骨水泥固定髋关节的动应力波失效机理研究及减振设计

Nowadays loosening is still one of major problems that restricts the fixture reliability of cemented type stem. Despite the continuous progress of clinical procedures and materials, the problems still occur frequently, whose underlying reason that the loosening mechanism of cemented total hip replacement is still unclear. Therefore, this project intends to use nonlinear viscoelastic wave dynamics theory to research the propagation mechanism of stress wave in cemented hip joint and reveal the cause of its failure. Firstly, based on the generalized fractional derivative operator theory, the nonlinear power function constitutive model of bone cement is established to provide theoretical guidance for later experiments. Secondly, the dynamic stress wave is monitored by the designed embedded distribution fiber Bragg grating system, which establishes the nonlinear viscoelastic dynamic stress wave model of the cement-type hip joint and explains its propagation mechanism. Moreover, according to Timoshenko beam-column nonlinear viscoelastic dynamic damage theory, the difference of bone cement-stem system that the response to dynamic stress wave is analyzed and its dynamic damage characteristics are studied. Finally, by means of the load mistuning and constant sinusoidal excitation experiment, it is established for the dynamic equation of the cemented hip joint at the time of load imbalance. The key parameters of loosening hip joint failure are investigated and the design method of optimizing vibration-damping and anti-loosening prosthesis is further proposed. The research results are expected to provide a theoretical evidence for the new hip prosthesis design in accordance to reduce cemented stem loosening vibration damage and the improvement of its reliability. It is of great significance to prolong the life of cemented hip joint and reduce the failure rate.

松动问题是制约骨水泥型髋关节柄可靠性关键因素。尽管临床手术和材料不断进步，但问题仍频繁出现，其根本原因是松动机理尚不清楚。为此，本项目拟利用非线性粘弹波动力学研究应力波在骨水泥型髋关节传播机理并揭示其失效本质，即首先基于广义分数阶导数算子理论建立骨水泥材料的非线性幂函数本构模型，为后期实验提供理论指导；其次，通过设计埋置式分布光纤光栅系统监测动应力波，建立骨水泥型髋关节非线性粘弹动应力波模型并解释其传播机理；接着，根据Timoshenko梁-柱非线性粘弹性动态损伤理论，分析骨水泥-柄对动应力波响应差异并研究其动态损伤特性；最后，通过对正弦激励载荷失调试验，建立骨水泥型髋关节构件载荷失调时动力学方程，发现该系统松动失效的关键参数，并提出减振型假体的设计方法。研究结果有望为改进假体减振抗损设计及提升其可靠性提供理论依据，对延长骨水泥型髋关节柄寿命和降低失效率具有重要意义。

骨水泥因其具有良好生物相容性和即时稳定的力学性能被作为关节植入填充物，但是植入体松动问题是制约骨水泥型髋关节柄可靠性的关键问题，其衍生“应力遮挡效应”和“磨屑疾病”的问题长期困扰患者康复。因此研究非线性粘弹动态应力波在骨水泥型髋关节传播机理成为剖析其松动失效机理，在基础理论和应用两方面都具有重要意义。本项目开展了骨水泥型髋关节脱粘试验研究，建立了骨水泥粘弹特性非线性幂函数本构模型；研究发现了骨水泥微孔裂纹萌生和扩展的机理主要是因骨水泥非饱和结晶度而造成聚合物链缺陷，以及径向和轴向应力耦合应力，导致骨水泥-柄界面的剪切滞后效应不能阻止界面和内部损伤的自上而下，从而形成不同位置的界面损伤和脱粘；骨水泥在劈裂失效阶段微裂纹增多形成损伤带削弱其力学强度，且其宽度随载荷增大而增大。通过自主设计仿人工髋关节微动试验机及埋置式分布光纤光栅系统监测骨水泥动应力波，提取骨水泥粘弹性参数储能模量、损耗模量、动态粘度和耗损因子与频率曲线，构建了骨水泥型髋关节非线性粘弹动应力波有限元模型并分析其传播机理。研究发现了骨水泥粘弹性三维模型中蠕变柔量、剪切模量和体积模量为优化设计匹配髓腔假体的关键参数。此外研究也发现骨水泥内部应力波传递从顶端呈现圆波向外传递，而从顶部向底部传递过程中波形与轴向夹角约为45°±0.8°。上百万动态周期后骨水泥微孔隙及微裂纹呈显著增长且形成贯通损伤带，而血清体液能够有效减少骨水泥裂纹扩展。长期松动导致骨水泥-钛合金界面微动磨损形成不可逆修复的热塑性和微小扭矩损伤，并发现了蛋白质能有效抗界面磨损能力却随载荷增大而降低故骨水泥磨损量要增大。骨水泥磨损斑痕呈现凹谷状，而钛合金磨损区域则呈现中间凸台周围环形凹谷的特征。研究磨屑轮廓进行分形统计发现了骨水泥和钛合金磨屑大致分为六种典型形态如球状，类球状，条状，块状，撕裂和片状等。磨屑最大分形维数均介于0.3-0.4区间，而0.3-0.6分形维数磨屑居多其主要为球状和类球状。为将研究结果应用临床发现骨水泥有利于患者术后康复，但体重(BMI)，骨质疏松和关节炎症等三个因素易引发术后失效，且失效影响率分别为37.31%，23.30%和30.64%，引发骨水泥松动及柄下沉和组织病变威胁患者康复。本项目工作为研究提升骨水泥型髋关节置换的可靠性提供实验和理论基础，有力促进适合国人体质生物医用置换术的发展。

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