Highly lubricated polymer interfaces for advanced artificial hip joints through biomimetic design

Abstract

For long-lasting artificial hip joint implants, it is necessary to reduce the wear of the acetabular liner composed of ultra-high-molecular-weight polyethylene (UHMWPE) and to eliminate periprosthetic osteolysis. An articular cartilage-mimicking technology has been developed for nanoscale surface modification by grafting poly(2-methacryloyloxyethyl phosphorylcholine) (MPC) onto a highly cross-linked UHMWPE (X-UHMWPE) using photoinduced polymerization. The thickness of the poly(MPC) graft layer is 100-200 nm. This treatment increases the surface hydrophilicity. Other hydrophilic polymers grafted onto the X-UHMWPE are not suitable for long-term functioning under biological conditions. Studies of the tribological and biological effects with poly(MPC) grafted onto the X-UHMWPE substrate revealed that this grafting decreases the production of wear particles and bone resorption responses. The poly(MPC)-grafted X-UHMWPE has been introduced onto an artificial hip joint as a liner for lubrication. This artificial hip joint has been used clinically since 2011 and has been implanted in more than 20 000 patients. This technology has also been applied to the surface modification of PMPC on poly(ether ether ketone) (PEEK), using self-initiated photoinduced grafting, for the development of a new type of artificial joint. This articular cartilage-mimicking technology, which is applied to obtain highly lubricating surfaces, is therefore suitable for preparing artificial hip joint substrates.