton conductivity. This study focuses on a new precise polymer synthesized by ring-opening polymerization, p5PhSA, that has a polyethylene backbone with a sulfonated phenyl group pendant on every 5th carbon. The structure of p5PhSA is characterized with X-ray scattering and the proton conductivity is measured by electrical impedance spectroscopy. Experiments are performed as a function of relative humidity and temperature. Atomistic molecular dynamics simulations are used to elucidate the structure of the acid aggregates in the amorphous polymer matrix. At 40°C and 95% relative humidity, the proton conductivity of p5PhSA is 0.28 S/cm, exceeding that of Nafion at the same conditions. The interaggregate distance increases by 50% from 1.9nm when dry to 2.7nm at 90% relative humidity. The reversible swelling of these aggregates in water facilitates the proton transport through p5PhSA.
Responsive, synthetic membrane-less organelles from recombinant proteins
Recently, many cellular proteins have been shown to phase separate, forming liquid droplets termed membrane-less organelles. Due to their fast formation and dissolution and their ability to sequester other biomolecules, these organelles have great potential to be used as a biomaterial. To achieve this, there is a need to develop strategies to control the formation of membrane-less organelles. To this end, the goal of our work was to engineer a phase separating protein to be responsive to light. This system was based on the RGG domain from the protein LAF-1. RGG has been shown to phase separate to form protein droplets in-vitro. To achieve light sensitivity, a photocleavable protein, PhoCl, was used. Upon exposure to 405 nm light, PhoCl irreversibly cleaves into two parts. We designed a construct that contained an N-terminal MBP domain, followed by PhoCl, followed by two RGG domains. MBP solubilizes the protein preventing phase separation. Upon exposure to 405 nm light, the PhoCl domain is cleaved and MBP is liberated. Within minutes after exposure, the remaining RGG phase separates to form liquid droplets. We demonstrated that this strategy results in light-induced membrane-less organelle formation both in-vitro and in yeast cells. This method provides novel ways to control protein droplets and will have applications in metabolic engineering, in the study of phase separating proteins, and as a mimic of membrane-less organelles in synthetic protocells.
Session II
Fibrinolytic products act as predictive biomarkers and mediators of platelet dysfunction in trauma patients
Trauma-induced coagulopathy (TIC) occurs in about 25% of severely injured patients and accounts for about 10% of deaths worldwide. Upon injury, hemostatic function may decline due to clotting factor deficiencies, hyperfibrinolysis, and/or platelet dysfunction. In this work, we aim to interrogate the potential link between elevated levels of fibrinolytic products (e.g. D-dimer) and hypofunctional platelets in an effort to improve mechanistic understanding of platelet dysfunction in trauma. In collaboration with Presbyterian Medical Center, platelets from trauma patients and healthy donors were fluorescently labeled and monitored via intracellular calcium mobilization and aggregometry following stimulation with a panel of agonists. Blood samples were also tested for plasma D-dimer by ELISA measurements and correlations were drawn between fibrinolytic product content and platelet function in both cohorts. To study mechanism, traumatic conditions were phenocopied in healthy blood by simulating fibrinolysis prior to observing downstream platelet response to potent stimuli, as well as observing platelet-mediated capture of D-dimer in solution. Through these and other methodologies, we demonstrate the ability for D-dimer and other fibrin-related species to interfere with platelet function, contributing to a fibrinolysis-dependent platelet loss-of-function phenotype that may influence both native and transfused platelets. These results provide insight into the potential lack of effective transfusions during clinical treatment of severely injured patients and give rise to consideration of a new target for future drug development.
Direct identification and quantification of bound polymer in polymer nanocomposite melts
The addition of nanoparticles (NPs) to a polymer matrix, forming a polymer nanocomposite (PNC), can significantly enhance the thermal, mechanical, and functional properties of the host material, making them relevant for a variety of fields. Due to the large surface area to volume ratio of NPs, PNC properties are often dominated by interfacial polymer near the NP surface. However, directly probing the static and dynamic properties of interfacial polymer remains an experimental challenge. Using ion scattering techniques, we separate, identify, and directly quantify the interfacial polymer in a model PNC system with strong NP-polymer attraction. By annealing thin PNC films deposited on bulk polymer matrices, free polymer from the PNC rapidly diffuses into the underlying matrix while the spontaneously-formed bound polymer remains with the slower NPs. By correlating the fraction of bound chains with the NP surface area, a bound layer thickness of ~Rg is observed and the average NP surface area occupied by adsorbed chains is found to be much smaller than that of an isolated chain or measured in solution. The bound polymer fraction decreases as a function of annealing time and decreases more rapidly at higher temperature and lower molecular weights. Although the bound polymer desorbs ~104 times slower than bulk diffusion, we measure strongly bound polymer that remains adsorbed after >106 reptation times. These results provide fundamental insights to help understand static and dynamic properties of interfacial polymer in PNCs and reveals non-equilibrium properties that can be used to engineer equilibrium dispersion of NPs in various polymer melts.
Bicontinuous biphasic emulsion gels for catalysis and separation applications
Simultaneous operation of catalysed reaction and separation had transformative impact increasing the efficiency of chemical processes; very successful particle-stabilized emulsion-based phase-transfer catalysis has been developed, however the traditional water in oil/oil in water emulsion cannot perform a steady and robust separation of the product. A bicontinuous particle-stabilized emulsion (bijel) can overcome this limitation, in our lab we developed the solvent-transfer induced phase separation (STRIPS) technique to produce such material in a simple, flexible and continuous fashion. We show how bijel chemistry can be tuned to improve its mechanical and chemical properties, as well as introducing catalytic nanoparticles in the bijel scaffold. We use this soft material to run simultaneous reaction and separation taking advantage of the different water affinity of reagent and products. We are able to perform a broad variety of chemical reactions in bijels: non catalytic, homogeneous catalysis and heterogeneous catalysis, accessing temperature ranges of about 100°C.
Session III
Enhanced molecular simulations of ice nucleation
Exercising control over the formation of ice and similar crystalline structures is important in a variety of contexts, from preserving organs for transplant to preventing clathrate hydrate plugs in natural gas pipelines. To achieve this control, it is crucial to understand nucleation phenomena at the molecular level. Studies have shown that heterogeneous nucleation proceeds orders of magnitude faster than homogeneous nucleation. Hence an understanding of ice nucleation phenomena in most real-world contexts hinges upon identifying the molecular-scale features of surfaces which promote or inhibit heterogeneous ice nucleation. Certain mineral surfaces and salts, such as kaolinite or silver iodide, are known to facilitate ice nucleation. However, recent work has shown that there is a complex interplay between a surface's morphology and its icephilicity: small variations in properties such as (surface flexibility and lattice mismatch) can significantly impact a material's ability to nucleate ice. We have developed novel approaches for characterizing surface icephilicity, and applied them to study a wide range of model surfaces. Our results shed new light on the molecular-scale features that govern a surface's propensity to nucleate ice and related crystalline structures.
The effect of substrate interactions on the dynamics of supported ultra-thin molecular glasses
As the thickness of films formed from polymers or small molecule glasses is reduced, it is well known that the glass transition temperature, Tg, can decrease, increase, or remain the same depending on the magnitude that the substrate and free surface perturb the dynamics. These deviations from bulk dynamics have important ramifications for technologies such as organic photovoltaics, light emitting diodes, protective coatings, and nano-imprint lithography where thin films of organic molecules are routinely employed. Recently, we have shown that when small molecule glass films of N,N′-Bis(3-methylphenyl)-N, N′-diphenylbenzidine (TPD) are reduced below ~30 nm the dynamics of the substrate and free surface interfaces are strongly correlated and this correlation cannot be described by simple 2- or 3-layer models. Furthermore, when TPD films are supported on a near-neutral substrate (wetting), obtained by modifying SiOx with an irreversibly adsorbed layer of polystyrene, as opposed to a weakly interacting (dewetting) SiOx substrate, the reduction in Tg is weaker but the ~30 nm length scale is unchanged. These results suggest that the length-scale for the correlated dynamics is independent of interfacial interactions and not unique to polymer glasses. However, little is known about how the dynamics of the irreversibly adsorbed layer used to modify the substrate may couple to the dynamics of the TPD films. Here, we explore SiOx substrates modified with chemically distinct irreversibly adsorbed layers to gain insight into how substrate effects might impact the dynamics of thin glassy films.
Feasibility of a single-use, point-of-care microfluidic chip for evaluation of platelet function and coagulation in whole blood under flow
Current diagnostic techniques used for point-of-care assessment of platelet function and coagulation, such as thromboelastography, are indirect and can be unreliable and difficult to interpret. Microfluidics has become a powerful tool for phenotyping platelet function and coagulation behavior of human blood while utilizing minimal fluid volumes but has thus far been restricted to laboratory settings with bulky equipment and significant manual technique required. While this technique can produce high quality data, a convenient single-use microfluidic chip, feasible for use in a clinical setting with minimal user training, has remained yet undemonstrated. For this work, the design of a previously published 8-channel PDMS microfluidic device was adapted for mass production in biocompatible plastic (COC) by injection molding for the construction of a single-use, disposable device. The 8-channel design allows for imaging of 8 independent clotting events, with up to 8 conditions, for up to 3 independent fluorescence channels. Platelet and fibrin signal can be imaged and quantified using fluorescently conjugated anti-CD61 and human fibrinogen respectively. The thrombogenic surface can be customized for either platelet function only, or platelet function and coagulation, using type I fibrillar collagen and lipidated tissue factor. COMSOL software was used to redesign the flow paths of the original PDMS device to allow for efficient multichannel pipetting analogous to a 96 well plate, while retaining equivalent fluid dynamics in each channel. Using a feedback controlled constant pressure source, whole blood can be perfused at venous shear rates for up to 20 minutes. Platelet and fibrin fluorescence data show parity with comparable data achieved with the previously published PDMS device data and can be obtained using a compact benchtop microscope.
Poster Presentations
Scaling analyses of cancer genome atlas transcriptomes for liver, lung, and breast link Lamin-B to matrix-insensitive proliferation and poor survival
The Cancer Genome Atlas (TCGA) enables unbiased analyses of transcriptomes and survival, but confidence in such data might increase if key trends agree with physico-chemical principles. Here, scaling concepts rooted in polymer physics and stoichiometry are applied to transcriptomes to identify non-linear links between polymerizing structural factors in nuclei and extracellular matrix in relation to tumor growth and patient survival. Primary tumors in Liver, Lung, and Breast show the nuclear lamin LMNB1 is always high, whereas LMNA and a co-regulated actomyosin-adhesion pathway are up only in Liver tumors. Proteomics confirm RNA trends, consistent with LMNB1 being a circulating biomarker for liver cancer; moreover, transcripts that scale with LMNB1 relate to proliferation and predict poor survival. The main fibrotic collagen, COL1A1, scales stoichiometrically with COL1A2, more strongly with basement membrane COL4A1, and in a given patient large increases predict survival. However, COL1A1 levels between patients do not correlate with survival nor with LMNB1 and proliferation, which link closely in vitro as well as in tumors. Although noisy data generally frustrates weak relationships, physico-chemical scaling is evident even in raw single cell RNA-Seq data, providing new means of data validation.
Colloidal organization at interfaces for advanced materials applications
Colloidal assembly can be used to form complex materials that depend on the organization and interaction of the constituent particles. Colloids are known to accumulate and organize at fluid interfaces via capillary interactions, the product of the surface tension and change in interfacial area that occurs when particles attach onto interfaces. Capillary interactions move colloids to particular locations to minimize the free energy of the system. These interactions are determined by the particle contact line and interface shape, and are typically orders of magnitude larger (~ 106 KBT for a 1 micron diameter colloid) than colloidal interactions in suspension. These energy fields can be used to direct, rotate, and assemble anisotropic particles on planar interfaces. Furthermore, even spherical objects have highly directional interactions owing to contact line pinning and associated leading order, long-range quadrupolar distortions. Particles with pinned contact lines make quadrupolar distortions, assemble with quadrupolar symmetries, and migrate to sites of high deviatoric curvature on curved interfaces. In this work we formulate the curvature capillary energy for two interacting particles on a curved interface. For pinned contact lines, we find curvature capillary energies using the method of reflections. The closed-form analytical expression for the interaction energy has contribution from the individual particle curvature interactions, as well as pair interaction from the two particles. The exact solution in bipolar coordinates agrees when the particles are far from each other, but near contact, the exact solution deviates, indicating that higher order distortions become important near field. In experiments, we study pair interactions of colloids on curved interfaces. Pairs interact with the curvature and migrate along deterministic trajectories when far apart but interact with each other when close enough to dimerize. Observed particle pair trajectories are compared to simulated trajectories obtained from a force balance on each particle equating the drag to the capillary attraction force. In addition to studying pairs, we study aggregates and structures formed at different regions of the interface. These are compared to Monte Carlo simulations base on pair interactions. By studying the underlying physics behind these interactions and assemblies, we develop new rules for organization by using the versatility in the energy landscapes that highly deformable fluid interfaces and colloids provide.
Enhanced molecular simulations of ice nucleation
Exercising control over the formation of ice and similar crystalline structures is important in a variety of contexts, from preserving organs for transplant to preventing clathrate hydrate plugs in natural gas pipelines. To achieve this control, it is crucial to understand nucleation phenomena at the molecular level. Studies have shown that heterogeneous nucleation proceeds orders of magnitude faster than homogeneous nucleation. Hence an understanding of ice nucleation phenomena in most real-world contexts hinges upon identifying the molecular-scale features of surfaces which promote or inhibit heterogeneous ice nucleation. Certain mineral surfaces and salts, such as kaolinite or silver iodide, are known to facilitate ice nucleation. However, recent work has shown that there is a complex interplay between a surface's morphology and its icephilicity: small variations in properties such as (surface flexibility and lattice mismatch) can significantly impact a material's ability to nucleate ice. We have developed novel approaches for characterizing surface icephilicity, and applied them to study a wide range of model surfaces. Our results shed new light on the molecular-scale features that govern a surface's propensity to nucleate ice and related crystalline structures.
Src-family kinase inhibition by dasatinib blocks both initial and subsequent platelet deposition on collagen under flow, but lacks efficacy when thrombin is generated
Driven by a triggering surface, platelet signaling evolves as clot growth either abates or reaches occlusion. Using microfluidics (200 s-1 wall shear rate) to perfuse FXIIa-inhibited whole blood (WB) over collagen ± tissue factor (TF), we explored the potency of the Src-family kinase (SFK) inhibitor dasatinib present at clot initiation or added after 90 sec (via rapid switch to dasatinib-pretreated WB). When initially present, dasatinib potently inhibited platelet deposition and Src-pY418 staining of collagen-adherent platelets (no TF). Furthermore, in this experiment, dasatinib immediately inhibited continued platelet deposition when introduced 90 sec after clot initiation. However, dasatinib was markedly less potent against clot growth on collagen/TF and had no effect when added 90 sec after clot initiation. Similarly, dasatinib added at 90 sec had no effect for clotting on collagen/TF when fibrin was also blocked with Gly-Pro-Arg-Pro, indicating that strong thrombin-induced signaling (but not fibrin-induced signaling) can bypass SFK inhibition. For WB perfused over collagen/TF (no dasatinib), the fibrin inhibitor Gly-Pro-Arg-Pro had no inhibitory effect on clot growth or Src-pY418 staining, indicating that fibrin provided no detectable stimulatory SFK signaling (via GPVI or α2bβ3 for example) beyond the stimuli distal of collagen and TF. SFKs are essential for primary hemostatic clotting on collagen without thrombin, but SFK function is bypassed by robust thrombin generation. SFK-inhibitors may have reduced antithrombotic activity in settings of high TF and thrombin.
Leaching induced capillary rise infiltration (LeCaRI) to make composite films
Leaching-enabled capillary rise infiltration (LeCaRI) is a powerful method to generate composites by inducing leaching and subsequent infiltration of uncross-linked chains from an elastomer network into the pores of a nanoparticle packing. Unlike conventional methods of patterning composites, this method can be performed at room temperature without the need for any sophisticated equipment and solvents to produce nanocomposite patterns with extremely high fill fractions. This method offers a unique and rapid capability to create both non-permanent and permanent patterned microdomains of composites. Laterally graded patterns and features can be fabricated to produce surface structures with laterally graded optical, mechanical and wetting properties. This method can potentially emerge as an environmentally friendly scalable method to manufacture polymer infiltrated nanoparticle films for applications in water collection and optical grating.
Gene regulation via interallelic interactions in the Drosophila embryo
Enhancers regulate the transcription of DNA during development, but the trans interaction between them is unclear. We use live-imaging methods and quantitative analysis to develop a mechanistic model of interallelic interactions between various enhancers of different developmental activities in living Drosophila embryos. We show that homologous genes regulated by strong enhancers interfere with one another, reducing the transcriptional activity of each allele. However, homozygous alleles driven by weakly active enhancers do not exhibit similar interference. We also provide evidence that interference between strong enhancers can be reduced by replacing one of the strong enhancers with a weak enhancer, while interference lacking between weak enhancers cannot be induced by replacing one of the weak enhancers with a strong enhancer. We propose that the level of enhancer activity determines the degree to which alleles engage in interference.
Modeling hybrid catalysts for hydrocarbon chemistry
Traditionally, there has been detailed focus on studying both heterogeneous and homogeneous catalysts, however, there has been little overlap between the two. They each provide their own benefits and drawbacks. For example, heterogeneous catalysts are the most widely used in industry due to easier separation from the products. However, they are not as easily tuned or as active as homogeneous catalysts, which on the other hand, suffer from fast degradation. We seek a material system, a so-called hybrid catalyst, that can have the benefits of both types of catalysts. One such approach involves the combination of a homogeneous catalyst by anchoring it to a heterogeneous surface using a linker molecule, thereby creating a hybrid catalyst. In a recent study, hybrid Ir-complexes have shown promise as viable catalysts for alkane dehydrogenation. Using density functional theory (DFT) calculations, we show how an Ir-POCOP complex is anchored to a heterogeneous surface at the atomic scale. The goal is to investigate the effects of geometry and site adsorption on the system’s stability and reactivity for different hydrocarbon reactions. Integration of our computational studies with experimentally realized hybrid catalysts, in collaboration with the groups of Prof. Ray Gorte (CBE) and Prof. Karen Goldberg (Chemistry), will provide valuable fundamental insight into the effects of hybridization of these materials and aid in the design of more efficient chemistries at atomically controlled active sites.
Reduced model to predict thrombin and fibrin generation during thrombosis on collagen/tissue factor under venous flow: roles of 𝛾’-fibrin and factor XI
Fibrin presents the weak sites in the E-domain for thrombin exosite 1 (~1.6-1.8 sites/monomer, Kd~2-4 µM) and a high affinity site that targets thrombin exosite 2 via the highly anionic and tyrosine-sulfated 𝛾’-chain sequence (~0.2-0.4 sites/monomer, Kd~0.1-0.4 µM). Based upon our recent measurements of thrombin and fibrin production under flow condition, we have developed a reduced model of clotting. We sought to establish the transient mass balance for clotting under venous flow by microfluidic measurements. Using a thin film approximation, we were able to simplify clotting under flow to 8 ODEs and 19 kinetic and stoichiometric parameters. A total of 16 parameters were from literature and only 3 needed adjustment in order to fit the measured thrombin generation (TAT and F1.2) and fibrin generation data. With fibrin polymerizing for 500 sec, 92000 thrombin molecules and 203000 clot-associated fibrin monomer equivalents were generated per TF molecule (or per m2). Fibrin reached 15 mg/mL in the pore space (porosity~0.5) of a 15-micron thick thrombus core by 500 sec and 30 mg/mL by 800 sec. This reduced model predicted the measured clot elution rate of thrombin-antithrombin (TAT) and fragment F1.2 in the presence and absence of the fibrin inhibitor Gly-Pro-Arg-Pro. The model required fibrinogen penetration into the clot to be strongly diffusion-limited (actual rate/ideal rate = 0.05), which is not unexpected given the size of fibrinogen. The model required free thrombin in the clot (~100 nM) to have an elution half-life of ~2 sec, consistent with measured albumin elution, with most thrombin (>99%) being fibrin-bound. Thrombin-feedback activation of FXIa became prominent and reached 5 pM at >500 sec in the simulation, consistent with anti-FXIa experiments. In a full convection/diffusion simulation, the velocity field and convective-diffusive transport solved by COMSOL and indicated that binding of thrombin onto fibrin was strong under venous shear rate with an apparent half-life in the clot of 1.1 hour. To sum up, this reduced model predicts thrombin and fibrin co-regulation during thrombosis under flow, which may be useful for multiscale simulation.
Alternative sustainable means to ammonia production: electrochemical nitrogen reduction reaction on metal catalysts supported on oxides
Ammonia synthesis is a critically important industrial chemical reaction that allows agriculture to operate at the scale necessary to feed the growing world population. Furthermore, ammonia has the potential to be a competitive carbon-free fuel source. Industrial ammonia synthesis is done using the Haber-Bosch process, which operates at high temperature and pressure, requiring large energy input and resulting in CO2 emissions. A possible alternative ammonia production route is through electrochemical synthesis using solid oxide proton conducting cells. These can be operated at ambient pressure and the reaction can be carbon neutral, but current experimental Faradaic efficiencies are low due to the parasitic hydrogen evolution reaction (HER). To overcome this, we use BaZrO3 and modifications thereof as the catalyst support because it is a stable material known to have high bulk proton conductivity and to be a poor HER catalyst. This study uses atomic scale computational tools such as density functional theory (DFT) to investigate the nitrogen reduction reaction (NRR) on different transition metal catalysts supported on the surfaces of BaZrO3. We model both proton diffusion from the bulk of the oxide to its surfaces and the atomistic details of the NRR at the surfaces. By constructing potential energy diagrams for different reaction pathways, we compare the suitability of different metal catalysts. This can guide and inform the experimental studies that are performed in the groups led by Prof. Gorte, Vohs and McIntosh and allow for a more complete fundamental understanding of NRR chemistry.
Responsive, synthetic membrane-less organelles from recombinant proteins
Recently, many cellular proteins have been shown to phase separate, forming liquid droplets termed membrane-less organelles. Due to their fast formation and dissolution and their ability to sequester other biomolecules, these organelles have great potential to be used as a biomaterial. To achieve this, there is a need to develop strategies to control the formation of membrane-less organelles. To this end, the goal of our work was to engineer a phase separating protein to be responsive to light. This system was based on the RGG domain from the protein LAF-1. RGG has been shown to phase separate to form protein droplets in-vitro. To achieve light sensitivity, a photocleavable protein, PhoCl, was used. Upon exposure to 405 nm light, PhoCl irreversibly cleaves into two parts. We designed a construct that contained an N-terminal MBP domain, followed by PhoCl, followed by two RGG domains. MBP solubilizes the protein preventing phase separation. Upon exposure to 405 nm light, the PhoCl domain is cleaved and MBP is liberated. Within minutes after exposure, the remaining RGG phase separates to form liquid droplets. We demonstrated that this strategy results in light-induced membrane-less organelle formation both in-vitro and in yeast cells. This method provides novel ways to control protein droplets and will have applications in metabolic engineering, in the study of phase separating proteins, and as a mimic of membrane-less organelles in synthetic protocells.
Computational study of functionalized 2D MXene materials for electrochemical N2 reduction (NRR)
Ammonia (NH3) is vital to the agricultural industry as an agent in manufacturing fertilizer, resulting in the dramatic population growth of the 20th century. There is an interest in discovering catalytic materials for the NRR under ambient conditions to overcome the current energy intensive Haber Bosch process. In this presentation, we use density functional theory calculations to study the mechanism of MXenes with chemical formula M2XT2, a new class of materials, for electrochemically producing NH3 (NRR) under ambient conditions. 2-D carbides and nitrides (M = Ti, Zr, V, Nb, Ta, Mo, W) and surface functionalization (T=Bare, H, O, and N) are varied to screen for their catalytic activity based on thermodynamic energy pathways. W2C, W2N, Mo2C, and Mo2N are selected candidate electrocatalysts, but are unstable under working conditions. The adsorption free energy of the intermediates defines a descriptor, ΔGN, which confirms that H-, O-, and N-terminated MXenes are unsuitable electrocatalysts due to their inability to stabilize the N2H* intermediate. A comparison of how H poisoning affects HER (Hydrogen Evolution Reaction) activity versus the limiting potential step shows that only unstable bare MXenes compete against the HER. Charge analysis is implemented to show that surface chemistry is related to charge transfer from the surface to adsorbate, dependent on the adsorption geometry and the termination on the basal planes. Finally, we investigate two routes closely to enhance and tune the basal plane chemistry for NRR, namely the impact of functional groups including S, F, and Cl and role of the crystal structure of the MXene.
Intrathrombus fibrin attenuates spatial sorting of phosphatidylserine-exposing platelets during clotting under flow
As thrombosis proceeds, certain platelets in a clot present phosphatidylserine (PS) and these PS-positive platelets subsequently spatially sort to the perimeter of the mass. Using an 8-channel microfluidic assay of whole blood clotting on collagen (± tissue factor) at 100 s-1 wall shear rate, we investigated sorting of PS-positive platelets in the presence of fibrin formation and fibrinolysis using image autocorrelation analysis of Annexin V staining. By 6 minutes, PS was randomly distributed throughout the platelet deposits and became spatially sorted by 15 minutes if thrombin, and thus fibrin, were blocked with PPACK. However, fibrin polymerization (no PPACK present) greatly reduced sorting. Intrathrombus fibrin also greatly reduced clot contraction. With GPRP added to block fibrin polymerization, PS sorting was prominent, as was clot contraction. Platelet monolayers that were formed on the collagen (± fibrin) through the use of αIIbβ3 inhibitor GR144053 failed to display sorting or contraction. Exogenously added tissue plasminogen activator (tPA) drove fibrinolysis in the clots which, in turn, promoted PS sorting as well as clot contraction. Overall, these findings are consistent with spatial sorting of PS-positive platelets being enhanced by clot contraction, while fibrin attenuates both clot contraction and PS sorting. For clotting under flow, fibrin has distinct roles, beyond mechanical stabilization, that include the attenuation of: (1) thrombin, (2) clot contraction, (3) shear-induced NETosis, and (4) spatial sorting of PS-positive platelets.
Multiscale dynamics of small, attractive nanoparticles and entangled polymers in polymer nanocomposites
Polymer segmental dynamics, center-of-mass chain diffusion, and nanoparticle (NP) diffusion are directly measured in a series of polymer nanocomposites (PNC) composed of very small (radius ≈ 0.9 nm) sticky NPs and poly(2-vinylpyridine) (P2VP). With increasing NP concentration, both the segment reorientational relaxation rate (measured by dielectric spectroscopy) and polymer chain center-of-mass diffusion coefficient (measured by elastic recoil detection) are substantially reduced, with reductions relative to bulk reaching ∼80% and ∼60%, respectively, at 25 vol % OAPS. This commensurate slowing of both the segmental relaxation and chain diffusion process is fundamentally different than the case of PNCs composed of larger, immobile nanoparticles, where the NP perturbation to segmental dynamics and chain dynamics are often decoupled. Using Rutherford backscattering spectrometry to probe the NP diffusion process, we find that small NPs diffuse anomalously fast in these PNCs, reaching diffusivities 10−10,000 times faster than predicted by the Stokes−Einstein relation. The OAPS diffusion coefficients are found to scale very weakly with molecular weight, Mw−0.7±0.1, and our analysis shows that this characteristic diffusion rate occurs on intermediate microscopic time scales, lying between the Rouse time of a Kuhn monomer and the Rouse time of an entanglement strand. Our results demonstrate the unique transport properties in PNCs comprised of small, attractive NPs in entangled polymer melts on various length and time scales and help guide the design of new PNC technology with tunable physical and functional properties.
Platelet activation leads to enhanced thrombus stability
Thrombus stability is a crucial part in determining the outcome of a thrombotic event. To measure thrombus stability, we used a two part 8-channel microfluidic assay of whole blood clotting over collagen ± tissue factor (TF) at 100 s-1 for 3 minutes subsequently followed by buffer at 1000 s-1. This allowed for precise control over both platelet activation and fibrin formation during the thrombotic event. Thrombi show shear-dependent stability as seen in a smaller platelet decay at a lower buffer shear rate (100s-1) versus a higher shear rate (1000s-1). The inclusion of thrombin through tissue factor lead to increased stability over a thrombin free system as seen in PPACK+TF and -TF conditions. However, there was no significant difference between +GPRP (fibrin free) and -GPRP, suggesting that platelet activation (measured with P-Selectin) is more important than fibrin at the experimental shear rates for clot stability. Overall, these findings show that high levels of platelet activation are crucial for stabilizing a thrombus.
In silico profiling of activating mutations in cancer
Clinical oncologists constantly confront the challenge of administering the right drugs for cancer-diagnosed patients. More often than not, these patients undergo genome sequencing and certain mutations are expressed which might be deleterious to protein structure and function. Therefore it is important to predict the effect of point mutations to be either activating or non-activating (passenger mutations). To classify the mutations, a detailed understanding of the structure of proteins in its active and non-active configuration is required. We implement statistical mechanics based approaches like enhanced molecular dynamics to obtain the differentiating features between these configurations of proteins and suggest to feed them as an input into a support vector machine algorithm which then classifies the mutation into activating or not. An expanded investigation to take into account the interactions of mutant proteins with inhibitor drugs is being pursued. Together, these studies would then guide the oncologists in factoring the effect of mutation in a given patient in customizing therapy regimen.
Surface modification of SOFC electrodes via ALD to enhance anode coking tolerance
Present-day Ni-YSZ cermet anodes are highly optimized to achieve good mechanical strength and electrochemical performance. However, they suffer from a tendency to form carbon fibers if the H2O:C ratio is too low or there are higher hydrocarbons in the feed to the cell. It has been reported that addition of CeO2 or BaO to Ni can increase the anodes’ tolerance and prevent coking. Adding too much BaO however, promotes reactions with YSZ and leads to volume expansion. This highlights an important opportunity for ALD as controlled amounts of CeO2 and BaO can be deposited onto the anode surface. The suppression of coke formation was studied on model anode surfaces, as well as on anode-supported Ni-YSZ cells under various H2O:C ratios.
Bicontinuous biphasic emulsion gels for catalysis and separation applications
Simultaneous operation of catalysed reaction and separation had transformative impact increasing the efficiency of chemical processes; very successful particle-stabilized emulsion-based phase-transfer catalysis has been developed, however the traditional water in oil/oil in water emulsion cannot perform a steady and robust separation of the product. A bicontinuous particle-stabilized emulsion (bijel) can overcome this limitation, in our lab we developed the solvent-transfer induced phase separation (STRIPS) technique to produce such material in a simple, flexible and continuous fashion. We show how bijel chemistry can be tuned to improve its mechanical and chemical properties, as well as introducing catalytic nanoparticles in the bijel scaffold. We use this soft material to run simultaneous reaction and separation taking advantage of the different water affinity of reagent and products. We are able to perform a broad variety of chemical reactions in bijels: non catalytic, homogeneous catalysis and heterogeneous catalysis, accessing temperature ranges of about 100°C.
Integrin crosstalk allows CD4+ T lymphocytes to continue migrating in the upstream direction after flow
In order to perform critical immune functions at sites of inflammation, circulatory T lymphocytes must be able to arrest, adhere, migrate and transmigrate on the endothelial surface. This progression of steps is coordinated by a complex combination of cellular adhesion molecules (CAMs), chemokines and selectins presented on the endothelial layer. Two important interactions are between LFA-1 and Intracellular Adhesion Molecule-1 (ICAM-1) and VLA-4 and Vascular Cell Adhesion Molecule-1 (VCAM-1); endothelial cells can alter the expression of both ICAM-1 and VCAM-1 during inflammation. Recent studies have shown that T lymphocytes and other cell types can migrate upstream (against the direction) of flow through the binding of LFA-1 to ICAM-1. The dependence of upstream migration on a specific adhesive pathway suggests mechanotransduction is critical to migration, and we hypothesized that signals might allow T-cells to remember their direction of migration after flow is terminated. Cells on ICAM-1 surfaces migrate against the shear flow, but the upstream migration reverts to random migration after the flow is stopped. Cells on VCAM-1 migrate with the direction of flow. However, on surfaces that combine ICAM-1 and VCAM-1, cells crawl upstream at a shear rate of 800 s-1 and continue migrating in the upstream direction for at least 30 minutes after the flow is terminated. Post-flow upstream migration on VCAM-1/ICAM-1 surfaces is reversed upon inhibition of PI3K, but conserved with cdc42 and arp2/3 inhibitors. These results indicate that, while upstream migration under flow is governed by LFA-1, simultaneous VLA-4 engagement, high shear rate, and PI3K activity are required for cells to continue its upstream direction after the absence of flow. These results indicate that crosstalk between integrins potentiates the signal of upstream migration.
Ion transport and aggregate morphology in precise sulfophenylated polyethylene ionomers
A set of new and amorphous precise ionomers synthesized by ring-opening polymerization exhibit decoupled ion transport. These precise ionomers consist of a polyethylene backbone with a sulfonated phenyl group pendant on every 5th carbon, that is fully neutralized by a counterion X (X is Li+, Na+, or Cs+), p5PhSA-X. The morphologies of these ionomers are characterized with X-ray scattering, and the ion transport properties are characterized with electrical impedance spectroscopy. Both experiments are performed under vacuum, from room temperature up to 200°C. Distance between aggregates appears independent of ion type, with an interaggregate spacing of ~1.9 nm present in the Li+, Na+, and Cs+ as-cast ionomers. Atomistic molecular dynamics simulations are used to elucidate the structure of aggregates in the ionomers and compared to absolute X-ray scattering data. The ionomers exhibit conductivity of 10-8 to 10-7 S/cm at 150°C. These materials demonstrate decoupled ion transport up to 200°C, a result of ions traveling within ionic aggregates and independent of chain dynamics.
Fibrinolytic products act as predictive biomarkers and mediators of platelet dysfunction in trauma patients
Trauma-induced coagulopathy (TIC) occurs in about 25% of severely injured patients and accounts for about 10% of deaths worldwide. Upon injury, hemostatic function may decline due to clotting factor deficiencies, hyperfibrinolysis, and/or platelet dysfunction. In this work, we aim to interrogate the potential link between elevated levels of fibrinolytic products (e.g. D-dimer) and hypofunctional platelets in an effort to improve mechanistic understanding of platelet dysfunction in trauma. In collaboration with Presbyterian Medical Center, platelets from trauma patients and healthy donors were fluorescently labeled and monitored via intracellular calcium mobilization and aggregometry following stimulation with a panel of agonists. Blood samples were also tested for plasma D-dimer by ELISA measurements and correlations were drawn between fibrinolytic product content and platelet function in both cohorts. To study mechanism, traumatic conditions were phenocopied in healthy blood by simulating fibrinolysis prior to observing downstream platelet response to potent stimuli, as well as observing platelet-mediated capture of D-dimer in solution. Through these and other methodologies, we demonstrate the ability for D-dimer and other fibrin-related species to interfere with platelet function, contributing to a fibrinolysis-dependent platelet loss-of-function phenotype that may influence both native and transfused platelets. These results provide insight into the potential lack of effective transfusions during clinical treatment of severely injured patients and give rise to consideration of a new target for future drug development.
“Intelligent” catalysts studied on high-surface area CaTiO3 films
CaTiO3-supported Pt is sometimes referred to as an “Intelligent” catalyst because Pt can reversibly leave or enter the perovskite lattice following high-temperature reduction or oxidation; however, slow egress-ingress kinetics associated with large perovskite crystallites make these systems impractical. In the present work, thin films (~1 nm) of CaTiO3 were deposited onto MgAl2O4 and then examined as catalyst supports for Pt and Pd. While Pd/CaTiO3/MgAl2O4 showed adsorption and CO-oxidation properties that were essentially the same as Pd/MgAl2O4, the Pt/CaTiO3/MgAl2O4 catalyst exhibited evidence for strong support interactions. Pt/CaTiO3/MgAl2O4 showed high activity for CO oxidation following reduction at 1073 K, even though CO adsorption was suppressed; but the catalysts were dramatically less active after oxidation at 1073 K and reduction at 773 K. Both Pt/CaTiO3/MgAl2O4 and a catalyst formed by ex-solution of CaTi0.95Pt0.05O3 exhibited very low rates for toluene hydrogenation in comparison to Pt/MgAl2O4. Scanning Transmission Electron Microscopy (STEM) and Energy Dispersive Spectroscopy (EDS) showed that the CaTiO3 films uniformly covered the MgAl2O4 surface after both reduction and oxidation at 1073 K. Pt particles on reduced Pt/CaTiO3/MgAl2O4 exhibited an unusual rhombohedral shape and may be flat, a further indication of strong interactions between the metal and the support. Low Energy Ion Scattering (LEIS) indicated that high-temperature reduction caused a restructuring of the CaTiO3. The implications of these results for understanding catalysts formed by ex-solution of metals from a perovskite lattice are discussed.
Role of epigenetic modifications in transcription and cell reprogramming
At a given time in development, each cell must regulate activation of tens to hundreds of genes to ensure normal development. One layer of regulation divides each chromosome into active euchromatin and inactive, or silenced, heterochromatin regions. While heterochromatin helps reduce ectopic activation of genes, it can also prevent stem cells from being properly reprogrammed. Many hepatic genes which cause stem cells to differentiate into hepatic cells remain silenced since they are located within the compacted heterochromatin domain. In order to screen for proteins that are responsible for the formation of heterochromatin, we treated fibroblast cells with siRNAs targeting each of the candidate protein and examined the change in expression level of key hepatic genes such as DSC2, NR1H4, and CRP. Using RNA-seq, we identified 90 proteins that led to overexpression of the hepatic genes. To further understand how each candidate protein affects the formation of heterochromatin, we stained the siRNA treated cells with H3K9me3 antibody which works as a marker for heterochromatin domain and analyzed the change in heterochromatin structure in a single cell resolution. We examined how diffuse and moderately compacted heterochromatin region and highly compacted focal region of heterochromatin are affected upon different siRNA treatment. Some siRNA-treated cells exhibited both fewer densely packed and moderately packed chromatin regions. Some other siRNA-treated cells showed changes in either focal heterochromatin regions or diffuse regions, but not both. Our results imply that heterochromatin proteins regulate heterochromatin formation and subsequent gene silencing in a differential manner. This study will provide better understanding on the mechanism of gene silencing via heterochromatin formation, as well as to suggest better stem cell reprogramming strategies.
Predicting trauma patient outcomes and survival probabilities with gradient boosting
Data analytic methods were performed on trauma data from the National Trauma Data Bank (NTDB) to predict trauma patient outcomes and quantify survival probabilities based upon single measurements of patient symptoms. The gradient boosting ensemble method was optimized, trained and tested by measuring accuracy with the area under the curve (AUC) of the receiver operating characteristic (ROC) since this metric is relatively insensitive to class imbalance resulting from the large ratio of patients who survived to patients who were deceased. With this metric, the model was able to obtain a 94% accuracy and correctly classified 1211 of the 1392 deceased patients and 600378 of the 703037 patients who survived. Furthermore, the permutation importance method, the Local Model-Agnostic Explanation (LIME) method, and partial dependence curves were used for understanding the local and global predictions of the model to gather a greater insight into which factors contribute most to patient outcomes. Key results were: (1) heart rate and blood pressure measurements can be a large predictor of patient outcome, (2) a modified severity score and the total Glasgow coma score are good for quantifying patient status, (3) patient age can be the final determining factor for patient survival.
Effects of Fe doping cobalt oxide nanoparticles on water adsorption and splitting
Earth abundant transition metal oxides and their mixed metal oxide counterparts have shown promise as viable catalysts for the oxygen evolution reaction (OER). OER is a valuable reaction for renewable alternate energy applications and necessity for these catalyst materials increases as the need for new clean energy grows. Understanding the chemistry of these complex multi-component oxide catalysts at the atomic scale is required to effectively design better catalysts. Previous work found binding energies of OER intermediates on CoFeW systems exhibit near optimal binding energies for OER and these materials were shown to have low overpotentials for OER. Nanoparticles of CoOx on Au (111) doped with Fe are among mixed oxide materials that are of interest as OER catalyst building off previous work having investigated pure CoOx on Au (111). Using density functional theory (DFT), Fe doping into CoO bilayers is studied to understand dopant cluster location, size and shape preferences. Integration of our computational studies with scanning tunneling microscopy (STM) studies by reveal the doping patterns of Fe in these CoO bilayers. The effects the discovered Fe doping provides valuable insight into the catalytic promotion affects seen from these binary oxides compared to their single metal oxides and aids towards our ultimate goal of identifying the active site for water adsorption, dissociation and OER.
Robust underwater anti-oil fouling coatings from spray assemblies of polyelectrolyte grafted silica nanochains for enhancing oil/water filtration membranes
Surfaces that have superhydrophilic characteristics are known to exhibit extreme oil repellency underwater, which is attractive for applications including anti-fogging, water-oil separations, and self-cleaning. However, superhydrophilic surfaces can also be easily fouled and lose their extreme oil repellency, thus limiting their usage in practical applications. In this work, we create a robust superhydrophilic coating by spray coating poly(acrylic acid) (PAA)-grafted SiO2 nanochains (approximately 45 nm wide and 300 nm long) onto silicon wafers, forming a nanoporous coating exhibiting superhydrophilicity (water contact angle in air ≈ 0°) and underwater superoleophobicity (dichloroethane contact angle ≥ 165°). The polymer-grafted nanochain assemblies exhibit extremely low contact angle hysteresis (< 1°) and small adhesion hysteresis (≈ −0.05 mN m-1), and thus oil can readily roll off from the surface when the coating is immersed in water. Compared to other superhydrophilic surfaces, we show that both the unique structure of spray-assembled nanochains and the hygroscopic nature of PAA are essential to enable robust anti-oil fouling. Even after the PAA-grafted nanochain coating is purposely fouled by oil, oil can be readily and completely expelled and lifted-off from the coating within 10 seconds when placed under water. Furthermore, the coating is tested on existing membranes and it shows enhancement on oil/water separation in terms of flux and oil rejection. Our approach offers a simple yet versatile method to create a robust superhydrophilic and anti-oil fouling coating via a scalable manufacturing method.
The nuclear to cytoplasmic ratio regulates zygotic transcription in Drosophila
Early embryos must rapidly generate large numbers of cells to form an organism. Many species accomplish this through a series of rapid, reductive, and transcriptionally repressed cleavage divisions. Previous work has demonstrated that the number of divisions for both cell cycle elongation and zygotic genome activation (ZGA) is regulated by the ratio of nuclei to cytoplasm (N/C). However, the mechanism by which the N/C ratio affects ZGA is not well characterized, mainly due to limited temporal resolution in assays using fixed tissues. We used MS2 tagging-based live imaging methods to understand how the N/C ratio affects the timing of ZGA in early Drosophila embryos. We visualized the transcriptional activity of several previously identified N/C ratio dependent genes in diploid and haploid embryos. For all the genes that we examined, we found that transcription is delayed by a nuclear cycle in haploids. However, the mechanism by which the N/C ratio affects transcriptional dynamics is gene specific. For many genes, the effect of ploidy can be mostly accounted for by changes in cell cycle duration. However, for a subset of genes, the N/C ratio directly affects the probability of transcription initiation, such that significantly fewer number of nuclei exhibited active transcription in haploids compared to diploids in a given cell cycle. We conclude that cell cycle duration is the dominant component in modulating transcriptional output for most genes, but a subset of genes is directly responsive to the N/C ratio independent of cell cycle length.
Thermodynamics of nanoplates inside a diblock copolymer matrix
The mechanical properties of polymer nanocomposites are coupled to the orientation and arrangement of nanoparticles inside polymer matrices. Understanding how to control nanoparticles could lead to the development of new and novel materials with prescribed properties. We used hybrid particle/field theory and collaborated with experimentalists to characterize the interactions between anisotropic polyethylene glycol (PEG) grafted nanoplates inside a poly(styrene-b-methyl methacrylate) (PS-b-PMMA) block copolymer (BCP). Using simulations, we visualized microdomain bulging caused by the introduction of a grafted nanoparticle, leading to an increase in interfacial area, something hypothesized but difficult to resolve experimentally. Our potential of mean force of two particles approaching end-on experiences a free energy minimum at 7.0 nm, consistent with a mean experimental separation distance of 6.42 nm. The probability distribution of nanoplate separations predicted from the simulations also agrees very well with those observed in experiments. Our simulations showed small angle rotations are minimally unfavorable, especially compared to larger rotations, explaining the tendency for particles to align in the plane of the BCP. These results provide opportunities to design nanocomposites with anisotropic nanoparticles in order to achieve orientation-dependent properties.
Effect of patterning of ICAM-1 on the upstream migration of CD4+ T cells under shear flow
The leukocyte adhesion cascade is crucial in leukocyte recruitment in response to pathogens, infections, and cancer treatments. There are four stages to the cascade: the initial capture and rolling of cells, firm adhesion to the endothelium, migration, and transmigration. CD4+ T Cells will migrate upstream under shear flow following firm adhesion arrest. CD4+ T cells adhere to the adhesion molecules ICAM-1 and VCAM-1 during migration. Valignet et. al. and previous studies in the Hammer lab have shown ICAM-1 is sufficient to support upstream migration, whereas adhesion to VCAM-1 alone results in downstream migration on uniformly coated surfaces. Understanding and controlling the migration of CD4+ T Cells will assist in combating Leukocyte adhesion deficiencies and cancers. Most studies have focused on uniform distributions of adhesion molecules in vitro. The objective of this study was to determine if the patterning of ICAM-1 or VCAM-1 had any influence on the direction of T cell migration under flow. Primary CD4+ T cells were seeded onto protein patterned surfaces for these experiments. Two pattern archetypes are utilized: Uniform distribution of adhesion proteins and striped surfaces of various widths, from 50 μm and 200 μm wide stripes. The surfaces were created with microcontact printing. Each surface either consisted of purely ICAM-1 or a 1:1 mass ratio of ICAM-1 to VCAM-1. Cells were tracked under static, 400 s-1 shear flow, and 800 s-1 shear flow conditions to determine whether upstream migration was present. Consistent with previous publications, uniform distributions result in upstream migration under flow and no directional migration at static conditions. On striped patterned surfaces, narrower width stripes result in overall downstream migration of T Cells which lessens in magnitude and turns towards upstream migration as the stripes widen. This migratory behavior is apparent on both mixed surfaces and ICAM-1 only surfaces.
Nanoparticle diffusion in tortuous polyacrylamide-silica hydrogels
Tortuosity of a material is a key component to understanding the probe dynamics of any system. By modifying the tortuosity of polyacrylamide hydrogels by incorporating static silica nanoparticles, we can artificially increase the tortuous path experienced by a probe nanoparticle. Using single particle tracking (SPT) with quantum dots as probes, we see that low concentrations of homogeneously dispersed silica creates two distinctive populations, where a portion of quantum dots are diffusive, and others are localized. At high loadings (10% volume), there is an increase in the correlation length compared to low loadings (0.5% volume), potentially because of the disruption of the mesh due to incorporated particles. A proposed mechanism for the localized particle behavior is that the PEG brush on the quantum dots hydrogen bonds to the surface of the incorporated silica at neutral pH, which was investigated via QCM-D experiments. This work offers important insights for predicting and controlling nanoparticle diffusion in gels through the addition of artificial tortuosity, applicable in drug delivery and in understanding nanoparticle diffusion in biofilms.
Directed micro assembly and manipulation of passive particles via capillarity using a magnetic micro-robot at oil/water interface
Assembly and manipulation of objects at the microscale can effectively be achieved by harnessing physico-chemical interactions that dominate at that scale. Capillary interactions are one such example. These interactions are ubiquitous on fluid interfaces. Passive colloidal particles disturb the shape of the fluid interface and migrate to minimize the area of the interface around them. In particular, the interfacial area of a disturbance created by a colloid depends on the interface curvature. By using a magnetic micro-robot as a programmable interface curvature source, the curvature can be controlled by changing the position and orientation of the robot. The aim is to attract passive colloids to the curvature source as it moves along the interface. Hydrodynamic interactions play an important role in this process. As the micro-robot moves under external field at the interface, it generates a flow field that can be approximated as a Stokeslet plus a potential dipole. Via the interplay of hydrodynamic and capillary interactions, controlled assembly of passive particles can be achieved. We demonstrate predictable directed assembly of passive microparticles toward high curvature sites without the need for high resolution position control of the micro-robot. The ability to tune the strength of the capillary bond creates opportunities for more complicated manipulation process, such as cargo delivery and release. Particle assembled on the microrobot and be passed to intentionally designed stronger attractive sites which makes it a powerful tool to generate desired 2-D structures.
Surface active layers of bacteria at oil-water interfaces
Active colloids can accumulate at fluid interfaces and move in manners strongly influenced by this complex 2D fluid environment. We seek to understand these motions and their consequences to develop building blocks for 2D materials that are truly surface active. The complex boundary conditions and asymmetric viscosities of fluid interfaces make them particularly rich environments. We study Pseudomonas aeruginosa PAO1 on or near hexadecane-water interfaces as a model system. We find several distinct modes of swimming behaviors, including rotational and other modes, which we characterize statistically under different interfacial conditions. To analyze hydrodynamic interaction between bacteria and the interface, we have developed an approach to measure the 2d displacement field induced by different modes of bacteria motion around the bacteria. Displacement fields of both the active colloids and passive colloidal tracers are constructed to reveal interaction fields.
Active sites for the selective hydrodeoxygenation of m-cresol on WOx-modified Pt
Adsorption and reaction of m-cresol on Pt(111) and WOx-modified Pt(111) surfaces was characterized using temperature programmed desorption (TPD), high resolution electron energy loss spectroscopy (HREELS), and X-ray photoelectron spectroscopy (XPS). The results of my study show that on Pt(111) a strong interaction between the aromatic ring and the Pt surface facilitates C-C bond cleavage resulting in decomposition at relatively low temperatures. In contrast, on WOx-modified Pt(111), m-cresol bonds to oxygen vacancy sites on the WOx deposits via the hydroxyl oxygen with the aromatic ring tilted away from the surface, resulting in a bonding configuration that promotes selective C-O bond cleavage and limits ring hydrogenation. XPS results also show that interactions at the Pt-WOx interface help stabilize submonolayer WOx deposits in a partially reduced state, thereby maintaining a high concentration of the oxygen vacancy adsorption sites.