Covalently crosslinked coacervates: immobilization and stabilization of proteins with enhanced enzymatic activity.

Coacervates represent models for membrane-free protocells and thus provide a simple route to synthetic cellular-like systems that provide selective encapsulation of solutes. Here, we demonstrate a simple and versatile post-coacervation crosslink method using the thiol-ene click reaction in aqueous media to prepare covalently crosslinked coacervates. The crosslinking of the coacervate enables stability at extreme pH where the uncrosslinked coacervate fully disassembles.

Sodium dodecyl sulfate modulates the structure and rheological properties of Pluronic F108-poly(acrylic acid) coacervates).

Micelles formed within coacervate phases can impart functional properties, but it is unclear if this micellization provides mechanical reinforcement of the coacervate whereby the micelles act as high functionality crosslinkers. Here, we examine how sodium dodecyl sulfate (SDS) influences the structure and properties of Pluronic F108-polyacrylic acid (PAA) coacervates as SDS is known to decrease the aggregation number of Pluronic micelles. Increasing the SDS concentration leads to larger water content in the coacervate and an increase in the relative concentration of PAA to the other solids.

Polyelectrolyte-micelle coacervates: intrapolymer-dominant vs. interpolymer-dominant association, solute uptake and rheological properties.

The effects of polyelectrolyte charge density, polyelectrolyte-to-surfactant ratio, and micelle species on coacervation were studied by turbidity, dynamic light scattering, and zeta potential measurements to examine the coacervation of the weak polyelectrolyte branched polyethylenimine (BPEI) and oppositely charged sodium dodecyl sulfate (SDS) micelles as well as BPEI and mixed micelles composed of SDS and poly(ethylene glycol) 4-nonylphenyl 3-sulfopropyl ether potassium salt (PENS). The results of dynamic light scattering and zeta potential measurements are discussed in terms of pH and BPEI-to-surfactant ratio. An intrapolymer-dominant to interpolymer-dominant association model for the BPEI-micelle coacervates was proposed based on the variation of size and zeta potential of coacervate particles by their BPEI-to-surfactant ratio.

Protein encapsulation via polyelectrolyte complex coacervation: Protection against protein denaturation.

Complex coacervation can be used as a route to compartmentalize a variety of solutes such as organic small molecules, inorganic nanoparticles, and proteins within microscale coacervate droplets. To obtain insight into the accumulation of proteins within complex coacervate phases, the encapsulation of Bovine Serum Albumin (BSA) within complex coacervates containing cationic polyelectrolyte poly(allylamine hydrochloride) (PAH) and anionic polyelectrolyte poly(acrylic aid) (PAA) was investigated as a function of mixing sequence, total polyelectrolyte concentration, BSA overall concentration, and the mixing molar ratio of PAA/PAH. Mixing BSA having a negative net charge with the polycation PAH before coacervation, increasing the total polyelectrolyte concentration and PAA/PAH molar ratio, or decreasing the BSA overall concentration led to more efficient protein encapsulation.

Mechanical properties of bulk graphene oxide/poly(acrylic acid)/poly(ethylenimine) ternary polyelectrolyte complex.

Ternary complexes formed in a single pot process through the mixing of cationic (branched polyethylenimine, BPEI) and anionic (graphene oxide, GO, and poly(acrylic acid), PAA) aqueous solutions exhibit superior mechanical performance in comparison to their binary analogs. The composition of the ternary complex can be simply tuned through the composition of the anionic solution, which influences the water content and mechanical properties of the complex. Increasing the PAA content in the complex decreases the overall water content due to improved charge compensation with the BPEI, but this change also significantly improves the toughness of the complex.

Slippery Liquid-Infused Porous Surfaces (SLIPS) Using Layer-by-Layer Polyelectrolyte Assembly in Organic Solvent.

Slippery liquid-infused porous surfaces (SLIPS) have potential impact on a wide range of industries, including healthcare, food packaging, and automobile. A tremendouseffort has been focused on developing novel fabrication methods for making SLIPS. However, current fabrication methods usually involve harsh conditions and complicated postfabrication modifications or are limited to specific substrates.

Effect of small molecules on the phase behavior and coacervation of aqueous solutions of poly(diallyldimethylammonium chloride) and poly(sodium 4-styrene sulfonate).

Hypothesis: Complex coacervates are capable of easily partitioning solutes within them based on relative affinities of solute-water and solute-polyelectrolyte pairs, as the coacervate phase has low surface tension with water, facilitating the transport of small molecules into the coacervate phase. The uptake of small molecules is expected to influence the physicochemical properties of the complex coacervate, including the hydrophobicity within coacervate droplets, phase boundaries of coacervation and precipitation, solute uptake capacity, as well as the coacervate rheological properties.

Experiments: Phase behavior of aqueous solutions of poly(diallyldimethylammonium chloride) (PDAC) and poly(sodium 4-styrene sulfonate) (SPS) was investigated in the presence of various concentrations of two different dyes, positively charged methylene blue (MB) or non-charged bromothymol blue (BtB), using turbidity measurements.

Tuning Wet Adhesion of Weak Polyelectrolyte Multilayers.

Weak polyelectrolyte multilayers (PEMs) assembled by the layer-by-layer method are known to become tacky upon contact with water and behave as a viscoelastic fluid, but this wet adhesive property and how it can be modified by external stimuli has not yet been fully explored. We present here a study on the wet adhesive performance of PEMs consisting of branched poly(ethylene imine) and poly(acrylic acid) under controlled conditions (e.g.

Surface Functionalization for a Nontextured Liquid-Infused Surface with Enhanced Lifetime.

Liquid-infused surfaces (LISs) are a new class of self-cleaning surfaces having superior properties compared to other self-cleaning surfaces. One challenge regarding these is the eventual washing away or drainage of the lubricant, limiting their longevity. Presented here is a surface functionalization strategy to compatibilize the lubricant and surface, enhancing the ability of the lubricant to remain on the surface even during washing.

Assembly of large area crack free clay porous films.

Porous materials with well-defined porosity have advantages in a wide range of applications, including filtration media, catalysis, and electrodes. The bottom-up fabrication of inverse opals have promised to provide those nanostructures, but fabrication of these materials is often plagued with large numbers of defects and macro-scale cracks. Here, we present a method for making nanostructured porous clay films with well defined pore size that are crack free over a large area (multiple cm).

A family of mechanically adaptive supramolecular graphene oxide/poly(ethylenimine) hydrogels from aqueous assembly.

Composite hydrogels containing graphene oxide (GO) offer advantageous mechanical properties, but tuning these properties generally requires the synthesis of new hydrogels or if the hydrogel is thermally responsive, utilization of a chemistry determined temperature window. Here, we demonstrate a simple route to generate a family of GO-based hydrogels from aqueous solution based assembly of GO with polycationic poly(ethylenimine), PEI, without any secondary chemical crosslinking. Tuning the ratio of GO : PEI during the assembly produces a family of hydrogels that responds to mechanical compression by irreversibly altering their equilibrium water content and mechanical properties in a controllable manner.

Self-Healing of Bulk Polyelectrolyte Complex Material as a Function of pH and Salt.

Self-healing materials are an emerging class of modern materials gaining importance due to environmental and energy concerns. Materials based on the complexation of oppositely charged polyelectrolytes, usually in the form of coatings and films, have been shown to have water activated self-healing properties. In this work, the self-healing of bulk branched poly(ethylene imine) and poly(acrylic acid) (BPEI/PAA) complex is studied as a function of the aqueous solutions used to activate the self-healing.

Accelerated Amidization of Branched Poly(ethylenimine)/Poly(acrylic acid) Multilayer Films by Microwave Heating.

Chemical cross-linking of layer-by-layer assembled films promotes mechanical stability and robustness in a wide variety of environments, which can be a challenge for polyelectrolyte multilayers in saline environments or for multilayers made from weak polyelectrolytes in environments with extreme pHs. Heating branched poly(ethylenimine)/poly(acrylic acid) (BPEI/PAA) multilayers at sufficiently high temperatures drives amidization and dehydration to covalently cross-link the film, but this reaction is rather slow, typically requiring heating for hours for appreciable cross-linking to occur. Here, a more than one order of magnitude increase in the amidization kinetics is realized through microwave heating of BPEI/PAA multilayers on indium tin oxide (ITO)/glass substrates.

Sequestration of Methylene Blue into Polyelectrolyte Complex Coacervates.

Polyelectrolyte complex coacervation is a process that has been proposed as a model for protocell formation due to its ability to compartmentalize chemicals in solution without a membrane. During the liquid-liquid phase separation that results in water rich and polyelectrolyte rich phases, small molecules present in solution selectively partition to one phase over the other. This sequestration is based on relative affinities.

Contraction of weak polyelectrolyte multilayers in response to organic solvents.

Weak polyelectrolyte multilayers (PEMs) prepared by the layer-by-layer assembly technique have recently been found to demonstrate a unique contraction upon exposure to organic solvents. This response is dependent upon which organic solvent is employed, and fundamental questions have not been clarified regarding the correlation of the magnitude of the film contraction with solvent type. In this work, we used solubility parameters to analyze the response of branched poly(ethylene imine)/poly(acrylic acid) (BPEI/PAA) multilayers when exposed to a variety of solvents.

Large-scale solvent driven actuation of polyelectrolyte multilayers based on modulation of dynamic secondary interactions.

Polyelectrolyte multilayers (PEMs), assembled from weak polyelectrolytes, have often been proposed for use as smart or responsive materials. However, such response to chemical stimuli has been limited to aqueous environments with variations in ionic strength or pH. In this work, a large in magnitude and reversible transition in both the swelling/shrinking and the viscoelastic behavior of branched polyethylenimine/poly(acrylic acid) multilayers was realized in response to exposure with various polar organic solvents (e.

Layer-by-layer rose petal mimic surface with oleophilicity and underwater oleophobicity.

Surfaces designed with specific wetting properties are still a key challenge in materials science. We present here a facile preparation of a surface assembled by the layer-by-layer technique, using a colloidal dispersion of ionomer particles and linear polyethylene imine. The colloidal ethylene-co-methacrylic acid (EMAA) particles are on the order of half a micron in size with surface features from 40 to 100 nm in width.

Facile Assembly Enhanced Spontaneous Fluorescent Response of Ag Ion Containing Polyelectrolyte Multilayer Films.

Fluorescent organic-inorganic composite materials exhibiting "turn-on" response are often based on conjugated small molecules. Conjugated polymers, however, often exhibit a "turn-off" response in combination with metal ions. Here we present fluorescent turn-on behavior of a branched poly(ethylene imine)-poly(acrylic acid)-Ag ion complex in a thin film.

Silver nanoparticle aided self-healing of polyelectrolyte multilayers.

Self-healing is the ability of a material to repair mechanical damage. The lifetime of a coating or film might be lengthened with this capacity. Water enabled self-healing of polyelectrolyte multilayers has been reported, using systems that grow via the interdiffusion of polyelectrolyte chains.

Formation and tunable disassembly of polyelectrolyte-Cu2+ layer-by-layer complex film.

Layer-by-layer assembly of films containing metal ions was investigated. A complex between various metal ions and branched polyethyleneimine is formed in solution and then assembled into multilayer films with poly(acrylic acid). The metal-ligand complex formation results in brightly colored materials that deposit as thick layers.

Omniphobic Slippery Coatings Based on Lubricant-Infused Porous Polyelectrolyte Multilayers.

Omniphobic and slippery coatings from lubricant-infused, textured surfaces have recently been shown to have superior properties including low contact angle hysteresis and low sliding angles. Here, we present an omniphobic slippery surface prepared by infusing a fluorinated lubricant into a porous polyelectrolyte multilayer. These surfaces repel water and decane with sliding angles as low as 3°.

Laser-written photonic crystal optofluidics for electrochromatography and spectroscopy on a chip.

Femtosecond laser processes were optimized for nonlinear interactions with various optical materials to develop a novel biophotonic lab-on-a-chip device that integrates laser-formed waveguides (WGs), microfluidic channels and photonic crystals (PCs). Such integration seeks the unique demonstration of dual PC functionalities: (1) efficient chromatographic separation and filtration of analytes through a porous PC embedded inside a microfluidic channel and (2) optofluidic spectroscopy through embedded WGs that probe PC stopband shifts as varying analyte concentrations flow and separate. The building blocks together with their integration were demonstrated, providing embedded porous PCs through which electrochromatography drove an accelerated mobile phase of analyte and an optical stopband was probed via integrated buried WGs.

Electric field induced morphological transitions in polyelectrolyte multilayers.

In this work, the morphological transitions in weak polyelectrolyte (PE) multilayers (PEMs) assembled from linear poly(ethylene imine) (LPEI) and poly(acrylic acid) (PAA) upon application of an electric field were studied. Exposure to an electric field results in the creation of a porous structure, which can be ascribed to local changes in pH from the hydrolysis of water and subsequent structural rearrangements of the weak PE constituents. Depending on the duration of application of the field, the porous transition gradually develops into a range of structures and pore sizes.