Key Engineering Materials Vols. 361-363

Abstract: Three types of calcium-deficient apatite fibers (Ca-def AF) were synthesized by a homogeneous precipitation method using starting solution with Ca/P ratios of 1.00, 1.50 and 1.67, and then the resulting fibers were characterized by XRD, FT-IR and SEM. Especially, the microstructure including strain and defect of individual Ca-def AF was examined by transmission electron microscopy (TEM). All the resulting Ca-def AFs had a single phase of apatite, and contained carbonate ions. These fibers were of single crystal, and highly strained. However, when Ca-def AFs were heated to higher than 800 °C, they changed to HAp and TCP biphases. The content of the carbonate group in the Ca-def AFs decreased with heating temperature.

Abstract: There is a clinical need for synthetic scaffolds that will promote bone regeneration. Important factors include obtaining an optimal porosity and size of interconnecting macropores whilst maintaining scaffold mechanical strength, enabling complete penetration of cells and nutrients throughout the scaffold, preventing the formation of necrotic tissue in the centre of the scaffold. To address this we investigated flexural strength of bimodal porous apatite ceramics prepared using apatite slurry and its slurry synthesis was studied. Slips with different contents of HAp (K-HAp and T-HAp) and deflocculant were prepared by milling in a pot mill. The viscosity of slurries made of commercial T-HAp powder showed a drop after 3 hours’ milling, but the viscosity of slurry with high solid content of k-HAp and 2.0 wt% deflocculant increased with an increase of milling time after 2 hours’ milling. The porosity and flexural strength of the porous HAp prepared by heating the foam dipped in K-HAp slip with 2.0 wt% of deflocculant and 0.5wt% of foaming regent heated at 1200°C were 62.4 % and 14.7 MPa, and those in T-HAp were 59.7 % and 15.2 MPa with 1.5 wt% of deflocculant and 0.5wt% of foaming regent heated at 1200°C.

Abstract: A edible cuttlefish(Zoological name : Sepia esculenta) bone has a porous structure with all pores interconnected The purpose of this research is to develop porous hydroxyapatite prepared by hydrothermal treatment from cuttlefish bone and evaluate the biocompatibility using undecalcified materials through the in-vivo test of rabbits. In this study, the phase and substructure of a porous hydroxyapatite, prepared by hydrothermal treatment using edible cuttlefish bone as a calcium source, has been confirmed by X-ray diffractometer and scanning electronic microscope. After preparing the specimens with 5mm diameter and 7mm length, the specimens were implanted into the femoral condyles of rabbits. Each rabbits were sacrificed at each time period of 1, 2, 3, 4 weeks after operation, respectively and the stained section was examined by a transmission light microscope. The X-ray diffraction patterns of the edible cuttlefish bone was confirm for aragonite phase and of the sample after hydrothermal treatment showed mostly into hydroxyapatite phase. There was more bone density increase in porous HA rod around implant site than natural edible cuttlefish bone. Because the edible cuttlefish bone is a very pure and good calcium source, porous hydroxyapatite developed from this study is expected to be a biomaterial having a good biocompatibility to be used as a suitable bone substitute.

Abstract: Zinc substituted hydroxyapatite of varying wt% was produced using a precipitation method based on reacting calcium and zinc nitrate with ammonium phosphate. Characterisation results from X-ray diffraction (XRD) and X-ray fluorescence spectroscopy (XRF) showed that zinc was successfully substituted up to 0.8wt% using this method. Rietveld analysis showed that the alattice parameter was reduced and c-lattice parameter was increased with increasing zinc content. Initial mechanical test results showed samples with a zinc content of 0.4% had the greatest compressive strength.

Abstract: We fabricated a small α-TCP ceramic unit having four pods, named “Tetra-bone” employing a ceramic injection molding. Tetra-bone can keep uniform concave geometry among the pods as well as immobilizing each other. Owing to the monotony of Tetra-bone, weight of Tetrabones used can be converted into the number of Tetra-bones, volume that can be filled with Tetrabones, and the number of functional structures. By using Tetra-bones, bone defects can be filled with intentional geometry that helps to discuss the relation between geometric features of pores and bone formation.

Abstract: Bioactivity of biomaterials is recognized to be of importance and the behavior of nanosized HA and β-TCP particles is described and compared. The study focuses on the influence of the phase transformation and grain size on the reprecipitation of calcium phosphate and the effect of immersion time in SBF on the surface characteristics of the samples. The HA and β-TCP samples were fabricated by mixing the powders in a ball mill, drying, uniaxial pressing and sintering at 1150oC for 240 minute using fixed heating and cooling rates. The densified samples were then immersed in a simulated body fluid (SBF) for controlled periods of time in order to investigate their bioactivities. Changes in the surface structure were examined to investigate and characterize phase formation and the chemical functionality of the samples.

Abstract: Hydroxyapatite powders characterized by substitutions of Mg2+, SiO4 4-, CO3 2- ions in biological like amounts, in the crystallographic site of calcium and phosphates, ions in biological like amounts, in the crystallographic site of calcium and phosphorus, were successfully prepared by synthesis in aqueous medium. The chemico-physical properties of the powders were investigated through several analytical techniques, among them: XRD, FTIR, TG-DTA, ICP-OES, HR-TEM. The entering of silicon in the HA structure progressively reduces its crystallinity, as also carbonate ions do. Silicate and carbonate ions can enter simultaneously into the HA structure, in biological-like amounts, although they compete for the occupation of the phosphate site. Solubility tests, carried out at physiological conditions, reveal an increased calcium release in the HA powders containing silicon compared to the silicon-free HA.

Abstract: Silicon substituted Hydroxyapatite coatings were prepared by Pulsed Laser Deposition from targets made of mixtures of Hydroxyapatite with Si powder at different concentrations. The properties of the Si-HA coatings with several degrees of Si substitution were analyzed by different techniques such as FTIR, XRD, XPS and solid-state NMR. It was found that the Si incorporation causes an amorphization of the structure together with a loss of carbonate groups. Furthermore, the Si atoms are incorporated in the form of SiO4 4- groups, and H(PO4)2- appears as the predominant phosphate group.

Abstract: Porous hydroxyapatite (HA) ceramic scaffolds are extensively used to induct the tissue growth for bone repair and replacement, and serve functions to support the adhesion, transfer, proliferation and differentiation of cells. Highly porous structure is always expected for its positive effect on the bone regeneration in vivo, nevertheless high porosity always accompanies a decrease in strength of the HA ceramic scaffolds. Therefore, it is significant to improve the strength of the HA ceramic scaffolds with highly interconnected porosity so that they are more suitable in clinic applications. The aim of this study is to investigate the effect of starting materials on mechanical property of final scaffold in order to optimize the preparation process. In this work, three starting HA particles with different morphologies are used to prepare highly porous HA ceramic scaffolds by the polymer impregnation approach in the same preparation process. The phase composition, microstructure and mechanical properties of the sintered porous HA scaffolds are investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM) and compressive test. The experimental results show that the particle morphologies have influence on the slurry viscosity and further affect the coating amount on the sponge. The porous HA ceramics fabricated by spherical HA particle hold the highest compressive strength than the other two HA scaffolds for better sintering property. It is an effectively method to improve the mechanical property of porous HA ceramic scaffolds by optimizing the starting particle morphology.

Abstract: Recently the creation of calcium compounds with a highly controlled ultrastructure is noted as next generation materials for biomedical applications. Here we propose the novel method for synthsizing calcium nanoparticles using iron strange protein, apoferritin. Apoferritin was incubated in saturated Ca(HCO3)2 solution at 18 °C. Temperature of the reaction solution was then increased to 37 °C and left for 2 hours to make CaCO3 sedimentated. After removing the sediments in the bulk solution by centrifugation, the supernatant was concentrated. Saturated Ca(HCO3)2 was added to it and the mixed solution was incubated at 37 °C for 30 min. This process was repeated four times. With a Transmission Electron Microscope (TEM), nearly spherical particles with a diameter of about 6 nm were observed to form in the cavity of apoferritin. The nanoparticles were observed to have a lattice structure of spacing about 0.22 nm with high resolution TEM. With Energy Dispersive X-ray spectroscopy (EDS) analysis, the peak of Ca (Kα; 3.7 keV) was detected from a synthesized nanoparticle. According to the solvent condition, nanoparticles formed in the apoferritin cavity would be CaCO3.