[1] Univ Penn, Dept Bioengn, Philadelphia, PA 19104 USA
[2] Univ Penn, Inst Med & Engn, Vagelos Res Lab 1170, Philadelphia, PA 19104 USA
[3] Univ Penn, Dept Pathol, Philadelphia, PA 19104 USA
[4] Inst Med & Engn, Vagelos Res Lab 1170, Philadelphia, PA 19104 USA