Key Engineering Materials Vols. 309-311

Abstract: Bonelike apatite formation abilities of β-tricalcium phosphate (β-TCP) and hydroxyapatite (HA) were enhanced by a simple and useful method of autoclaving in distilled water. By immersion tests using simulated body fluid, the apatite formation was observed on the surfaces of the autoclaved β-TCP and HA after 10 days and confirmed to be controllable by the autoclaving temperature, although the formation was not or dispersedly observed on non-autoclaved samples. Surface potentials and morphologies of the samples were decreased and roughed after the autoclaving

Abstract: Apatite formation behavior of tricalcium phosphate (TCP) ceramics with different phases and porosity was investigated in a simulated body fluid (SBF, Kokubo solution). The pure α-TCP with 80% porosity did not form hydroxyapatite (HAp) on its surface after soaking in SBF for 7 days. On the other hand, the pure α-TCP with 20% porosity formed HAp on its surface after soaking in SBF within 7 days, and the biphasic TCP, which consisted of mixture of α-TCP and β-TCP and had 20% porosity, formed HAp within 1 day. The low porosity and coexistence of α-TCP and β-TCP phases in TCP ceramics were effective for apatite formation in SBF.

Abstract: Dehiscence bone defects, frequently observed on dental implants placed in periodontitis-affected alveolar bone or extraction sockets were treated with β-tricalcium phosphate (β –TCP) and chitosan membrane for guided bone regeneration, and the new bone formation on the treated sites were studied. Beagle dogs were used for the experiment. First to fourth mandibular premolars were extracted, and the post extraction alveolar bone surface was planed. After 8 weeks of healing, 3 by 4mm dehiscence defects were created using straight fissure burs. Total of 16 oxidized titanium surface implants were placed on the bone defects of the subjects, two on each side. Control sites were treated with implants only. Experimental Group 1 sites were treated with implants and chitosan membrane. Experimental Group 2 sites were treated with implants, β-TCP and chitosan membrane. Experimental Group 3 sites were treated with implants, β-TCP, autogenous bone and chitosan membrane. The animals were sacrificed 12 weeks after implant placement, and the specimens from the treated sites were histologically studied with following results. Limited amount of new bone formation was observed in control group with unexposed membrane. Slightly greater amount of bone formation was observed on sites treated with β-TCP+membrane or autogenous bone+ β-TCP+membrane compared to control group. Remnants of chitosan membrane and β-TCP encapsulated with connective tissue were observed during experimental periods. These results suggest that further studies are needed on membrane rigidity and infection control for space maintenance underneath the membrane and bone substitutes in the treatment of dehiscence defects.

Abstract: Titanium alloy(Ti-6Al-4V, Samsung techwin, Korea) rods with diameter of 2.5mm were used as the implant materials. Polymethyl methacrylate(PMMA) bone cements(CMW, USA) were used as bone cement and
-tricalcium phosphate(TCP)-based bone filler powder was used as osteoconductive additives. Hydroxyapatite(HA) was the desired end product after hydrolysis of the
-TCP-based bone filler powder mixed with the blood. In animal study using rabbits, we divided the group into A, B, C and D. Rabbits were sacrificed at 1, 3, 9 weeks after implantation and the affinity index and bone density were calculated. X-ray diffraction patterns of HA formed by hydrolysis of
-TCP-based bone filler powder showed higher and higher intensity in HA peak with increase of time period. There was more bone density increase in the group B and D containing
- TCP-based bone filler powder around implant site than in the group A and C(p<0.05). It is suggested that HA formed by hydrolysis of
-TCP-based bone filler powder will play some parts in enhancing osteconducting ability in clinical settings.

Abstract: The cytotoxicity of five calcium phosphate ceramics, hydroxyapatite (HAp), flouroapatite (FAp), α-tricalcium phosphate (α-TCP), β-tricalcium phosphate (β-TCP) and tetracalcium phosphate (TTCP), was investigated. Based on the guidelines of biological test for medical devices in Japan, a cytotoxicity test of these calcium phosphates was carried out using Chinese hamster V79 lung fibroblasts. The cytotoxic study revealed that FAp and α-TCP showed high cytotoxicities. From various analyses, it was considered that the cytotoxicity of the FAp was due to fluorine ions extracted in a culture medium and the cytotoxicity of α-TCP resulted from a decrease in pH of the medium by the phosphoric acid, which produced by hydrolysis of( the α-TCP.

Abstract: The influence of several sinter additives (three glasses, magnesium acetate, bismuth trioxide) on the compressive strength and also on the solubility of a sintered ceramics, which is composed of 57.6Mol% CaO, 26.2Mol% P2O5, 10.4Mol% ZrO2 and 5.8Mol% CaF2 was tested. The amount of sinter additives, pre-mixing of the powders, pressure power, sintering temperature and sintering time were varied. The most dense samples were produced with the finest powders (D50 ~ 1/m) and the highest sintering temperatures (1200°C). The mechanical stability of the samples was more influenced by the particle size of the powders than by the kind of binder as well as the pressure power. The compressive strength of the sintered samples ranged between 180MPa (D50 of the powder = 2.4/m) and 530MPa (D50 of the powder < 1/m). Storing of the samples in simulated body fluid for 4 weeks at a temperature of 37°C did not influence the compressive strength significantly. The sintered ceramics can be finished, for instance by grinding or polishing.

Abstract: In vitro method has often been used in the biodegradation/bioactivity evaluation of bioactive ceramics for its convenience and saving in time and outlay. The simulated body fluid (SBF) suggested by Kokubo was a good simulation of the osteoproduction environment in osseous tissue and has been proved to be a good method to study the bioactivity of biomaterials and the mechanism of bone bonding. But SBF is not a suitable method to research the osteoinduction of biomaterials. The results from SBF were not consistent with that from in vivo in muscle. The local ion concentration is the key factors to affect the nucleation and growth of apatite. In muscle the effect of body fluid flowing on local ion concentration cannot be ignored. A dynamic SBF suggested by these authors of this paper not only simulated the ion concentration of body fluid, but also simulated the effect of body fluid flowing on the local ion concentration near the surface or in biomaterials in muscle. The results from the dynamic SBF were in good agreement with that of the implantation experiments in muscle. The results from dynamic SBF showed that apatite only formed on the walls of macropores of the porous CaP, no apatite formed on the surface of both dense and porous CaP. The new bone only formed on the walls of macropores of porous CaP implanted in muscles, no apatite or osseous tissue could be found on the surfaces of both porous and dense CaP. The dynamic SBF preferably simulated the osteoinduction environment in non-osseous tissue and can be used in osteoinductivity evaluation of bioceramics.

Abstract: Bioactive polymeric microspheres can be produced by pre-coating them with a calcium silicate solution and the subsequent soaking in a simulated body fluid (SBF). Such combination should allow for the development of bioactive microspheres for several applications in the medical field including tissue engineering. In this work, three types of polymeric microspheres with different sizes were used: (i) ethylene-vinyl alcohol co-polymer (20-30 'm), (ii) polyamide 12 (10-30 'm) and (iii) polyamide 12 (300 'm). These microspheres were soaked in a calcium silicate solution at 36.5°C for different periods of time under several conditions. Afterwards, they were dried in air at 100°C for 24 hrs. Then, the samples were soaked in SBF for 1, 3 and 7 days. Fourier transformed infrared spectroscopy, thin-film X-ray diffraction, and scanning electron microscopy showed that after the calcium silicate treatment and the subsequent soaking in SBF, the microspheres successfully formed a bonelike apatite layer on their surfaces in SBF within 7 days due to the formation of silanol (Si-OH) groups that are quite effective for apatite formation.

Abstract: In cell culture medium containing serum proteins, a layer with a great role in ostelblast-like cell’s growth formed on a HAp ceramics by a coprecipitation with a deposition of a bone-like apatite and an adsorption of serum proteins. The adsorption of proteins is influential in the apatite deposition and the cell adhesion. A component of serum albumin is forming < 80% of total serum proteins, therefore we focused on the serum albumin. The serum albumin was removed from fetal bovine serum by using an albumin removal kit, and then the albumin free cell culture medium was prepared. The bone-like apatite layer was quickly formed on the HAp ceramics in the albumin free medium, however the high cell adhesion property was not confirmed. As a result of investigation of an initial cell adhesion, the initial cell adhesion property of the bone-like apatite layer was not excellent even though the layer contained the serum proteins. Moreover, the layer without serum proteins showed a meager cell adhesion property in every time of the cultivation. Therefore, it was revealed that the adsorption of the serum proteins only on the surface was not enough to the improvement of the cell growth. And a few days cultivation was required for an appearance of the remarkable effect on the cell growth on the layer formed by a coprecipitation reaction about the bone-like deposition apatite and the serum proteins adsorption.