1. Department of Mechanical & Materials Engineering, University of Nebraska–Lincoln, Lincoln, Nebraska 68588, USA
2. Department of Surgery, University of Nebraska Medical Center, Omaha, Nebraska 68198, USA
3. Cardiovascular Biology and Biomechanics Laboratory, Cardiovascular Division, University of Nebraska Medical Center, Omaha, Nebraska 68198, USA
4. SRI International, Ann Arbor, Michigan 48105, USA