Key Engineering Materials Vols. 361-363

Abstract: Comparison of two experimental techniques of silicon-contained and/or silica-substituted calcium phosphate preparation from Ca(NO3)2·4H2O, NH4H2PO4, fumed silica and aqueous solution of NH4OH was performed. The first technique was a traditional one, in which the final product was synthesized in an aqueous solution by the well-known sol-gel process, followed by phase separation, washing off, drying and high-temperature sintering. An environmentally friendly direct preparation route was the second technique, in which the initial chemicals were mixed in the necessary proportions inside a crucible, followed by a high-temperature sintering of the entire mixture. The sintered powders were analyzed by the standard measurement techniques. Intentional variations from the stoichiometry within ±10% of the amounts of the mixed chemicals were employed to compare the vulnerability of both preparation techniques to random fluctuations of the processing parameters. The results revealed a better reproducibility and a higher yield of the direct preparation technique but the traditional sol-gel technique was found to be able to compensate accidental technological imperfections.

Abstract: The present work was performed to improve the mechanical strength of porous calcium phosphate blocks by adding a little amount of montmorillonite mineral to the calcium phosphate composition. 3.5 wt % of the montmorillonite mineral was added to the slurry of precipitated hydroxyapatite and the porosity was produced by infiltration of a polymer template. After the firing process (1200 oC), the compressive strength, phase composition, morphology and dissolution behavior of the porous bodies were evaluated by appropriate techniques. It was found that the additive improved the mechanical strength but decreased the dissolution rate of the porous calcium phosphate body. Also the final composition of the porous block (i.e. hydroxyapatite, HA, and β- tricalcium phosphate, β-TCP) was not influenced through the presence of the additive. It is suggested that the montmorillonite mineral can improve the sintering performance of the HA and β- TCP.

Abstract: Long HA whiskers with uniform morphology, high aspect ratio, and good crystallinity could be prepared using a hydrothermal technique at 180 oC for 10 h. Whisker morphology was sensitively-dependent on preparation conditions. Compared with formamide and urea, acetamide showed a low hydrolysis rate; it was found to be an appropriate additive to synthesize HA whiskers. Length and aspect ratio could be controlled by selecting solution conditions with the Ca/P ratio at 1.67 in the range 42 - 84 mmol/L calcium and 25 - 50 mmol/L phosphate and 0.75 – 1.25 mol/L additive concentration (as amide, -NH2).

Abstract: An appropriate scaffold, which provides structural support for transplanted cells and acts as a vehicle for the delivery of biologically active molecules, is critical for tissue engineering. We developed a fully interconnected globular porous biphasic calcium phosphate ceramic scaffold by adopting a foaming method, and evaluated its efficiency as a bone substitute and a scaffold for bone tissue engineering by in vitro and in vivo biocompatible analysis and its osteogenic healing capacity in rat tibial bone defects. They have spherical pores averaging 400um in diameter and interconnecting interpores averaging 70um in diameter with average 85% porosity. They elicited no cytotoxicity and noxious effect on cellular proliferation and osteoblastic differentiation during the cell-scaffold construct formation. Also the bone defects grafted with fully interconnected globular porous biphasic calcium phosphate ceramic blocks revealed excellent bone healing within 3 weeks. These findings suggest that the fully interconnected porous biphasic calcium phosphate scaffold formed by the foaming method can be a promising bone substitute and a scaffold for bone tissue engineering.

Abstract: Several novel methods for the production of calcium phosphate based functional gradient materials have been explored. The processes involved the use of polyurethane foams with a different number of pores per inch which were joined together in a variety of ways to form unique templates prior to vacuum impregnation with a ceramic slip. Before processing, rectangular blocks of foam were joined by stitching or trapezoidal blocks were compressed into rectangular shapes to produce a gradient of porosity along the length of the template. Four-point bend testing of the sintered samples which combined two porous structures showed them to have comparable mechanical properties to homogeneous ceramics based on foam templates with uniform pore sizes, with no evidence of weakness at the interface. The method was further developed to make a cylindrical sample with two diverse porous structures which more closely mimic the natural bone morphology. The two very different areas, which represented cortical and cancellous bone, had good structural integrity at the interface.

Abstract: Adsorption experiments of bovine serum albumin on hydroxyapatite previously annealed at temperatures up to 1100°C was performed at 37°C and phosphate buffer, pH 6.0. Kinetic process was very efficient and irreversible for low phosphate buffer concentration. Thermal treatment contributed to the decrease of bovine serum albumin immobilization indicating that sorption process depended on HA specific surface area and the number of surface active sites. However, it was verified that particle size was also an important parameter for bovine serum albumin immobilization.

Abstract: A porous silicon-containing hydroxyapatite has been prepared using natural coral as a calcium source to obtain a biomaterial having an improved biocompatibility. From the XRD analysis, it was confirmed that the single-phase hydroxyapatite containing silicon has formed without revealing the presence of extra phases related to silicon dioxide or other calcium phosphate species. Silicon content is ranged from 0.5wt% to 1wt% by weight. The porous silicon-containing hydroxyapatite blocks were inserted into the 5mm diameter of drill holes made through the lateral femoral condyles of New Zealand white rabbits. The new bony formation did not begin after 1 week. At 3 week, bony ongrowth to the inserted porous silicon-containing hydroxyapatite block could be found, and the new bone surrounded the inserted block entirely after 24weeks. Based on in-vivo test, Si-containing porous hydroxyapatite derived from coral possesses high biodegradability and can be considered a useful material for bone implants.

Abstract: The purpose of this study was to evaluate synthetic calcium phosphates and animal bones using Raman spectroscopy and explore the possibility of its application in characterizing newly formed bone around implants. Synthetic calcium phosphates (monobasic calcium phosphate, dibasic calcium phosphate, tribasic calcium phosphate, fiber apatite, hydroxyapatite and carbonate hydroxyapatite) and animal bones (from pig, cow, rabbit with and without implants) were analyzed in this study. Slight differences in the Raman bands among the 7 types of synthetic calcium phosphate were observed. Furthermore, a 3 cm-1 difference was noted in the bands of the main PO4 3- in rabbit’s bone formed around the implant, compared to the existing bone, suggesting a difference in the molecular structure between the existing and newly formed bones.

Abstract: In order to modify the biological properties of pure hydroxyapatite (HAp), two kinds of zinc-containing HAp, which had zinc content of 5.10wt% and 2.54wt%, respectively, were synthesized via sol-gel technique. The obtained coatings were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Then the antibacterial effects were evaluated through bacteriostatic test on Streptococcus mutans (S.mutans) in vitro and zinc ions releasing ability was investigated through detecting the zinc ions concentration by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The obtained coatings were observed to possess typical apatite peaks in XRD patterns and high homogeneous and porous surfaces in SEM morphology. The coating layer demonstrated good releasing ability in Brain Heart Infusion (BHI) liquid and obviously inhibitory effects to the growth and proliferation of S. mutans. Based on the results obtained above, it is concluded that the sol-gel derived zinc-containing hydroxyapatite could be applied as an antibacterial effective biomaterial.

Abstract: Calcium is generally determined by EDTA titration after separation of phosphate radicals, and the phosphorus is determined by weigh method. This traditional analytical process is time consuming and unfavourable for quality controlling. In contrast, the ICP-AES is simple and fast, and can simultaneously determine multielements. In this paper, the ICP-AES method was used to simultaneously determine calcium and phosphorous in calcium phosphate based bioceramics, and wavelengths of 317.933 nm and 213.618 nm were selected for the measuring of the calcium and phosphorus, respectively. The results obtained by ICP-AES are well consistent with the results determined by the traditional EDTA titration and weigh method, and suggest that the ICP-AES analysis is a simple, fast and accurate method for simultaneous determination of calcium and phosphorous in calcium phosphate based bioceramics.