Takuya Katashima

Polyelectrolyte gels comprising fixed ions exhibit swelling behaviors because of external solution conditions. Such behaviors are usually explained by using the Flory–Rehner model that considers the Donnan equilibrium. However, this model assumes a homogeneous distribution for fixed ions; therefore, its applicability to the case of heterogeneous distributions remains unclear. Here, we successfully designed a hydrogel with alternating neutral/highly charged sequences (i.e., tetrapoly(acrylic acid

Silk fibers show high toughness, ductility, biocompatibility, and biodegradability due to their high-order structure. Silk materials are not limited to native fibers and also include regenerated silk materials, such as chemically modified silk materials, composite materials, and silk-inspired artificial materials synthesized through chemoenzymatic polymerization. Here, we present the concepts and methodologies associated with the different types of silk-based materials for a wide range of fields

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 e

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 leng

Summary Polymer gels exhibit some unique features that are not seen in the uncrosslinked polymer system, rubber elasticity and swelling. In this paper, we review our recent studies towards the molecular understanding of the relationship between the elasticity and the swelling ratio using the Tetra‐PEG gels. The dependence of the polymer volume fraction of interest state ( ϕ m ) on the elasticity exhibits the power‐law behaviors and the crossovers at ϕ * and ϕ c due to the presence of the exclude

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., the vanishing of the cross effect in regular networks with no trapped entanglemen

Transient polymer networks are formed by dynamic crosslinks with a finite lifetime and therefore exhibit significant viscoelasticity, including non-Newtonian behaviors. Using the combination of multiple experimental techniques, such as viscoelastic measurements and spectroscopic analyses, these properties can be understood at the molecular level. This review classified transient polymer networks as side-chain and end-chain crosslinks, and viscoelastic studies of each type were presented. A combi

The effect of network connectivity on viscoelastic relaxation in transient networks with well-defined structures (Tetra-PEG slime) was experimentally evaluated and compared to bond dissociation kinetics. To control the connectivity and discuss the pure effect precisely, we mixed the precursors in off-stoichiometric ratio. With decreasing network connectivity, the viscoelastic relaxation time accelerated and became shorter than the bond dissociation time. With increasing polymer concentration, th

Cluster growth process during the gelation is attractive from both scientific and biomedical point of views. Until now, there have been many attempts from theoretical and experimental approaches. However, the comparison of the experimen tal results with the theoretical prediction is ambiguous, because it is impossible to quench the gelation reaction and directly estimate the connectivity in experiments. In this study, we fabricated the states near the critical points using the Tetra-PEG gel syst

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 ap

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 th

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 deformat