1. Department of Thoracic and Cardiovascular SurgerySapporo Medical University School of Medicine Sapporo 060‐8543 Japan
2. Department of Material‐Based Medical Engineering, Institute of Biomaterials and BioengineeringTokyo Medical and Dental University Tokyo 101‐0023 Japan
3. Japan Society for the Promotion of Science Tokyo 102‐8472 Japan
4. Faculty of Textile Science and TechnologyShinshu University Nagano 386‐8567 Japan