Actuation based on thermo/photosalient effect: a biogenic smart hybrid driven by light and heat†
Aimed at the design of efficient smart actuating materials, we have fabricated a self-actuating material that sets the platform for conceptually new, hybrid biocompatible actuators capable of dual mechanical response—by changes in temperature and by stimulation with weak ultraviolet or blue visible light. We demonstrate herein that microcrystallites of thermosalient and photosalient (leaping) solids can effectively utilize thermal or light energy and act as a robust and dynamically active “skeleton” to actuate sodium caseinate films as an elastic, flexible, biocompatible, natural protein matrix, similar to artificial muscle. The spectroscopic, kinematic and mechanical profiles of the new material are all consistent with a mechanism whereby the cooperative strains induced by reshaping and motions of the thermosalient crystals trigger macroscopic mechanical deformation of the matrix. The elastic medium absorbs the stress, thus providing reinforcing feedback to the brittle crystals. The hybrid material conveniently combines fast energy absorption and conversion within single crystals and elasticity of polymers and displays a remarkable improvement in the tensile properties relative to the non-doped caseinate. Being based on natural protein, this thermally and photoresponsive artificial muscle is also biologically compatible and environmentally benign.