Synthesis and characterization of a novel UHMWPE interpenetrating polymer network.

A novel, biomimetic, interpenetrating polymer network (IPN) between poly-L-lysine (PLL) and ultra high molecular weight polyethylene (UHMWPE) has been synthesized in an attempt to decrease wear in joint prostheses. A biomaterial with a gradient IPN of cationic PLL and UHMWPE has been synthesized, in the surface of bulk UHMWPE, to recruit the poly-anion, hyaluronic acid, from the synovial fluid. It is hypothesized that the hyaluronic acid molecules and their associated hydration layer will improve lubrication between the articulating surfaces, thus lowering both friction and wear. The synthesis involves four steps. Silylation of the PLL-HBr to PLL-SiMe3 utilizing bis(trimethylsiyl)acetamide (BSA). Swelling of the UHMWPE in a solution of PLL-SiMe3/xylenes at 60 degrees C with ultrasonics. Crosslinking of the PLL-SiMe3 within the UHMWPE with 1,8-diisocyanatooctane (a.k.a. OMDI). Finally, de-swelling and drying of the IPN under vacuum at 50 C. Visual observations show an adhered film on the IPN surface. Reflective FTIR spectra contain the characteristic peaks associated with UHMWPE. Two additional peaks, at 3410 and 1690 cm-1, are associated with PLL. SEM shows a morphology dominated by PLL spheres with diameters ranging from < 1 micron up to 3 micron. This shows that the PLL-SiMe3 has been crosslinked by the OMDI and was not rinsed away by either xylenes or sonicated water rinses. High contact angle of the PLL in contact with the UHMWPE demonstrate that the PLL has been de-silylated and returned to its hydrophilic nature. The spheres attached to the surface of the UHMWPE indicate that PLL has infiltrated the UHMWPE physical network and is entangled there. XPS confirms the presence of nitrogen by a 3-5 atomic percent signal in the outer 100 A of the IPN surface.