Key Engineering Materials Vols. 309-311

Abstract: Human osteoclasts derived from CD14+ precursors were cultured on discs of stoichiometric hydroxyapatite (HA) and carbonate substituted hydroxyapatite (CHA) of varying carbonate contents. Resorption of the ceramic increased with increasing carbonate content up to 2.35 wt. %. Development of osteoclasts is qualitatively different on ceramics compared to dentine, occurring in discrete, confluent subpopulations, which suggests local cell signalling may be important in the process. Resorption appears to drive further development of osteoclasts. Controlling carbonate content may be one way of controlling the rate of resorption of synthetic HA ceramics.

Abstract: It has been shown that fluoride ions enhance OCP hydrolysis into Ca-deficient apatite and that fluoridation in hydroxyapatite (HA) affects osteoblast activity. The present study was designed to investigate whether fluoridated Ca-deficient apatite (F-HA) formed via OCP enhances bone regeneration. F-HA was obtained through hydrolysis of the OCP in a solution containing 2 ppm fluoride at 37 °C and pH 7.4. A standardized critical-sized defect was made in the rat calvarium, and granules of F-HA were implanted into the defect. Five rats from each group were fixed through four to twelve weeks after implantation. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) confirmed that F-HA corresponded well to apatite structure. In week four, new bone matrix was formed around F-HA. In week twelve of F-HA group, newly formed bone matrix was more abundant, whereas the implanted F-HA was unresorbed and still remained. A statistical analysis in week twelve showed that the newly formed bone in the defect with F-HA was higher than that with untreated group. The fact that new bone was directly formed on F-HA implant suggests F-HA formed via OCP could be used as a bone substitute material.

Abstract: Abstract. Fluoride (F-)-substituted type-B carbonate-containing hydroxyapatites (CHAPs) were prepared as bone substitutes with a F-releasing ability. The F- contents in the F-substituted CHAPs were 16-22 times larger than that in normal adult human bones. The carbonate contents in the F-substituted CHAPs corresponded to that in human bones. The F-substituted CHAPs released F- in an acetic acid – sodium acetate buffer at pH 4.9; within only 3 h, the F- concentration in the buffer increased to more than 63.9 µg L-1, which was 1.5~8.9 times higher than that in a body fluid of normal adult humans. Although the F- concentration rapidly decreased probably due to the precipitation of a certain phase containing F-, the F-substituted CHAPs exhibited the ability to increase the F- concentration in a body fluid by bone resorption. Therefore, it is expected that the F-substituted CHAPs will be feasible as a F-releasing material for promoting bone formation.

Abstract: An electrovector effect of the polarized hydroxyapatite (HA) on crystal growth in a simulated body fluid was clarified to discuss the role of the polarization energy in the effect. The polarization of the HA carried out in high dc field at 300-600°C was confirmed by thermally stimulated depolarization current measurements. The dependence of the thickness of the crystal grown layer on the induced charge was remarkably indicated in the modification of the growth rates. The growth rate under an optimum polarization condition was estimated to be almost 3 times of that by the biomimetic method. At the early stage of the crystal growth, the grown crystals were spherical and their sizes were dependent on the field strength and time for polarization. The polarization is therefore considered to effect the nucleation as well as the crystal growth.

Abstract: We investigated the immediate response in the vicinity of the implanted polarized hydroxyapatite (HA). One of the important immediate events was found to be the fibrin adsorption on the implanted HA. The activation of the fibrin adsorption on the polarized HA was confirmed by the observation by SEM observation and immunohistochemical detection. After the implantation, the coagulation cascade induced the wound healing. The adsorbed fibrin was formed network structure and worked for later cell responses as the scaffolds. The acceleration of fibrin scaffolds formation in the vicinity of the implanted polarized HA contributed to the stimulation and activation of platelets and osseous cells. The platelets were activated from the results of the signal transduction and cytoskeleton changes and released growth factors. The growth factors released from platelets led to bone regeneration by stimulating migration and proliferation of the osseous cells. In the vicinity of the implanted HA samples, the coagulation cascade reaction to repair wound healing led to the new bone formation by mediation of the platelets and osseous cells. The mechanism of osteoconduction at earlier stage had close relationships to the electrostatic properties of the implant.

Abstract: Surface charges of biomaterials are recognized as one of the important factors to determine cell and tissue responses. The HA ceramics polarized at various temperatures were estimated by implantation tests. The HA ceramic samples with the polarization treatment at temperature ranging from 250 to 500°C were implanted into bones. These phenomena were observed regard less the polarization temperature. It was obvious that the negatively chargedsurfaces acquired the excellent osteoconductivity at the polarization temperature from 250 to 500°C. The similarity of the tissue reactions implied that the variation of stored charges was within a tolerance of an effective stimulation and that the enhancement mechanism of the osteoconduction had not a linear sensibility of electrostatic charges.

Abstract: Four rabbits received human derived HA to their left tibias. After 16 weeks bioglass was implanted to their right tibias. After other 16 weeks bone scintigraphies were taken with 99mTc- MDP. Three phase bone scan images showed no evidence of inflammation and superior vascularization rates at implantation sites. In this study, bioglass demonstrated higher uptake of 99mTc-MDP comparing to HA, suggesting a higher vascularization rate and better osseointegration.