Design, Preparation and Tribological Performance Study of Bionic Layered Polyvinyl Alcohol Hydrogel Lubricating Materials

PVA hydrogel is a promising candidate for cartilage replacement materials due to its favorable mechanical properties and biocompatibility. However, its structure poses challenges in meeting the demands of complex conditions encountered in practical applications. The mechanical and lubricating performances of PVA hydrogels fall short compared to human tissues, lacking the intricate architecture and functionality inherent in natural tissues. This deficiency results in suboptimal deformation, shock absorption and lubrication capabilities for cartilage substitutes. Consequently, researchers have shifted the focus towards simulating the natural lubricating tissues within the human body to address functional issues related to cartilage replacement materials and friction and wear concerns. Natural articular cartilage with a composite structure is important for supporting, cushioning, and lubricating human joints. The rapid hydration function of brush-like biomacromolecules, in conjunction with the synovial fluid present in the joint cavity, collaborates to sustain a low friction coefficient and minimize friction loss on the cartilage surface. Together with the superior mechanical properties of the cartilage itself, they establish a joint lubrication system characterized by high load-bearing capacity, low friction coefficient, and extended longevity. Inspired by the composite structure of natural articular cartilage and its lubrication mechanism, this paper constructed the interpenetration of molecular chains by casting a composite lubricating layer with CMCS molecules as lubricants on the bearing layer. At the same time, the structure was strengthened and toughed by solvent exchange, and a biomimetic layered PVA hydrogel with excellent mechanical and lubricating properties was prepared. The lubricating layer consisted of a low-concentration PVA hydrogel with CMCS aimed at reducing the friction coefficient while the load-bearing layer comprised highly concentrated PVA hydrogel with high mechanical performance. In addition, by changing the solvent exchange time and the mass fractions of CMCS molecules in the preparation process, the mechanical properties was optimized and the lubricating mechanism was investigated. During the solvent exchange process, the crosslinking network underwent shrinkage and the intercrystal spacing diminishes over time, leading to a denser cross-linked structure that enhanced surface modulus. An increase in CMCS content resulted in a progressive reduction of intercrystal spacing, indicating tighter crystal packing and further augmenting surface modulus. By optimizing both the solvent exchange time and the mass fraction of CMCS, an ideal contact surface with optimal surface modulus could be achieved, facilitating superior hydration lubrication effects without excessive deformation while minimizing the total friction coefficient. In comparison to PVA hydrogel with a single network structure, the biomimetic layered PVA hydrogel exhibited a lower friction coefficient, which remained stable (friction coefficient<0.05) over an extended duration of testing (36 000 cycles). These research findings offerred novel insights for the design of PVA-based lubrication materials.