1. Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, W342 Nebraska Hall, Lincoln, NE 68588-0526
2. Department of Surgery, University of Nebraska Medical Center, 4400 Emile Street, Omaha, NE 68198
3. Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, W342 Nebraska Hall, Lincoln, NE 68588-0526 e-mail: