Key Engineering Materials Vols. 309-311

Abstract: The mechanism by which carbonate substitution within the hydroxyapatite (HA) lattice improves osteoconduction is unclear. Discs of dense, sintered, phase-pure HA and carbonate substituted hydroxyapatite (CHA) were cultured with human CD14+ cells in the presence of macrophage-colony stimulating factor (M-CSF) and soluble receptor activator of nuclear factor (NF)-κB (sRANKL), during which time osteoclasts developed and resorbed the ceramic surface. Discs were then seeded with human osteoblasts (HOBs), and proliferation and collagen synthesis measured. Proliferation was increased on resorbed compared to control (unresorbed) surfaces on both materials. Collagen synthesis was increased on CHA compared to HA, an increase accelerated on a previously resorbed surface. The results suggest that osteoclasts can condition synthetic bioceramic surfaces and alter the responses of osteoblasts which subsequently populate them. Carbonate substitution may enhance osteoconduction via effects on enhanced bioresorption.

Abstract: Degradation characteristics of calcium metaphosphate (CMP) ceramics substituted by 5, 10, 15, 20 mol% of NaPO3 and KPO3, respectively, was evaluated in revised simulated body fluid (R-SBF) by measuring the weight change, flexural strength, crystalline phases, and surface morphology with immersion period. The weight loss of CMP substituted by KPO3 was significantly higher than that of CMP substituted by NaPO3. The weight loss in the KCa(PO3)3–CMP samples was due to the dissolution of KCa(PO3)3 phase. The flexural strength of NaCa(PO3)3–CMP samples increased, however, that of KCa(PO3)3–CMP samples decreased significantly due to the dissolution of KCa(PO3) phase with immersion period. The dissolution of KCa(PO3)3 phase formed a pore structure in KCa(PO3)3–CMP samples.

Abstract: For effective bone regeneration, various surface modifications have been tried. In an effort to improve osteogenic repair potential, we evaluated recombinant peptides containing the RGD domain as a bioactive molecule for tissue-engineered bone regeneration. The synthetic peptides slightly suppressed cellular proliferation in the in vitro culture system but induced favorable osteoblastic differentiation, which was determined by MTT and ALP activity staining, respectively. The synthetic peptide coated CMP granules, which were implanted into the mandibular bone defects showed more favorable bone repair compared to the non-coated CMP implantation. In addition, there were not any sign of inflammatory reaction. These findings suggest that synthesized peptides containing the RGD domain enhance cellular attachment and osteogenic activity in vivo condition and that the peptide-coated CMP granules can serve as a biocompatible bone substitute.

Abstract: An amorphous calcium phosphate precursor way was utilized to prepare submicron biphasic α-tricalcium phosphate (TCP)/hydroxyapatite (HA) powders. The results showed that the addition of carbonate during the precipitation reaction could eventually lead to the formation of HA phase in the resulting powders, and even determine the relative content of HA to the range from 0 percent (pure α-TCP) to 100 percent (pure HA). Similarly, the particle size of the resulting biphasic powders depended on the carbonate content, ranging from 100nm to 500nm. The biphasic Ca phosphate with tailored α-TCP/HA ratio could be a new combination of calcium phosphate for promoting early bone formation.

Abstract: Submicron α-tricalcium phosphate (α-TCP), β-tricalcium phosphate (β-TCP) and biphasic α/β-TCP powders were prepared by an amorphous calcium phosphate (ACP) precursor way. For the biphasic TCP powders, primary particle size was 300nm, α-TCP and β-TCP primary particles were homogeneously mixed in the submicron powders. When the TCP powders were soaked in acetate buffer solution with pH 5, the Ca ion concentration in the soaked solutions and the resulting morphology variations were measured and observed. The results showed that the dissolution behavior of the biphasic TCP powders was different from α-TCP and β-TCP, and had a higher dissolved Ca ion concentration. This is attributed to a high supersaturation which is cased by the distribution homogeneity of two phase primary particles in submicron powders. These demonstrate the biphasic TCP to have potential to extend biological applications of Ca phosphates.

Abstract: Surface morphology and degradation behavior of mechanically mixed and chemically precipitated biphasic calcium phosphate (M-BCP and P-BCP) were compared. For the M-BCP powder, commercial HA and TCP powders were used. In order to prepare P-BCP powder, precipitation method was used. The particle size of P-BCP was smaller than that of M-BCP. The disk-type specimens of each powder were prepared for the morphology comparison and degradation test. The surface morphology of sintered samples was porous in M-BCP and dense in P-BCP. The degradation test was conducted in the revised simulated body fluid (R-SBF) for 1, 7, and 21 days. Surface morphology and degradation rate of two samples were different. The weight gain in both samples increased linearly with immersion period due to apatite-like layer formation. However, the weight gain in M-BCP was much higher than that in P-BCP. The weight gain was related to the surface morphology and degradation with immersion period.

Abstract: The purpose of this study was to develop a feasible technique for bone reparation and further explore the possible applications of Ca-P ceramics in segmental load-bearing bone reparation. HA/TCP ceramics sintered at 1250oC were fabricated into tube-like columns of Φ15mm×30mm with a central canal of Φ4mm. Bone-like apatite was precipitated on the ceramics before implantation. 12 male dogs were used in this study, and a 30mm long segmental bone defect was made in the middle of one femur of each dog. Supported by the fixation of net-cage-structured TC4, the osteoinductive Ca-P ceramic cylinder was used to repair the segmental defect in dog femur. Stress was analyzed by ANSYS. The morphology recovery, function restoration, gait analyses and bone regeneration were evaluated. After implantation at 2, 4 and 8 months, the specimens were harvested respectively. The specimens were evaluated with morphological observation and mechanical testing. Stress analysis showed that the thickness of TC4 net cage was 0.3mm. The morphology recovery of the experimental animal was good and function was restored after 2 months gradually. Aided by stress analysis and by optimizing the design and fixation of implants, Ca-P materials with excellent osteoinductivity could be applied in repairing segmental bone defects.

Abstract: We synthesized tricalcium phosphate (TCP) microspheres using an ultrasonic spray-pyrolysis technique, and investigated the effect of the concentrations of the starting solution on the powder properties. The XRD pattern showed that the crystalline phases of the resulting powders were β-TCP/HAp biphase in the case of pyrolysis temperature at 850 °C and TCP single phase at 1000 °C. The Ca/P molar ratios were determined by XRF to be at 1.50±0.03. The particle shapes of the powders were observed by SEM; the diameters of the microspheres were narrowly distributed from 0.5 to 4 µm. The mean particle diameters of the resulting powder increased with the concentration of the starting solutions and could be controlled in the range of 0.85-1.4 µm. When the compressed powder was sintered at 1050 °C for 5 h , the relative density of the sintered compact attained to 97%. The TCP microspheres had good sinterability.

Abstract: The purpose of this study was to determine the solubility of magnesium-containing tricalcium phosphate (MgTCP) over a magnesium content range from 0 to 10 mol%, and to compare it with that of zinc-containing tricalcium phosphate (ZnTCP). MgTCP powders with various Mg contents were immersed in 0.08M acetic acid and sodium acetate buffer solution of pH 5.5 at 25±2 °C. Solubility product, Ksp = (Ca2+)3-x(Mg2+)x(PO4 3-)2, was calculated. From the Ksp data, the solubility of MgTCP in the pH range from 5 to 7.5 was inversely calculated. The solubility of MgTCP decreased with increasing Mg content. The negative logarithm of solubility product (Ksp) was regressed as pKsp = 29.041+0.90467C-0.18069C2+0.025962C3-0.00192C4-0.000055199C5 , where C is the Mg content of MgTCP in mol%. In the magnesium content range from 0 to 10 mol%, the solubility of MgTCP is higher than that of ZnTCP containing the same amount of zinc.

Abstract: The purpose of this study was to evaluate the efficacy of magnesium (Mg), zinc (Zn) and fluoride (F)-containing calcium phosphate compounds (Mg/Zn/F-CaP) in correcting the bone mineral deficiency noted in ovariectomized (OVX) rats. In order to evaluate therapeutic effect of selected Mg/Zn/F-BCP preparations (G2: 1.13%Mg/13.6%Zn/2.5%F, G3:7.76%Mg/1.89%Zn /3.01%F and G4:2.72%Mg/3.75%Zn/1.35%F), suspensions consisting of Mg/Zn/F-CaP preparations and of Zn-TCP (G1: 6.17%Zn) powder were injected in the right thigs of OVX rats for 4 weeks. Injection of Zn-TCP powder suspension in G1 and G2 groups led to the recovery of plasma Zn levels in OVX rats. The area under the curve of plasma Zn for the G2, G1 and Normal (not ovariectomized) control group (GN) groups were significantly lower than those of the group G3, G4 and OVX /untreated control (GC) groups (p<0.05). The bone mineral density (BMD) of the right femur was significantly higher than that of the left in G1, G2, G3 and G4 groups on day 28. However, there was no significant difference in the BMD between the left and right femur in the GC and GN groups.