| Lubricin is the primary boundary lubricant of articular cartilage.Its boundary lubricating ability arises from two key structural features:a dense mucin-like domain consisting of hydrophilic oligosaccharides and a terminal binding domain that anchors the molecule to the surface of the joint.When bound to cartilage,lubricin molecules attract and trap water near the surface of cartilage,reducing friction and facilitating sliding.In this study,a brush-like copolymer of poly(hydroxyethyl acrylate)grafted with poly(methacryloyloxyethyl)choline(p HEA-g-PMPC)was designed based on the structure of lubricin.The PMPC moiety was designed to attract water molecules and anchor the polymer to cartilage surfaces,thereby achieving the purpose of simulating the lubricating function of lubricin.In this study,the target copolymer was synthesized by reversible addition-fracture chain transfer(RAFT)and atom transfer radical polymerization(ATRP).The structure and elemental analysis of the product were performed by GPC,~1H NMR and XPS.The results show that the contour length of backbone was 263～310nm,and the molecular weight is positively correlated with the monomer/chain transfer agent ratio;when the monomer/chain transfer agent ratio is too large,the polymer molecular weight distribution is uneven.Both the esterification reaction of the main chain and the ATRP growth of the MPC monomer were in line with the expected results.Biomimetic lubricant has excellent biocompatibility and some clinical significance.In this study,spin-coating and immersion methods were used to combine bionic lubricant with silicon wafer substrate,and a"worm-like"structure of lubricant molecules was observed on the surface of the silicon wafer.The morphology of the surface boundary layer of the silicon wafers produced by the two methods is different.In the spin coating method,due to the entanglement of the bionic lubricant molecules,aggregates are formed on the surface of the silicon wafer,with a height of 28.2 nm and a diameter of 1 to 2.5μm.After the immersion sample preparation,it was found that mimLUB molecules self-assembled on the surface of the silicon wafer to form a network structure.The increase in solution concentration and molecular length made the coverage area of mimLUB more continuous and the network structure more complete.AFM was used to perform friction tests on the above two types of boundary layers.The results show that the friction and normal load obey the Amontons law.The addition of mimLUB reduced the surface friction coefficient of the silicon wafer from 0.11 to 0.02.Concentration and molecular contour size determine the coverage and continuity of the boundary layer,while the friction coefficient is affected by the synergistic effect of the two.At the same time,the chemical interaction between the atom probe and the boundary layer also affects the friction coefficient.The friction coefficient of the network boundary layer(0.024～0.049)is lower than that of the planar boundary layer(0.021～0.10),which provides ideas for reducing friction from the construction of atomic-scale corrugated surfaces.Macro friction study on the surface of the silicon wafer also revealed that mimLUB lubricated the surface of the silicon wafer.The static self-assembled film has better lubricity than the dynamic self-assembled boundary film,and the low-friction surface may have a large amount of wear.The dip coating was preferred as the boundary layer preparation method.When mimLUB bond to cartilage,it improved the hydrophilicity of the surface.The increase of normal load and sliding speed increased the friction coefficient of cartilage surface.Both the increase in molecular size and the concentration of solution will lead to a decrease in the friction coefficient of cartilage surface. |
