Abstract：
Intra-articular injections of hyaluronic acid (HA) are the cornerstone of osteoarthritis (OA) treatments. However, the mechanism of action and efficacy of HA viscosupplementation are debated. As such, there has been recent interest in developing synthetic viscosupplements. Recently, a synthetic 4 wt% polyacrylamide (pAAm) hydrogel was shown to effectively lubricate and bind to the surface of cartilage in vitro. However, its ability to localize to cartilage and alter the tribological properties of the tissue in a live articulating large animal joint is not known. The goal of this study was to quantify the distribution and extent of localization of pAAm in the equine metacarpophalangeal or metatarsophalangeal joint (fetlock joint), and determine whether preferential localization of pAAm influences the tribological properties of the tissue. An established planar fluorescence imaging technique was used to visualize and quantify the distribution of fluorescently labeled pAAm within the joint. While the pAAm hydrogel was present on all surfaces, it was not uniformly distributed, with more material present near the site of the injection. The lubricating ability of the cartilage in the joint was then assessed using a custom tribometer across two orders of magnitude of sliding speed in healthy synovial fluid. Cartilage regions with a greater coverage of pAAm, that is, higher fluorescent intensities, exhibited friction coefficients nearly 2-fold lower than regions with lesser pAAm (Rrm = -0.59, p < 0.001). Collectively, the findings from this study indicate that intra-articular viscosupplement injections are not evenly distributed inside a joint, and the tribological outcomes of these materials is strongly determined by the ability of the material to localize to the articulating surfaces in the joint.
摘要：
关节内注射透明质酸(HA)是骨关节炎(OA)治疗的基石。然而,HA黏贴补充剂的作用机制和功效存在争议。因此，最近有兴趣开发合成粘胶补充剂。最近,合成的4重量%聚丙烯酰胺(pAAm)水凝胶被证明在体外有效地润滑和结合到软骨的表面。然而,它在活的大型动物关节中定位软骨并改变组织的摩擦学特性的能力尚不清楚。这项研究的目的是量化pAAm在马掌指骨或meta趾关节（fetlock关节）中的分布和定位程度，并确定pAAm的优先定位是否会影响组织的摩擦学特性。已建立的平面荧光成像技术用于可视化和量化关节内荧光标记的pAAm的分布。虽然pAAm水凝胶存在于所有表面上，它不是均匀分布的，在注射部位附近存在更多的物质。然后使用定制的摩擦计在健康滑液中两个数量级的滑动速度上评估关节中软骨的润滑能力。软骨区域具有更大的pAAm覆盖率，也就是说,更高的荧光强度，显示摩擦系数比pAAm较小的区域低近2倍（Rrm=-0.59，p<0.001）。总的来说，这项研究的结果表明，关节内注射粘胶补充剂不是均匀地分布在关节内，并且这些材料的摩擦学结果强烈地由材料的局部化到关节中的关节表面的能力决定。
