Matrix mechanics as a modular aspect of biomaterials. β-sheet forming peptide-thioesters self-assemble into fibrils and undergo native chemical ligation, leading to matrix stiffening (a). Ligated peptides retain the ability to fibrillize (b), and stiffening leads to significantly improved proliferation of human endothelial cells over un-stiffened matrices (c, blue DAPI, green CD31). Reprinted with permission from Jung et. al, Biomaterials, 2008.28