PubMed · 7186982
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E Masuhara, Y Kadoma. 1982. [Biomaterials].. https://pubmed.ncbi.nlm.nih.gov/7186982/
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The purpose of this pilot study was to evaluate surface-induced mineralization (SIM) as a potential technique to apply ceramic coatings to metal orthopaedic implants. Cylindrical titanium porous-coated implants were either coated by SIM or plasma-spray (PLS) techniques with calcium phosphate, or left uncoated (CTL). The implants were bilaterally implanted into the intramedullary canal of the proximal femur of 24 adult New Zealand white rabbits segregated into the following groups: PLS/CTL, SIM/CTL, and SIM/PLS. After 6 weeks in vivo, biomechanical and histologic evaluations were completed. Biomechanically, SIM had consistently greater mechanical interlock than PLS implants. However, CTL implants had greater mechanical interlock than both PLS and SIM. The small sample size prevented statistical evaluation and definitive biomechanical conclusions. Histologically, SIM and PLS had significantly greater ingrowth than CTL implants (p < 0.05). The SIM coating technique produced similar ingrowth characteristics as standard PLS coatings, yet may prevent osteolysis by providing a stronger, more reliable, covalent bond between the ceramic and metal.
Hip replacement implants fabricated using the ASTM F-75 alloy sometimes fail in a sudden catastrophic way. In general, fractures start at microstructural defects subjected to stress-corrosion under chemical attack by body fluids. In this paper the results of a study on the effect of casting parameters on the microstructure of ASTM F-75 are presented. The preheating mold temperature and the liquid temperature were varied between 900 and 1000 degrees C, and 1410 and 1470 degrees C, respectively. Optimum static strength and ductility were obtained when shrinkage microporosity and the volume fraction of M23C6 "eutectic" carbides precipitated at grain boundaries were minimized by increasing the preheating mold temperature to 1000 degrees C and by using intermediate pouring temperatures of 1455 degrees C. Under these casting conditions, however, the solidification rates are low, leading to large grain sizes, which, in turn, reduce the strength of the material under dynamic loading conditions. The volume fraction of the M23C6 "blocky" carbides appears to be independent of the casting conditions; however, their size and spatial distributions determine the strength of the as-cast alloys.
This study investigated the vascular effect of ferromagnetic obstruction of cochlear blood vessels in the guinea pig using dual-channel laser Doppler flowmetry. To improve this technique, we tested new types of magnets and iron spheres. In so doing, the cochlear temperature was lowered selectively and general hypothermia was avoided. The success of vascular impairment in the inner ear was found to depend on the experimental conditions used. Given normothermic conditions (38 degrees C body temperature), a clear reduction in cochlear blood flow (CBF) was found in only about 30% of the animals tested when an aluminium-nickel-cobalt alloy magnet and carbonyl iron spheres were used, while this ratio increased to about 80% under general hypothermia (33 degrees C). Using a stronger neodymium-iron-boron magnet and smaller-sized iron spheres, we found the success of vascular obstruction to be approximately 70% under normothermia and 100% with local hypothermia (to 33 degrees C) of the cochlea. Although the extent of vascular impairment revealed a considerable interindividual variation, the present findings demonstrate that ferromagnetic intervention in CBF with dual-channel laser Doppler flowmetry can be used to investigate the effect of quantified cochlear ischemia on inner ear physiology in the guinea pig model and test various therapeutic strategies.