1. Division of Biomedical Engineering, Chonbuk National University, Deokjin-Dong 1-Ga, Jeonju, Jeonbuk 561-756, South Korea
2. Institute of Fluid Science, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan
3. Bioengineering Research Center for the Aged, Chonbuk National University, Jeonju, Jeonbuk 561-756, South Korea