1. Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0656
2. Stanley Truhlsen Eye Institute, University of Nebraska Medical Center, Omaha, NE 68105-1119;
3. Center for Advanced Surgical Technology, University of Nebraska Medical Center, Omaha, NE 68198-6245
4. Department of Neurological Sciences, University of Nebraska Medical Center, Omaha, NE 68198-8440
5. Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0656;
6. Center for Advanced Surgical Technology, University of Nebraska Medical Center, Omaha, NE 68198-6245;
7. Nebraska Center for Materials and Nanoscience, Lincoln, NE 68588-0656 e-mail: