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

生物问题和系统有能力根据环境和日常行为的变化来生长、吸收和/或变形。这种通过重塑进行机械适应的能力只存在于生物问题和系统中。定量观测及其模型描述是理解此类现象和将此类函数应用于工程领域的基础。从这个角度出发，本研究从实验/数学的角度探讨了以下主题。骨内残余应力及重建模型采用切割法释放兔胫骨-腓骨系统残余应力。观察到的残余应力与自重的残余应力相当，其在胫骨上的分布很复杂。提出了一种允许骨内残余应力存在的骨重构模型。结合观察到的残余应力，通过简单的实例研究验证了模型的基本能力。采用手术干预法建立小鼠实验性颈椎病模型及作用。机械失稳加速了椎间盘退变的进程，长期失稳导致椎体病。对家兔脊柱进行反复伸屈负荷，观察纤维环剥离和早期骨赘形成。这表明过度使用是颈椎病发病的一个因素。对大鼠高血压大鼠进行了主动脉和髌骨肌腱的机械适应实验，发现主动脉壁先发生形态变化，再发生力学性能变化，使其适应机械环境。兔髌骨肌腱的应力屏蔽导致其力学性能立即下降，再加载使其逐渐恢复。这些结果显示了软组织的快速机械适应性。

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.