1. Department of Bioengineering, National Cardiovascular Center Research Institute, 5-7-1 Fujishiro-dai, Suita, Osaka 565-8565, Japan, Department of Materials Synthesis, Johnson & Johnson Corporate Biomaterials Center, A Division of Ethicon, Inc., Route 22 West, PO Box 151, Somerville, New Jersey 08876-0151, and Department of Biomedical Engineering, Graduate School of Medicine, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan