Regenerative Biology, Morgridge Institute for Research, Madison, WI 53707, Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, CA 93106, Departments of Mechanical Engineering and Materials, University of California, Santa Barbara, CA 93106 and Department of Cell and Regenerative Biology, University of Wisconsin, Madison, WI 53706, USA Regenerative Biology, Morgridge Institute for Research, Madison, WI 53707, Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, CA 93106, Departments of Mechanical Engineering and Materials, University of California, Santa Barbara, CA 93106 and Department of Cell and Regenerative Biology, University of Wisconsin, Madison, WI 53706, USA Regenerative Biology, Morgridge Institute for Research, Madison, WI 53707, Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, CA 93106, Departments of Mechanical Engineering and Materials, University of California, Santa Barbara, CA 93106 and Department of Cell and Regenerative Biology, University of Wisconsin, Madison, WI 53706, USA.