In previous studies, we have reported that the BMP-2-derived peptide KIPKASSVPTELSAISTLYL, corresponding to BMP-2 residues 73-92, binds to a BMP-2-specific receptor, and elevates both alkaline phosphatase activity and osteocalcin mRNA in the murine mesenchymal cell line, C3H10T1/2. This 73-92 peptide conjugated to a covalently crosslinked alginate gel induced ectopic bone formation in rat calf muscle, and activated osteoblasts to promote the repair of rat tibial bone defects. Here, we report repair of 20-mm long rabbit radial bone defects using the 73-92 peptide combined with a porous alpha-tricalcium phosphate (TCP) scaffold. In vitro, the 73-92 peptide was released from the porous alpha-TCP scaffold over more than one week. In vivo, radiomorphometric analysis showed that the 73-92 peptide combined with the porous alpha-TCP scaffold promoted calcification in the implanted area in a dose-dependent manner, and that 5 mg of the 73-92 peptide induced connection of 20-mm long defects, defects of critical size, 12 weeks after implantation. Histological examination revealed newly formed bone and a marrow cavity in the implanted area. The area of bone denser than 690 mg/cm(3) induced by the 73-92 peptide was nearly equal to that of the contralateral radius.
Wear performance and mechanical properties of cross-linking polyethylene (XLPE) tibial inserts were investigated using a knee simulator, scanning electron microscopy (SEM), and a small punch test (SPT). Ultrahigh molecular weight PE made from GUR1050 resin was irradiated at doses ranging from 0 to 200 kGy and then machined into tibial inserts followed by annealing. The knee simulator was run for up to four million cycles. As the radiation dose increased from 0 to 100 kGy, the wear rate decreased dramatically, yielding 95% wear reduction at 100 kGy. The microwear features observed by SEM supported the dose-dependent wear reduction. The SPT for XLPE after the simulation test showed that, as the radiation dose increased from 0 to 200 kGy, the ultimate displacement decreased dose-dependently, while the ultimate load increased from 0 to 75 kGy and decreased from 75 to 200 kGy. The resulting toughness of the PE increased to its maximum at a dose of 50 kGy and then decreased with higher doses up to 200 kGy. PE cross-linked with radiation doses from 25 to 75 kGy had greater toughness than virgin, nonirradiated PE. However, PE irradiated with 100 kGy or more had lower toughness than virgin PE. These data suggest that a certain amount of irradiation enhances both wear performance and toughness of PE tibial inserts. Although a certain amount of cross-linking would be effective for clinical application of PE tibial inserts, an optimal radiation dose should be much smaller than that used in current XLPE in total hip arthroplasty.
The purpose of this study was to evaluate the mechanical and chemical characteristics of gamma-irradiated, cross-linked polyethylene after long-term service in vivo. Two gamma-irradiated ultra high molecular weight polyethylene (RCH 1000, molecular weight: 10(6)) total hip replacement sockets were retrieved at 15 and 16 years after implantation. Mechanical and chemical characteristics of the sockets were evaluated in comparison with nonirradiated sockets. Significant surface oxidation occurred in the nonirradiated sockets; up to 75% of that seen in the irradiated ones. The mechanical properties of the irradiated sockets were not subject to increased deterioration in the presence of high free radical content. The cross-link was stable and was retained for a long period both in vivo and in ambient air. These data indicate that gamma-irradiated polyethylene was not subject to increased oxidative degradation during long-term service in vivo and confirmed the usefulness of this material as an articulating surface in total hip replacement.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.