In situsaxs characterization of thermoresponsive behavior of a poly(ethylene glycol)-graft-(poly(vinyl caprolactam)-co-poly(vinyl acetate)) amphiphilic graft copolymer.

We report the thermoresponsive assembly and rheology of an amphiphilic thermosensitive graft copolymer, poly(ethylene glycol)-graft-(poly(vinyl caprolactam)-co-poly(vinyl acetate)) (commercial name Soluplus®), which has been investigated for potential biomedical applications. It has received attention due to is ability to solubilize hydrophobic drugs and for its thickening behavior close to body temperature. Through use of the synchrotron at Brookhaven National Lab, and collaboration with the department of energy, the nanoscale structure and properties can be probed in greater detail. Soluplus®undergoes two structural changes as temperature is increased; the first, a concentration independent change where samples become turbid at 32 °C. Increasing the temperature further causes the formation of physically associated hydrogels. This sol-gel transition is concentration dependent and occurs at 32 °C for 40 wt% samples, and increases to 42 °C for 10 wt% samples. From variable temperature SAXS characterization micelles of 20-25 nm in radius can be seen and maintain their size and packing below 32 °C. A gradual increase in the aggregation of micelles corresponding to a thickening of the material is also observed. Close to and above the gelation temperature, micelles collapse and form a physically associated 3D network. A model is proposed to explain these physical effects, where the poly(vinyl caprolactam) group transitions from the hydrophilic corona at room temperature to the hydrophobic core as temperature is increased.

Dynamics and microrheology of colloidal clay-polymer glasses and gels: Size-dependent phenomena and re-entrant behavior at early aging times.

Colloidal clay Laponite forms a variety of arrested states that display interesting aging behavior. Microrheology has been applied to Laponite-based glasses and gels, but few studies evaluate the influence of probe particle size. In this work, we report the dynamics and microrheology of Laponite-polymer dispersions during aging using passive microrheology with three different probe particle sizes. At early aging times, the neat Laponite dispersion forms an arrested state; the nature of this state (e.g., a repulsive glass or gel) has remained the subject of debate. The addition of polymer retards gelation and melts the arrested state. While this melting has been observed at the macroscale and has been attributed to a re-entrant transition of a repulsive glass to a liquid state, to our knowledge, it has not been observed at the microscale. The delay of the gelation time needed to form an arrested state was found to depend on the polymer concentration and could vary from ∼24 h for neat Laponite to seven days for some Laponite-polymer samples. Significant effects of probe particle sizes are observed from the mean-squared displacement (MSD) curves as small and intermediate probe particles show diffusive motion, while the motion of large particles is restricted. By examining the factor of ⟨Δr2 (τ)⟩a, structural heterogeneity can be confirmed through the strong size-dependence displayed. Different MSD trends of probe particles are obtained at longer aging times, but no significant changes occur after 30 days of aging. Our microrheology results also reveal significant effects of probe particle size.

Techniques to characterize dynamics in biomaterials microenvironments: XPCS and microrheology of alginate/PEO-PPO-PEO hydrogels.

Many recent studies have highlighted the timescale for stress relaxation of biomaterials on the microscale as an important factor in regulating a number of cell-material interactions, including cell spreading, proliferation, and differentiation. Relevant timescales on the order of 0.1-100 s have been suggested by several studies. While such timescales are accessible through conventional mechanical rheology, several biomaterials have heterogeneous structures, and stress relaxation mechanisms of the bulk material may not correspond to that experienced in the cellular microenvironment. Here we employ X-ray photon correlation spectroscopy (XPCS) to explore the temperature-dependent dynamics, relaxation time, and microrheology of multicomponent hydrogels comprising of commercial poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer F127 and alginate. Previous studies on this system have shown thermoreversible behavior in the bulk oscillatory shear rheology. At physiological temperatures, bulk rheology of these samples shows behavior characteristic of a soft solid, with G' > G'' and no crossover between G' and G'' over the measurable frequency range, indicating a relaxation time >125 s. By contrast, XPCS-based microrheology shows viscoelastic behavior at low frequencies, and XPCS-derived correlation functions show relaxation times ranging from 10-45 s on smaller length scales. Thus, we are able to use XPCS to effectively probe the viscoelasticity and relaxation behavior within the material microenvironments.

Targeting Multiple Binding Sites on Cholera Toxin B with Glycomimetic Polymers Promotes the Formation of Protein-Polymer Aggregates.

The canonical binding site on the B subunit of cholera toxin (CTB) binds to GM1 gangliosides on host cells. However, the recently discovered noncanonical binding site on CTB with affinity for fucosylated molecules has raised the possibility that both sites can be involved in initiating intoxication. Previously, we showed that blocking CTB binding to human and murine small intestine epithelial cells can be increased by simultaneously targeting both binding sites with multivalent norbornene-based glycopolymers [ACS Infect. Dis. 2020, 6, 5, 1192-1203]. However, the mechanistic origin of the increased blocking efficacy was unclear. Herein, we observed that mixing CTB pentamers and glycopolymers that display fucose and galactose sugars results in the formation of large aggregates, which further inhibits binding of CTB to human granulocytes. Dynamic light scattering analysis, small-angle X-ray scattering analysis, transmission electron microscopy, and turbidimetric assays revealed that the facial directionality of CTB promotes interchain cross-linking, which in turn leads to self-assembly of protein-polymer networks. This cross-linking-induced self-assembly occurs only when the glycopolymer system contains both galactose and fucose. In an assay of the glycopolymer's ability to block CTB binding to human granulocytes, we observed a direct correlation between IC50 and self-assembly size. The aggregation mechanism of inhibition proposed herein has potential utility for the development of low-cost macromolecular clinical therapeutics for cholera that do not have exotic architectures and do not require complex synthetic sequences.

Emulsions Stabilized by Inorganic Nanoclays and Surfactants: Stability, Viscosity, and Implications for Applications.

Pickering emulsions, or emulsions with solid particles at the interface, have attracted significant interest in Enhanced Oil Recovery (EOR) processes, cosmetics, and drug delivery systems due to their ability to resist coalescence. Here, a synthetic clay nanoparticle, laponite®, is utilized to create oil-in-water (o/w) emulsions, and the addition of small-molecule surfactants induces a more stable emulsion. In this study, the stability of laponite® Pickering emulsions with and without the surfactants (dodecyltrimethylammonium bromide (DTAB), Pluronic F68 (F68), and sodium dodecyl sulfate (SDS) is investigated using dynamic light scattering (DLS), ζ-potential, optical microscopy, and rheology. With laponite® and no added surfactants, the DLS and ζ-potential results show formation of emulsion droplets with a diameter of 3 µm and a ζ-potential of -90 mV. With the addition of surfactants, both the droplet diameter and ζ-potential increase, suggesting adsorption of surfactants on the surface of laponite® particle. Optical microscopy suggests that the Pickering emulsion without surfactant undergoes flocculation, while the emulsion becomes stable to coalescence and creaming with addition of surfactants due to formation of a network structure. Regardless of the formation of network structure, the laponite®-F68 emulsion rheologically behaves as a Newtonian fluid, while the laponite®-SDS and laponite®-DTAB emulsions display shear thinning behavior. The difference in the rheological behavior can be attributed to the weak adsorption of F68 on laponite® and electrostatic interactions between laponite® and charged surfactants at oil-water interface.

Impact of stereochemistry on rheology and nanostructure of PLA-PEO-PLA triblocks: stiff gels at intermediate l/d-lactide ratios.

We report rheology and structural studies of poly(lactide)-poly(ethylene oxide)-poly(lactide) (PLA-PEO-PLA) triblock copolymer gels with various ratios of l-lactide and d-lactide in the PLA blocks. These materials form associative micellar gels in water, and previous work has shown that stereoregular triblocks with a l/d ratio of 100/0 form much stiffer gels than triblocks with a 50/50 l/d ratio. Our systems display an unexpected maximum in the storage modulus, G', of the hydrogels at intermediate l/d ratio. The impact of stereochemistry on the rheology is very striking; gels with an l/d ratio of 85/15 have storage moduli that are ∼1-2 orders of magnitude higher than hydrogels with l/d ratios of 100/0. No stereocomplexation is observed in the gels, although PLLA crystals are found for gels with l/d ratios of 95/5 and 90/10, and SANS results show a decrease in the intermicellar spacing for intermediate l/d ratios. We expect the dominant contribution to the elasticity of the gels to be intermicellar bridging chains and attribute the rheology to a competition between an increase in the time for PLA endblocks to pull out of micelles as the l/d ratio is increased and PLLA crystallization occurs, and a decrease in the number of bridging chains for micelles with crystalline PLA domains, as formation of bridges may be hindered by crowded crystalline PLA domains. These results provide a new strategy for controlling the rheology of PLA-based hydrogels for potential applications in biomaterials, as well as fundamental insights into how intermicellar interactions can be tuned via stereochemistry.

Sugars Require Rigid Multivalent Displays for Activation of Mouse Sperm Acrosomal Exocytosis.

As a prerequisite to mammalian fertilization, the sperm acrosomal vesicle fuses with the plasma membrane and the acrosome contents are exocytosed. Induction occurs through engagement of the sperm receptors by multiple sugar residues. Multivalent polymers displaying mannose, fucose, or GlcNAc are effective synthetic inducers of mouse sperm acrosomal exocytosis (AE). Each carbohydrate is proposed to have a distinct binding site on the sperm cell surface. To determine the role of the scaffold structure in the efficiency of AE induction, different polymer backbones were employed to display the different activating sugar residues. These glycopolymers were prepared by ruthenium-catalyzed ring-opening metathesis of 5-substituted norbornene or cyclooctene. The conformations of the glycopolymers were characterized by small-angle X-ray scattering. Polynorbornene displaying mannose, fucose, or GlcNAc forms flexible cylinders in aqueous solution. However, polycyclooctenes displaying any of these same sugars are much more flexible and form random coils. The flexible polycyclooctenes displaying fucose or GlcNAc were less effective inducers of AE than their norbornene counterparts. In contrast, polycyclooctene displaying mannose was the most effective AE inducer and had a more collapsed spherelike structure. Our results suggest that the AE efficacy of fucose, GlcNAc, and mannose polymers relies on a relatively rigid polymer that can stabilize receptor signaling complexes.

Translating Thermal Response of Triblock Copolymer Assemblies in Dilute Solution to Macroscopic Gelation and Phase Separation.

The thermal response of semi-dilute solutions (5 w/w%) of two amphiphilic thermoresponsive poly(ethylene oxide)-b-poly(N,N-diethylacrylamide)-b-poly(N,N-dibutylacrylamide) (PEO45 -PDEAmx -PDBAm12 ) triblock copolymers, which differ only in the size of the central responsive block, in water was examined. Aqueous PEO45 -PDEAm41 -PDBAm12 solutions, which undergo a thermally induced sphere-to-worm transition in dilute solution, were found to reversibly form soft (G'≈10 Pa) free-standing physical gels after 10 min at 55 °C. PEO45 -PDEAm89 -PDBAm12 copolymer solutions, which undergo a thermally induced transition from spheres to large compound micelles (LCM) in dilute solution, underwent phase separation after heating at 55 °C for 10 min owing to sedimentation of LCMs. The reversibility of LCM formation was investigated as a non-specific method for removal of a water-soluble dye from aqueous solution. The composition and size of the central responsive block in these polymers dictate the microscopic and macroscopic response of the polymer solutions as well as the rates of transition between assemblies.

Magnetic Hydrogels from Alkyne/Cobalt Carbonyl-Functionalized ABA Triblock Copolymers.

A series of alkyne-functionalized poly(4-(phenylethynyl)styrene)-block-poly(ethylene oxide)-block-poly(4-(phenylethynyl)styrene) (PPES-b-PEO-b-PPES) ABA triblock copolymers was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. PESn[Co2(CO)6]x-EO800-PESn[Co2(CO)6]x ABA triblock copolymer/cobalt adducts (10-67 wt % PEO) were subsequently prepared by reaction of the alkyne-functionalized PPES block with Co2(CO)8 and their phase behavior was studied by TEM. Heating triblock copolymer/cobalt carbonyl adducts at 120 °C led to cross-linking of the PPES/Co domains and the formation of magnetic cobalt nanoparticles within the PPES/Co domains. Magnetic hydrogels could be prepared by swelling the PEO domains of the cross-linked materials with water. Swelling tests, rheological studies and actuation tests demonstrated that the water capacity and modulus of the hydrogels were dependent upon the composition of the block copolymer precursors.

SANS study of highly resilient poly(ethylene glycol) hydrogels.

Polymer networks are critically important for numerous applications including soft biomaterials, adhesives, coatings, elastomers, and gel-based materials for energy storage. One long-standing challenge these materials present lies in understanding the role of network defects, such as dangling ends and loops, developed during cross-linking. These defects can negatively impact the physical, mechanical, and transport properties of the gel. Here we report chemically cross-linked poly(ethylene glycol) (PEG) gels formed through a unique cross-linking scheme designed to minimize defects in the network. The highly resilient mechanical properties of these systems (discussed in a previous publication) [J. Cui, M. A. Lackey, A. E. Madkour, E. M. Saffer, D. M. Griffin, S. R. Bhatia, A. J. Crosby and G. N. Tew, Biomacromolecules, 2012, 13, 584-588], suggests that this cross-linking technique yields more homogeneous network structures. Four series of gels were formed based on chains of 35,000 g mol(-1), (35k), 12,000 g mol(-1) (12k) g mol(-1), 8000 g mol(-1) (8k) and 4000 g mol(-1) (4k) PEG. Gels were synthesized at five initial polymer concentrations ranging from 0.077 g mL(-1) to 0.50 g mL(-1). Small-angle neutron scattering (SANS) was utilized to investigate the network structures of gels in both D2O and d-DMF. SANS results show the resulting network structure is dependent on PEG length, transitioning from a more homogeneous network structure at high molecular weight PEG to a two phase structure at the lowest molecular weight PEG. Further investigation of the transport properties inherent to these systems, such as diffusion, will aid to further confirm the network structures.

Triblock Glycopolymers with Two 10-mer Blocks of Activating Sugars Enhance the Activation of Acrosomal Exocytosis in Mouse Sperm.

Carbohydrate recognition is imperative for the induction of sperm acrosomal exocytosis (AE), an essential phenomenon in mammalian fertilization. In mouse sperm, polynorbornene 100-mers displaying fucose or mannose moieties were effective at inducing AE. In contrast, glycopolymers exhibiting glucose sugars resulted in no AE activation. To further elucidate the role of ligand density on the activation of AE in mouse sperm, a triple-stain flow cytometry assay was employed to determine the efficacy of polynorbornene block copolymers with barbell-like sequences as initiators of AE. Triblock (ABA or ABC) copolymers were synthesized by ring-opening metathesis polymerization (ROMP) with one or two activating sugars, mannose or fucose, and one nonactivating sugar, glucose. The active ligand fractions in the polymers varied from 10, 20, or 40%. Simultaneously, random copolymers comprising 20% activating ligands were prepared to confirm the importance of ligand positionality in AE activation in mouse sperm. Polynorbornene 100-mers possessing two 10-mer blocks of activating sugars were the most effective copolymers at inducing AE with levels of AE comparable to their homopolymer counterparts and more effective than their random analogues. Small-angle X-ray scattering (SAXS) was then performed to verify that there were no differences in the conformations of the glycopolymers contributing to their varying AE activity. SAXS data analysis confirmed that all of the glycopolymers assumed semiflexible cylindrical structures with similar radii and Kuhn lengths. These findings suggest that the overall ligand density of the sugar moieties in the polymer is less important than the positionality of short blocks of high-density ligands for AE activation in mouse sperm.

Polymer-mediated clustering of charged anisotropic colloids.

Formation of stable, dense nanoparticle clusters is interesting due to both the underlying physics and use of nanoclusters in applications such as digital printing, imaging and biosensing, and energy storage. Here, we explore formation of nanoparticle clusters in dispersions of the model disk-shaped colloid Laponite. Under basic conditions, the model disk-shaped colloid Laponite forms a repulsive glass in water due to strong electrostatic interactions. Addition of a nonadsorbing polymer, the sodium salt of poly(acrylic acid) (PAA), induces a depletion attraction between particles. Through dynamic light scattering (DLS) and rheology, we see that the polymer initially causes a transition from the glassy phase to an ergodic fluid. Samples at higher particle concentration age to a weak nonergodic state, while samples at lower Laponite remain as fluids. As the strength of attraction between particles is increased, we find an increase in the fast relaxation time measured via dynamic light scattering (e.g., slowing of the short-time diffusion of a single particle). While this may in part be attributed to an increase in the ionic strength, the aging behavior and glass-fluid transition we observe appear to be unique to the presence of polymer, suggesting that depletion plays an important role. DLS data on the fluid samples were consistent with two widely spaced diffusive relaxation modes, corresponding to motion of single particles and motion of large clusters, although other slow dynamic processes may be present. On the basis of the estimated volume fraction and depletion attraction, we believe the Laponite-PAA suspensions to be either fluids of stable clusters or glasses of clusters, although it is possible that the nonergodic state we observe is instead a gel of clusters. Additionally, the cluster size was found to be stable for at least 120 days and was directly related to the polymer concentration. This may serve as an important means of tuning cluster size in products and processes based on dense nanoparticle assemblies.

Alginate/PEO-PPO-PEO composite hydrogels with thermally-active plasticity.

Stimuli-responsive hydrogels with high strength and toughness have received significant interest in recent years. Here, we report thermally active composite hydrogels comprising alginate and one of two poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers. Temperature-sensitive structural and mechanical changes are probed using calorimetry, neutron scattering, shear rheology, unconfined compression, and fracture. Below the lower gelation temperature, LGT, the mechanical properties are dominated by alginate. As the LGT is reached, the contribution of PEO-PPO-PEO to the mechanical properties is activated, resulting in order-of-magnitude increases in elastic modulus. Under compression, we show the evolution of plasticity for the composite hydrogels as the LGT is approached and surpassed, resulting in dramatic increases in fracture stress compared to neat alginate hydrogels. Plasticity was observed above the LGT and may be attributed to restructuring from the sliding of packed micelles and strain-hardening due to stress concentration on alginate cross-links and junction zones, ultimately leading to fracture.

Structural properties of optically clear bacterial cellulose produced by Komagataeibacter hansenii using arabitol.

Bacterial cellulose (BC) exhibits beneficial properties for use in biomedical applications but is limited by its lack of tunable transparency capabilities. To overcome this deficiency, a novel method to synthesize transparent BC materials using an alternative carbon source, namely arabitol, was developed. Characterization of the BC pellicles was performed for yield, transparency, surface morphology, and molecular assembly. Transparent BC was produced using mixtures of glucose and arabitol. Zero percent arabitol pellicles exhibited 25% light transmittance, which increased with increasing arabitol concentration through to 75% light transmittance. While transparency increased, overall BC yield was maintained indicating that the altered transparency may be induced on a micro-scale rather than a macro-scale. Significant differences in fiber diameter and the presence of aromatic signatures were observed. Overall, this research outlines methods for producing BC with tunable optical transparency, while also bringing new insight to insoluble components of exopolymers produced by Komagataeibacter hansenii.

Structural insights into perilipin 3 membrane association in response to diacylglycerol accumulation.

Lipid droplets (LDs) are dynamic organelles that contain an oil core mainly composed of triglycerides (TAG) that is surrounded by a phospholipid monolayer and LD-associated proteins called perilipins (PLINs). During LD biogenesis, perilipin 3 (PLIN3) is recruited to nascent LDs as they emerge from the endoplasmic reticulum. Here, we analyze how lipid composition affects PLIN3 recruitment to membrane bilayers and LDs, and the structural changes that occur upon membrane binding. We find that the TAG precursors phosphatidic acid and diacylglycerol (DAG) recruit PLIN3 to membrane bilayers and define an expanded Perilipin-ADRP-Tip47 (PAT) domain that preferentially binds DAG-enriched membranes. Membrane binding induces a disorder to order transition of alpha helices within the PAT domain and 11-mer repeats, with intramolecular distance measurements consistent with the expanded PAT domain adopting a folded but dynamic structure upon membrane binding. In cells, PLIN3 is recruited to DAG-enriched ER membranes, and this requires both the PAT domain and 11-mer repeats. This provides molecular details of PLIN3 recruitment to nascent LDs and identifies a function of the PAT domain of PLIN3 in DAG binding.

Autostratification in drying colloidal dispersions: effect of particle interactions.

When particles differing in size or charge are mixed and cast, vertical segregation is an inevitable phenomenon in the produced films. Apart from the Peclet number, which is the ratio of evaporation to diffusion rates, particle interactions play a crucial role in determining the distribution of particles in the dried films. Trueman et al. (1) developed a model for vertical segregation of particles during drying. Their numerical solution assumed that the chemical potentials were determined entirely by entropy. We report the effect of particle interactions in various systems: (i) charged particles with different Peclet numbers and (ii) charged particles with the same Peclet numbers. An experimental study has also been carried out for particles with Peclet numbers straddling unity; the experimental results conform with the behavior predicted theoretically.

Synthetically simple, highly resilient hydrogels.

Highly resilient synthetic hydrogels were synthesized by using the efficient thiol-norbornene chemistry to cross-link hydrophilic poly(ethylene glycol) (PEG) and hydrophobic polydimethylsiloxane (PDMS) polymer chains. The swelling and mechanical properties of the hydrogels were controlled by the relative amounts of PEG and PDMS. The fracture toughness (G(c)) was increased to 80 J/m(2) as the water content of the hydrogel decreased from 95% to 82%. In addition, the mechanical energy storage efficiency (resilience) was more than 97% at strains up to 300%. This is comparable with one of the most resilient materials known: natural resilin, an elastic protein found in many insects, such as in the tendons of fleas and the wings of dragonflies. The high resilience of these hydrogels can be attributed to the well-defined network structure provided by the versatile chemistry, low cross-link density, and lack of secondary structure in the polymer chains.

Controlling Rheology of Fluid Interfaces through Microblock Length of Sequence-Controlled Amphiphilic Copolymers.

Previous studies have demonstrated that films of sequence-controlled amphiphilic copolymers display contact angles that depend on microblock size. This suggests that microblock length may provide a means of tuning surface and interfacial properties. In this work, the interfacial rheology of a series of sequence-controlled copolymers, prepared through the addition of bicyclo[4.2.0]oct-1(8)-ene-8-carboxamide (monomer A) and cyclohexene (monomer B) to generate sequences up to 24 monomeric units composed of (A m B n ) i microblocks, where m, n, and i range from 1 to 6. Interfacial rheometry is used to measure the mechanical properties of an air-water interface with these copolymers. As the microblock size increases, the interfacial storage modulus, G', increases, which may be due to an increase in the size of interfacial hydrophobic domains. Small-angle X-ray scattering shows that the copolymers have a similar conformation in solution, suggesting that any variations in the mechanics of the interface are due to assembly at the interface, and not on solution association or bulk rheological properties. This is the first study demonstrating that microblock size can be used to control interfacial rheology of amphiphilic copolymers. Thus, the results provide a new strategy for controlling the dynamics of fluid interfaces through precision sequence-controlled polymers.

Self-Patterned Nanoscale Topography of Thin Copolymer Films Prepared by Evaporative Assembly-Resist Early-Stage Bacterial Adhesion.

Biofilm formation on the surfaces of indwelling medical devices has become a growing health threat due to the development of antimicrobial resistance to infection-causing bacteria. For example, ventilator-associated pneumonia caused by Pseudomonas and Staphylococci species has become a significant concern in treatment of patients during COVID-19 pandemic. Nanostructured surfaces with antifouling activity are of interest as a promising strategy to prevent bacterial adhesion without triggering drug resistance. In this study, we report a facile evaporative approach to prepare block copolymer film coatings with nanoscale topography that resist bacterial adhesion. The initial attachment of the target bacterium Pseudomonas aeruginosa PAO1 to copolymer films as well as homopolymer films was evaluated by fluorescence microscopy. Significant reduction in bacterial adhesion (93-99% less) and area coverage (>92% less) on the copolymer films was observed compared with that on the control and homopolymer films [poly(methacrylic acid) (PMAA)─only 40 and 23% less, respectively]. The surfaces of poly(styrene)-PMAA copolymer films with patterned nanoscale topography that contains sharp peaks ranging from 20 to 80 nm spaced at 30-50 nm were confirmed by atomic force microscopy and the corresponding surface morphology analysis. Investigation of the surface wettability and surface potential of polymer films assists in understanding the effect of surface properties on the bacterial attachment. Comparison of bacterial growth studies in polymer solutions with the growth studies on coatings highlights the importance of physical nanostructure in resisting bacterial adhesion, as opposed to chemical characteristics of the copolymers. Such self-patterned antifouling surface coatings, produced with a straightforward and energy-efficient approach, could provide a convenient and effective method to resist bacterial fouling on the surface of medical devices and reduce device-associated infections.

Self-assembly and thermoreversible rheology of perfluorocarbon nanoemulsion-based gels with amphiphilic copolymers.

Perfluorocarbon (PFC) nanoemulsions have great potential in biomedical applications due to their unique chemical stability, biocompatibility, and possibilities for enhanced oxygen supply. The addition of amphiphilic block copolymers promotes the formation and long-term stability of emulsion-based gels. In this work, we report the systematic study of the impact of adding amphiphilic triblock copolymers to water-in-perfluorocarbon nanoemulsions on their structure and viscoelasticity, utilizing small-angle neutron and X-ray scattering (SANS and SAXS) and rheology. We find that an intermediate concentration of copolymer yields the highest strength of attraction between droplets, corresponding to a maximum in the elasticity and storage modulus. The stability and viscoelastic moduli can be tuned via the amount of copolymer and surfactant along with the volume fraction of aqueous phase. SANS provides the detail on nanostructure and can be fit to a spherical core-shell form factor with a square-well hard sphere structure factor. The PFC nanoemulsion system displays thermoresponsive and thermoreversible properties in temperature sweeps.