Elucidating Nonlinear Stress Relaxation in Transient Networks through Two-Dimensional Rheo-Optics.

This study aims to elucidate the origin of nonlinear stress relaxation behaviors in transient networks using a systematically controlled model system consisting of the tetra-armed polyethylene glycols (Tetra-PEG slime) in conjunction with two-dimensional rheo-optics observations. Transient networks, characterized by their temporary cross-links, are extensively utilized in self-healing and robust materials. However, the molecular mechanisms governing their viscoelastic responses to large deformations have remained elusive.

Probing the Molecular Mechanism of Viscoelastic Relaxation in Transient Networks.

Hydrogels, which have polymer networks through supramolecular and reversible interactions, exhibit various mechanical responsibilities to its surroundings. The influence of the reversible bonds on a hydrogel's macroscopic properties, such as viscoelasticity and dynamics, is not fully understood, preventing further innovative material development. To understand the relationships between the mechanical properties and molecular structures, it is required to clarify the molecular understanding of the networks solely crosslinked by reversible interactions, termed "transient networks".

Percolation-induced gel-gel phase separation in a dilute polymer network.

Cosmic large-scale structures, animal flocks and living tissues can be considered non-equilibrium organized systems created by dissipative processes. Replicating such properties in artificial systems is still difficult. Herein we report a dissipative network formation process in a dilute polymer-water mixture that leads to percolation-induced gel-gel phase separation.

In situ-formable, dynamic crosslinked poly(ethylene glycol) carrier for localized adeno-associated virus infection and reduced off-target effects.

The adeno-associated virus (AAV) is a potent vector for in vivo gene transduction and local therapeutic applications of AAVs, such as for skin ulcers, are expected. Localization of gene expression is important for the safety and efficiency of genetic therapies. We hypothesized that gene expression could be localized by designing biomaterials using poly(ethylene glycol) (PEG) as a carrier.

Molecular Weight-Dependent Diffusion, Biodistribution, and Clearance Behavior of Tetra-Armed Poly(ethylene glycol) Subcutaneously Injected into the Back of Mice.

Four-armed poly(ethylene glycol) (PEG)s are essential hydrophilic polymers extensively utilized to prepare PEG hydrogels, which are valuable tissue scaffolds. When hydrogels are used , they eventually dissociate due to cleavage of the backbone structure. When the cleavage occurs at the cross-linking point, the hydrogel elutes as an original polymer unit, i.

Decoupling between Translational Diffusion and Viscoelasticity in Transient Networks with Controlled Network Connectivity.

The mobility of sustained molecules is influenced by viscoelasticity, which is strongly correlated with the diffusional property in polymeric liquid. However, the study of transient networks formed by a reversible crosslink, which is the viscoelastic liquid, was insufficient due to the absence of a model system. We compare the viscoelastic and diffusional properties of the transient networks, using the model system with controlled network connectivity (Tetra-PEG slime).

Analysis of the sustained release ability of bevacizumab-loaded tetra-PEG gel.

Multiple intravitreal injections, which are painful and costly, are often required in the treatment of retinal disorders. Therefore, a novel drug delivery system using hydrogels is currently being evaluated as an alternative. This study aimed to evaluate the ability of tetra-armed polyethylene glycol (tetra-PEG) gel for sustained release in vitro.

Experimental Comparison of Bond Lifetime and Viscoelastic Relaxation in Transient Networks with Well-Controlled Structures.

We demonstrate an experimental comparison of the bond lifetime, estimated using surface plasmon resonance (SPR), and the viscoelastic relaxation time of transient networks with well-controlled structures (dynamically cross-linked Tetra-PEG gel). SPR and viscoelastic measurements revealed that the temperature dependences of the two characteristic times are in agreement, while the viscoelastic response is delayed with respect to the lifetime by a factor of 2-3, dependent on the network strand length. Polymers cross-linked by temporary interactions form transient networks, which show fascinating viscoelasticity with a single relaxation mode.

Tri-branched gels: Rubbery materials with the lowest branching factor approach the ideal elastic limit.

Unlike hard materials such as metals and ceramics, rubbery materials can endure large deformations due to the large conformational degree of freedom of the cross-linked polymer network. However, the effect of the network's branching factor on the ultimate mechanical properties has not yet been clarified. This study shows that tri-branching, which entails the lowest branching factor, results in a large elastic deformation near the theoretical upper bound.

Star-Polymer-DNA Gels Showing Highly Predictable and Tunable Mechanical Responses.

Dynamically crosslinked gels are appealing materials for applications that require time-dependent mechanical responses. DNA duplexes are ideal crosslinkers for building such gels because of their excellent sequence addressability and flexible tunability in bond energy. However, the mechanical responses of most DNA gels are complicated and unpredictable.

Temperature Dependence of Polymer Network Diffusion.

The swelling dynamics of polymer gels are characterized by the (collective) diffusion coefficient D of the polymer network. Here, we measure the temperature dependence of D of polymer gels with controlled homogeneous network structures using dynamic light scattering. An evaluation of the diffusion coefficient at the gelation point D_{gel} and the increase therein as the gelation proceeds ΔD≡D-D_{gel} indicates that ΔD is a linear function of the absolute temperature with a significantly large negative constant term.

Effect of Nonlinear Elasticity on the Swelling Behaviors of Highly Swollen Polyelectrolyte Gels.

Polyelectrolyte gels exhibit swelling behaviors that are dependent on the external environment. The swelling behaviors of highly charged polyelectrolyte gels can be well explained using the Flory-Rehner model combined with the Gibbs-Donnan effect and Manning's counterion condensation effect (the FRGDM model). This study investigated the swelling properties of a series of model polyelectrolyte gels, namely tetra-polyacrylic acid-polyethylene glycol gels (Tetra-PAA-PEG gels), and determined the applicability of the FRGDM model.

Spider silk self-assembly via modular liquid-liquid phase separation and nanofibrillation.

Spider silk fiber rapidly assembles from spidroin protein in soluble state via an incompletely understood mechanism. Here, we present an integrated model for silk formation that incorporates the effects of multiple chemical and physical gradients on the different spidroin functional domains. Central to the process is liquid-liquid phase separation (LLPS) that occurs in response to multivalent anions such as phosphate, mediated by the carboxyl-terminal and repetitive domains.

Mechanistic insights into silk fibroin's adhesive properties via chemical functionalization of serine side chains.

-derived silk fibroin (SF) has recently gained interest for its intrinsic or engineered adhesive properties. In a previous study by our group, the mechanism of the protein's intrinsic adhesiveness to biological substrates such as leather has been hypothesized to rely on hydrogen bond formation between amino acid side chains of SF and the substrate. In this study, the serine side chains of SF were chemically functionalized with substituents with different hydrogen bonding abilities.

Supercoiling transformation of chemical gels.

The swelling/deswelling behavior of chemical gels has been an unsolved problem disputed over for a long time. The Obukhov-Rubinstein-Colby model depicts the influence that swelling/deswelling has on elasticity, but its physical picture is too complicated to be sufficiently validated by experiment. In this study, we use molecular dynamics simulation to verify the validity of the molecular picture of network strands predicted by the Obukhov-Rubinstein-Colby model.

Probing the cross-effect of strains in non-linear elasticity of nearly regular polymer networks by pure shear deformation.

The pure shear deformation of the Tetra-polyethylene glycol gels reveals the presence of an explicit cross-effect of strains in the strain energy density function even for the polymer networks with nearly regular structure including no appreciable amount of structural defect such as trapped entanglement. This result is in contrast to the expectation of the classical Gaussian network model (Neo Hookean model), i.e.

Silk-pectin hydrogel with superior mechanical properties, biodegradability, and biocompatibility.

A new method is developed to prepare silk hydrogels and silk-pectin hydrogels via dialysis against methanol to obtain hydrogels with high concentrations of silk fibroin. The relationship between the mechanical and biological properties and the structure of the silk-pectin hydrogels is subsequently evaluated. The present results suggest that pectin associates with silk molecules when the silk concentration exceeds 15 wt%, suggesting that a silk concentration of over 15 wt% is critical to construct interacting silk-pectin networks.

Mechanical properties of tetra-PEG gels with supercoiled network structure.

We investigate the effects of swelling and deswelling on the mechanical properties of tetra-polyethylene glycol gels with the precisely tuned polymerization degree of network strand (Nc) and polymer volume fraction at preparation (ϕ0) by varying the fraction of interest (ϕm). The ϕm-dependence of the elastic modulus exhibits a crossover at ϕc due to large contraction of the network strands (supercoiling) accompanying deswelling. The Obukhov model successfully describes the ϕm-dependence of the elastic modulus.

State of water, molecular structure, and cytotoxicity of silk hydrogels.

A novel technique was developed to regulate the bulk water content of silk hydrogels by adjusting the concentrations of silk proteins, which is helpful to investigate the effects of the state of water in polymeric hydrogel on its biological functions, such as cytotoxicity. Gelation of the silk hydrogel was induced with ethanol and its gelation behavior was analyzed by rheometry. The silk hydrogels prepared at various silk concentrations were characterized with respect to their water content, molecular and network structures, state of water, mechanical properties, and cytotoxicity to human mesenchymal stem cells.