Alternatively, natural polymers (e.g. peptides, saccharides, nucleic acids), can form networks in response to temperature, light, and solvents by partially unfolding, thus exposing previously buried, or "cryptic", binding sites. Of particular interest to us, these cryptic binding sites can also be revealed in response to a mechanical stimulus . For example, fibronectin will dynamically unfold and polymerize into fibrils in response to cell-generated forces . In contrast, synthetic polymers commonly weaken or even rupture under force .