Fig. 5. Growth of cardiomyocytes on recombinant proteins, and effects of elastic modulus on cardiomyocyte differentiation.

The elastin-like proteins (ELPs) used by Chung and colleagues (a) consist of a bioactive domain translationally fused to one or more elastin-like domains; these domains contain lysine groups to facilitate crosslinking by tetrakis hydroxymethyl phosphonium chloride (THPC). By varying the ratio of THPC to ELP reactive groups, it is possible to tune the elastic modulus of the resulting culture matrix (b) without significantly altering the diffusion of nutrients or other vital factors through the gel (c). Embryoid bodies embedded in the matrix undergo differentiation into cardiomyocytes most favorably in the gels with the lowest elastic modulus (d); the cells show the greatest contractility when grown in protein crosslinked with a 0.5:1 ratio of THPC:ELP reactive groups. The image is from ref. ¹⁹⁰ and is reproduced with permission.