Converting “sliding” to “rolling” design for high-performance lubricating hydrogel

Despite the excellent lubricity of conventional hydrogel materials due to their wet-soft properties, they produce severe mechanical elastic deformation at higher interfacial contact stresses. Balancing the load-bearing capacity and lubricating properties of hydrogel material is the difficulty of the current research work for articular cartilage substitutes. Great progress has been made in developing bionic joint materials with high load-bearing and low-friction hydrogels based on gradient designs. However, most bionic materials are based on sliding friction greatly limiting the improvement of lubrication performance. Herein, we designed and prepared a new hydrogel material with high load-bearing capacity and stable lubrication performance, breaking through the traditional friction method and turning to "sliding" for "rolling". The network on the hydrogel surface was dissociated by UV irradiation and the pores on the surface were filled with SiO2 nanoparticles. The dense network structure of the underlying layer endows the hydrogel material with good load-bearing properties, while the high degree of hydration of the surface layer and the rolling friction effect of SiO2 nanoparticles greatly enhance the lubrication property. With the synergistic effect of these designs, the multi-layered hydrogel with nanoparticles on the surface achieved an ultra-low average coefficient of friction (COF) of ∼0.00809 at a high load of 50 N during 30,000 cycles. This idea of hydrogel material design provides a new strategy for the replacement of biomimetic articular cartilage materials.