Creation of Cartilage-Like Hydrogels with High Toughness and Low Friction

我们的研究表明，水凝胶具有较低的表面滑动摩擦。特别是聚电解质刷在水凝胶表面的存在，可以有效地将表面滑动摩擦系数降低到10^<-4>。凝胶的低摩擦特性使其在关节软骨、半月软骨等需要低摩擦的领域得到广泛应用。然而，传统的水凝胶，特别是聚电解质凝胶，在机械上太弱，不能实际用于任何应力或应变承载应用。水凝胶通常在不高于0.1 MPa的压应力下分解。然而，关节软骨，尤其是膝盖和臀部的关节软骨，每天承受几十到几十兆帕的压力，在很大的滑动速度范围内，其摩擦系数低至10^<-3>。这种机械缺陷不仅阻碍了水凝胶作为工业和生物医用材料的广泛应用，也阻碍了对水凝胶在高于MPa压力下可能发生脱溶的摩擦行为的基础研究。我们发现了一种通过诱导各种亲水性聚合物组合的双网络（DN）结构来获得含有60- 90%水的非常强的水凝胶的一般方法。DN水凝胶的断裂强度可高达几至几十兆帕斯卡（即100 kg/cm^2）。在此基础上，我们进一步开发了一种新型材料，即含有弱交联3^<rd>网络或非交联3^<rd>线性链的高强度DN凝胶，其断裂强度高达9 MPa，摩擦系数μ低至10^<-4>。这种具有高强度和极低表面摩擦的凝胶不仅在工业上有广泛的应用，而且在生物医学领域也有广泛的应用，例如作为关节软骨或其他生物组织的替代品。

Our study shows that hydrogel shows a low surface sliding friction. Especially the presence of polyelectrolyte brushes on a hydrogel surface can effectively reduce the surface sliding frictional coefficient to a value as low as 10^<-4>.The low friction of gel should have enabled the gel to find a wide application in many fields where low friction is required, such as articular cartilage, semi lunar cartilage. However, conventional hydrogels, especially polyelectrolyte gels, are mechanically too weak to be practically used in any stress or strain bearing applications. A hydrogel usually breaks down under a compressive stress not higher than 0.1 MPa. However, an articular cartilage, especially those of kneels and hips, sustains a daily compression of several to decades MPa, exhibits a friction coefficient as low as 10^<-3> over a wide range of sliding velocity. The mechanical weakness has hindered not only the extensive application of hydrogels as an industrial and biomedical materials, but also the fundamental researches on the friction behavior of gel under a pressure higher than MPa where desolvation might occur.We discovered a general method to obtain very strong hydrogels containing 60-90 % water by inducing a double-network (DN) structure for various combinations of hydrophilic polymers. The DN hydrogel can exhibit fracture strength as high as a few to several tens of megapascals, that is, 100 kg/cm^2).Based on these researches, we further developed a novel material, a high strength DN gel containing either a weakly cross-linked 3^<rd> network or non-cross-linked 3^<rd> linear chains which shows a fracture strength as high as 9 MPa and frictional coefficient μ as low as 10^<-4>.The gel with both a high strength and an extremely low surface friction would find wide applications not only in industry but also in biomedical field, for example, as substitutes of articular cartilage or other bio-tissues.