A muscle mimetic polyelectrolyte-nanoclay organic-inorganic hybrid hydrogel: its self-healing, shape-memory and actuation properties.

Sovan Lal Banerjee,Thomas Swift,Richard Hoskins,Nikhil K. Singha,Stephen Rimmer

doi:10.1039/c8tb02852d

Abstract

In this investigation, we report a non-covalent (ionic interlocking and hydrogen bonding) strategy of self-healing in a covalently crosslinked organic-inorganic hybrid nanocomposite hydrogel, with specific emphasis on tuning its properties fitting into a muscle mimetic material. The hydrogel was prepared via an in situ free radical polymerization of sodium acrylate (SA) and successive crosslinking in the presence of starch grafted with poly(2-(methacryloyloxy)ethyl trimethyl ammonium chloride) (PMTAC) and montmorillonite modified with cetyl ammonium bromide (OMMT). This hydrogel shows stimuli triggered self-healing following damage in both neutral and acidic solutions (pH = 7.4 and pH = 1.2). This behavior was reported using stress-strain experiments and rheological analyses of the hydrogel segments joined at their fracture points. The hydrogel was also able to display shape memory properties in the presence of water as well as stimuli (salt, acid and electric impulse) driven actuation behavior. It was observed that the ultimate tensile strength (UTS) of the self-healed hydrogel at pH = 7.4 was comparable to the extensor digitorum longus (EDL) muscle of a New Zealand white rabbit and the as synthesized self-healable hydrogel was found to be non-cytotoxic against NIH 3T3 fibroblast cells.

Highlights

Self-healable hydrogels can be prepared by using different physical and chemical interactions
The formation of starch-g-poly(2-(methacryloyloxy)ethyl trimethyl ammonium chloride) (PMTAC) was confirmed by 1H NMR and diffusion-ordered NMR spectroscopy (DOSY) NMR analyses
The hydrogel was synthesized utilizing conventional free radical polymerization reactions to generate a brush like cationic starch and anionic poly(sodium acrylate) moieties along with cetyl trimethyl ammonium bromide (CTAB) modified MMT clay

Summary

Introduction

Self-healable hydrogels can be prepared by using different physical and chemical interactions. The main disadvantages observed in most physically interacting self-healable hydrogels are their poor mechanical stability (i.e. contractility, extensibility and elasticity), which is an important factor to mimic a muscle system. Interacting hydrogels have poor elasticity and are unable to dissipate the absorbed energy, so they are unsuitable for use as an artificial muscle, cartilage, tendons etc. They require high loadbearing capacity without permanent shape deformation (shape memory effect) as well as self-healing properties. Many researchers have focused on the preparation of stronger hydrogels. Possible solutions in this area include different

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Conclusion