Fabrication and characterization of hydrogels formed from designer coiled-coil fibril-forming peptides

Hydrogels are soft solids that represent attractive matrices for tissue engineering, wound healing and drug delivery. We previously reported an alpha-helical peptide, AFD19, that forms fibrils and hydrogels at pH 6, but precipitates under physiological conditions. We now show that a single targeted change in AFD19 yields peptide AFD36, which gels at physiological pH and in the presence of salt. Furthermore, we present a simple method for homogeneous sol-gel conversion through pH titration with sodium bicarbonate followed by loss of carbon dioxide. Chemical and thermal denaturation studies show AFD36 self-assembles to give stable alpha-helical structures, forming fibrils of 3.8-3.9 nm diameter at pH 4.0-7.0 as shown by small-angle X-ray scattering and atomic force microscopy. An AFD36 gel at 0.35% (w/v) showed an elastic modulus of 350 Pa. Mouse fibroblasts exhibited low cellular toxicity and spread morphologies when grown on the gel as a preliminary proof of principle towards cell culture studies. These peptide gels offer a molecularly simple, biodegradable alternative to polymer-based systems for biomedical applications.