Almost every laboratory that grows mammalian cells today grows their cells on tissue culture plastic, which was introduced to cell culture decades ago based on properties such as inertness, transparency, and so forth. However, plastic is rigid and unlike the many soft tissues in the body. Polymer gel systems that mimic the softness of various tissues have been developed over the past decade to test and understand the effects of rigidity on cells such as muscle cells. One recent study even shows that muscle stem cells expand much better in vitro on muscle-mimetic gels and that such cells prove optimal for engraftment in muscle.