Calcium phosphate coating formed in infusion fluid mixture to enhance fixation strength of titanium screws.

A novel technique was developed to coat a calcium phosphate (CaP) layer on titanium screws with a titanium oxide surface layer, using infusion fluids officially approved for clinical use. A calcium-containing solution, a phosphate-containing solution, and a sodium bicarbonate solution prepared from the infusion fluids were mixed at a Ca/P molar ratio of 2.0. Each screw was immersed in 10 mL of the resulting mixture at 37 degrees C for 2 days. A low-crystalline apatite layer (Ca/P molar ratio = 1.681 +/- 0.038) was formed on the screws. The layer consisted of a few 100 nm diameter particles fixed on the screw surface. In animal experiments, the screws were percutaneously implanted in both proximal tibial metaphyses of rabbits. The insertion torque was not significantly different between the CaP-coated screws (0.132 +/- 0.002 Nm, n = 10) and uncoated screws (0.140 +/- 0.002 Nm, n = 10) (p = 0.5785). After the insertion torque test, the apatite layer remained on the surface of the screws, which means that the apatite layer survived the friction of screw insertion. The extraction torque of the screws in the CaP-coated group (0.239 +/- 0.066 Nm, n = 19) was significantly higher (by 29.9%) than that in the uncoated group (0.184 +/- 0.062 Nm, n = 18) 4 weeks after the operations (p = 0.0132). Histologically, a larger amount of new bone formation was observed around the CaP-coated screws than that around the uncoated screws. Even after the removal of the screw, the CaP layer remained on the screw at the site where soft tissues were attached. The coating technique with the use of the infusion fluids is an effective method of improving bone-screw interface strength.

Formation of a FGF-2 and calcium phosphate composite layer on a hydroxyapatite ceramic for promoting bone formation.

Fibroblast growth factor-2 (FGF-2) was immobilized on a hydroxyapatite (HAP) ceramic in supersaturated calcium phosphate solution prepared using solutions corresponding to clinically approved infusion fluids. To avoid the risk of FGF-2 denaturation, FGF-2 immobilization was carried out at 25 degrees C. FGF-2 was successfully immobilized on HAP ceramic surfaces by deposition with calcium phosphate to form a FGF-2 and calcium phosphate composite layer. A maximum of 2.72 +/- 0.01 microg cm(-2) of FGF-2 was immobilized in the composite layer formed on the HAP ceramic under the optimum condition. A FGF-2-immobilized HAP ceramic is likely to have the ability to release a sufficient amount of FGF-2 to promote bone formation. FGF-2 released from a FGF-2-immobilized HAP ceramic maintained its biological activity, since the proliferation of fibroblastic NIH3T3 was promoted. Therefore, the FGF-2-immobilized HAP ceramic is expected to be a useful material for promoting new bone formation.

Formation of an ascorbate-apatite composite layer on titanium.

An ascorbate-apatite composite layer was successfully formed on NaOH- and heat-treated titanium by coprecipitating L-ascorbic acid phosphate and low-crystalline apatite in a supersaturated calcium phosphate solution at 37 degrees C for 48 h. The supersaturated calcium phosphate solutions used have chemical compositions attainable by mixing infusion fluids officially approved for clinical use. The amount of immobilized L-ascorbic acid phosphate ranged from 1.0 to 2.3 microg mm(-2), which is most likely to be sufficient for the in vitro osteogenic differentiation of mesenchymal stem cells on titanium. Since ascorbate is important for the collagen synthesis and subsequent osteogenesis of mesenchymal stem cells, titanium coated with the ascorbate-apatite composite layer would be useful as a scaffold in bone tissue engineering and as a bone substitute.

Effect of controlled zinc release on bone mineral density from injectable Zn-containing beta-tricalcium phosphate suspension in zinc-deficient diseased rats.

The purpose of this study was to evaluate the efficacy of zinc (Zn)-containing beta-tricalcium phosphate (Zn-TCP) in correcting the bone mineral deficiency noted in osteoporosis using ovariectomized rat model. Four rats were used for each of the four experimental groups: D0, D10, D20, and N10. The rats in D0, D10, and D20 groups were ovariectomized, and fed a vitamin D-, Ca-, and Zn-deficient diet, and induced Zn-deficient osteoporoses for 9 weeks. In contrast, the N10 group was the normal rats fed normal healthy diet for 9 weeks. D0 group was injected with pure beta-TCP suspension, D10 and D20 groups were injected with suspensions containing 10 mg of 10 mol % (6.17 wt % Zn) and 20 mol % (12.05 wt % Zn) Zn-TCP, respectively, and the healthy group, N10 were injected with 10 mol %. Zn-TCP suspensions. Injections were administered intramuscularly in the left thigh once a week in all rats, and fed a vitamin D- and Zn-deficient diet for 9 weeks. The plasma calcium (Ca) and Zn levels, plasma alkaline phosphatase activity (ALP) and bone mineral density (BMD) of the lumbar vertebra and femora were measured. The plasma Zn levels in all the rats were between 1.1 and 2.8 microg/mL. The areas under the curves for the Ca, Zn, and ALP (Ca-AUC, Zn-AUC, and ALP-AUC) levels between 0 and 63 days were calculated. Results for the AUCs were as follows: (1) the Zn-AUCs were in the order of N10 = D20 > D10 > D0; (2) the Ca-AUCs for D0, D10 groups were significantly lower than that for the N10 group; (3) the ALP-AUCs for the D10 and D20 groups were significantly higher than that for the N10 group, and that of the D0 group was in between those. The body weight of D10 and D20 groups significantly increased with time, that of the D0 group increased slightly, and that of the N10 group remained unchanged for the entire experimental period. The BMD of the lumbar vertebrae of the D10 and D20 groups (about 100 mg/cm(2)) was significantly higher than that of the D0 group but lower than that of the N10 group. The BMD of the left femur increased more than that of the right femur with the increase in the amount of Zn in the suspension. The results of this study suggest that the local effect on BMD was more pronounced than the effect on the whole body.

Effect of particle size on zinc release from zinc containing tricalcium phosphate (ZnTCP) in Zn-deficient osteoporosis rats.

The effect of particle size on in vivo and in vitro Zn release of ZnTCP was investigated for the purpose of understanding Zn release behavior from a sustained-release device. The tricalcium phosphate powders (Ca2.7 Zn0.3(PO4)2), with particle size of 7.5 and 553 microm (S-ZnTCP and L-ZnTCP), including a 10 mol% of Zn (6.17 w/w%), as new sustained-release preparations, were synthesized by heating, after then ground and sieved using 38 and 300 microm screens. The different powder samples were characterized by the X-ray powder diffractometry and scanning electron microscopy. The release rates from Zn-TCP powders (10 mg) were measured in 10 ml of simulated body fluid (SBF) containing 10 mg/100 ml Ca2+(SBF/H), SBF containing 5 mg/100 ml Ca2+ (SBF/L) or SBF without Ca2+ (SBF/-) at 37.0 degrees C. The in vitro Zn release profiles for the smallest and the largest particles size of ZnTCP powders (L-ZnTCP and S-ZnTCP) at various Ca concentrations in SBF were significantly higher in SBF/- and SBF/L than in SBF/H. The Zn release rate from ZnTCP with different particle sizes were found to be inversely proportional to the concentration of calcium in SBF. After injection of a ZnTCP suspension containing 30 mg of S-ZnTCP powder on the backs of the rats, the plasma Zn level increased rapidly, reaching a concentration range of around 2 microg/ml. The area under the curve values of the plasma Zn concentration (Zn-AUC) over 6 days post injection of S-ZnTCP and L-ZnTCP were significantly higher than that of the control experiment. After the injection of S-ZnTCP and L-ZnTCP suspension, the plasma alkaline phosphatase activity (AIP) levels increased to more than 300 IU/l. In contrast, the AIP for the control decreased after 2 days. The area under the curve of the AIP (AIP-AUC) for 6 days of S-ZnTCP was significantly higher than that of other groups.