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Longer and stronger; stiff but not brittle Hydrogels are highly water-swollen, cross-linked polymers. Although they can be highly deformed, they tend to be weak, and methods to strengthen or toughen them tend to reduce stretchability. Two papers now report strategies to create tough but deformable hydrogels (see the Perspective by Bosnjak and Silberstein). Wang et al . introduced a toughening mechanism by storing releasable extra chain length in the stiff part of a double-network hydrogel. A high applied force triggered the opening of cycling strands that were only activated at high chain extension. Kim et al . synthesized acrylamide gels in which dense entanglements could be achieved by using unusually low amounts of water, cross-linker, and initiator during the synthesis. This approach improves the mechanical strength in solid form while also improving the wear resistance once swollen as a hydrogel. —MSL

Recent experimental and theoretical work has shown that sticker clustering can be used to enhance properties such as toughness and creep resistance of polymer networks. While it is clear that the changes in properties are related to a change in network topology, the mechanistic relationship is still not well understood. In this work, the effect of sticker clustering was investigated by comparing the dynamics of random copolymers with those where the stickers are clustered at the ends of the chain in the unentangled regime using both linear mechanics and diffusion measurements. Copolymers of N,N-dimethyl acrylamide (DMA) and pendant histidine groups were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. The clustered polymers were synthesized using a bifunctional RAFT agent, such that the midblock consisted of PDMA and the two end blocks were random copolymers of DMA and the histidine-functionalized monomer. Upon addition of Ni ions, transient metal-coordinate crosslinks are formed as histidine-Ni complexes. Combined studies of rheology, neutron scattering and self-diffusion measurements using forced Rayleigh scattering revealed changes to the network topology and stress relaxation modes. The network topology is proposed to consist of aggregates of the histidine-Ni complexes bridged by the non-associative midblock. Therefore, stress relaxation requires the cooperative dissociation of multiple bonds, resulting in increased relaxation times. The increased relaxation times, however, were accompanied by faster diffusion. This is attributed to the presence of defects such as elastically inactive chain loops. This study demonstrates that the effects of cooperative sticker dissociation can be observed even in the presence of a significant fraction of loop defects which are known to alter the nonlinear properties of conventional telechelic polymers.

This two-dimensional computational study investigates the effect of external magnetic fields on thin film nanocomposites comprised of superparamagnetic nanoparticles dispersed within block copolymer melts, which display a variety of morphological transitions based on the field orientation, nanoparticle loading, and selectivity of the nanoparticles for the blocks. In-plane magnetic fields lead to chaining of the nanoparticles; when selective for the minority block in a hexagonal block copolymer nanostructure, this chaining results in the formation of stripe phases oriented parallel to the magnetic field. When selective for the majority block of the hexagonal structure, nanoparticle chains of sufficient persistence length drive the orientation of the hexagonal morphology with the ⟨100⟩ direction oriented parallel to the magnetic field. Out-of-plane magnetic fields induce repulsive dipolar interactions between the nanoparticles that annihilate the defects in the hexagonal morphology of the block copolymer when the nanoparticle is selective for the minority block. When the nanoparticles are selective for the majority block and the field is oriented out of plane, repulsive dipolar interactions lead to the formation of honeycomb lattices. In all cases, the nanoparticle size and volume fraction must be chosen to maximize the commensurability with the block copolymer structure to optimize the ordering of the final composite.

The diffusion of entangled rod–coil block copolymers is investigated by molecular dynamics (MD) simulations, and theories are introduced that describe the observed features and underlying physics. The reptation of rod–coil block copolymers is dominated by the mismatch between the curvature of the rod and coil entanglement tubes, which results in dramatically slower diffusion of rod–coils compared to the rod and coil homopolymers. For small rods, a local curvature-dependent free energy penalty results in a rough energy surface inside the entanglement tube, causing diffusivity to decrease with rod length. For large rods, rotational hindrances on the rod dominate, causing the coil block to relax by an arm retraction mechanism and diffusivity to decrease exponentially with coil size.

This work presents scattering functions of conjugates consisting of a colloid particle and a self-avoiding polymer chain as a model for protein–polymer conjugates and nanoparticle–polymer conjugates in solution. The model is directly derived from the two-point correlation function with the inclusion of excluded volume effects. The dependence of the calculated scattering function on the geometric shape of the colloid and polymer stiffness is investigated. The model is able to describe the experimental scattering signature of the solutions of suspending hard particle–polymer conjugates and provide additional conformational information. This model explicitly elucidates the link between the global conformation of a conjugate and the microstructure of its constituent components.

The Flory-Rehner and Bray-Merrill swelling theories are venerable theories for calculating the swelling of polymer networks and are widely applied across polymer materials. Here, these theories are revised to include cyclic topological defects present in polymer networks by using a modified phantom network model. These closed-form equations assume defect contributions to the swelling elasticity to be linear and additive and allow different assumptions regarding prestrain of larger loops to be incorporated. To compare to the theories, swelling experiments are performed on end-linked poly(ethylene glycol) gels in which the topological defects (primary and secondary loops) have been previously measured. Gels with higher loop densities exhibit higher swelling ratios. An equation is derived to compare swelling models independent of knowledge of the Flory-Huggins χ parameter, showing that the revised swelling models for loop defects are more accurate than both the phantom network model that neglects loops and the Bray-Merrill equation.

Physics-based models are the primary approach for modeling the phase behavior of block copolymers. However, the successful use of self-consistent field theory (SCFT) for designing new materials relies on the correct chemistry- and temperature-dependent Flory-Huggins interaction parameter

The failure properties of a polymer network, including toughness, ultimate strain, and ultimate stress, are some of the most critical properties for network performance. The polymer networks often ...

While protein self-assembly has been used to improve the performance of biosensors and biocatalysts, few general techniques have been demonstrated to achieve well-ordered protein arrays under the h...

Luminescence thermometry has substantially progressed in the last decade, rapidly approaching the performance of concurrent technologies. Performance is usually assessed through the relative thermal sensitivity, Sr, and temperature uncertainty, ����T. Until now, the state-of-the-art values at ambient conditions do not exceed maximum Sr of 12.5% K���1 and minimum ����T of 0.1 K. Although these numbers are satisfactory for most applications, they are insufficient for fields that require lower thermal uncertainties, such as biomedicine. This has motivated the development of materials with an improved thermal response, many of them responding to the temperature through distinct photophysical properties. This paper demonstrates how the performance of multiparametric luminescent thermometers can be further improved by simply applying new analysis routes. The synergy between multiparametric readouts and multiple linear regression makes possible a tenfold improvement in Sr and ����T, reaching a world record of 50% K���1 and 0.05 K, respectively. This is achieved without requiring the development of new materials or upgrading the detection system as illustrated by using the green fluorescent protein and Ag2S nanoparticles. These results open a new era in biomedicine thanks to the development of new diagnosis tools based on the detection of super-small temperature fluctuations in living specimens., This project has received funding from the European Union's Horizon 2020 FET Open programme under grant agreement No 801305 (NanoTBTech). This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement No. 823941.

Proteins films have been developed for use in food packaging materials in order to replace synthetic polymers because of environment pollution. Despite their advantages, the use of protein films in a wide range of food products is still limited due to their hydrophilic behavior. Thus, this study aimed to decrease the sensitivity of fish protein films to water through the application of glow discharge plasma. Plasma parameters (power, pressure and time of exposure) were studied according to a 23 factorial design, and the physicochemical properties of the films including moisture content, water vapor permeability, and solubility in water were evaluated. The microstructure and thermal properties of the films were also characterized. In general, glow discharge plasma caused different effects in films properties, such as cleaning and etching which were responsible for the changes observed in physicochemical properties. Power and time of exposure, as well as their interaction, were the most influent parameters. Decrease in water vapor permeability and solubility were observed in some treatments, which are important characteristics for a material to be used as food packaging. Then, the plasma setting might be changed through the adjustment of parameters of exposure according to the specificity of the application intended.

Proteins have great potential as biomass-derived feedstocks for material synthesis and can form strong materials due to their highly hydrogen-bonded nature. Elastomers comprised of proteins and a synthetic rubbery polymer were prepared by copolymerizing a methacrylated protein and a vinyl monomer, where proteins function as macro-cross-linkers and reinforcing fillers. Selecting a hydrophobic synthetic polymer block partially mitigates the moisture absorption of protein-based materials while maintaining desirable levels of mechanical properties. The use of a hydrophobic monomer is enabled by the use of surfactants that function as compatibilizers, since proteins are generally insoluble in organic solvents and vinyl monomers. Surfactants also lower the softening temperature of proteins, allowing materials to be fabricated solvent free using thermoplastic processing techniques. The preparation of a polyacrylate network toughened through incorporation of protein cross-linking domains is demonstrated using whe...

Myofibrillar proteins have good film forming ability, that leads to the formation of polymers with interesting properties for food packaging development. However, as other bio-sourced macromolecules, they have limited performance compared to synthetic materials and cold plasma represents a promising strategy to change polymer properties. Alternating current (AC) glow discharge plasma is a novel and innovative approach for surface modification of agro-based films in order to improve their properties. Then, the effects of exposure to AC glow discharge plasma were studied on the physicochemical, microstructural and thermal properties of myofibrillar protein films from fish. Films treated for 2 min showed increased elongation at break and decreased tensile strength, while the opposite behavior was observed after 5 min of treatment. Solubility in water increased with 5 min and water vapor permeability increased with 2 min of plasma treatment. Color and opacity also increased probably as a result of chemical changes because of plasma application. Slight changes were observed in microstructure of the films. Thermal properties results agreed with the modifications observed in physicochemical performance, which might be attributed to polymer surface functionalization and etching. Thus, the AC glow discharge is a promising alternative to other strategies in order to advance properties of myofibrillar protein films for food packaging because it is a dry process, does not cause damage by heating in the material, and does not pollute the environment.

The vast differences in material properties accessible via crosslinking of sidechain-functionalized polymers are driven by topology., The vast differences in material properties accessible via crosslinking of sidechain-functionalized polymers are driven by topology. For example, vulcanized rubbery networks feature intermolecular connections and loop topologies of various orders while single-chain nanoparticles (SCNPs) are comprised, in principle, entirely of primary loops. Despite this fact, precise quantification of loops in sidechain crosslinked polymers has not been accomplished. Here, it is demonstrated that by introducing cleavable linkers and mass labels onto the pendant functional groups of reactive polymers, the number of primary loops in sidechain crosslinked materials ranging from rubbery networks (gels) to soluble SCNPs can be precisely quantified. This study sheds new light on the topology of sidechain-crosslinked networks, providing design principles for augmenting the properties of this industrially and academically important class of materials through topological control.

Bioconjugates made of the model red fluorescent protein mCherry and synthetic polymer blocks show that topology, i.e. the BA, BA2, ABA and ABC chain structure of the block copolymers, where B represents the protein and A and C represent polymers, has a significant effect on ordering transitions and the type and size of nanostructures formed during microphase separation. ABA and ABC type block copolymers were synthesized by using two site-specific bioconjugation reactions: the thiol–ene reaction with a cysteine on mCherry and maleimide functionalized polymers, and the sortase A ligation reaction with an LPETG sequence at the C-terminus on mCherry and a triglycine functionalized polymer. The phase behaviors of mCherry–poly(N-isopropylacrylamide) (PNIPAM) and mCherry–(PNIPAM)2 show that the shapes of the phase diagrams are similar overall, but mCherry–(PNIPAM)2, i.e. BA2 type, yields a narrower domain spacing than mCherry–PNIPAM, i.e. BA type. PNIPAM–mCherry–PNIPAM (ABA type) shows only lamellar phases in the range of conditions under which ordered structures appear. PDMAPS–mCherry–PNIPAM (ABC type) shows an ordered structure across the widest range of conditions in the four bioconjugates and also the widest range of different nanodomain structures. The phase behavior of the ABC type implies that the repulsive interaction between two water-soluble coil polymers can be a key factor in enhancing the self-assembly of globular protein–polymer block copolymers.

Contrast-variation small-angle neutron scattering (CV-SANS) is a widely used technique for quantifying hydration water in soft matter systems, but it is predominantly applied in the dilute regime or for systems with a well-defined structure factor. Here, CV-SANS was used to quantify the number of hydration water molecules associating with three water-soluble polymers with different critical solution temperatures and types of water–solute interactions in dilute, semidilute, and concentrated solution through the exploration of novel methods of data fitting and analysis. Multiple SANS fitting workflows with varying levels of model assumptions were evaluated and compared to give insight into SANS model selection. These fitting pathways ranged from general, model-free algorithms to more standard form and structure factor fitting. In addition, Monte Carlo bootstrapping was evaluated as a method to estimate parameter uncertainty through simulation of technical replicates. The most robust fitting workflow for dilute solutions was found to be form factor fitting without CV-SANS (i.e. polymer in 100% D2O). For semidilute and concentrated solutions, while the model-free approach can be mathematically defined for CV-SANS data, the addition of a structure factor imposes physical constraints on the optimization problem, suggesting that the optimal fitting pathway should include appropriate form and structure factor models. The measured hydration numbers were consistent with the number of tightly bound water molecules associated with each monomer unit, and the concentration dependence of the hydration number was largely governed by the chemistry-specific interactions between water and polymer. Polymers with weaker water–polymer interactions (i.e. those with fewer hydration water molecules) were found to have more bound water at higher concentrations than those with stronger water–polymer interactions due to the increase in the number of forced water–polymer contacts in the concentrated system. This SANS-based method to count hydration water molecules can be applied to polymers in any concentration regime, which will lead to improved understanding of water–polymer interactions and their impact on materials design.

Polymers are stochastic materials that represent distributions of different molecules. In general, to quantify the distribution, polymer researchers rely on a series of chemical characterizations that each reveal partial information on the distribution. However, in practice, the exact set of characterizations that are carried out, as well as how the characterization data are aggregated and reported, is largely nonstandard across the polymer community. This scenario makes polymer characterization data highly disparate, thereby significantly slowing down the development of polymer informatics. In this work, a proposal on how structural characterization data can be organized is presented. To ensure that the system can apply universally across the entire polymer community, the proposed schema, PolyDAT, is designed to embody a minimal congruent set of vocabulary that is common across different domains. Unlike most chemical schemas, where only data pertinent to the species of interest are included, PolyDAT deploys a multi-species reaction network construct, in which every characterization on relevant species is collected to provide the most comprehensive profile on the polymer species of interest. Instead of maintaining a comprehensive list of available characterization techniques, PolyDAT provides a handful of generic templates, which align closely with experimental conventions and cover most types of common characterization techniques. This allows flexibility for the development and inclusion of new measurement methods. By providing a standard format to digitalize data, PolyDAT serves not only as an extension to BigSMILES that provides the necessary quantitative information but also as a standard channel for researchers to share polymer characterization data.

Here, we report covalent polymer gels in which the macroscopic fracture “reaction” is controlled by mechanophores embedded within mechanically active network strands. We synthesized poly(ethylene glycol) (PEG) gels through the end-linking of azide-terminated tetra-arm PEG (Mn = 5 kDa) with bis-alkyne linkers. Networks were formed under identical conditions, except that the bis-alkyne was varied to include either a cis-diaryl (1) or cis-dialkyl (2) linked cyclobutane mechanophore that acts as a mechanochemical “weak link” through a force-coupled cycloreversion. A control network featuring a bis-alkyne without cyclobutane (3) was also synthesized. The networks show the same linear elasticity (G' = 23~24 kPa, 0.1 – 100 Hz) and equilibrium mass swelling ratios (Q = 10~11 in tetrahydrofuran), but they exhibit tearing energies that span a factor of 8 (3.4 J∙m-2, 10.5 J∙m-2, and 27.1 J∙m-2 for networks with 1, 2, and 3, respectively). The difference in fracture energy is well aligned with the force-coupled scission kinetics of the mechanophores observed in single-molecule force spectroscopy experiments, implicating local resonance stabilization of a diradical transition state in the cycloreversion of 1 as a key determinant of the relative ease with which its network is torn. The connection between macroscopic fracture and small molecule reaction mechanism suggests opportunities for molecular understanding and optimization of polymer network behavior.

The utility and lifetime of materials made from polymer networks, including hydrogels, depend on their capacity to stretch and resist tearing. In gels and elastomers, those mechanical properties are often limited by the covalent chemical structure of the polymer strands between cross-links, which is typically fixed during the material synthesis. Here, we report polymer networks in which the constituent strands lengthen through force-coupled reactions that are triggered as the strands reach their nominal breaking point. Reactive strand extensions of up to 40% lead to hydrogels that stretch 40-50% further than, and exhibit tear energies twice that of, networks made from analogous control strands. The enhancements are synergistic with those provided by double network architectures, and complement other existing toughening strategies.

The authors use neutron spin-echo spectroscopy and forced Rayleigh scattering to study the interplay between conformational fluctuations and transient binding in associative protein hydrogels.

Transient network theory is the state of the art for understanding the mechanical response of associative networks. However, the predictions of the models are difficult to verify in the absence of direct observations of the bond states. This manuscript introduces a method to quantitatively measure force-induced bond dissociation in associative networks through the design of an opto-mechanically coupled model polymer system and a rheo-fluorescence set-up. The findings show that shear thinning in the model associative polymers cannot be explained by classical theories, and likely involves alternative modes as suggested by newer models.

Dynamic networks formed by physically crosslinked, entangled polymers have emerged as self-healing, stretchable, and functional materials. Entangled associative gels with remarkable toughness and extensibility have been produced by several distinct chemical approaches, suggesting that these enhanced mechanical properties result from molecular-scale topology. Previously, artificially engineered associative proteins were designed to provide an ideal model system to investigate the role of entanglement on gel mechanics via well-defined entangled or unentangled physical gels. Herein, uniaxial strain-induced structural changes in these model gels were observed using in situ small-angle x-ray scattering (SAXS) and in situ polarized optical microscopy (POM) up to 2000% engineering strain. Anisotropic optical responses to uniaxial strain at the nano-, micro-, and macroscales suggest that stress dissipation mechanisms enable high extensibility and toughness. Nano- and microscopic anisotropy observed by SAXS indicate stretching and alignment of flexible polymer strands along the straining axis, and nonmonotonic macroscopic anisotropy observed by POM suggests relaxation within the hydrogel due to rearrangement of associative network junctions. Unentangled hydrogels exhibit low toughness and a strain-rate-dependent transition from ductile to brittle tensile behavior, which is typical for associative polymer solutions. These findings indicate that topological entanglements and the freedom of individual chains to align at the nanoscale due to junction relaxation are both critical to achieving high toughness and elongation in entangled physical gels.

Recent experiments have revealed that a variety of associative polymers with different architecture (linear and branched) and different nature of the associating interaction (associative protein domains and metal–ligand bonds) exhibit unexplained superdiffusive behavior. Here, Brownian dynamics simulations of unentangled coarse-grained associating star-shaped polymers are used to establish a molecular picture of chain dynamics that explains this behavior. Polymers are conceptualized as particles with effective Rouse diffusivities that interact with a mean field background through attachments by stickers at the end of massless springs that represent the arms of the polymer. The simulations reveal three mechanisms of molecular diffusion at length scales much larger than the radius of gyration: hindered diffusion, walking diffusion, and molecular hopping, all of which depend strongly on polymer concentration, arm length, and the association/dissociation rate constants. The molecular model establishes that su...

To predict and understand the properties of polymer networks, it is necessary to quantify network defects. Of the various possible network defects, loops are perhaps the most pervasive and yet difficult to directly measure. Network disassembly spectrometry (NDS) has previously enabled counting of the simplest loops-primary loops-but higher-order loops, e.g., secondary loops, have remained elusive. Here, we report that the introduction of a nondegradable tracer within the NDS framework enables the simultaneous measurement of primary and secondary loops in end-linked polymer networks for the first time. With this new "NDS2.0" method, the concentration dependences of the primary and secondary loop fractions are measured; the results agree well with a purely topological theory for network formation from phantom chains. In addition, semibatch monomer addition is shown to decrease both primary and secondary loops, though the latter to a much smaller extent. Finally, using the measured primary and secondary loop fractions, we were able to predict the shear storage modulus of end-linked polymer gels via real elastic network theory (RENT).

Accurate prediction of the gel point for real polymer networks is a long-standing challenge in polymer chemistry and physics that is extremely important for applications of gels and elastomers. Here, kinetic Monte Carlo simulation is applied to simultaneously describe network topology and growth kinetics. By accounting for topological defects in the polymer networks, the simulation can quantitatively predict experimental gel point measurements without any fitting parameters. Gel point suppression becomes more severe as the primary loop fraction in the networks increases. A topological homomorphism theory mapping defects onto effective junctions is developed to qualitatively explain the origins of this effect, which accurately captures the gel point suppression in the low loop limit where cooperative effects between topological defects are small.

Poly(oligoethylene glycol)-poly(2-vinylpyridine) is a model diblock for studying the effect of block-localized charge on block copolymer self-assembly because in the absence of charge the polymers are perfectly miscible, and upon protonation of the vinylpyridine block the polymer undergoes an order–disorder transition. Seven model block copolymers with molecular weights of approximately 60 kDa containing poly(2-vinylpyridine) volume fractions spanning 0.069–0.700 were synthesized using reversible addition fragmentation transfer polymerization and then studied to understand the effect of protonation level, diblock composition, and temperature on the location of the ordering transition and the type of nanostructures formed in a charge asymmetric system. All of the polymers displayed lower critical solution-type behavior, with the order–disorder transition temperature decreasing with increasing acid content. Polymers with symmetric compositions showed the highest degree of incompatibility for a given degree of protonation, and the observed morphologies for all polymers were consistent with those observed at similar compositions for classical hydrophobic block copolymers. The observed protonation-induced phase transition can be explained by the shift of the Flory–Huggins parameter due to the alternation of the identity of monomers, consistent with the prediction of Nakamura and Wang's theory. The use of polyvalent ions promotes self-assembly at lower concentrations, consistent with ionic crosslinking effects between polymer chains that are promoted at high concentration due to exchange entropy in crosslinked polymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1181–1190

Controlling the molecular structure of amorphous cross-linked polymeric materials is a longstanding challenge. Herein, we disclose a general strategy for precise tuning of loop defects in covalent polymer gel networks. This "loop control" is achieved through a simple semibatch monomer addition protocol that can be applied to a broad range of network-forming reactions. By controlling loop defects, we demonstrate that with the same set of material precursors it is possible to tune and in several cases substantially improve network connectivity and mechanical properties (e.g., ∼600% increase in shear storage modulus). We believe that the concept of loop control via continuous reagent addition could find broad application in the synthesis of academically and industrially important cross-linked polymeric materials, such as resins and gels.

The junction functionality of polymer networks is a key design variable to tune the material properties through changing the network connectivity. Here, we perform a Monte Carlo simulation to study the topology and elasticity of end-linked polymer networks constructed by junctions with different functionalities. The effect of junction functionality on the topological structure of the network displays both universal features and odd–even effects. For all junction functionalities, the primary loop fraction shows a linear dependence on the dimensionless product of concentration with single chain pervaded volume. The slopes of the lines exhibit strong odd–even alternation: primary loops are formed more frequently for junctions with an odd number of functional groups. The secondary loop fraction has a maximum when plotted against the normalized primary loop fraction, where the value of the maximum also shows odd–even alternation. The topological information obtained through Monte Carlo simulation is then incor...

Bio-sourced macromolecules such as cyanophycin are an attractive source for alternative, sustainable plastics. While the chemical structure and biological function of cyanophycin have been previously investigated, its material properties remain largely unexplored. This study investigates the structural, thermal, mechanical, and solution properties of cyanophycin produced from recombinant Escherichia coli . Unplasticized, it has an elastic compression modulus of about 560 MPa and undergoes brittle failure at 78 MPa. Cyanophycin exhibits thermal stability in air up to 200 °C and does not undergo glass transition within its limit of thermal stability. The polypeptide is amorphous and has no long-range ordering in the solid state. In solution, water-soluble cyanophycin is thermoresponsive, exhibiting both upper and lower critical solution temperatures. Because the feasibility of industrial scale cyanophycin production through fermentation has been well studied, an expanded understanding of its materials properties should contribute to the development of new applications for this biopolymer.

Dual-associative protein di- and triblock copolymers composed of sticker-decorated midblocks and micelle-forming elastin-like polypeptide (ELP) endblocks form shear-thinning, thermoresponsively reinforceable hydrogels that are potentially useful as injectable materials for a variety of applications. Here, the combination of rheological and in situ scattering measurements under shear on these dual-associative gels is employed in order to better understand how block architecture plays a role in controlling microscopic structural rearrangement and the resulting macroscopic mechanical responses. These gels, which form a disordered sphere phase due to endblock aggregation under quiescent conditions with the midblock domains physically crosslinked by protein associations, exhibit both viscoelastic and thixotropic signatures with relative magnitudes dependent upon gel concentration and block architecture. In situ SAXS measurements during flow indicate that these thixotropic responses correspond to the development of ordered domains following start-up of shear. For both architectures, the rate of alignment increases with increasing concentration. However, the rate of domain formation when increasing the temperature from 35 to 50 °C depends on the interplay between thermoresponsive toughening of the endblocks and softening of the coiled-coil domains such that rate of rearrangement decreases in the triblock while it increases in the diblock. Following a step-down in shear flow, structural rearrangement within the samples results in a thixotropic stress response. Upon cessation of flow, gel recovery is characterized by a concentration-dependent restoration of the micellar network over time, with two timescales observed that correspond to two different length scales of network relaxation.

Three-dimensional (3D) ordered arrays of human immunoglobulin G (IgG) were fabricated using well-defined full-length antibody–polymer conjugates (APCs). The conjugates were prepared through a two-step sequential click approach with a combination of oxime ligation and strain promoted alkyne–azide cycloaddition. They were able to self-assemble into lamellar nanostructures with alternating IgG and poly(N-isopropylacrylamide) (PNIPAM) nanodomains. As a proof-of-concept, these materials were fabricated into thin films and their specific binding ability was tested. The nanostructure not only improves the packing density and the proper orientation of the IgG, but also provides nanochannels to facilitate substrate transport.

Self-assembly of protein-polymer block copolymers is an attractive route for preparing biocatalytic materials. To clarify the effect of bioconjugate shape on self-assembly without changing the chemical details of either block, four different conjugation sites are selected on the surface of the model globular protein mCherry at residues 3, 108, 131, and 222 to alter the colloidal shape of the bioconjugate. All four mCherry-b-poly(N-isopropylacrylamide) bioconjugates show qualitatively similar phase diagrams, indicating that self-assembly is robust with respect to changes in conjugation site. However, protein orientation has an effect on the location of the order-disorder transition concentration, and the stability of the disordered micellar phase is shown to be different for each conjugate. Differences in domain spacing also suggest changes in protein orientation within the lamellae.

Fish protein films present promising properties for use in food packaging; however, their hydrophilic behavior still limits their use. In the present study, cold plasma and a carnauba wax coating were combined as a strategy to reduce the sensitivity to water of films produced with myofibrillar proteins from fish. Bi-layer films were produced by protein solution casting, followed by plasma-treatment (glow discharge) and coating with carnauba wax. The effects of plasma and wax coating on the packaging-related properties of protein films (thickness, mechanical and barrier performance, water solubility, color and opacity), microstructure, and glass transition and melting temperatures were evaluated. The importance of cold plasma to produce bi-layer films was confirmed since inferior properties were obtained for coated samples without plasma application. The glow discharge plasma application followed by carnauba wax coating resulted in 175% higher tensile strength and 65% lower water vapor permeability of fish protein films under the best conditions identified in comparison to control films. The modifications of fish protein films properties were confirmed by the scanning electron microscopy images, X-ray diffraction pattern and thermal transitions. The combination of cold plasma and carnauba wax coating is an alternative to improve the packaging properties of fish protein films, addressing the need to reduce synthetic plastics accumulation in nature, while using environmentally friendly resources and technologies.

Plants accumulate solid carbon mass and self-repair using atmospheric CO2 fixation from photosynthesis. Synthetic materials capable of mimicking this property can significantly reduce the energy needed to transport and repair construction materials. Here, a gel matrix containing aminopropyl methacrylamide (APMA), glucose oxidase (GOx), and nanoceria-stabilized extracted chloroplasts that is able to grow, strengthen, and self-repair using carbon fixation is demonstrated. Glucose produced from the embedded chloroplasts is converted to gluconolactone (GL) via GOx, polymerizing with APMA to form a continuously expanding and strengthening polymethacrylamide. The extracted spinach chloroplasts exhibit enhanced stability and produce 12 µg GL mg-1 Chl h-1 after optimization of the temporal illumination conditions and the glucose efflux rate, with the insertion of chemoprotective nanoceria inside the chloroplasts. This system achieves an average growth rate of 60 µm3 h-1 per chloroplast under ambient CO2 and illumination over 18 h, thickening with a shear modulus of 3 kPa. This material can demonstrate self-repair using the exported glucose from chloroplasts and chemical crosslinking through the fissures. These results point to a new class of materials capable of using atmospheric CO2 fixation as a regeneration source, finding utility as self-healing coatings, construction materials, and fabrics.

Hybrids of protein biopolymers and synthetic polymers are a promising new class of soft materials, as the advantages of each component can be complementary. A recombinant elastin-like polypeptide (ELP) was conjugated to poly(ethylene glycol) (PEG) by macromolecular coupling in solution to form multiblock ELP-PEG copolymers. The hydrated copolymer preserved the thermoresponsive properties from the ELP block and formed hydrogels with different transition temperatures depending on salt concentration. Small angle scattering indicates that the copolymer hydrogels form sphere-like aggregates with a "fuzzy" interface, while the films form a fractal network of nanoscale aggregates. The use of solutions with different salt concentrations to prepare hydrogels was found to influence the transition temperature, the mechanical properties, and the size of the nanoscale structure of the hydrogel without changing the secondary structure of the ELP. The salt variation and the addition of a plasticizer also affected the nanoscale structure and the mechanical characteristics of the films., This research was supported by the MIT Portugal Program. SAXS measurements were performed at the 12-ID-C,D beamline at the Advanced Photon Source at Argonne National Lab, supported by the National Science Foundation., info:eu-repo/semantics/publishedVersion

Through the use of macromolecular design and efficient chemical reactions it is now possible to control the composition of polymer networks and gels with excellent precision. In contrast, topological defects are still impossible to avoid and are generally difficult to quantify. For example, primary loops that form when a bifunctional monomer (A2) reacts twice with the same f functional (f > 2) monomer (Bf) during formation of an end-linked A2 + Bf network represent a pervasive defect that has a detrimental effect on mechanical integrity. Methods for the quantitative analysis of primary loops in such materials have recently emerged; however, these methods have only been applied to the simplest network structure: A2 + B3. Herein, we report strategies for counting primary loops in tetrafunctional (A2 + B4) networks and networks with mixed tri- and tetrafunctional (A2 + B3/B4) junctions. We apply these strategies to the quantitative analysis of primary loops in a series of end-linked poly(ethylene glycol) hyd...

A method for fabricating nanostructured biocatalysts using bioconjugate block copolymer self-assembly is demonstrated, yielding very high protein loadings and activity per unit area, compared to more-established enzyme encapsulation methods. Self-assembled heterogeneous biocatalysts are fabricated by flow coating myoglobin-b-poly(N-isopropylacrylamide) (myoglobin-PNIPAM) block copolymers onto solid supports, and films are stabilized by lightly cross-linking with glutaraldehyde. The conjugates form weakly ordered, nonbirefringent micellar and lamellar assemblies in concentrated solution and disordered but micro-phase-separated structures in thin solid films. The low diffusion resistance in the bioconjugate film imparted by the water-swollen PNIPAM nanostructures, the high enzyme density within the film, and high retention of protein activity results in extremely high catalytic activity: 5-10 times greater than catalysts fabricated using other well-established methods.

Nucleoporin-like polypeptide (NLP) hydrogels are developed by mimicking nucleoporins, proteins that form gel filters regulating transport into the nucleus. Using protein polymers of a minimal consensus repeat, the NLPs selectively enhance transport of cargo–carrier complexes similar to the natural nuclear pore system. The engineered protein gels additionally have tunable mechanical and transport properties and can be biosynthesized at high yield, making them promising materials for advanced separation technologies., United States. Defense Threat Reduction Agency (Grant HDTRA1-13-1-0038), National Institutes of Health (U.S.) (Grant 5-T32-GM008834), National Institute for Biomedical Imaging and Bioengineering (U.S.) (Grant P41EB015871-28), MIT Skoltech Initiative

Understanding dynamic relaxation mechanisms in self-diffusion and constraint release processes of rod–coil block copolymers is important for many technological applications that employ neat melts or concentrated solutions. Using a model system composed of poly(alkoxyphenylenevinylene) rods and polyisoprene coils, reptation theories of entangled rod–coil block copolymers are investigated in the isotropic melt state. Self-diffusion was measured by forced Rayleigh scattering using a red laser line and a new blue photoswitchable dye that allow operation above the bandgap of most semiconducting polymers. In contrast to previous tracer studies where the diffusion of rod–coils through a coil homopolymer matrix is slowed relative to coil homopolymers because of a mismatch in the curvature of the rod and coil entanglement tubes, slowed diffusion is only present in self-diffusion measurements above a critical molecular weight. An activated reptation mechanism with constraint release is proposed as a modification to...

Polymers exhibiting lower critical solution behavior in water have found broad use as thermoresponsive moieties in soft materials, particularly in biomedical applications for triggered actuation, gelation, accumulation, or release. In this work, changing the thermoresponsive block in a self-assembling hydrogel is shown to be a useful approach to control the viscoelastic behavior and mechanical reinforcement of the gel above its transition temperature. Triblock copolymers were prepared with artificial associative protein midblocks from either site-specific bioconjugation of narrowly disperse poly(N-isopropylacrylamide) (PNIPAM) or as biosynthetic genetic fusions to monodisperse elastin-like polypeptide (ELP) sequences. Both synthetic approaches yield responsively reinforceable hydrogels that can be stiffened by up to an order of magnitude to approximately 105 Pa at 30% (w/w). However, end block chemical composition and linear block copolymer architecture could be manipulated to yield high-temperature plate...

Proteins possess an impressive array of functionality ranging from catalytic activity to selective binding and mechanical strength, making them highly attractive for materials engineering. Conjugation of synthetic polymers to proteins has the potential to improve the physical properties of the protein as well as provide functionality not typically found in native proteins, such as stimuli-responsive behavior and the programmable ability to self-assemble. This viewpoint discusses the design of protein-polymer conjugates, an important class of block copolymers. Use of these hybrid molecules in biological and catalytic applications is highlighted, and the ability of the polymer to direct the solution and solid-state self-assembly of the hybrid block copolymers is reviewed. Future challenges in polymer and material science that will enable these hybrid molecules to reach their potential as protein-based materials are outlined.

Perfectly defined, monodisperse fusion protein block copolymers of a thermoresponsive coil-like protein, ELP, and a globular protein, mCherry, are demonstrated to act as fully biosynthetic analogues to protein-polymer conjugates that can self-assemble into biofunctional nanostructures such as hexagonal and lamellar phases in concentrated solutions. The phase behavior of two mCherry-ELP fusions, E10-mCherry-E10 and E20-mCherry, is investigated to compare linear and bola fusion self-assembly both in diluted and concentrated aqueous solution. In dilute solution, the molecular topology impacts the stability of micelles formed above the thermal transition temperature of the ELP block, with the diblock forming micelles and the bola forming unstable aggregates. Despite the chemical similarity of the two protein blocks, the materials order into block copolymer-like nanostructures across a wide range of concentrations at 30 wt% and above, with the bola fusion having a lower order-disorder transition concentration than the diblock fusion. The topology of the molecule has a large impact on the type of nanostructure formed, with the two fusions forming phases in the opposite order as a function of temperature and concentration. This new system provides a rich landscape to explore the capabilities of fusion architecture to control supramolecular assemblies for bioactive materials.

Ionic interactions between proteins and polyelectrolytes are demonstrated as a method to trigger responsive transitions in block copolymer (BCP) photonic gels containing one neutral hydrophobic block and one cationic hydrophilic block. Poly(2-vinylpyridine) (P2VP) blocks in lamellar poly(styrene-b-2-vinylpyridine) block copolymer thin films are quaternized with primary bromides to yield swollen gels that show strong reflectivity peaks in the visible range; exposure to aqueous solutions of various proteins alters the swelling ratios of the quaternized P2VP (QP2VP) gel layers in the PS-QP2VP materials due to the ionic interactions between proteins and the polyelectrolyte. Parameters such as charge density, hydrophobicity, and cross-link density of the QP2VP gel layers as well as the charge and size of the proteins play significant roles on the photonic responses of the BCP gels. Differences in the size and pH-dependent charge of proteins provide a basis for fingerprinting proteins based on their temporal and equilibrium photonic response. The results demonstrate that the BCP gels and their photonic effect provide a robust and visually interpretable method to differentiate different proteins.

Internal hemorrhaging is a leading cause of death after traumatic injury on the battlefield. Although several surgical approaches such as the use of fibrin glue and tissue adhesive have been commercialized to achieve hemostasis, these approaches are difficult to employ on the battlefield and cannot be used for incompressible wounds. Here, we present shear-thinning nanocomposite hydrogels composed of synthetic silicate nanoplatelets and gelatin as injectable hemostatic agents. These materials are demonstrated to decrease in vitro blood clotting times by 77%, and to form stable clot-gel systems. In vivo tests indicated that the nanocomposites are biocompatible and capable of promoting hemostasis in an otherwise lethal liver laceration. The combination of injectability, rapid mechanical recovery, physiological stability, and the ability to promote coagulation result in a hemostat for treating incompressible wounds in out-of-hospital, emergency conditions.

Block copolymers composed of poly(oligo ethylene glycol methyl ether methacrylate) and poly(2-vinylpyridine) are disordered in the neat state but can be induced to order by protonation of the P2VP block, demonstrating a tunable and responsive method for triggering assembly in thin films. Comparison of protonation with the addition of salts shows that microphase separation is due to selective protonation of the P2VP block. Increasing acid incorporation and increasing 2-vinylpyridine content for P2VP minority copolymers both promote increasingly phase-separated morphologies, consistent with protonation increasing the effective strength of segregation between the two blocks. The self-assembled nanostructures formed after casting from acidic solutions may be tuned based on the amount and type of acid incorporation as well as the annealing treatment applied after casting, where both aqueous and polar organic solvents are shown to be effective. Therefore, POEGMA-b-P2VP is a novel ion-containing block copolymer whose morphologies can be facilely tuned during casting and processing by controlling its exposure to acid.

Stimuli-responsive photonic gels are made from the lamellar block copolymer (BCP) poly(styrene-b-2-vinylpyridine) (PS–P2VP), where the photonic responses are triggered by swelling/deswelling of the P2VP block with a selective solvent. When compared to isotropic swelling in chemically cross-linked homopolymer gels, the P2VP block in the lamellar BCP shows significantly lower degrees of swelling in alcohol–water cosolvents. The glassy PS layers completely constrain the lateral expansion of the P2VP gel layers and the dislocation defect network that develops during BCP self-assembly provides a counter force to vertical swelling. A model based on Flory–Huggins mixing and dislocation network strain energy is proposed to capture the swelling behavior of the BCP and is then used to estimate the dislocation network density in the lamellar BCP. This work establishes the quantitative relationship between the reflective color of the photonic gel, the effective χ parameter of the swellable block and the solvent, and ...

Mechanisms of entangled rod–coil diblock copolymer diffusion are investigated using tracer diffusion simulations and experiments in a matrix of entangled coil homopolymers, demonstrating that the d...