BIOTRIBOLOGY OF DIARTHRODIAL JOINTS

描述（由申请人提供）：近年来，我们对关节软骨润滑的基础工程科学的理解取得了很大进展，这主要是由本基金前期（1995- 2008）取得的进展所推动的。从20世纪30年代开始，虽然在过去的几十年里提出了许多相互竞争的假设，但现在已经从理论和大量实验中确定并验证了关节软骨间质流体加压驱动润滑的基本机制。加载后，接触关节层间质液明显受压，支撑了大部分接触力；因此，只有一小部分的接触力是由接触的胶原-蛋白聚糖基质支撑的，产生的摩擦力可以忽略不计，因此摩擦系数很低。虽然滑液中存在的边界润滑剂有助于进一步降低摩擦系数，但我们最近的研究表明，摩擦的减少主要是由这种间隙流体增压机制贡献的。在一定的载荷条件下，如果间隙流体压力减小，摩擦系数会急剧上升，我们的实验表明，软骨磨损也会随之增加。由于有了一个有效的理论框架来解释间隙流体增压的润滑机制，因此有可能预测间隙流体增压可能消退的加载条件。这一竞争性延续应用的具体目的是将这些基础科学发现转化为重要的、与关节半关节置换术临床相关的见解。半关节置换术是一种外科手术，用光滑的不透水的人工承托面代替一半的关节，使相邻的关节层保持完整。临床经验表明，半关节置换术后，骨性关节炎患者原有关节层退变的进展速度可能比预期的要快。本研究的总体目标是：a)研究半关节置换术效果不佳是否因为未能充分促进软骨间质液加压而导致摩擦系数升高；b)研究人工承载面为可变形多孔透水材料的半关节置换术是否比传统的不透水承载材料产生更低的持续摩擦和磨损。其他目标旨在进一步加深我们对软骨润滑和磨损的基础科学理解，为设计用于半关节置换术的改进承载表面奠定基础。

DESCRIPTION (provided by applicant): In recent years much progress has been made in our understanding of the basic engineering science of articular cartilage lubrication, driven significantly by the progress achieved in the prior funding periods (1995- 2008) of this grant. Though many competing hypotheses had been advanced over past decades, starting from the 1930's, a fundamental mechanism of lubrication driven by interstitial fluid pressurization of articular cartilage has now been identified and validated from theory and numerous experiments. Upon loading, the interstitial fluid of contacting articular layers pressurizes significantly, supporting most of the contact force; consequently, only a small fraction of this contact force is supported by the contacting collagen-proteoglycan matrixes, producing a negligible friction force, and thus a low friction coefficient. Though boundary lubricants present in synovial fluid help to further reduce the friction coefficient, our recent study has shown that the dominant reduction in friction is contributed by this interstitial fluid pressurization mechanism. If the interstitial fluid pressure subsides, as may occur under certain loading conditions, the friction coefficient rises dramatically, and evidence from our experiments indicates that cartilage wear increases concomitantly. Thanks to the availability of a validated theoretical framework explaining the mechanism of lubrication by interstitial fluid pressurization, it is possible to anticipate those loading conditions where interstitial fluid pressurization may subside. The specific aims of this competing continuation application are to translate these basic science findings into important, clinically relevant insights for joint hemiarthroplasties. Hemiarthroplasty is a surgical procedure that replaces one half of a diarthrodial joint with a smooth impermeable artificial bearing surface, leaving the apposing articular layer intact. Clinical experience suggests that, following hemiarthroplasty, degeneration of the native articular layer may progress at a faster rate than expected in osteoarthritis. The overall objective of this application is to a) investigate whether hemiarthroplasties fare poorly because they produce elevated friction coefficients by failing to promote sufficient cartilage interstitial fluid pressurization; and b) investigate whether hemiarthroplasties where the artificial bearing surface is a deformable porous-permeable material can produce lower sustained friction and wear than traditional impermeable bearing materials. Additional objectives aim to further deepen our basic science understanding of cartilage lubrication and wear, setting the stage for designing improved bearing surfaces for hemiarthroplasties. PUBLIC HEALTH RELEVANCE: There are more than 120,000 hip hemiarthroplasties performed each year in the US. The two principal aims of this application are to (1) provide an explanation for the observation that hemiarthroplasties lead to a faster wear of the native articular surface of an operated joint than otherwise expected in osteoarthritis, based on principles of friction and wear; and (2) propose an engineering solution for redesigning hemiarthroplasties to reduce friction and wear. If successful, these studies can lead to a significant improvement in hemiarthroplasty procedures.