Meredith N. Silberstein

High Resolution Image Download MS PowerPoint Slide The severe, long-lasting harm caused by plastic pollution to marine ecosystems and coastal economies has led to the development of biodegradable plastics; however, their limited decomposition in marine environments remains a challenge. Here, technologies are presented for creating 3D-bioprinted living materials as a proof of concept for bioplastic degradation, with specific use in marine environments. The approach developed here integrates the halotolerant bioplastic-degrading bacterium Bacillus sp. NRRL B-14911 into alginate-based bio-ink to print an engineered living material (ELM) termed a “bio-sticker.” Quantification of bacteria viability reveals that bioprinted marine bacteria survive within biostickers for more than 3 weeks. The rate at which the biostickers degrade the bioplastic polyhydroxybutyrate (PHB) can be tuned by altering biosticker biomass concentration, bioplastic concentration, or incubation temperature. Biostickers that are transferred to a different PHB sample still retain high biodegradation activity, demonstrating their reusability. Strain sweep oscillatory tests demonstrate that the biostickers display predominantly viscoelastic behavior. Monotonic tensile tests indicate that the elastic modulus and the adhesion of the biostickers are not negatively impacted by bacteria growth or incubation temperature. This work paves the way for the development of ELMs to facilitate the inclusion of bioplastics within the blue economy, promoting the emergence of more sustainable and eco-friendly materials.

Abstract Air-liquid interfaces (ALIs) at the upper layer of oceans, lakes and rivers cover the majority of the earth’s surface. Microbes are known to accumulate at these resource-rich boundaries, but the mechanisms of ALI colonization are often assumed to mirror the formation of pellicle biofilms by non-aquatic organisms. Here, we analyzed ALI colonization by natural aquatic bacteria. We used samples from a freshwater lake to enrich for microbes that colonize the ALI in liquid growth medium. Mixed-species pellicles formed rapidly in these enrichments, were structurally stable for weeks and displayed a pronounced ecological succession. We isolated 31 members of the genus Pararheinheimera from early stages of mixed-species pellicle maturation. Five phylogenetically distinct Pararheinheimera clades were identified, each with a shared colony morphology. We used representative isolates to show that only one Pararheinheimera clade formed thin, adherent films at the ALI resembling classical pellicles. Isolates from the four remaining clades formed floating structures that could be categorized either as non-adhesive films or large viscous masses. Viscous mass (VM) pellicle formation was a polyphyletic trait that correlated with a highly mucoid appearance on agar plates, suggesting that the process is driven by copious secretion of extracellular matrix. Matrices from VM biofilms were largely non-adhesive, contained a mixture of acidic polysaccharides and proteins and formed thermally stable, shear-thinning hydrogels. Our results demonstrate that ALI colonization strategies vary widely even among closely related aquatic bacteria and identify VM pellicles as a distinct biofilm architecture with unique mechanical properties. Importance Lakes, rivers and oceans contain a boundary between the air and the water’s surface known as the air-liquid interface (ALI). Microbial communities that populate the ALI play crucial roles in nutrient cycling, but how aquatic microbes partition to these sites remains poorly characterized. Our study investigated how bacteria from a freshwater lake accumulate at the ALI. Lake water samples incubated in nutrient medium formed a layer of cells known as a pellicle biofilm at the ALI, and we isolated 31 different bacteria from a genus ( Pararheinheimera ) that was abundant during the early stages of pellicle formation. Only a subset of Pararheinheimera isolates formed traditional pellicle biofilms. Most formed either thin, non-adhesive films or large, gelatinous aggregates that appeared to persist at the ALI due to buoyancy. These findings expand our understanding of biofilm diversity in aquatic systems and suggest that the production of buoyant hydrogels may play an important role in structuring microbial communities at air–water boundaries.

, spatial structure-function relationships, with particular regard to strength and toughness. While this approach has driven fundamental advancements in the design of robust hydrogel structures, further complementary perspectives are needed to enable holistic, rational design schemes that integrate considerations such as fabrication and advanced functions like response and adaptation. To these ends, this review focuses on the dynamics of temporal-function relationships and their fundamental bases in order to highlight how the dynamic regulation of polymer interactions programs: 1) polymer assembly and material structure; 2) response to deformation and fracture behavior; 3) dynamic modulation of properties and structural remodeling/self-healing. By exploring this intersection of hydrogel formation, function, and remodeling, this review seeks to shed light on the fundamental relationship between molecular structure, material assembly, and performance in order to connect the emerging area of bioinspired materials processing with tough hydrogel design, and further provides a lasting inspiration and impetus for future hydrogel development that enables valuable scientific and technological advancements.

A biohybrid coating for crack detection: when the substrate is damaged, the coating cracks, causing spores to germinate and fluoresce.

During plant development, the mechanical properties of the cell walls must be tuned to regulate the growth of the cells. Cell growth involves significant stretching of the cell walls, yet little is known about the mechanical properties of cell walls under such substantial deformation, or how these mechanical properties change to regulate development. Here, we investigated the mechanical behavior of the Arabidopsis leaf epidermal cells being stretched. We found that the mechanical properties arise from the cell wall, which behaves as a fibrous network material. The epidermis exhibited a non-linear stiffening behavior that fell into three regimes. Each regime corresponded to distinct nonlinear behaviors in terms of transverse deformation (i.e., Poisson effect) and unrecoverable deformation (i.e., plasticity). Using a model, we demonstrated that the transition from reorientation and bending-dominated to stretch-dominated deformation modes of cellulose microfibrils cause these nonlinear behaviors. We found the stiffening behavior is more pronounced at later developmental stages. Finally, we show the spiral2-2 mutant has anisotropic mechanical properties, likely contributing to the spiraling of leaves. Our findings reveal the fibrous network nature of cell walls gives a high degree of tunability in mechanical properties, which allows cells to adjust these properties to support proper development.

Early detection of fatigue cracking is crucial to extend the life‐cycle of materials and structures. To reduce the risk of fatigue, parts are often over‐engineered or retired early, leading to material waste. Current methods for crack detection, including strain sensors or ultrasonic testing, can be costly, require regular maintenance, and do not respond to cracks directly via a repair mechanism. People are leveraging biology to create materials that can sense and respond. Engineered living materials have been primarily limited to porous matrices and hydrogels, which facilitate viability of organisms. We present an engineered living coating that can be applied to conventional structural materials to detect cracks. The coating integrates bacterial spores into a tailored synthetic matrix. This biohybrid coating approach unlocks potential, beyond crack detection, for crack mitigation through leveraging the biological component. This study: 1) describes the design of a spore‐polymer coating for in situ crack detection for structural materials and 2) demonstrates detection for different loading mechanisms, geometries, and materials. This work demonstrates how living materials can be used to enhance conventional materials and creates a valuable approach for crack detection. Our coating will reduce waste, increase product lifespan, and improve safety by preventing failure due to cracks.

The mucus layer lining the gastrointestinal tract is essential for gut health, providing a protective barrier while maintaining host-microbiome symbiosis. Its disruption is a hallmark of diseases like ulcerative colitis, yet how bacterial activity impacts mucus structure remains unclear. We developed a method to collect human-cell-derived mucus that mimics human colonic mucus and used it to investigate mucus degradation by commensal bacteria. Glycan foraging by species such as Bacteroides thetaiotaomicron and Bacteroides fragilis did not alter mucus rheology. Instead, secreted proteases were the primary drivers of degradation. Protease activity by B. fragilis and Bifidobacterium longum subsp. infantis was nutrient-dependent, while Enterococcus faecalis was further influenced by oxygen. Under oxidative stress, E. faecalis upregulated carbohydrate metabolism and virulence genes. These results reveal that bacterial mucus degradation is context-dependent and shaped by environmental factors. Our findings underscore the value of human cell-derived mucus models for understanding bacteria-mucus interactions in health and disease.

Soft ionic circuitry promises to create soft control systems and active materials that can sense, assess information, and respond to their environment. This complex behavior is enabled by charged polymers that act as ionic semiconductors, but their widespread use is inhibited by a lack of suitable design tools. The authors develop a lumped-element model that incorporates key effects and enables the design and analysis of large-scale ionic systems. Their tool illuminates the performance and limits of existing devices, and principles for designing a fully ionic soft-robot control system. This model will enable the field of ionics to move from building single devices to whole systems.

Polydimethylsiloxane (PDMS) with metal-ligand coordinating bonds has shown exceptional mechanical properties like high stretchability and toughness, combined with advanced properties like self-healing and tunable stress relaxation. Being able to dissolve the network and reclaim PDMS is important, allowing us both to retrieve expensive metal ions at material's end-of-life and change properties by inserting different ions. Yet methods to realize metal removal without chemical change are unclear. We present a decantation-like method to measure the dissolution kinetics of metal-ligand coordinating network while preserving the PDMS chemical integrity. We find a similar dissolution rate regardless of dramatic mechanical response changes caused by different counterions. Compared to our reference zinc coordinated polymer, copper and higher molecular weight are shown to slow down dissolution process, while cobalt completely prevents it. The novel experimental method and results can lead to guidelines for design of dynamically adaptable metal-ligand coordination networks and specifically, for reclaimable PDMS.

Inspired by how forces facilitate molecule immobilization in biological tissues to provide localized functionalization, tough hydrogel networks with stretch activated mechanochemistry are developed by utilizing disulfide bonds as dynamic covalent crosslinks. Specifically, disulfide linked polyethylene glycol hydrogels are reinforced with a second ionically bonded sodium alginate network to simultaneously achieve stretchability and mechanochemical functionalization. To demonstrate and quantify the mechanochemical response, thiols produced by disulfide bond rupture are sensed during stretching using a reaction activated fluorophore dissolved in the hydrating solution. By monitoring the increase in fluorescence intensity upon stretching, it is determined that disulfide bond breakage in the double network hydrogels becomes more activated in hydrogels with high stretchability under low stress. Such results provide guidance regarding how the molecular weights and mass fractions of the monomers must be chosen to design double network hydrogels that balance favorable mechanical properties and mechanochemical responsiveness. Finally, for the most mechanochemically active hydrogel, we demonstrate how the stretch-activated immobilization of a maleimide containing peptide can functionalize the gels to promote the growth of human fibroblasts. Results of this work are anticipated to encourage further research into the development of stretchable and multifunctionalizable hydrogels for biotechnology and biomedical applications. STATEMENT OF SIGNIFICANCE: Inspired by the mechanochemical dynamics in biological tissues, this work demonstrates the development of hydrogel-based biomaterials that can achieve stretch activated functionalization by molecule immobilization in multiple distinct ways. Using disulfide linked polyethylene glycol hydrogels reinforced with a second alginate network, we have elucidated the structure-property relationships of our hydrogels by functionalizing them with fluorophore to ensure a robust combination of stretchability and mechanochemical responsiveness. We also have demonstrated the capability for using stretch activated immobilization of functional peptides to guide human fibroblasts activity. By demonstrating how hydrogel network properties impact both mechanical and functional performance, this work opens pathways for designing multifunctionalizable hydrogels that adapt to mechanical forces, potentially broadening the application of hydrogels in biotechnology and biomedical applications.

Conventional building materials, such as concrete, steel, and brick, are energy-intensive to produce, contribute to significant carbon emissions, and deplete finite natural resources. In response to critical environmental issues caused by these non-renewable materials, mycelium-based composites (MBCs) have attracted widespread attention. MBCs provide a renewable alternative where mycelium grows on lignocellulosic fibers forming a lightweight, low energy cost, and an effective insulating material. However, the bottleneck of large-scale architectural applications of MBCs lies in conventional mold-based manual manufacturing processes. Even though 3D-printable mycelium composites facilitate automated production and greater design freedom, the size is still limited at the centimeter scale due to the extended time required for layers to fuse from hyphal growth. The development of shootable MBCs, which can potentially overcome these constraints for flexible forms and automated large-scale construction, has not yet been explored. This study investigates biopolymer modification methods for psyllium husk gels to engineer shootable MBCs with high cohesive and adhesive properties that enable deposition on vertical surfaces. Engineered formulations demonstrated consistent shootability over a span of 50 minutes with minimal material loss (<10%), and robust mycelium growth at both the surface and throughout the cross section. The resulting composition exhibits circular building lifecycle principles as all ingredients are biodegradable and compostable at the end of building life. Additionally, a shootable composite broadens the fabrication methods and applications of MBCs, showing promise for use with shotcrete-like spraying techniques in the building industry.

The severe, long-lasting harm caused by plastic pollution to marine ecosystems and coastal economies has led to the development of biodegradable plastics; however, their limited decomposition in cold, dark marine environments remains a challenge. Here, we present our newly developed technologies for creating 3D-bioprinted living materials for bioplastic degradation with specific use in marine environments. Our approach integrates halotolerant bioplastic-degrading bacterium Bacillus sp. NRRL B-14911 into alginate-based bio-ink to print an engineered living material (ELM) termed a “bio-sticker.” Quantification of bacteria viability reveals that bioprinted marine bacteria survive within bio-stickers for more than three weeks. The rate at which the bio-stickers degrade the bioplastic polyhydroxybutyrate (PHB) can be tuned by altering bio-sticker biomass concentration, bioplastic concentration, or incubation temperature. Bio-stickers that are transferred to a new PHB sample still retain high biodegradation activity, demonstrating their durability. Strain sweep oscillatory tests demonstrate viscoelastic behavior of the bio-stickers. Monotonic tensile tests indicate that the elastic modulus and the adhesion of the bio-stickers are not negatively impacted by bacteria growth or incubation temperature. Our work paves the way for development of ELMs to facilitate the inclusion of bioplastics within the blue economy, promoting the emergence of more sustainable and eco-friendly materials.

ABSTRACT The mucus layer lining the gastrointestinal tract is essential for gut health, providing a protective barrier against pathogens while maintaining symbiosis with the microbiome. Its disruption is a hallmark of gastrointestinal diseases like ulcerative colitis. While glycan foraging by gut bacteria is thought to initiate mucus disruption, its impact on mucus structural properties remains poorly understood, largely due to the lack of physiologically relevant models. To address this gap, we developed a method to collect human-cell-derived mucus that closely mimics the mechanical properties of human colonic mucus. Using this system, we investigated mucus utilization and degradation by a panel of commensal bacteria with distinct metabolic profiles. Glycan utilization by species such as Bacteroides thetaiotaomicron and Bacteroides fragilis showed no correlation with changes in mucus rheology. Instead, secreted proteases were identified as the primary driver of mucus degradation. Protease activity by B. fragilis and Bifidobacterium longum was influenced by nutrient availability, whereas in Enterococcus faecalis, it was additionally affected by oxygen exposure . E. faecalis also adapted to oxidative stress by enhancing carbohydrate metabolism and upregulating several virulence genes. Together, our findings reveal that bacterial mucus degradation is context-dependent and shaped by environmental factors. This study provides key insights into the mechanisms underlying mucus degradation and underscores the value of human cell-derived mucus models for understanding bacteria-mucus interactions in health and disease.

. We utilized wide-angle X-ray scattering to elucidate the molecular structural changes that led to this thermal conductivity enhancement. Furthermore, we conducted a device-cooling experiment and showed a 39% hot spot temperature reduction compared to a commercial ceramic-filled silicone thermal pad under a heating power of 3.6 W. Thus, this bulk-scale thermally conductive PE bar with nanoscale structural refinement demonstrated superior cooling performance, offering potential as an advanced thermal interface material for thermal management in microelectronics.

MP particles. The presence of a mucus layer also provides critical protection against cytotoxicity, reactive oxygen species production, and uptake for all particles tested, although certain functionalizations, such as streptavidin, are particularly harmful to cells with high toxicity and inflammation. Understanding the properties that assist of impede the diffusion of MPs through mucus is relevant to the overall bioaccumulation and health effects of MPs as well as drug delivery purposes.

Stimuli-responsive polymeric materials have attracted significant attention due to their ability to change properties in response to various external stimuli. Using an electric field as the stimulus is of particular interest as it possesses the potential for seamless integration of materials with electronic systems. While many materials with electric field responsive actuation have an associated mechanical property change, it is beneficial to develop materials that exhibit mechanical property changes without accompanying significant shape deformation. To address this challenge, here we designed a semi-interpenetrating polymer network (semi-IPN) hydrogel system containing both polyelectrolytes and salt ions, which enables electric field induced changes in mechanical properties while minimizing actuation. We first successfully verified the viability of our design by removing salt ions through a diffusion-only method where we witnessed the stiffness increased to 4.5 times the initial value while still being highly deformable. After this, we applied an electric field to transport the salt ions out of the hydrogel, as shown by both Raman spectroscopy and scanning electron microscopy. We were able to show a time-dependent stiffness increase, the maximum of which was 5 times the original stiffness. We quantified ion transport and water-splitting in the hydrogel by both experiments and simulations. Following this, we showed functional system reversibility by reversing the direction of the current to reinject salt ions into the semi-IPN hydrogel and reducing its stiffness to below the initial value. It's worth noting that our simulations enable us to understand the governing mechanisms behind ion generation and salt transport that leads to mechanical property changes. Finally, we were able to fabricate a spatially variable stiffness haptic interface with our hydrogel, with demonstrated reversibility and cyclability. This research can possibly find applications in soft robotics and haptics and also inspire the development of bio-compatible electronics related devices.

Polymer matrix fiber composites often suffer from residual stresses due to differences in coefficients of thermal expansion between the fibers and resins, as well as contractile strain of the resins during curing. To address residual stress driven composite failure, we propose the use of vitrimers as composite resins, which can undergo thermally activated, stress alleviating, bond exchange reactions (BERs). We conduct fiber Bragg grating measurements for a single glass fiber within bulk vitrimer. These show that the fiber strain in vitrimers with 5% catalyst is significantly lower than in those with 0% catalyst (minimal BER expected) during both curing and post-curing phases. We developed a finite deformation, micromechanically-inspired model that incorporates curing, thermal processes, and BERs, and then implemented this model it into finite element software to simulate stress evolution within single fiber composite systems. The combination of experimental and computational results reveals that BERs can effectively mitigate, but not eliminate, the residual stress in polymer matrix fiber composites.

Discrete mesoscale network models, in which explicitly modeled polymer chains are replaced by implicit pairwise potentials, are capable of predicting the macroscale mechanical response of polymeric materials such as elastomers and gels, while offering greater insight into microstructural phenomena than constitutive theory or macroscale experiments alone. However, whether such mesoscale models accurately represent the molecular structures of polymer networks requires investigation during their development, particularly in the case of dynamic polymers that restructure in time. We here introduce and compare the topological and mechanical predictions of an idealized, reduced-order mesoscale approach in which only tethered dynamic bonding sites and crosslinks in a polymer's backbone are explicitly modeled, to those of molecular theory and a Kremer-Grest, coarse-grained molecular dynamics approach. We find that for short chain networks at intermediate polymer packing fractions, undergoing relatively slow loading rates, the mesoscale approach reasonably reproduces the chain conformations, bond kinetic rates, and ensemble stress responses predicted by molecular theory and the bead-spring model. Further, it does so with a 90% reduction in computational cost. These savings grant the mesoscale model access to larger spatiotemporal domains than conventional molecular dynamics, enabling simulation of large deformations as well as durations approaching experimental timescales (e.g., those utilized in DMA). While the model investigated is for monodisperse polymer networks in theta-solvent, without entanglement, charge interactions, long-range dynamic bond interactions, or other confounding physical effects, this work highlights the utility of these models and lays a foundational groundwork for the incorporation of such phenomena moving forward.

Abstract During plant development, the mechanical properties of the cell walls must be tuned to regulate the growth of the cells. Cell growth involves significant stretching of the cell walls, yet little is known about the mechanical properties of cell walls under such substantial deformation, or how these mechanical properties change to regulate development. Here, we investigated the mechanical behavior of the Arabidopsis leaf epidermal cells being stretched. We found that the mechanical properties arise from the cell wall, which behaves as a fibrous network material. The epidermis exhibited a non-linear stiffening behavior that fell into three regimes. Each regime corresponded to distinct nonlinear behaviors in terms of transverse deformation (i.e., Poisson effect) and unrecoverable deformation (i.e., plasticity). Using a model, we demonstrated that the transition from reorientation and bending-dominated to stretch-dominated deformation modes of cellulose microfibrils cause these nonlinear behaviors. We found the stiffening behavior is more pronounced at later developmental stages. Finally, we show the spiral2-2 mutant has anisotropic mechanical properties, likely contributing to the spiraling of leaves. Our findings reveal the fibrous network nature of cell walls gives a high degree of tunability in mechanical properties, which allows cells to adjust these properties to support proper development.

Stimuli-responsive polymeric materials have attracted significant attention due to their ability to change properties in response to various external stimuli. Using an electric field as the stimulus is of particular interest as it possesses the potential for seamless integration of materials with electronic systems. While many materials with electric field responsive actuation have an associated mechanical property change, it is beneficial to develop materials that exhibit mechanical property changes without accompanying significant shape deformation. To address this challenge, here we designed a semi-interpenetrating polymer network (semi-IPN) hydrogel system containing both polyelectrolytes and salt ions, which enables electric field induced changes in mechanical properties while minimizing actuation. We first successfully verified the viability of our design by removing salt ions through a diffusion-only method where we witnessed the stiffness increased to 4.5 times the initial value while still being highly deformable. After this, we applied an electric field to transport the salt ions out of the hydrogel, as shown by both Raman spectroscopy and scanning electron microscopy. We were able to show a time-dependent stiffness increase, the maximum of which was 5 times the original stiffness. We quantified ion transport and water-splitting in the hydrogel by both experiments and simulations. Finally, we showed functional system reversibility by reversing the direction of the current to reinject salt ions into the semi-IPN hydrogel and reducing its stiffness to below the initial value. It's worth noting that our simulations enable us to understand the governing mechanisms behind ion generation and salt transport that leads to mechanical property changes. This research can possibly find applications in soft robotics and also inspire the development of bio-compatible electronics related devices.

Stimuli-responsive polymeric materials have attracted significant attention due to their ability to change properties in response to various external stimuli. Using an electric field as the stimulus is of particular interest as it possesses the potential for seamless integration of materials with electronic systems. While many materials with electric field responsive actuation have an associated mechanical property change, it is beneficial to develop materials that exhibit mechanical property changes without accompanying significant shape deformation. To address this challenge, here we designed a semi-interpenetrating polymer network (semi-IPN) hydrogel system containing both polyelectrolytes and salt ions, which enables electric field induced changes in mechanical properties while minimizing actuation. We first successfully verified the viability of our design by removing salt ions through a diffusion-only method where we witnessed the stiffness increased to 4.5 times the initial value while still being highly deformable. After this, we applied an electric field to transport the salt ions out of the hydrogel, as shown by both Raman spectroscopy and scanning electron microscopy. We were able to show a time-dependent stiffness increase, the maximum of which was 5 times the original stiffness. We quantified ion transport and water-splitting in the hydrogel by both experiments and simulations. Finally, we showed functional system reversibility by reversing the direction of the current to reinject salt ions into the semi-IPN hydrogel and reducing its stiffness to below the initial value. It's worth noting that our simulations enable us to understand the governing mechanisms behind ion generation and salt transport that leads to mechanical property changes. This research can possibly find applications in soft robotics and also inspire the development of bio-compatible electronics related devices.

Since the 1950s, soft ionic devices have evolved from individual components to an expanding library of sensors, actuators, signal transmitters, and processors. However, integrating these components into complex, multi-functional systems remains challenging due to the non-intuitive and non-linear interactions between ionic elements. In this work, we address these fundamental challenges by developing a lumped element model that enables interrogation of the physics that govern ionic circuits, as well as rapid design and optimization. Our model captures features specific to ionic charge carriers, while preserving the hierarchical design flexibility and computational efficiency of traditional circuit modeling. We demonstrate that our model can not only fit individual device behavior but also accurately predict the behavior of larger circuits formed by combining those devices. Additionally, we show how our tool utilizes the intrinsic non-linearities of ionic systems to enable novel functionality, revealing how factors such as ion enrichment, ion leakage, and polymer charge density influence performance. Finally, we present a fully ionic power supply, sensor, control system, and actuator for a soft robot that adapts its motion in response to environmental salt, illustrating the tool's potential to accelerate advancements in chemical sensing, biointerfacing, biomimetic systems, and adaptive materials.

Discrete mesoscale network models, in which explicitly modeled polymer chains are replaced by implicit pairwise potentials, are capable of predicting the macroscale mechanical response of polymeric materials such as elastomers and gels, while offering greater insight into microstructural phenomena than constitutive theory or macroscale experiments alone. However, whether such mesoscale models accurately represent the molecular structures of polymer networks requires investigation during their development, particularly in the case of dynamic polymers that restructure in time. We here introduce and compare the topological and mechanical predictions of an idealized, reduced-order mesoscale approach in which only tethered dynamic bonding sites and crosslinks in a polymer's backbone are explicitly modeled, to those of molecular theory and a Kremer-Grest, coarse-grained molecular dynamics approach. We find that for short chain networks at intermediate polymer packing fractions, undergoing relatively slow loading rates, the mesoscale approach reasonably reproduces the chain conformations, bond kinetic rates, and ensemble stress responses predicted by molecular theory and the bead-spring model. Further, it does so with a 90% reduction in computational cost. These savings grant the mesoscale model access to larger spatiotemporal domains than conventional molecular dynamics, enabling simulation of large deformations as well as durations approaching experimental timescales (e.g., those utilized in DMA). While the model investigated is for monodisperse polymer networks in theta-solvent, without entanglement, charge interactions, long-range dynamic bond interactions, or other confounding physical effects, this work highlights the utility of these models and lays a foundational groundwork for the incorporation of such phenomena moving forward.

Biomaterials such as spider silk and mussel byssi are fabricated by the dynamic manipulation of intra- and intermolecular biopolymer interactions. Organisms modulate solution parameters, such as pH and ion co-solute concentration, to effect these processes. These biofabrication schemes provide a conceptual framework to develop new dynamic and responsive abiotic soft material systems. Towards these ends, the chemical diversity of readily available ionic compounds offers a broad palette to manipulate the physicochemical properties of polyelectrolytes via ion-specific interactions. In this study, we show for the first time that the ion-specific interactions of biomimetic polyelectrolytes engenders a variety of phase separation behaviors, creating dynamic thermal- and ion-responsive soft matter that exhibits a spectrum of physical properties, spanning viscous fluids to viscoelastic and viscoplastic solids. These ion-dependent characteristics are further rendered general by the merger of lysine and phenylalanine into a single, amphiphilic vinyl monomer. The unprecedented breadth, precision, and dynamicity in the reported ion-dependent phase behaviors thus introduce a broad array of opportunities for the future development of responsive soft matter; properties that are poised to drive developments in critical areas such as chemical sensing, soft robotics, and additive manufacturing.

Abstract Biomaterials such as spider silk and mussel byssi are fabricated by the dynamic manipulation of intra‐ and intermolecular biopolymer interactions. Organisms modulate solution parameters, such as pH and ion co‐solute concentration, to effect these processes. These biofabrication schemes provide a conceptual framework to develop new dynamic and responsive abiotic soft material systems. Towards these ends, the chemical diversity of readily available ionic compounds offers a broad palette to manipulate the physicochemical properties of polyelectrolytes via ion‐specific interactions. In this study, we show for the first time that the ion‐specific interactions of biomimetic polyelectrolytes engenders a variety of phase separation behaviors, creating dynamic thermal‐ and ion‐responsive soft matter that exhibits a spectrum of physical properties, spanning viscous fluids to viscoelastic and viscoplastic solids. These ion‐dependent characteristics are further rendered general by the merger of lysine and phenylalanine into a single, amphiphilic vinyl monomer. The unprecedented breadth, precision, and dynamicity in the reported ion‐dependent phase behaviors thus introduce a broad array of opportunities for the future development of responsive soft matter; properties that are poised to drive developments in critical areas such as chemical sensing, soft robotics, and additive manufacturing.

Abstract Biologically produced materials are an attractive alternative to traditional materials such as metals and plastics and offer improved functionalities such as better biodegradability and biocompatibility. Polysaccharides are an example of a biologically produced materials that can have a range of chemical and physical properties including high stiffness to weight ratios and thermal stability. Biomanufactured bacterial polysaccharides can come with many advantages such as being non-toxic and are mechanically robust relative to proteins and lipids, which are also secreted by bacteria to generate a biofilm. One major goal in biomanufacturing is to produce quality material quickly and cost-effectively. Biomanufacturing offers additional benefits compared to traditional manufacturing including low resource investment and equipment requirements, providing an alternative to sourcing fossil fuel byproducts, and relatively low temperatures needed for production. However, many biologically produced materials require complex and lengthy purification processes before use. This paper 1) identifies the material properties of a novel polysaccharide, dubbed promonan, isolated from the extracellular polymeric substances of Sphingomonas sp. LM7; 2) demonstrates that these properties can be manipulated to suit specific applications; and 3) presents two alternative methods of processing to shorten purification time by more than 50% while maintaining comparable material.

Biomaterials such as spider silk and mussel byssi are fabricated by the dynamic manipulation of intra- and intermolecular biopolymer interactions. Organisms modulate solution parameters, such as pH and ion co-solute concentration, to effect these processes. These biofabrication schemes provide a conceptual framework to develop new dynamic and responsive abiotic soft material systems. Towards these ends, the chemical diversity of readily available ionic compounds offers a broad palette to manipulate the physicochemical properties of polyelectrolytes via ion-specific interactions. In this study, we show for the first time that the ion-specific interactions of biomimetic polyelectrolytes engenders a variety of phase separation behaviors, creating dynamic, thermal and ion responsive soft matter. that exhibits a spectrum of physical properties, spanning viscous fluids, to viscoelastic and viscoplastic solids. These ion dependent characteristics are further rendered general by the merger of lysine and phenylalanine into a single, amphiphilic vinyl monomer. The unprecedented breadth, precision, and dynamicity in the reported ion dependent phase behaviors thus introduce a broad array of opportunities for the future development of responsive soft matter, properties that are poised to drive developments in critical areas such as chemical sensing, soft robotics, and additive manufacturing.

sp. LM7; (2) demonstrates that these properties can be manipulated to suit specific applications; and (3) presents two alternative methods of processing to shorten purification time by more than 50% while maintaining comparable material properties.

Abstract Ionic circuitry formed from soft charged polymers promises to enable a new kind of analog computing and usher in a new age of human–computer interaction, but devices remain in their infancy. Ionic diodes, created by the interface between two oppositely charged polymers, form one of the most fundamental elements of ionic circuitry. However, it is currently not well understood how the boundary conditions and geometry of a diode influence its transient response and performance. A consistent set of metrics with which to analyze these diodes is first developed, then a continuum model based on the Nernst–Planck–Poisson equations is used to study how device construction and three types of boundary conditions affect performance. This model is solved using the finite volume method and gives insight into transient diode behavior not described by previous analyses. It is demonstrated how different parts of a diode's construction, thickness, and operating voltage act as the limiting factors for different regimes. To conclude, it is demonstrated how blocking electrodes limit both diode lifetime and rectification behavior and how neutral bath boundary conditions play an important role in the performance of some diodes, with recommendations for building higher performance devices in the future.

Mechanochemistry can lead to the degradation of the properties of covalent macromolecules. In recent years, numerous functional materials have been developed based on block copolymers (BCPs), however, like homopolymers, their chains could undergo mechanochemical damage during processing, which could have crucial impact on their performance. To investigate the mechanochemical response of BCPs, multiple polymers comprising different ratios of butyl acrylate and methyl methacrylate were prepared with similar degree of polymerization and stressed in solution via ultrasonication. Interestingly, all BCPs, regardless of the amount of the methacrylate monomer, presented a mechanochemistry rate constant similar to that of the methacrylate homopolymer, while a random copolymer reacted like the acrylate homopolymer. Size-exclusion chromatography showed that, in addition to the typical main peak shift towards higher retention times, a different daughter fragment was produced indicating a secondary selective scission site, situated around the covalent connection between the two blocks. Molecular dynamics modeling using acrylate and methacrylate oligomers were carried out and indicated that dynamic phase separation occurs even in a good solvent. Such non-random conformations can explain the faster polymer mechanochemistry. Moreover, the dynamic model for end-to-end chain overstretching supports bond scission which is not necessarily chain-centered.

Abstract Mechanochemistry can lead to the degradation of the properties of covalent macromolecules. In recent years, numerous functional materials have been developed based on block copolymers (BCPs), however, like homopolymers, their chains could undergo mechanochemical damage during processing, which could have crucial impact on their performance. To investigate the mechanochemical response of BCPs, multiple polymers comprising different ratios of butyl acrylate and methyl methacrylate were prepared with similar degree of polymerization and stressed in solution via ultrasonication. Interestingly, all BCPs, regardless of the amount of the methacrylate monomer, presented a mechanochemistry rate constant similar to that of the methacrylate homopolymer, while a random copolymer reacted like the acrylate homopolymer. Size‐exclusion chromatography showed that, in addition to the typical main peak shift towards higher retention times, a different daughter fragment was produced indicating a secondary selective scission site, situated around the covalent connection between the two blocks. Molecular dynamics modeling using acrylate and methacrylate oligomers were carried out and indicated that dynamic phase separation occurs even in a good solvent. Such non‐random conformations can explain the faster polymer mechanochemistry. Moreover, the dynamic model for end‐to‐end chain overstretching supports bond scission which is not necessarily chain‐centered.

Phase-segregated polyureas (PU) have received considerable interest due to their use as tough, impact-resistant coatings. Polyureas are favored for these applications due to their mechanical strain rate sensitivity and energy dissipation. Predicting and tailoring the mechanical response of PU remains challenging due to the complex interaction between its elastomeric and glassy phases. To elucidate the role of PU microstructure on its mechanical properties, we developed a finite element modeling framework in which each phase is represented by a volume fraction within a representative volume element (RVE). Critically, we used separate constitutive models to describe the elastomeric and glassy phases. We developed a plasticity-driven breakdown process in which we model the glassy phase disaggregating into a new phase. The overall contribution of each phase at a material point is determined by their respective volume fractions within the RVE. We applied our modeling methods to two compositions of PU with differing elastomeric segment lengths derived from oligoether diamines, Versalink P650 and P1000. Our simulations show that a combination of microstructural differences and elastomeric phase properties accounts for the difference in mechanical response between P650 and P1000. We show our model's ability to predict PU behavior in various loading conditions, including low-rate cyclic loading and monotonic loading over a wide range of strain rates. Our model produces microstructure transformations that mirror those indicated by small-angle X-ray scattering (SAXS) experiments. Fourier transform analysis of our RVEs reveals glassy phase fibrillation due to deformation, a finding consistent with SAXS experiments.

Phase-segregated polyureas (PU) have received considerable interest due to their use as tough, impact-resistant coatings. Polyureas are favored for these applications due to their mechanical strain rate sensitivity and energy dissipation. Predicting and tailoring the mechanical response of PU remains challenging due to the complex interaction between its elastomeric and glassy phases. To elucidate the role of PU microstructure on its mechanical properties, we developed a finite element modeling framework in which each phase is represented by a volume fraction within a representative volume element (RVE). Critically, we used separate constitutive models to describe the elastomeric and glassy phases. We developed a plasticity-driven breakdown process in which we model the glassy phase disaggregating into a new phase. The overall contribution of each phase at a material point is determined by their respective volume fractions within the RVE. We applied our modeling methods to two compositions of PU with differing elastomeric segment lengths derived from oligoether diamines, Versalink P650 and P1000. Our simulations show that a combination of microstructural differences and elastomeric phase properties accounts for the difference in mechanical response between P650 and P1000. We show our model's ability to predict PU behavior in various loading conditions, including low-rate cyclic loading and monotonic loading over a wide range of strain rates. Our model produces microstructure transformations that mirror those indicated by small-angle X-ray scattering (SAXS) experiments. Fourier transform analysis of our RVEs reveals glassy phase fibrillation due to deformation, a finding consistent with SAXS experiments.