Papers by Keyword: Bone Growth

Abstract: The Success of Hydroxyapatite-Coated Acetabular Components Has Not Been Consistent. Plasma-Sprayed Hydroxyapatite Coatings Work Well on Nonporous Substrates but Do Not Coat the Inner Surfaces of Open-Porous Substrates. Solution Deposition Can Generate Consistent Bioceramic Coats on Porous Surfaces that More Closely Mimic the Trabecular Pattern and Biochemistry at the Bone Interface. we Compared Bone Response to the Following Implants: Porous-Coated Ti6al4v Cylinders with 1 of 3 Treatments: Plasma Sprayed with Hydroxyapatite (HA), Coated with a Solution-Deposited Biomimetic Apatite Coating (BA), and Untreated (Control). Bilateral Femurs in 36 Rabbits Were Implanted with One of the above Implants. Bone Ingrowth for HA and BA Surfaces Was Significantly Higher than that for Control Surfaces. No Fragmentation or Debris Production Was Evident in the Apatite Coat of the BA Group. A Biomimetic Coat of Solution-Deposited Apatite May Be Resistant to Coating Delamination and Particle Generation.

Abstract: A microbeam X-ray diffractometer is a powerful tool to analyze oriented biological apatite (BAp) crystallites in bones since BAp orientation is one of the dominant controlling factors for bone mechanical function. The formation of BAp orientation seems to be partly affected by the bone formation process, including membranous or intracartilaginous ossification, the direction and the rate of bone growth, the mineral apposition rate, etc. However, the detailed process and the mechanisms of the organization of BAp orientation during the bone formation process are still not understood. In this study, we focused on a calvarial bone as a flat bone to establish a procedure to analyze BAp orientation in calvarial bone and examined the variation in BAp orientation with age and position in growing rats. Microbeam X-ray diffraction analysis was performed on the extracted calvaria of 5- to 10-week-old Wister rats. The transmission optical system was selected to analyze the orientation of the BAp c-axis along the bone surface. An incident molybdenum (Mo)-K X-ray, which was collimated into a 300-m diameter, was vertically radiated on the calvaria surface, and the diffraction pattern was registered on an imaging plate. Diffraction peak intensities from the (002) and (310) planes of the hexagonal BAp were detected, and then an intensity ratio of (002)/(310) was calculated to evaluate the degree of BAp orientation. BAp orientation in a calvarial bone was successfully analyzed, and the two-dimensional distribution of the BAp c-axis along the calvarial bone surface was identified. A parietal bone, which is a part of the calvarial bone, showed a unique two-dimensional distribution of the BAp c-axis. The distribution remarkably changed depending on the position on a parietal bone and age. The anisotropy in the preferred BAp orientation was very significant at a region that showed high growth rate. Even though the bone formation process seems to affect BAp orientation in the parietal bone, further investigation is needed to understand the mechanism for the development of BAp texture, which is closely related to bone mechanical function.

Abstract: Typical plasma-sprayed hydroxyapatite coatings work well on non-porous substrates but do not coat the inner surfaces of open-porous substrates. Solution deposition can produce consistent bioceramic coats of precise thickness on porous surfaces. The resultant “biomimetic” surface more closely mimics the trabecular pattern and biochemistry at the bone interface. This report compares bone response to porous surfaces with biomimetic hydroxyapatite coatings. Implants were manufactured as Ti6Al4V cylinders (5-mm diameter, 41-mm long) coated with c.p-Ti PorocoatÒ porous layer with a thickness of 750 (± 250 µm). Implants were divided into three groups based on surface treatments. The porous surfaces of control group implants did not receive any treatment. The porous surfaces of HA group implants were plasma sprayed with hydroxyapatite. The porous surfaces of BAp group implants were coated with a biomimetic apatite (BAp) coating using a lowtemperature solution-based process that mimics bone mineralization. BAp coating is pure apatite coating of uniform structure and composition, with a thickness of approximately 15 µm on the outer beads. Because of the reduced thickness, the BAp coating does not block the pores or alter the porous structure. Bilateral femurs in thirty-six rabbits were implanted with one of the above groups. Twelve rabbits each were euthanized at 2, 4, and 12 weeks. Osseointegration was measured by automated computerized histomorphometry of scanning electron microscopy images of sections taken through the implant. Bone ingrowth on the Control surface was 45 % at 2 weeks and 47% at 12 weeks. Bone ingrowth on the PS surface increased from 51% at 2 weeks to 67% at 12 weeks. Bone ingrowth on the BAp surface increased from 45 % at 2 weeks to 71% at 12 weeks. At both time points mean bone ingrowth on PS and BAp coated implants was significantly higher than the control uncoated implants (p < 0.01). By 12 weeks the PS hydroxyapatite coat began showing evidence of fragmentation and debris production on SEM. This was not evident in the BAp coat. This study supports the hypothesis that apatite coating benefits osseointegration. A biomimetic coat of solution deposited apatite may not show the disadvantages of coating delamination and particle generation. Biomimetic apatite coatings may be attractive alternatives for noncemented total hip arthroplasty.