Key Engineering Materials Vols. 342-343

Abstract: To develop a suitable scaffold optimizing bone regeneration, we developed bovine bone ash derived fully connected porous HA ceramic scaffolds adopting a foaming method. They revealed excellent biocompatibility. The attached cells on the scaffolds proliferated in multi-layers with osteoblastic differentiation. The bone defects grafted with bovine bone ash derived fully interconnected porous HA ceramics having average 500 μm sized spherical pores and average 150 μm sized interconnecting interpores with average 80% porosity were favorably healed without any pathologic changes within 3 weeks. New bone ingrowth with excellent osteoconduction through the spherical pores along the inner surface was noted from 1 week after implantation. Each spherical pore was filled with hematopoietic marrow and newly formed bone which with time was well integrated with the porous HA ceramic scaffold with time. These findings suggest that the bovine bone ash-derived fully interconnected porous HA ceramic formed by foaming method can be a promising bone substitute and a scaffold for bone tissue engineering.

Abstract: Particle separations occurred frequently in sintered hydroxyapatite when immersed in distilled water or simulated body fluid. This dissolution initiated at grain boundary creating nano-size defects such as small pores and grew up to micro scale by increasing immersion time. The dissolution, probably due to the appearance of secondary phases in grain boundary, resulted in grain separation at the surfaces and finally in degradation and fracture. And the dissolution concentrated on those grains adjacent to pores rather than those in the dense region. Hydroxyapatite ceramics incorporated with calcium silicate glass were prepared by slip casting to enhance the sinterability as well as to reduce dissolution. Glass phase was incorporated into hydroxyapatite to act as sintering aids followed by crystallization in order to improve the mechanical properties without reducing biocompatibility. From dissolution test, significant damage was reduced even more than 7 days and the dissolution pattern somewhat changed than pure hydroxyapatite. X-ray diffraction and SEM showed no decomposition of secondary phases in grain boundary and fracture toughness somewhat increased.

Abstract: The study is aimed at to explore the construction of bone graft with calcium phosphate ceramics implanted in subcutaneous fat, and provide applying technique for the in vivo bone tissue engineering. Forty-eight calcium phosphate ceramics (Ca-P ceramics) columns with Φ 5×8 mm were prepared, and eight dogs were used in this experiment. Six samples were implanted in each dog. Three in dorsal muscles while the others in subcutaneous fat. The specimens were harvested at 4, 6, 12 and 24 weeks post operation, for gross observation, SPECT and histological studies. The osseous or osteoid tissue formation at different times in the two non-osseous sites was compared and the new bone grafts in subcutaneous fat and intramuscular implantations were evaluated. The results demonstrated that the bone graft could be constructed not only in muscle but also in subcutaneous fat. Compared to that in muscle, constructing bone graft in subcutaneous fat could have brighter prospect to clinical application.

Abstract: Zirconia toughened alumina (ZTA) nano-ceramic composite has excellent mechanical properties. Preparation of ZTA was conducted in the present study with an attempt to use as dental ceramics. On the basis of the study on the effect of the die pressing forces on the density and Vickers hardness of the sintered ZTA, additive aids TiO2, MgO, SiO2 and CaO were introduced in order to reduce the sintering temperature of ZTA nano-ceramic composite with good densification. Scanning electron microscopy was employed to evaluate the microstructural morphology. Phase composition was confirmed by using X-ray diffraction. Thermal analysis was further used to study the structural change. The results indicated that the ZTA product sintered at 1450°C had dense and uniform microstructure due to the combinative effect of additive aids, including the formation of an intermediate compound. This study suggested that such ZTA nano-ceramics had potential applications as dental prosthetic materials.

Abstract: Various composition of calcium-silicate thinfilms were deposited to the thickness of 1μm by electron-beam deposition. The composition was varied by changing the composition of source. The Si concentration of thinfilm was ranged from 25 at% to 85 at%, evaluated by EDS. The specimens were immersed into PBS solution at 37 °C. Changes of the morphology and calcium phosphate formation on the specimens were examined by SEM. If the concentration of calcium is high, the calcium phosphate was quickly formed on the specimen. However, the calcium phosphate formed on the high calcium oxide concentration exhibited very poor adhesion onto the substrate. There is a range of appropriate calcium oxide concentration to use as a surface modification method for dental or orthopedic implants.

Abstract: Dissolution of calcium phosphate powders with different compositions in simulated body fluid was investigated. Hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) powders were synthesized by a precipitation method and by controlling pH of the solution. Biphasic calcium phosphate (BCP) powders were prepared by mixing the HA and β-TCP powders with ratio of 80:20 and 60:40 in weight % in a planetary mill for 4 h. For dissolution test, 0.5g of each β-TCP, HA and BCP powders were immersed in 50 ml of SBF at 37°C for 3-28 days. HA powders with stoichiometric composition showed no significant morphological change regardless of the immersion time. β-TCP powders were not dissolved in SBF in spite of its high solubility. The surface of BCP powders became rough due to dissolution with increasing immersion time. This surface dissolution gradually extended into the core region of the particles resulting in disintegration of the dense particle into fine crystallites. It may be caused that the milling process during preparation of BCP powders may induce stress concentration or formation of dislocation on the surface of particles.

Abstract: Hydroxyapatite derived from human teeth was sintered at 1200°C for 2 h. Dissolving behavior of the biologically derived HA (BHA) in distilled water was investigated and compared with an artificial hydroxyapatite (HA) made of synthetic HA powder. All disks were immersed in 40 ml of pH 7.4 distilled water (buffered using 0.05 M Tris.) for 7 and 14 days at 37°C. All detectable peaks in the HA are identical only to HA lattice planes, whereas BHA consisted of a mixture of HA and β-tricalcium phosphate (TCP). In the case of the HA specimen, the surface dissolution was initiated at grain boundaries followed by generated many separated grains and large defect like cavities. On the other hand, biologically derived HA showed that definite grains considered as β-TCP was predominantly dissolved and the grains were separated from the matrix leaving pores. In the mean time, the rest region, mainly consisting of HA, did not show any evidence of dissolution. It seems that BHA is more stable than the artificial HA in liquid environment.

Abstract: Calcium phosphate ceramics (CPC) have been attractively used in different areas of biomedical applications, such as substances of artificial hard tissue replacement implants, drug delivery system due to their biocompatibility and bioactivity. In this work, three calcium phosphate powders between Ca/P molar ratio 1.50-1.67 were synthesized by aqueous precipitation method, using the mixture of Ca(NO3)2·4H2O and H3PO4 solutions to ammonia solution. During the precipitation reaction, Ca/P molar ratio was adjusted by controlling pH of the solution between 8.0 and 10.5 by the addition of ammonium hydroxide solution. All powders were treated at 800 oC for 2 hrs. The calcined powders were immersed in pH 7.4 distilled water at 37°C for 3 and 7 days. Decomposition and related dissolution with the various Ca/P ratios were investigated by XRD, FTIR, and TEM observation.

Abstract: Osseointegration (OI) could be described as the modality for stable fixation of titanium implant to bone structure. The OI has become a realized phenomenon of importance in the dental and rehabilitation sciences since recently developed dentures and artificial limbs are directly attached to human skeleton by using osseointegrated implants. Previously, a study showed that bone strain generated potential (SGP) that is an electrical potential and considered to be generated by fluid flow in bone could be used as a parameter to examine the amount of OI on implant-bone interface. Since no study was performed to understand SGP behavior as a function of position for the implant-bone composite, a one-dimensional map of SGP was constructed along the longitudinal direction of the composite. For the purpose, nine electrodes including one reference were instrumented on the wet composite for the one-dimensional mapping of SGP during compression tests. The peak magnitudes of SGP were found to be significantly increased when the measurement position was approached for the interface of implant-bone. The results could indicate that the spatial SGP behavior of osseointegrated implant-bone composite could be caused by the interface of the implant-bone.

Abstract: α-Tricalcium phosphate (α-TCP) is one of the main reactants of the powder phase of several bioactive calcium phosphate bone cements. After preparing TCP, the TCP was determined by the measurement of X-ray diffraction, particle size, and scanning electron microscopy. Cements were characterized using viscosity measurements, X-ray diffraction, scanning electron microscopy, and compressive and tensile strengths etc. When citric acid was added as dispersant at different concentration to α-tricalcium phosphate bone cements, it was found to act as a fluidizing agent during the first stages of cement mixing. The setting time for cement without citric acid was 300 min, while setting times for cements prepared with 0.5-2.5 M citric acid were at a minimum of 4 min and a maximum of 35 min, respectively. The dissolution-precipitation reaction of α-tricalcium phosphate was accelerated by adding citric acid and compressive and diametral tensile strength increased.