Supramolecular peptidic dopants for inducing photoconductivity and mechanical tunability in digital light processable hydrogels†

This work presents a strategy for generating composite hydrogels bearing photoconductive conduits held by supramolecular interactions that are compatible with digital light processing (DLP) printing. Conductive polymers are typically processed with organic solvents as the film, yet if used as biomaterials, excitable cells often require matching with the mechanical and structural properties of their native, aqueous three-dimensional (3-D) microenvironment. Here, we utilize peptide-functionalized porphyrin units capable of self-assembling into photoconductive nanostructures with defined nanomorphologies under aqueous conditions. In addition to the DXXD peptide arms (X = V, F), the sequence variants studied here include a peptidic moiety bearing allyloxycarbonyl (alloc) groups that can serve as crosslinking sites of the acrylate-based monomers that ultimately form the base 3-D covalent network for the hydrogels. We investigate the impact of pre-templating polymeric gelators with supramolecular assemblies vs. printing a dispersed peptide–porphyrin in a polymer composite, specifically, the potential impact of the morphologies of the supramolecular additives or “dopants” on the resulting mechanical property, conductivity, and printability of the hydrogels, comprised of a hybrid between acrylated polymers and supramolecular peptide–porphyrin assemblies. Lastly, we demonstrate the role of photophysical properties that emerge from peptide-tuned porphyrin assemblies as a photoabsorber additive that influences the printing outcomes of the composite hydrogel. Overall, we present a covalent-supramolecular composite hydrogelator system where the self-assembled networks offer a pathway for energy transport and mechanical reinforcement/dissipation at the same time, leading to the formation of a hydrogel with optoelectronic, mechanical, and printable behavior that can be influenced by self-assembled dopants.