Study on the lubrication behavior of tannic acid/ poly (vinyl alcohol) hydrogel enhanced by protein adsorption for articular cartilage applications

Poly (vinyl alcohol) (PVA)-based hydrogels are widely regarded as ideal cartilage replacement materials because of their excellent properties. However, they have drawbacks such as high coefficient of friction (COF) and insufficient wear resistance. As important components of the synovial fluid, proteins are involved in counter-pairs and effect their tribological behavior via denaturation. Tannic acid (TA), which is rich in hydroxyl groups, can bind strongly proteins and change their conformation. In this study, the structure and lubrication performance of TA/PVA hydrogels in phosphate buffer saline (PBS) and bovine serum albumin (BSA) solutions were investigated. The results indicated that TA molecules enhanced the stiffness of the hydrogel by forming hydrogen bonds with PVA, reducing its COF in the PBS solution. In BSA solution, the tribological behavior of the PT hydrogels is altered by the BSA adsorbed at the hydrogel interface owing to the addition of TA. The COF of the PVA hydrogels with a TA content of 0.5 wt% is as low as 0.045, which was approximately 2.67 times lower than that of the PVA hydrogel under the same conditions. The benzene rings and hydroxyl groups in TA were connected to BSA molecules through hydrogen bonding, inducing a conformational change in the BSA from an α-helix structure to β-sheet structure, which further improves the lubricating properties of the hydrogel.