精密重合法による自励振動ポリマーブラシ表面の設計と機能創出

学位の種別: 課程博士審査委員会委員 : （主査）東京大学教授 吉田 亮, 東京大学教授 石原 一彦, 東京大学准教授 山崎 裕一, 東京大学准教授 坂田 利弥, 東京大学准教授 酒井 崇匡, 東京大学講師 秋元 文University of Tokyo(東京大学

Delayed mechanical response to chemical kinetics in self- oscillating hydrogels driven by the Belousov−Zhabotinsky reaction

We show experimentally that chemical and mechanical self-oscillations in Belousov−Zhabotinsky hydrogels are inherently asynchronous, that is, there is a detectable delay in swelling−deswelling response after a change in the chemical redox state. This phenomenon is observable in many previous experimental studies and potentially has farreaching implications for the functionality and response time of the material in future applications; however, so far, it has not been quantified or reported systematically. Here, we provide a comprehensive qualitative and quantitative description of the chemical-tomechanical delay, and we propose to explain it as a consequence of the slow nonequilibrium swelling−deswelling dynamics of the polymer material. Specifically, standard hydrogel pieces are large enough that transport processes, for example, counterion migration and water diffusion, cannot occur instantaneously throughout the entire gel piece, as opposed to previous theoretical considerations. As a result, the volume response of the polymer to a chemical change may be governed by a characteristic response time, which leads to the emergence of delay in mechanical oscillation. This is supported by our theoretical calculations

A Thermoresponsive Cationic Comb-Type Copolymer Enhances Membrane Disruption Activity of an Amphiphilic Peptide

Membrane active peptides (MAPs) have potential applications in drug delivery systems and as antimicrobials. We previously showed that a cationic comb-type copolymer, poly­(allylamine)-<i>graft</i>-dextran (PAA-<i>g</i>-Dex), forms a soluble inter-polyelectrolyte complex with an anionic MAP, the E5 peptide, resulting in significant enhancement of the membrane disruption activity of E5. In this study, we designed a novel comb-type cationic copolymer composed of a PAA main chain and thermoresponsive poly­(<i>N</i>-isopropyl­acrylamide) graft chains (PAA-<i>g</i>-PNIPAAm). We hypothesized that the thermoresponsive hydrophilic/hydrophobic transition of the grafted polymer would regulate the membrane disruption activity of E5 peptide. Both the binding affinity of the complex and the membrane disruption activity of E5/PAA-<i>g</i>-PNIPAAm were found to be enhanced above the phase transition temperature of the grafted chain. Our analysis suggests that the hydrophilic/hydrophobic environment around the cationic polymer chain plays important roles in the enhancement of the activity of the anionic peptide

Superior antibacterial surfaces using hydrophilic, poly(MPC) and poly(mOEGMA) free chains of amphiphilic block copolymer for sustainable use

Surface modification of electrically neutral hydrophilic polymers is one of the most promising methods for preventing biofouling and biological contamination by proteins and bacteria. Surface modification of inorganic materials such as silica-based glass can render them more durable and thus help in achieving the sustainable development goals. This study reports a novel method for the simple and effective surface modification of glass surfaces with amphiphilic block copolymers possessing the silane coupling segment composed of 3-(methacryloyloxy)propyltris (trimethylsilyloxy) silane and 3-methacryloxypropyltrimethoxysilane. The ability of hydrophilic segments composed of either 2-methacryloyloxyethyl phosphorylcholine (MPC) or poly(ethylene glycol) methyl ether methacrylate (mOEGMA) to prevent bacterial adhesion was investigated. The target block copolymers were prepared by reversible addition-fragmentation chain transfer polymerization and the monomer units of the hydrophilic segments were controlled to be either 120 or 160. The polymers were modified on the substrate by dip-coating. Contact angle measurements indicated that the block copolymer with the PMPC hydrophilic segment formed a hydrophilic surface without pre-hydration, while those with the PmOEGMA hydrophilic segment-coated surface became hydrophilic upon immersion in water. The block copolymer-coated surfaces decreased S. aureus adhesion, and a significant reduction was observed with the MPC-type block copolymer. The following surface design guidelines were thus concluded: (1) the block copolymer is superior to the random copolymer and (2) increasing the hydrophilic segment length further decreases bacterial adhesion

Thermoresponsive Surface-Grafted Gels: Controlling the Bulk Volume Change Properties by Surface-Localized Polymer Grafting with Various Densities

We prepared poly(N-isopropylacrylamide-r-N-3-(aminopropyl)methacrylamide) (poly(NIPAAm-r-NAPMAm)) gels with poly NIPAAm (PNIPAAm) grafted only in the surface region (so-called thermoresponsive surface-grafted gels) with various graft densities and investigated the effect of the graft density on the bulk volume change properties, shrinking and swelling, in response to temperature changes. Initiators for atom-transfer radical polymerization (ATRP) and structurally analogous compounds were introduced at certain ratios onto the surface regions of the gels, and a subsequent activator regeneration by electron transfer ATRP of NIPAAm was conducted in aqueous media. The graft densities and molecular weights of the grafted polymers were evaluated from the increment in the dry mass of the gels and the amount of introduced ATRP initiators, which was measured by elemental analyses. Three-dimensional measuring laser microscopy revealed that the prepared gels had graft-density-dependent fine wrinkle structures on their surfaces. The surface-grafted gels induced the formation of skin layers during the shrinking process in response to a temperature increase, and their permeability strongly depended on the graft density. The graft density also controlled the kinetics of the swelling behavior in response to a temperature decrease. These physical properties were discussed on the basis of Young&apos;s modulus of the surface determined by an atomic force microscopy force curve measurement and the homogeneity of the surface polymer network observed by cryo-scanning electron microscopy. This makes it possible to arbitrarily control the characteristics of gels as open or semiclosed systems, which was uniquely determined by the designs of the surface gel networks.111sciescopu

Harmonic resonance and entrainment of propagating chemical waves by external mechanical stimulation in BZ self-oscillating hydrogels

Smart polymer materials that are non-living yet exhibit complex “life-like” or biomimetic behaviours have been the focus of intensive research over the past decades, in the quest to broaden our understanding of how living systems function under nonequilibirum conditions. Discovery of how chemical and mechanical coupling can generate resonance and entrainment with other cells or external environment is an important research question. We prepared Belousov-Zhabotinsky (BZ) self-oscillating hydrogels which convert chemical energy to mechanical oscillation. By cyclically applying external mechanical stimulation to the BZ hydrogels, we found that when the oscillation of a gel sample entered into harmonic resonance with the applied oscillation during stimulation, the system kept a "memory" of the resonant oscillation period and maintained it post stimulation, demonstrating an entrainment effect. More surprisingly, by systematically varying the cycle length of the external stimulation, we revealed the discrete nature of the stimulation-induced resonance and entrainment behaviours in chemical oscillations of BZ hydrogels, i.e., the hydrogels slow down their oscillation periods to the harmonics of the cycle length of the external mechanical stimulation. Our theoretical model calculations suggest the important roles of the delayed mechanical response caused by reactant diffusion and solvent migration in affecting the chemomechanical coupling in active hydrogels and consequently synchronising their chemical oscillations with external mechanical oscillations