Bioceramics 24

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Authors: Fu Zeng Ren, Yang Leng, Xiong Lu
Abstract: ab initio simulations were employed to investigate the crystal structure of carbonated apatite (CAp). Two possible sites for the carbonate ions in the apatite lattice were considered: carbonate substituting for OH- ion (type-A) and for PO43- ion (type-B). A combined type-AB substitution was also proposed and numerous possible charge compensation mechanisms were treated. The results show that the most stable type-A CAp had its carbonate triangular plane almost parallel to c-axis, making an angle of about 2° at z = 0.46. In the most stable type-B CAp structure, the nearest Ca (2) ion was replaced by a sodium ion and the carbonate group was lying almost flat in b/c-plane. Of all the models considered, mixed substitution type-AB where two carbonate ions replacing one phosphate group and one hydroxyl group shows the most stable structure.
Authors: Ill Yong Kim, Koichi Kikuta, Chikara Ohtsuki
Abstract: Morphological control on hydroxyapatite (HAp) crystals is one of attractive researches to produce novel bioactive materials for repairing bone defects. Hydrothermal processing has been applied to fabricate well-grown crystals of HAp, through a reaction from appropriate calcium and phosphate sources. We recently found that oriented structure was observed when single crystal of calcium carbonate was used as a starting material for the hydrothermal processing. However, the detailed process on the orientation of HAp crystals has been not clarified yet. In the present study, we investigated the effects of the crystalline planes of calcite on HAp formation through the hydrothermal condition. Calcite single crystals with either of {100} or (111) plane was used as a starting material to examine the difference of the reactivity in a phosphate solution. After the hydrothermal treatment at 160 °C for 24 h, the surfaces and cross-sections of starting materials were characterized. Rod-shaped HAp crystals were oriented on the surface of the starting material with {100} plane, whereas small HAp crystals formed on the starting material with (111) plane followed by growth to same direction that were observed on the sample with the {100} plane. The difference in the morphology of the formed HAp was caused by the reactivity of each crystal plane.
Authors: Natsuko Ito, Masanobu Kamitakahara, Koji Ioku
Abstract: Octacalcium phosphate (OCP) is regarded as a precursor of hydroxyapatite (HA) which is a main inorganic comstituent of human bones and teeth. OCP is becoming regarded as an important biomaterial. Recently, implanted OCP was found to be converted to apatitic phase in the body and support bone regeneration. Therefore, it is important to reveal the transformation mechanism of OCP to HA for revealing the mechanism of bone formation and for the development of biomedical materials for bone. In this study, we focused on the dissolution of OCP and precipitation of HA. OCP particles were immersed in distilled water at 60 °C. The temporal change of the immersed powders and immersing solution were examined, and the transformation mechanism of OCP to HA was discussed. As there was an unreactive period in the first stage of the transformation, HA crystals seemed to grow easily once HA nuclei were formed. It is speculated that HA nuclei formed on OCP crystals by heterogeneous nucleation, and then HA crystals grow using calcium and phosphoric ions supplied from dissolved OCP.
Authors: Taro Nikaido, Kanji Tsuru, Giichiro Kawachi, Melvin L. Munar, Shigeki Matsuya, Seiji Nakamura, Kunio Ishikawa
Abstract: The present study reports the synthesis of βTCP foam with fully interconnecting pores based on phase transformation of αTCP foam precursor by employing heat treatment. First, the αTCP foam precursor was fabricated by sintering the ceramics slurry-coated polyurethane foam template at 1,500°C. The resultant αTCP foam was again heated below α,β transition temperature for an extended period of times. After heating at 800°C for 150 hours, 900°C for 100 hours and 1,000°C for 300 hours, βTCP foam was obtained. The compressive strength of βTCP foam was approximately 46 kPa and the porosity was approximately 93%. The long heating period as well as heating temperature were the key to the transformation of βTCP phase. βTCP foam could be an ideal bone replacement since the invasion of bone cells into the pores provides optimum bone growth or repair.
Authors: G. Daculsi, Thomas Miramond, Pascal Borget, Serge Baroth
Abstract: The development of CaP ceramics involved a better control of the process of resorption and bone substitution. Micro Macroporous Biphasic CaP, (MBCP+) is a concept based on an optimum balance of the more stable phase of HA and more soluble TCP. The material is soluble and gradually dissolves in the body, seeding new bone formation as it releases Ca and P ions into the biological medium. The MBCP+ is selected for tissue engineering in a large European research program on osteoinduction and mesenchymal stem cell technology (REBORNE 7th EU frame work program, Regenerative Bone defects using New biomedical Engineering approaches, We have optimized the matrices in terms of their physical, chemical, and crystal properties, to improve cell colonization and to increase kinetic bone ingrowth. The fast cell colonization and resorption of the material are associated to the interconnected macropores structure which enhances the resorption bone substitution process. The micropore content involves biological fluid diffusion and suitable adsorption surfaces for circulating growth factors. The bioceramics developed for this project was fully characterized using X-Ray diffraction, FTIR, X-rays micro tomography, Hg porosimetry, BET specific surface area, compressive mechanical test, and SEM. Preclinical tests on the optimized scaffold were realized in critical size defects in several sites of implantation and animals (rats, rabbits, goats, dogs).The smart scaffold has a total porosity of 73%, constituted of macropores (>100µm), mesopores of 10 to 100µm and high micropores (<10µm) content of more or less 40%. The crystal size is <0.5 to 1 µm and the specific surface area was around 6m2/g. The in vivo experiment indicated higher colonization by osteogenic cells demonstrating suitable matrices for tissue engineering. The HA/TCP ratio of 20/80 was also more efficient for combination with total bone marrow or stem cell cultivation and expansion before to be implanted.
Authors: Taishi Yokoi, Ill Yong Kim, Kawashita Masakazu, Chikara Ohtsuki
Abstract: Calcium phosphatepolymer composites have been produced for bone-repairing. We have focused development of composites by a crystal growth technique in a hydrogel matrix, that is regarded as gel-mediated processing. Under the gel-mediated condition, reaction temperature is one of the major parameter to determine microstructure of the precipitated crystals. In the present study, we investigated effects of the reaction temperature on formation of calcium phosphates through gel-mediated processing where double diffusion technique was applied. Crystalline phases of calcium phosphate formed in the hydrogel were varied from octacalcium phosphate (OCP) to hydroxyapatite (HAp) with increasing the reaction temperature. OCP crystals formed at 4 and 40 °C had granular or spherical shape, while HAp crystals formed at 80 °C had rod shape. The HAp crystals were composed of a large number of fibrous crystals. The rod-shaped HAp crystals were oriented in the direction of ion diffusion. Formation of oriented HAp crystals was generated by increase in diffusion rate of ions in the hydrogel matrix after increasing reaction temperature in gel-mediated processing.
Authors: N. Demirkol, F.N. Oktar, E.S. Kayali
Abstract: The goal of this study is to produce and to investigate the mechanical and microstructural properties of composite materials made of hydroxyapatite, obtained from both natural sheep bone and commercial synthetic hydroxyapatite with niobium oxide addition ( 5 and 10 wt%). The samples were subjected to sintering at different temperatures between 1000°C and 1300°C. Microstructures and mechanical properties of sheep hydroxyapatite (SHA) and commercial synthetic hydroxyapatite (CSHA)-niobium oxide composites were investigated. The production of hydroxyapatite (HA) from natural sources is preferred due to economical reason. The aim of development of SHA and CSHA based niobium oxide composites is to improve mechanical properties of HA. The physical and mechanical properties were determined by measuring density, compression strength and Vickers microhardness (HV). Structural characterization was carried out with X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies. In all composites, density values and mechanical properties increased with increasing sintering temperature. The increase of niobium oxide content in all composites showed better mechanical properties. Both of SHA and CSHA composites with at 1300°C sintering temperature showed nearly the same compression strength value.
Authors: J. Feng, M. Chong, J. Chan, Z.Y. Zhang, S.H. Teoh, Eng San Thian
Abstract: The current available microcarriers were mainly targeted towards pharmaceutical industries, and might not be suitable for therapeutic implantation. As such, apatite-based microcarriers intended for bone tissue engineering applications would be featured here. Hydroxyapatite-Alginate (HA-Alg) suspension was extruded drop-wise into a calcium chloride (CaCl2) crosslinking solution. The HA-Alg microcarriers were then sintered to form microcarriers of uniform size. The physicochemical properties were analysed by scanning electron microscopy (SEM), X-ray diffractometery (XRD), and fourier transform infrared (FTIR) spectrophotometry. Cell viability on these microcarriers was evaluated using human fetal mesenchymal stem cells (hfMSCs). SEM images revealed that sintered apatite-based microcarriers exhibited a rough surface topology with interconnected pores. XRD results showed that these microcarriers remained phase pure since no other secondary calcium phosphate phases were detected. FTIR analysis indicated several sharp phosphate bands coupled with a hydroxyl band (all belonging to HA). Live/dead staining showed that hfMSCs remained viable after 14 days of culture, and cells have spread and covered the surfaces of the microcarriers. Certainly, these cell-loaded microcarriers could be potentially used in bone implant science.
Authors: Daiki Honda, Akari Takeuchi, Ishikawa Kunio
Abstract: Feasibility of starfish bone to be a source material for apatite bone substitute was investigated in the present study because starfish bone is known to be porous calcium carbonate. Starfish bone was assembly of Mg containing calcite granules. And the calcite granules had fully interconnected porous structure with approximately 20 µm of pore size. After the hydrothermal treatment of the calcite granules in Na2HPO4 aqueous solution, the granules were gradually transformed to apatite. Therefore, starfish derived calcium carbonate would be a candidate of a source material for carbonate apatite bone substitute.

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