1. From the University of California at Berkeley/San Francisco, Joint Graduate Group in Bioengineering (S.T.W., J.C.W., K.E.H., M.B.R., J.M.G.); Departments of Material Science and Engineering (K.E.H.) and Bioengineering (K.E.H.), University of California at Berkeley; Department of Surgery, University of California at San Francisco (M.B.R., J.M.G.); and Veterans Affairs Medical Center, San Francisco, Calif (M.B.R., J.M.G.).