Molecular Dynamics Simulation of the Hydration Lubrication Mechanism of HEA-MPC-Based Joint Lubricants

Osteoarthritis and lubrication failure in artificial joints remain major clinical challenges. In this study, molecular dynamics (MD) simulations were performed to investigate the hydration lubrication behavior of a bottlebrush-inspired biomimetic lubricant system consisting of MPC side chains grafted onto a pHEA backbone at the alumina (Al2O3) interface. The effects of the backbone length, grafting ratio, and concentration on lubrication performance were systematically analyzed. The results show that appropriate structural parameters are critical for achieving efficient lubrication. When the backbone degree of polymerization (DP) was 8 and the MPC grafting ratio was 50%, the system showed favorable load-bearing and frictional performance, with a minimum coefficient of friction (COF) of about 0.053. In contrast, shorter backbones showed limited interfacial coverage and water retention, whereas longer backbones exhibited more pronounced overall motion, conformational fluctuations, and persistent interchain proximity. In addition, increasing the polymer concentration generally reduced interfacial friction. These results indicate that the hydration lubrication performance of HEA-MPC is not governed by hydration ability alone but by the combined effects of local hydration, interfacial water dynamics, and polymer-chain conformational response. This study provides molecular-scale guidance for the structural design and performance optimization of MPC-based biomimetic joint lubricants.