Safaei Mohsen, Meneghini R Michael, Anton Steven R
Department of Mechanical Engineering, Tennessee Technological University, Cookeville, TN 38505 USA.
Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, IN 46202 USA.
Smart Mater Struct. 2018 Nov;27(11). doi: 10.1088/1361-665X/aad755. Epub 2018 Sep 25.
Recent developments in the field of orthopedic materials and procedures have made the total knee replacement (TKR) an option for people who suffer from knee diseases and injuries. One of the ongoing debates in this area involves the correlation of postoperative joint functionality to intraoperative alignment. Due to a lack of in vivo data from the knee joint after surgery, the establishment of a well-quantified alignment method is hindered. In order to obtain information about knee function after the operation, the design of a self-powered instrumented knee implant is proposed in this study. The design consists of a total knee replacement bearing equipped with four piezoelectric transducers distributed in the medial and lateral compartments. The piezoelectric transducers are utilized to measure the total axial force applied on the tibial bearing through the femoral component of the joint, as well as to track the movement in the center of pressure (CoP). In addition, the generated voltage from the piezoelectrics can be harvested and stored to power embedded electronics for further signal conditioning and data transmission purposes. Initially, finite element (FE) analysis is performed on the knee bearing to select the best location of the transducers with regards to sensing the total force and location of the CoP. A series of experimental tests are then performed on a fabricated prototype which aim to investigate the sensing and energy harvesting performance of the device. Piezoelectric force and center of pressure measurements are compared to actual experimental quantities for twelve different relative positions of the femoral component and bearing of the knee implant in order to evaluate the performance of the sensing system. The output voltage of the piezoelectric transducers is measured across a load resistance to determine the optimum extractable power, and then rectified and stored in a capacitor to evaluate the realistic energy harvesting ability of the system. The results show only a small level of error in sensing the force and the location of the CoP. Additionally, a maximum power of 269.1 is achieved with a 175 optimal resistive load, and a 4.9 V constant voltage is stored in a 3.3 mF capacitor after 3333 loading cycles. The sensing and energy harvesting results present the promising potential of this system to be used as an integrated self-powered instrumented knee implant.
骨科材料和手术领域的最新进展使全膝关节置换术（TKR）成为患有膝关节疾病和损伤的患者的一种选择。该领域正在进行的争论之一涉及术后关节功能与术中对线的相关性。由于缺乏术后膝关节的体内数据，阻碍了一种量化良好的对线方法的建立。为了获取术后膝关节功能的信息，本研究提出了一种自供电的仪器化膝关节植入物的设计。该设计包括一个全膝关节置换轴承，配备有四个分布在内侧和外侧腔室的压电换能器。压电换能器用于测量通过关节的股骨部件施加在胫骨轴承上的总轴向力，以及跟踪压力中心（CoP）的移动。此外，压电产生的电压可以被收集和存储，以为嵌入式电子设备供电，用于进一步的信号调节和数据传输目的。最初，对膝关节轴承进行有限元（FE）分析，以选择换能器在感测总力和CoP位置方面的最佳位置。然后对一个制造的原型进行一系列实验测试，旨在研究该装置的传感和能量收集性能。将压电式力和压力中心测量值与膝关节植入物的股骨部件和轴承的十二个不同相对位置的实际实验量进行比较，以评估传感系统的性能。在负载电阻上测量压电换能器的输出电压，以确定最佳可提取功率，然后进行整流并存储在电容器中，以评估系统实际的能量收集能力。结果表明，在感测力和CoP位置方面只有很小的误差水平。此外，在175Ω的最佳电阻负载下实现了269.1μW的最大功率，并且在3333次加载循环后，在一个3.3mF的电容器中存储了4.9V的恒定电压。传感和能量收集结果表明该系统有望用作集成的自供电仪器化膝关节植入物。
