Construction and Friction Behavior of High Strength and Low Friction Lipid Lubricated Hydrogel Materials

Articular cartilage is an important tissue for the support, cushioning, and lubrication of human joints. Articular cartilage will be damaged and degenerated with age, congenital diseases, trauma, and other factors, and eventually lead to the occurrence of osteoarthritis, which is currently one of the world's leading disabling diseases. However, there are almost no blood vessels and nerve tissue around the articular cartilage, which is difficult to heal after injury. Clinically, artificial joint replacement is one of the most effective methods to treat joint injury. Traditional artificial joint materials are mainly metal, ceramic, and polymer materials, and the contact modes are mainly hard-hard contact and hard-soft contact, which are easy to wear and cause foreign body reactions and eventually lead to loose failure after implantation. Inspired by the effective mitigation of impact and wear of natural joint surface cartilage, the primary way to solve the problems of wear and loosening of artificial joint materials is to construct high-performance cartilage replacement materials. Hydrogels are similar to biological soft tissues with both solid-liquid phase properties, and have the characteristics of natural cartilage microstructure similarity, high water content, excellent biocompatibility, stable physical and chemical properties, etc., and have been developed as the best alternative materials for articular cartilage. However, the lubrication and mechanical properties of traditional hydrogels are poor, which limits their application in the field of artificial cartilage replacement materials. In this paper, based on the non-fluid and lipid lubrication characteristics of articular cartilage, 1,2-Dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes were introduced into PVA/PAA hydrogels, and liposome composite hydrogels with excellent mechanical strength and lubrication properties were constructed by freezing-thawing and annealing methods. The findings suggested that liposome composite hydrogel had excellent mechanical strength (tensile strength was 10.4±1.2 MPa, tensile modulus was 4.1±0.8 MPa, compressive strength was 9.5±1 MPa, compressive modulus was 8.2±0.9 MPa), good fatigue resistance (the maximum stress could retain 93% of the first cyclic stress under 100 cycles of compression). In addition, the presence of lipid vesicles on the surface of the liposome composite hydrogel significantly reduced the friction coefficient of the hydrogel (0.049), and the friction reduction was observed under a wide range of sliding velocities and normal loads. The improvement of lubrication performance was mainly because the lipids in the hydrogel were exposed to the gel surface under the action of load. With the extension of time, the grease would spread to the entire hydrogel contact area, forming a lipid boundary layer and reducing the friction through the hydration lubrication mechanism. Therefore, this study opened up a new way to construct high-strength and low-friction cartilage imitation materials, providing potential applications for cartilage replacement and artificial joints.