Development of light-responsive materials for biomedical applications - A perspective on the use of Liquid Crystalline Elastomers as artificial muscles and cell culture substrates

Smart soft materials possess an unmatched potential in biomedical applications. Among them, liquid crystalline elastomers (LCEs) exhibit various properties exploited in the fabrication of microrobots and responsive coatings, and, very recently, also in the design of biomedical implants and devices. LCEs are shape-changing materials able to modify their structure upon stimulation, generating tension during this process. Biocompatibility and cell-instructiveness have been demonstrated for different classes of LCEs, whose mechanical properties and response time can be easily tuned. The research presented in this Thesis follows two applications of LCEs in the biomedical field. In the first part of the study, LCEs were investigated as artificial muscles. Starting from the demonstration of the ability of films obtained from a light-responsive LCE mixture in assisting cardiac contraction, its composition was tuned to improve its performance, and completely characterized in terms of efficiency, level of tension developed upon stimulation and kinetics of force development. The aims of the work were to find the correct light stimulation pattern and azobenzene-based dye to enhance its capabilities in muscle assistance and to miniaturize an implantable LCE-miniLED device. In the second part of the research, the ability of different supports to direct cell culturing was approached. The effect of different surface patterning methods on two different materials on cell adhesion and growth was evaluated. In the first study, the ability of linear motifs in directing cell alignment and growth of cardiomyocytes derived from human induced pluripotent stem cells, on hydrogels made of commercially available polymers, was pinpointed. Substrate rigidity was modulated to assess the relation between this parameter and cell functionality. The focus of the second study was the development of reconfigurable coatings based on light-responsive LCEs. Surfaces were patterned with fingerprint-like structures, which arose from self-assembly of a mixture of mesogenic monomers doped with a chiral crosslinker. The surfaces possessed hills and valleys with different molecular alignment, that underwent topography inversion upon irradiation. Different types of coatings were prepared, tuning pattern spacing, roughness and actuation level. The biocompatibility of the materials was studied in view of their use as active cell culture scaffolds capable of live stimulation of cultured cells.