The longevity of metal-on-polyethylene (MoP) prosthetic hip joint bearings, in which a polished CoCrMo femoral head articulates with a polyethylene liner, may be limited by mechanical instability or inflammation resulting from osteolysis caused by polyethylene wear debris. This study uses laser surface texturing to manufacture a pattern of shallow spherical microtexture features on a polished CoCrMo surface. Gravimetric wear measurements of a highly-crosslinked polyethylene pin articulating with a CoCrMo disc under multi-directional shear demonstrate that polyethylene wear is reduced by more 50% when articulating with a microtextured as opposed to a polished CoCrMo disc. Electrochemical measurements also show that laser texturing does not negatively affect the corrosion potential of CoCrMo.
A novel hybrid coating of biomimetic apatite(BAp) and osteocalcin (OC) was prepared by incubating BAp-coated Ti6A14V coupons in an osteocalcin-containing medium. A significant amount (up to 1.0 wt %) of OC was adsorbed by the BAp coating within 3 h of incubation as demonstrated by high-performance liquid chromatography. Characterizations of the hybrid coating with environmental scanning microscopy and X-ray diffraction indicated that protein adsorption does not alter the microstructure of the coating. The presence of OC in the hybrid coating was visualized with fluorescence microscopy using an immuno-labeling procedure. The affinity of OC to the BAp coating was examined using a 20-h elution test in phosphate-buffered saline and only a minimal amount (<10%) of the loaded OC was eluted out. When the coating was fully dissolved in hydrochloric acid solution after elution, about 78% of the loaded OC could be recovered. Enzyme-linked immunosorbent assay and peptide sodium dodecylsulfate-polyacrylamide gel electrophoresis confirmed the integrity and activity of OC molecules throughout the tests. The preliminary cell culture tests showed a significant effect of OC on the attachment and proliferation of osteoblasts. The quick loading profile and high affinity of OC to the BAp coating make it an ideal candidate for the hybrid coating preparation in clinical environment.
Hydroxyapatite (HA) coating applied on metallic orthopedic joint implants can improve bone apposition, presumably through selective protein adsorption from blood plasma. However, the detailed interaction mechanism of HA coating with serum proteins remains to be largely elucidated. Protein adsorption behavior of a biomimetic apatite (BAp) coating in bovine calf serum and alpha calf fraction was investigated in this study. Plasma sprayed HA (PSHA) coating was tested in alpha calf fraction. The microstructure and composition of the coatings before and after serum incubation were characterized and the proteins adsorbed during the incubation were extracted from the coatings and analyzed. Microstructural transformation of the BAp coating accompanied by selective serum protein adsorption was observed after incubation in both media. The total protein amount adsorbed by the BAp coating in alpha calf faction was about three times that of the PSHA coating. To test the potential use of BAp coating as a carrier of therapeutic agents, interaction between the BAp coating and transforming growth factor (TGF)-β1 was studied. The growth factor was successfully loaded onto the coating in a sodium acetate buffer. Because of its high affinity to the coating, TGF-β1 could not be easily eluted in a bovine serum albumin containing solution but could be recovered after coating dissolution in acid. The strong protein adsorption property of the BAp coating was found to be due mainly to its unique nanoporous structure. The BAp coating can serve as an ideal carrier of therapeutic agents for aiding in the healing of bone and soft tissues.
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