Key Engineering Materials Vols. 280-283

Abstract: Porous tricalcium phosphate ceramics were immersed in static and dynamic revised simulated body fluid (RSBF) at 37°C. Morphology, composition and phase of precipitates on TCP were identified by SEM, FTIR and TEM methods. FTIR and TEM results indicated the deposits on the inner pore walls of TCP were OCP, and SEM results implied that the deposited way of precipitates in static system was different from that in dynamic system.

Abstract: Bioactive glasses are known to have the ability to regenerate bone, but their use has been restricted mainly to powder, granules, or small monoliths. This work reports on the development of bioactive glasses with macroporosity of controlled size and volume through sol-gel and pore forming technologies. The macroporous structure (greater than 100µm) can provide the potential for tissue ingrowth. Simultaneously the samples exhibit mesoporous (2-50nm) texture and high specific surface which can enhance bioactivity and release of ionic products. The most important advantage is that these samples show satisfactory mechanical strength. This method should be a useful approach for preparation scaffolds with applications to repair and reconstruct damaged tissue.

Abstract: The mechanism of apatite formation on the surface of novel PDMS modified SiO2-CaO- P2O5 hybrids is presented. The bioactive hybrids with different P2O5 content were synthesized by sol-gel method and soaked in the simulated body fluid (SBF) for different periods. The surface and the cross-section of the specimens were examined by use of Fourier transform infrared reflection spectroscopy, thin-film X-ray diffraction technique and scanning electron microscopy. The PDMS-SiO2-CaO-P2O5 hybrid containing 0.03 mole ratio of TEP(triethyl phosphate) / TEOS (tetraethoxysilane) exhibited faster apatite formation compared to P2O5-free hybrids. This composition resulted in the thickest apatite layer (~6µm) and this might be attributed to faster formation of the silica hydrogel on the surface of the P2O5-containing hybrids than on the surface of the P2O5-free hybrids. Resultingly, the apatite nucleation on the surface of the P2O5-containing hybrids is effectively induced by the hydrated silica at a lower degree of supersaturation. Changes in concentrations of the calcium, silicon and phosphorus in the SBF and the SEM-EDS line analysis depicting the variation of Si, Ca and P elements for the bulk, the interface and the apatite are reported. These were found to be quite correlative with each other. The rate of the concentration changes for the P2O5-containing hybrids is higher than that of the P2O5-free hybrids. The increases in the calcium and silicon concentrations are attributed to dissolution of the calcium and silicate ions from the hybrids, and the decrease in the phosphorus concentration is ascribed to formation of the amorphous calcium phosphate and crystalline apatite on the surface of hybrids by consuming the phosphate ion from the fluid.

Abstract: In the present paper, nanocrystalline diamond films (NDFs) were fabricated on optical glass using microwave plasma assisted chemical vapor deposition (MPACVD). The suitable processing parameters are as followings: methane concentration 3% in argon, total deposition pressure 13.3 kPa, substrate temperature 500 °C. The diamond films were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. In vitro osteoblast cell cultures and platelet adhesion tests were applied to evaluate the biocompatibility of the nanocrystalline diamond films (NDFs). All results indicate that the diamond films exhibit better tissue compatibility and hemocompatibility which are very suitable for biomedical applications.

Abstract: A porous bioglass reinforced tricalcium phosphate scaffold was prepared. The microstructure, degradability and reaction products of the scaffold after immersed in a simulated body fluid for different days were emphatically investigated using scanning electron microscopy, energy-dispersive X-ray analysis, X-ray diffraction, Fourier transformed infrared spectroscopy and induced coupled plasma spectroscopy. The results showed that a homogeneous hydroxy-carbonate-apatite (HCA) layer forms on the surface of the scaffold for over 30- day immersion and the oriented growth of the HCA occurs. In addition, this paper discussed the competing mechanism between the dissolution and the precipitation via the measurement of calcium and silicon ionic concentrations in the SBF.

Abstract: The influence of leucite on dental porcelain properties is investigated in this paper. The nanosized leucite powder prepared by sol-gel method was added into a low-fusing temperature frit to fabricate dental porcelain fused to metal. The porcelains with different leucite contents were sintered at the temperatures ranging from 780° to 900°C. The flexural strength and the thermal expansion coefficient (TEC) of the dental porcelain containing leucite particles are evaluated. The micro- structure and phases of the porcelain are characterized and the mechanism that nanosized leucite particles strengthening the porcelain is discussed.

Abstract: The biomaterials in system CaO-P2O5-SiO2 were synthesized via sol-gel method. The biomaterials can be applied to bone reparation and bone tissue engineering scaffolds The nano-pore structure, degradability, bioactivity and bio-mineralization characteristic of the biomaterials were investigated in details using XRD, SEM/EDX, FTIR, BET and DSC/TG techniques. It was indicated that the sol-gel derived biomaterials have a higher bioactivity than that of the melt derived bioactive glasses or glass-ceramics. It just takes 4-8 hours for HCA to form on the surface of the sol-gel samples in SBF solution at 37°C. The spherical HCA crystal clusters formed on the surface of the sol-gel derived samples immersed in SBF for 8 hours have a low crystallinity. Owing to their interconnected nano-sized pores, the sol-gel samples possess much higher surface areas and the hydrous porous SiO2 gel layer containing a great amount of ºSi-OH groups can be rapidly formed on the biomterials’ surface through a quick ion exchange between H3O+ in the solution and Ca2+ in the surface of the materials. ºSi-OH groups can play a very important role in inducing formation of HCA. They make the material surfaces electronegative, which resulted in a double electrode layer formed between the samples surface and SBF solution. The double electrode layer is in favor of formation of HCA on the surface of the materials.

Abstract: The addition of b-tricalcium phosphate improves the biocompatibility and the bioactivity of scaffolds made from poly(lactic acid)(PLA). In this paper, a developed method was used to prepare poly(lactic acid)/ b-tricalcium phosphate microsphere-based tissue engineered scaffolds. It was found that the porosity and the compressive modulus of the scaffolds increased with increasing stirring time. The PLA scaffolds with a higher strength and porosity could be obtained under the optimum conditions (i.e., 2.0 g of PLA, 0.2 g of b-tricalcium phosphate, 300 rpm, stirring time for 2h ). In addition, the corresponding mechanism has been discussed.

Abstract: Bioactive composite coatings containing sub-layer and working-layer with different ingredients were prepared using subsonic thermal spraying technology and then heat-treated at 700°C for 1h. Two types of bioglasses, named BG1 and BG2, and Y2O3 were used as additives of the sublayer and working layer respectively. Phase transformation and structure changes of the coatings were investigated with XRD, DSC and SEM. Results showed that the phases of as-sprayed Ti/BG1 sub-layer were TiN, TiO2 (rutile and anatase), etc. Post-heat treatment changed the phase composition. TiN and anatase transformed into rutile and some new phases generated, which often enriched at pores and cracks. In the working-layer, part of nano-hydroxyapatite powders decomposed during coating preparation. Y2O3 impaired the decomposition to some extent and BG2 enhanced greatly. Post-heat treatment increased the crystallinity of all coatings effectively. The analysis of TG-DSC showed that BG2 added in working-layer crystallized at 700°

Abstract: Abstract. The improvement of subcritical crack growth (SCG) resistance for alumina glass dental composites was explored in this study. The addition of nitrogen to the glass phases in the composite was found to increase the SCG resistance, where the SCG exponent n increases from 22 for the oxide glass composites to 30 for the composites containing 0.5 mol% nitrogen in the glass phases. The improvement was tentatively attributed to the nitrogen addition, which makes the glass network stronger through forming the non-flexible Si-N bonds and thus inhibits the hydrolysis reactions under the SCG conditions. Analyses demonstrated that the increase of the n value from 22 to 30 offers the potential to greatly extend the lifetime and improve the long-term reliability for the alumina glass dental composites.