REVERSIBLE SIZE AND SHAPE CHANGING SMART MATERIALS AND THEIR APPLICATIONS

Abstract

Stimuli-responsive smart materials are one of the principal components of soft matter research because they enable creation of multi-functional, reconfigurable, and adaptive structures at many length scales. These functional materials can be actuated by various stimuli such as temperature, pH, salt, biomolecules, etc. This work focuses on the use of pH responsive hydrogels to harness their pH-dependent change in volume. We have established two novel ways of inducing dynamic shape-transformation to convert an initially flat two-dimensional (2D) piece of hydrogel into a bent three-dimensional (3D) one, and subsequently back into a flat two-dimensional form. We studied this 2D-3D-2D dynamic transformation in both single-composition monolayer and elastomer-hydrogel hybrid bilayer systems and employed novel design principles to demonstrate applications in pH-gradient sensing and self-regulation of pH. We have also devised a novel method of introducing structured anisotropy in the orientation of pores of pH-responsive hydrogels inspired by natural materials such as wood, marine diatoms, and honeycombs. This method is inexpensive compared to conventional fabrication methods such as stereo-lithography or photolithography. We hope that the new fabrication method introduced would find widespread use in specialized applications such as tissue engineering.