Blending polymers, proteins, and/or peptides with complementary stereochemistry yields ‘stereocomplexed’ materials that exhibit remarkable enhancements in thermal and mechanical properties, binding affinity, and stability relative to materials comprised of either component alone. This talk will describe our labs efforts to understand and employ interactions between d- and l-peptides to tune material properties. After finding that blending d- and l-peptides, which on their own form fibrous hydrogels, transforms morphology, mechanics, and stability of these materials, we investigated the role of peptide stereocomplexes as dynamic cross-links in polymer hydrogels. While solutions of 4-arm star polyethylene glycol (PEG) decorated with d- or l-peptides flow in aqueous solution, blending solutions of complementary conjugates generates strain-stiffening hydrogels, even in the presence of repulsive electrostatic interactions. By tuning the charge, length, and hydrophobic content of the peptides comprising the cross-links, we found these molecular-scale changes to modulate hydrogel rheology and stability. We also found the secondary structure (or conformation) adopted by the peptide cross-links to influence the dynamic nature of hydrogels: peptides that adopt a β-sheet conformation recover just 20% of their shear storage modulus after applying and removing high shear, whereas helical peptide cross-links recover nearly 100% of their initial modulus. Going forward, we are excited to continue the development of design rules correlating peptide sequence to the properties of peptide stereocomplexes so as to highlight peptide stereochemistry as a prominent tool for designing precision materials.
