Effect of ZnO addition on bioactive CaO-SiO2-P2O5-CaF2 glass-ceramics containing apatite and wollastonite.

Some ceramics show bone-bonding ability, i.e. bioactivity. Apatite formation on ceramics is an essential condition to bring about direct bonding to living bone when implanted into bony defects. A controlled surface reaction of the ceramic is an important factor governing the bioactivity and biodegradation of the implanted ceramic. Among bioactive ceramics, glass-ceramic A-W containing apatite and wollastonite shows high bioactivity, as well as high mechanical strength. In this study, glass-ceramics containing zinc oxide were prepared by modification of the composition of the glass-ceramic A-W. Zinc oxide was selected to control the reactivity of the glass-ceramics since zinc is a trace element that shows stimulatory effects on bone formation. Glass-ceramics were prepared by heat treatment of glasses with the general composition: xZnOx(57.0-x)CaOx35.4SiO(2)x7.2P(2)O(5)x0.4CaF(2) (where x=0-14.2mol.%). Addition of ZnO increased the chemical durability of the glass-ceramics, resulting in a decrease in the rate of apatite formation in a simulated body fluid. On the other hand, the release of zinc from the glass-ceramics increased with increasing ZnO content. Addition of ZnO may provide bioactive CaO-SiO(2)-P(2)O(5)-CaF(2) glass-ceramics with the capacity for appropriate biodegradation, as well as enhancement of bone formation.

Effect of polyacrylic acid on the apatite formation of a bioactive ceramic in a simulated body fluid: fundamental examination of the possibility of obtaining bioactive glass-ionomer cements for orthopaedic use.

Glass-ionomer cements, which consist of CaO-Al2O3-SiO2-CaF2 glass powders and a polyalkenoic acid solution, such as polyacrylic acid (PAA), have been widely used in dentistry. They set rapidly without any shrinkage, the lack of temperature increase on reaction, and develop high mechanical strength. Therefore, if bioactive glass-ionomer cements can be obtained, such cements are expected to be useful as cements for fixing orthopaedic implants to the surrounding bone. In the present study, to examine the possibility of obtaining bioactive glass-ionomer cements, the effect of PAA on the apatite formation on bioactive ceramics in a simulated body fluid was investigated. It was revealed that presence of even a small quantity of PAA inhibits the apatite formation in the body environment. It is speculated that when glass-ionomer cements are implanted into the body, PAA can be released from the glass-ionomer cements and inhibits the apatite formation on their surfaces. It is reasonable to suppose that this will occur with any glass-ionomer cement that contains PAA. Therefore, it might be considered difficult to obtain bioactive glass-ionomer cements.

Bioactivity and mechanical properties of polydimethylsiloxane (PDMS)-CaO-SiO2 hybrids with different calcium contents.

Polydimethylsiloxane (PDMS)-CaO-SiO(2) hybrids with starting compositions containing PDMS/(Si(OC(2)H(5))(4)+PDMS) weight ratio=0.30, H(2)O/Si(OC(2)H(5))(4) molar ratio=2, and Ca(NO(3))(2)/Si(OC(2)H(5))(4) molar ratios=0-0.2, were prepared by the sol-gel method. The apatite-forming ability of the hybrids increased with increasing calcium content in the Ca(NO(3))(2)/Si(OC(2)H(5))(4) molar ratio range 0-0.1. The hybrids with a Ca(NO(3))(2)/Si(OC(2)H(5))(4) molar ratio range 0.1-0.2 formed apatite on their surfaces in a simulated body fluid (SBF) within 12 h. The hybrid with a Ca(NO(3))(2)/Si(OC(2)H(5))(4) molar ratio of 0.10 showed an excellent apatite-forming ability in SBF with a low release of silicon into SBF. It also showed mechanical properties analogous to those of human cancellous bones. This hybrid is expected to be useful as a new type of bioactive material.

Apatite formation on CaO-free polydimethylsiloxane (PDMS)-TiO2 hybrids.

Polydimethylsiloxane (PDMS)-TiO(2) hybrids with PDMS (M=550)/tetraethylorthotitanate molar ratios at 0.27, 0.68 and 1.35, i.e. Si/Ti atomic ratios at 2, 5 and 10 (hybrids PD2, PD5 and PD10, respectively) were prepared by a sol-gel method. Hybrid PD2 formed many cracks. Hybrids PD5 and PD10 were subjected to hot-water treatment 80 degrees C for 7 d. Hybrid PD5 produced cracks, whereas hybrid PD10 was crack-free after the hot-water treatment. Hybrid PD10 took a homogeneous amorphous structure before the hot-water treatment, and precipitated anatase particles 10-20 nm in size after the hot-water treatment. Hybrid PD10 did not form apatite on its surface in a simulated body fluid before the hot-water treatment, but formed it after the hot-water treatment. The obtained hybrid showed elastic deformation as large as 200% after the hot-water treatment. This kind of hybrid could be useful as a new type of bone-repairing material.