A Study on Biomechanics of Growth/resorption of Biological Tissue as Functional Adaptation

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The biological issues and systems have the ability to grow, resorb, and/or deform themselves according to the changes of their environments and routine behaviors. Such ability of mechanical adaptation by remodeling is intrinsic only to the biological issue and systems. The quantitative observation and its model description are fundamental in understanding such phenomena and applying such a function in engineering field. From this viewpoint, this study investigates the following topics from experimental/mathematical approaches.1. Residual stress in bone and model of remodelingThe residual stress was released from the rabbit tibia-fibula system by the cutting method. It is found that the observed residual stress is comparable to that by the selfweight and its distribution is complex over the tibia. A model was proposed for the bone remodeling permitting the existence of the residual stress in the bone. The basic capability of the model was examined by simple case studies combined with the observed residual stress.2. Experimental spondylosis model and effect of overuseThe experimental spondylosis was established by surgicalintervention in mice. Mechanical instability accelerates the process of intervertebral disc degeneration and the long term instability brings the spondylosis. Repetitive extension-flexion was loaded on spine of rabbits, and the delamination of annulus fibrosus and the early osteophyte formation are observed. This suggests the overuse is a factor in the pathogenesis of spondylosis.3. Mechanical adaptation of aorta and patellar tendonGoldblatt hypertension was induced in rats and it is found that the aortic wall changes in morphology first and then in the mechanical properties adoptng itself to the mechanical environment. The stress shielding in the patellar tendon of rabbits leads the immediate decrease of the mechanical properties and the reloading brings the gradual recovery. These results show the rapid mechanical adaptation in soft tissues.