Biomechanics on the Growth and Deformation of Living Tissues and its Applications to Engineering

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1. Mechanical adaptation of rat aorta to hypertension.The wall thickness significantly correlated with systolic blood pressure (Psys). The aortic hoop stress calculated for Psys was almost independent of Psys at 2-16 weeks after the operation. The incremental elastic modulus (H_<00>) of wall at Psys significantly correlated with Psys at 2-8 weeks. However, the correlation disappeared at 16 weeks after operation.2. Mechanical properties of aortic walls in atherosclerotic rabbits.There were no significant changes in the mechanical properties of walls if the percent fraction of the area involved with sudanophilic lesions on the luminal surface (As) was under 80%. Even if As was over 80%, only 20% of walls gave significantly higher H_<00> values compared with the remaining walls. Remarkable calcification was observed in the walls which had high H_<00> values.3. Effects of stress shielding and restressing on the mechanical properties of rabbit patellar tendon.The stress shielding decreased the tensile strength and tangent modulus markedly, for example to 10% of the control value by 2 weeks. The restressing increased the tensile strength and tangent modulus gradually, for example to 50% of the control value after 2-week stress-shielding followed by 6-week restressing.4. Effects of over-stressing on the mechanical properties of rabbit patellar tendon.The over-stressing caused no significant changes in the mechanical properties, although the cross sectional area was increased significantly, for example to 150% of the initial area by the 6-week stress elevation, which means that the overstressing increases the maximum failure load of whole patellar tendon.These results indicate that biological soft tissues adapt themselves to the changes of mechanical environment by altering the mechanical properties and/or tissue dimensions.