[1] Stanford Univ, Dept Bioengn, Stanford, CA 94305 USA
[2] Stanford Univ, Dept Mat Sci & Engn, Stanford, CA 94305 USA
[3] Ecole Polytech Fed Lausanne EPFL, Lab Stem Cell Bioengn, Inst Bioengn, Sch Life Sci, Lausanne, Switzerland
[4] Ecole Polytech Fed Lausanne EPFL, Sch Engn, Lausanne, Switzerland
[5] Ecole Polytech Fed Lausanne EPFL, Sch Basic Sci, Inst Chem Sci & Engn, Lausanne, Switzerland