Preparation and tribological properties of high density polyethylene based hydrogel composite coating

Inspired by the natural joint structure, a hydrogel coating is constructed on the surface of high density polyethylene (HDPE) to improve the wettability and bearing capacity of materials. However, the adhesion between hydrogel and HDPE matrix is poor and easy to fall off, so UV induced dopamine (DA) polymerization is used to form polydopamine (PDA) grafted onto HDPE to obtain HDPE-PDA sample, and then nano hydroxyapatite polyvinyl alcohol (HA-PVA) hydrogel coating is constructed on the surface of HDPE-PDA to obtain HDPE-PDA-HA-PVA sample. Studied the wetting performance, biocompatibility, interface bonding performance and tribological characteristics of the sample. The effect of metal ions on friction pairs was investigated by placing HDPE-PDA-HA-PVA in a diluted lubrication (BSA) solution of calf serum containing Na⁺, Ca²⁺ and Al³⁺, respectively. To sum up: It is found that the static water contact angle of HDPE-PDA is reduced from 94.57° before grafting to 26.87°, the antibacterial performance is increased by 98%, and the adhesion with hydrogel is increased by 84%. In the study of tribological properties, it was found that the friction coefficient of HDPE PDA-HA-PVA under 2 N load water lubrication conditions was as low as 0.012, with only slight wear. When the load increased to 5 N, the average friction coefficient and wear amount decreased by 73% and 46% respectively compared to HDPE. In exploring the effect of lubrication solutions containing metal ions on tribological properties, it was found that under a 3 N load, lubrication solutions containing Ca²⁺ exhibited better lubrication performance. This is because Ca²⁺ can enhance the material's adsorption of lubricating proteins, easily forming a lubrication layer, and exhibiting better lubrication characteristics than other lubrication solutions containing metal ions.