Effect of UV‐irradiation intensity on graft polymerization of 2‐methacryloyloxyethyl phosphorylcholine on orthopedic bearing substrate

Abstract

Photoinduced grafting of 2-methacryloyloxyethyl phosphorylcholine (MPC) onto cross-linked polyethylene (CLPE) was investigated for its ability to reduce the wear of orthopedic bearings. We investigated the effect of UV-irradiation intensity on the extent of poly(MPC) (PMPC) grafting, and found that it increased with increasing intensity up to 7.5 mW/cm(2), and the remained fairly constant. It was found to be extremely important to carefully control the UV intensity, as at higher values, a PMPC gel formed via homopolymerization of the MPC, resulting in the formation of cracks at the interface of the PMPC layer and the CLPE substrate. When the CLPE was exposed to UV-irradiation during the graft polymerization process, some of its physical and mechanical properties were slightly changed due to cross-linking and scission effects in the surface region; however, the results of all of the tests exceed the lower limits of the ASTM standards. Modification of the CLPE surface with the hydrophilic PMPC layer increased lubrication to levels that match articular cartilage. The highly hydrated thin PMPC films mimicked the native cartilage extracellular matrix that covers synovial joint surface, acting as an extremely efficient lubricant, and providing high-wear resistance.

Revolutionary advances in 2‐methacryloyloxyethyl phosphorylcholine polymers as biomaterials

“…MPC polymers have been clearly demonstrated over the years as extremely wettable, and remain hydrated even when exposed to the atmosphere. The substrates modified with MPC polymer have high lubricity, and have low friction coefficients similar to that of natural cartilage . Hence, developing new joints using poly(MPC) at interfaces is an intriguing possibility …”

“…Extremely low‐friction poly(MPC)‐modified surfaces are obtained using established methods of surface‐initiated graft polymerization. However, a new and simple technique of photoinduced MPC polymerization was reported . In this approach, the water‐insoluble photoinitiator benzophenone is deposited onto the substrate from acetone, and is then exposed to ultraviolet light in an aqueous solution of MPC to trigger polymerization.…”

Prevention of bacterial adhesion and biofilm formation on a vitamin E-blended, cross-linked polyethylene surface with a poly(2-methacryloyloxyethyl phosphorylcholine) layer

“…The CLPE, HD-CLPE(VE), and PMPC-grafted HD-CLPE(VE) samples obtained using the range of UV-irradiation intensities were stained using an aqueous solution of 200 ppm (mass) rhodamine 6G (Wako Pure Chemical Industries, Ltd.) because it rapidly associates with the MPC polymer, which is structurally highly similar to lipids [30]. All samples were immersed in the rhodamine 6G solution for 30 s, washed twice with distilled water for 30 s, and dried.…”

“…The BP-coated HD-CLPE(VE) sample was then immersed in the MPC aqueous solution. Photoinduced-radical graft polymerization was carried out on the HD-CLPE(VE) surfaces using ultraviolet (UV) irradiation (UVL-400HA ultra-high pressure mercury lamp; Riko-Kagaku Sangyo Co., Ltd., Funabashi, Japan) with an intensity of 5.0 mW/cm 2 at 60°C for 90 min [29,30]; a filter (model D-35; Toshiba Corp., Tokyo, Japan) was used to permit the passage of only UV light with a wavelength of 350 ± 50 nm. After polymerization, the PMPC-grafted HD-CLPE(VE) sample was removed, washed with pure water and ethanol, and dried at room temperature for 1 h in a vacuum.…”

Effects of extra irradiation on surface and bulk properties of PMPC‐grafted cross‐linked polyethylene

“…MPC was dissolved in degassed water at a concentration of 0.50 M . After soaking the CLPE sample in MPC aqueous solution, photoinduced graft polymerization of MPC was carried out at 60°C for 90 min under UV light irradiation (UVL‐400HA ultra‐high pressure mercury lamp; Riko‐Kagaku Sangyo, Funabashi, Japan) with an intensity of 5.0 mW cm −2 ; a filter (UV‐D35; Toshiba, Tokyo, Japan) was used to restrict the passage of UV light to wavelengths of 350 ± 50 nm. After polymerization, the samples were removed from the reaction solution and washed with pure water and ethanol to remove ungrafted (free)‐polymer and monomer, and then dried under vacuum.…”