Recent progress of hydrogel-based biomimetic articular cartilage in mechanical and lubricated enhancement

Articular cartilage covering a joint surface provides excellent lubrication and a load-bearing interface for the daily activities of the human body, which is characterized by high load-bearing, low friction, and wear resistance. Articular cartilage is damaged and degenerated with age, congenital diseases, trauma, and other factors; however, the vascularization of articular cartilage leads to its weak self-repair ability, which ultimately accelerates the occurrence of osteoarthritis and seriously affects the quality of life of patients. Hydrogels are similar to biological soft tissue and have both solid and liquid properties, which have the characteristics of natural cartilage microstructure similarity, high water content, excellent biocompatibility, stable physical and chemical properties, etc., and have been developed into the best alternative material for articular cartilage. However, the mechanical properties and lubricating properties of traditional hydrogels are insufficient, which makes it difficult to apply artificial articular cartilage. Therefore, the development of mechanical enhancement and biomimetic lubrication technology to improve the mechanical properties and lubrication properties of biomimetic cartilage hydrogel materials has attracted extensive attention. In this work, the research progress of hydrogel-based cartilage replacements is reviewed from the aspects of mechanical enhancement and biomimetic lubrication; the design strategies and mechanisms of mechanical enhancement, such as nanocomposites, multi-network, hydrophobic associations, topological structures, supramolecular polymers, and biomimetic ordered structures, are introduced; the design ideas and lubrication mechanisms of biomimetic lubrication based on interfacial modulation, polymer brushes, lubricant boundary lubrication, and stimulus response are summarized. Furthermore, based on the structural and functional biomimicry of the natural articular cartilage system, the research progress on high-mechanical properties and low-friction biomimetic articular cartilage substitutes is reviewed, and their potential value as articular cartilage substitutes is discussed. Finally, the current problems associated with biomimetic articular cartilage materials, as well as future research focus and development directions, are discussed.