1. Kevin E. Healy is the Jan Fandrianto Distinguished Chair, Department of Bioengineering, University of California at Berkeley, Berkeley, CA 94720, USA.
2. Todd C. McDevitt is Associate Professor in the Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, and Director, Stem Cell Engineering Center, Georgia Institute of Technology, Atlanta, GA 30332, USA.
3. William L. Murphy is the Harvey D. Spangler Professor, Biomedical Engineering and Co-Director, Stem Cell and Regenerative Medicine Center, University of Wisconsin Madison, Madison, WI 53705, USA. E-mail: wlmurphy@wisc.edu
4. Robert M. Nerem is Parker H. Petit Distinguished Chair for Engineering in Medicine and Institute Professor Emeritus, and Founding Director of the Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA 30332, USA. E-mail: robert.nerem@ibb. gatech.edu