This research was conducted as part of the Center for Excellence for Self-Healing, Regeneration and Structural Remodeling, supported by the United States Air Force Office of Scientific Research through award FA9550-16-1-0017. We thank J. Sung for preparing the micropatterned silicon substrates, T. Ross for sample photography, D. Loudermilk for graphics assistance, and the Beckman Institute for Advanced Science and Technology for use of their facilities and equipment. I.D.R. thanks the US Department of Defense for a National Defense Science and Engineering Graduate Fellowship. L.M.D. thanks the National Science Foundation for a Graduate Research Fellowship.

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Nature thanks J. Pojman and the other anonymous reviewer(s) for their contribution to the peer review of this work.