Fabrication of Tough Stretchable Light-Responsive Hydrogels and their Application as Biohybrid Robots

Abstract

Living cells assemble into actuating tissues to perform bodily functions, however, these may be impeded by diseases that cause muscle, bone, or organ atrophy. The perfect transplant to replace these damaged organs would require smart-materials that can be programmed to execute directed functions and movements. This can be achieved by developing bio-hybrid devices that incorporate living cells within environment-responsive dynamic systems. Focusing specifically on muscle analogues, a smart-material would require hierarchical systems where changes at the molecular level trigger functional behaviours in bulk.
Actuating materials and life-supporting materials intersect in hydrogels, which may be functionalised for electrical, thermal, or pH-sensing capabilities. However, many limitations arise from direct contact with the stimuli, and harsh environmental changes which may create, resulting in low biocompatibility. Light-responsive systems offer the advantage of remote activation, wavelength selectivity, and localized actuation. Previously, azo-moieties have been used due to their photo-isomerizable properties. However, harnessing the molecular folding to create tough, photo-responsive hydrogels with appreciable actuation strain is still a significant challenge.
In this study, the interface between living cells with movement-generating smart materials is evaluated on the synergistic effect of movement, and bio-application. Highly elastic and stimuli-responsive hydrogels, with reversible mechanisms, are investigated at the material level; this includes the incorporation of Chrysophenine (CHP), a light-isomerisable sensitiser, and its stabilisation from single molecules to actuating nanoclusters that enhances the hydrogel’s actuation performance. The material stretches up to 500% and contracts up to 17% upon light-stimulation, both outstanding marks for hydrogel-based materials.
This material is functionalised to host living cells, resulting in a light-responsive active hydrogel, which exhibits mechanical properties like native biological tissues and high biocompatibility. The effects of its achievable mechanical contraction are expanded to include living muscle cells which differentiate from single units to fused muscle-like fibres. Further refinement of these systems may lead to biohybrid devices with an on-demand light-induced contraction complemented with a cell-powered one.

Date of Award	27 Sept 2022
Original language	English
Awarding Institution	University of Bristol
Supervisor	Adam W Perriman (Supervisor), Mark Schenk (Supervisor) & Michael Dicker (Supervisor)