Enhancing the Self-Propelled Motion of Hydrogen Peroxide Fueled Active Particles with Formic Acid and Other Oxygen Scavengers.

We report enhanced active particle motion in hydrogen peroxide-fueled self-diffusiophoretic active particle systems of up to 400% via addition of low concentrations of oxygen scavenging agents such as formic acid (as well as other organic acids, hydrazine, and citric acid), whereas active motion was inhibited at higher concentrations. Control experiments showed that enhanced motion was decoupled from catalytic hydrogen peroxide decomposition rate and insensitive to particle surface chemistry. Experimental results point to bulk oxygen scavenging as the cause for the enhanced active motion, representing a realization of recently predicted promotional effects of product sinks on self-diffusiophoretic motion.

Bridging Macroscopic Diffusion and Microscopic Cavity Escape of Brownian and Active Particles in Irregular Porous Networks.

While irregular and geometrically complex pore networks are ubiquitous in nature and industrial processes, there is no universal model describing nanoparticle transport in these environments. 3D super-resolution nanoparticle tracking was employed to study the motion of passive (Brownian) and active (self-propelled) species within complex networks, and universally identified a mechanism involving successive cavity exploration and escape. In all cases, the long-time ensemble-averaged diffusion coefficient was proportional to a quantity involving the characteristic length scale and time scale associated with microscopic cavity exploration and escape ( ∼ /), where the proportionality coefficient reflected the apparent porous network connectivity.

Stabilization of an Infectious Enveloped Virus by Spray-Drying and Lyophilization.

Enveloped viruses are attractive candidates for use as gene- and immunotherapeutic agents due to their efficacy at infecting host cells and delivering genetic information. They have also been used in vaccines as potent antigens to generate strong immune responses, often requiring fewer doses than other vaccine platforms as well as eliminating the need for adjuvants. However, virus instability in liquid formulations may limit their shelf life and require that these products be transported and stored under stringently controlled temperature conditions, contributing to high cost and limiting patient access.

Combinatorial High-Throughput Screening of Complex Polymeric Enzyme Immobilization Supports.

Recent advances have demonstrated the promise of complex multicomponent polymeric supports to enable supra-biological enzyme performance. However, the discovery of such supports has been limited by time-consuming, low-throughput synthesis and screening. Here, we describe a novel combinatorial and high-throughput platform that enables rapid screening of complex and heterogeneous copolymer brushes as enzyme immobilization supports, named combinatorial high-throughput enzyme support screening (CHESS).

Supra-biological performance of immobilized enzymes enabled by chaperone-like specific non-covalent interactions.

Designing complex synthetic materials for enzyme immobilization could unlock the utility of biocatalysis in extreme environments. Inspired by biology, we investigate the use of random copolymer brushes as dynamic immobilization supports that enable supra-biological catalytic performance of immobilized enzymes. This is demonstrated by immobilizing Bacillus subtilis Lipase A on brushes doped with aromatic moieties, which can interact with the lipase through multiple non-covalent interactions.

Computational and experimental approaches to quantify protein binding interactions under confinement.

Crowded environments and confinement alter the interactions of adhesion proteins confined to membranes or narrow, crowded gaps at adhesive contacts. Experimental approaches and theoretical frameworks were developed to quantify protein binding constants in these environments. However, recent predictions and the complexity of some protein interactions proved challenging to address with prior experimental or theoretical approaches.

Nanomotor-enhanced transport of passive Brownian particles in porous media.

Artificial micro/nanomotors are expected to perform tasks in interface-rich and species-rich environments for biomedical and environmental applications. In these highly confined and interconnected pore spaces, active species may influence the motion of coexisting passive participants in unexpected ways. Using three-dimensional super-resolution single-nanoparticle tracking, we observed enhanced motion of passive nanoparticles due to the presence of dilute well-separated nanomotors in an interconnected pore space.

Effect of mechanical stresses on viral capsid disruption during droplet formation and drying.

Identification of the mechanisms by which viruses lose activity during droplet formation and drying is of great importance to understanding the spread of infectious diseases by virus-containing respiratory droplets and to developing thermally stable spray dried live or inactivated viral vaccines. In this study, we exposed suspensions of baculovirus, an enveloped virus, to isolated mechanical stresses similar to those experienced during respiratory droplet formation and spray drying: fluid shear forces, osmotic pressure forces, and surface tension forces at interfaces. DNA released from mechanically stressed virions was measured by SYBR Gold staining to quantify viral capsid disruption.

Similarly slow diffusion of BAM and SecYEG complexes in live E. coli cells observed with 3D spt-PALM.

The β-barrel assembly machinery (BAM) complex is responsible for inserting outer membrane proteins (OMPs) into the Escherichia coli outer membrane. The SecYEG translocon inserts inner membrane proteins into the inner membrane and translocates both soluble proteins and nascent OMPs into the periplasm. Recent reports describe Sec possibly playing a direct role in OMP biogenesis through interactions with the soluble polypeptide transport-associated (POTRA) domains of BamA (the central OMP component of BAM).

Tuning Polymer Composition Leads to Activity-Stability Tradeoff in Enzyme-Polymer Conjugates.

Protein-polymer conjugation provides an opportune means to adjust the local environment of proteins and enhance protein stability, performance, and solubility. Although much attention has been focused on tuning protein-polymer interactions, the properties of polymer-modified proteins may also be altered by polymer-polymer interactions. Herein, we sought to better understand the influence of polymer-polymer interactions on lipase, which was modified with random co-polymers composed of sulfobetaine methacrylate (SBMA) and poly(ethylene glycol) methacrylate (PEGMA).

Tuning the surface charge of phospholipid bilayers inhibits insulin fibrilization.

The interactions between proteins and materials, in particular lipid bilayers, have been studied extensively for their relevance in diseases and for the formulation of protein-based therapeutics and vaccines. However, the precise rules by which material properties induce favorable or unfavorable structural states in biomolecules are incompletely understood, and as a result, the rational design of materials remains challenging. Here, we investigated the influence of lipid bilayers (in the form of small unilamellar vesicles) on the formation of insulin amyloid fibrils using a fibril-specific assay (thioflavin T), polyacrylamide gel electrophoresis, and circular dichroism spectroscopy.

Protein Desorption Kinetics Depends on the Timescale of Observation.

The presence of so-called reversible and irreversible protein adsorption on solid surfaces is well documented in the literature and represents the basis for the development of nanoparticles and implant materials to control interactions in physiological environments. Here, using a series of complementary single-molecule tracking approaches appropriate for different timescales, we show that protein desorption kinetics is much more complex than the traditional reversible-irreversible binary picture. Instead, we find that the surface residence time distribution of adsorbed proteins transitions from power law to exponential behavior when measured over a large range of timescales (10-10 s).

Effects of Surface Hydrophobicity on Catalytic Transfer Hydrogenation of Styrene with Formic Acid in a Biphasic Mixture.

Transfer hydrogenation (TH) of unsaturated hydrocarbons with formic acid (FA) is an attractive processing pathway for the reduction of lignocellulosic pyrolysis oils. The low solubility of hydrophobic bio-oil species in water and FA in oil necessitates the use of a biphasic system as the reaction environment. Here, we report the effects of Pd/silica catalyst surface wettability on the TH reaction rate.

Biocatalytic 3D Actuation in Liquid Crystal Elastomers via Enzyme Patterning.

Liquid crystal elastomers (LCEs) are stimuli-responsive materials that undergo large shape transformations after undergoing an order-disorder transition. While shape reconfigurations in LCEs are predominantly triggered by heat, there is a considerable interest in developing highly specific triggers that work at room temperature. Herein, we report the fabrication of biocatalytic LCEs that respond to the presence of urea by covalently immobilizing urease within chemically responsive LCE networks.

Diffusion of Short Semiflexible DNA Polymer Chains in Strong and Moderate Confinement.

In many technological applications, DNA is confined within nanoenvironments that are smaller than the size of the unconfined polymer in solution. However, the dependence of the diffusion coefficient on molecular weight and characteristic confinement dimension remains poorly understood in this regime. Here, convex lens-induced confinement (CLiC) was leveraged to examine how the diffusion of short DNA fragments varied as a function of slit height by using single-molecule fluorescence tracking microscopy.

Enhanced Facilitated Diffusion of Membrane-Associating Proteins under Symmetric Confinement.

The facilitated surface diffusion of transiently adsorbing molecules in a planar confined microenvironment (i.e., slit-like confinement) is highly relevant to biological phenomena, such as extracellular signaling, as well as numerous biotechnology systems.

Probing surface-adsorbate interactions through active particle dynamics.

Adsorbate molecules present in a reaction mixture may bind to and block catalytic sites. Measurement of the surface coverage of these molecules via adsorption isotherms is critical for modeling and design of catalytic reactions on surfaces. However, it is challenging to measure isotherms in solution in a way that is directly relevant to catalytic activity under reaction conditions, particularly since adsorbates may bind with an enormous range of surface affinity parameters.

Chemically Triggered Changes in Mechanical Properties of Responsive Liquid Crystal Polymer Networks with Immobilized Urease.

Liquid crystal polymer networks (LCNs) are stimuli-responsive materials that can be programmed to realize spatial variation in mechanical response and undergo shape transformation. Herein, we report a process to introduce chemical specificity to the stimuli response of LCNs by integrating enzymes as molecular triggers. Specifically, the enzyme urease was immobilized in LCN films via acyl fluoride conjugation chemistry.

Mechanisms of transport enhancement for self-propelled nanoswimmers in a porous matrix.

Micro/nanoswimmers convert diverse energy sources into directional movement, demonstrating significant promise for biomedical and environmental applications, many of which involve complex, tortuous, or crowded environments. Here, we investigated the transport behavior of self-propelled catalytic Janus particles in a complex interconnected porous void space, where the rate-determining step involves the escape from a cavity and translocation through holes to adjacent cavities. Surprisingly, self-propelled nanoswimmers escaped from cavities more than 20× faster than passive (Brownian) particles, despite the fact that the mobility of nanoswimmers was less than 2× greater than that of passive particles in unconfined bulk liquid.

Understanding Design Rules for Optimizing the Interface between Immobilized Enzymes and Random Copolymer Brushes.

A long-standing goal in the field of biotechnology is to develop and understand design rules for the stabilization of enzymes upon immobilization to materials. While immobilization has sometimes been successful as a strategy to stabilize enzymes, the design of synthetic materials that stabilize enzymes remains largely empirical. We sought to overcome this challenge by investigating the mechanistic basis for the stabilization of immobilized lipases on random copolymer brush surfaces comprised of poly(ethylene glycol) methacrylate (PEGMA) and sulfobetaine methacrylate (SBMA), which represent novel heterogeneous supports for immobilized enzymes.

Faster Surface Ligation Reactions Improve Immobilized Enzyme Structure and Activity.

During integration into materials, the inactivation of enzymes as a result of their interaction with nanometer size denaturing "hotspots" on surfaces represents a critical challenge. This challenge, which has received far less attention than improving the long-term stability of enzymes, may be overcome by limiting the exploration of surfaces by enzymes. One way this may be accomplished is through increasing the rate constant of the surface ligation reaction and thus the probability of immobilization with reactive surface sites (i.

Enhanced Diffusive Transport in Fluctuating Porous Media.

Mass transport within porous structures is a ubiquitous process in biological, geological, and technological systems. Despite the importance of these phenomena, there is no comprehensive theory that describes the complex and diverse transport behavior within porous environments. While the porous matrix itself is generally considered a static and passive participant, many porous environments are in fact dynamic, with fluctuating walls, pores that open and close, and dynamically changing cross-links.

Single molecule characterization of anomalous transport in a thin, anisotropic film.

The diffusion of small, charged molecules incorporated in an anisotropic polyelectrolyte multilayer (PEM) was tracked in three dimensions by combining single-molecule fluorescence localization (to characterize lateral diffusion) with Förster resonance energy transfer (FRET) between diffusing molecules and the supporting surface (to measure diffusion in the surface-normal direction). Analysis of the surface-normal diffusion required model-based statistical analysis to account for the inherently noisy FRET signal. Combining these distinct single-molecule methods, which are inherently sensitive to different length-scales, permitted simultaneous characterization of severely anisotropic diffusion, which was more than three orders of magnitude slower in the surface-normal direction.

Cadherin cis and trans interactions are mutually cooperative.

Cadherin transmembrane proteins are responsible for intercellular adhesion in all biological tissues and modulate tissue morphogenesis, cell motility, force transduction, and macromolecular transport. The protein-mediated adhesions consist of adhesive trans interactions and lateral cis interactions. Although theory suggests cooperativity between cis and trans bonds, direct experimental evidence of such cooperativity has not been demonstrated.

Antimicrobial peptide activity is anticorrelated with lipid a leaflet affinity.

The activity of antimicrobial peptides (AMPs) has significant bacterial species bias, the mechanisms of which are not fully understood. We employed single-molecule tracking to measure the affinity of three different AMPs to hybrid supported bilayers composed of lipid A extracted from four different Gram negative bacteria and observed a strong empirical anticorrelation between the affinity of a particular AMP to a given lipid A layer and the activity of that AMP towards the bacterium from which that lipid A was extracted. This suggested that the species bias of AMP activity is directly related to AMP interactions with bacterial outer membranes, despite the fact that the mechanism of antimicrobial activity occurs at the inner membrane.