1. Departments of Mechanical and Industrial Engineering, Ophthalmology, and Institute for Biomaterials and Biomedical Engineering, University of Toronto, Ontario, M5S 3G8, Canada;
2. Department of Biomedical Engineering, Northwestern University, Evanston, Illinois 60208;
3. Cambridge Polymer Group, Inc., Somerville, Massachusetts 02143, and Adjunct Assistant Scientist, Schepens Eye Research Institute, Boston, Massachusetts 02114-2500;