Substrate elasticity can direct stem cell differentiation. (A) Native tissues exhibit a range of stiffness. (B) Stem cells cultured on hydrogel with varying elasticity modified with cell-adhesive type I collagen directed differentiation into different lineages (neurogenic, 0.1–1 kPa; myogenic, 8–17 kPa; osteogenic, 25–40 kPa). (C) Microarray profiles of transcription factors show neurogenic markers (left) are highest on 0.1–1 kPa gels, myogenic markers (center) are highest on 11 kPa gels, and osteogenic markers (right) are highest on 34 kPa gels. Reprinted with permission from ref. 26. Copyright 2006 Elsevier.