1. Department of Biomedical Engineering, Bioengineering Bldg, State University of New York at Stony Brook, Stony Brook, New York 11794-5281, United States
2. Polymer Science and Engineering Department, University of Massachusetts Amherst, Amherst, Massachusetts 10003, United States
3. National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973, United States