Key Engineering Materials Vols. 361-363

Abstract: Silicate-substituted calcium phosphates have been shown to result in enhanced biological performance compared to the corresponding, silicate-free, calcium phosphates. We have produced a range of silicate-substituted alpha-TCP compositions using two different synthesis methods and two different substitution mechanisms. Single phase compositions were only observed for a silicate substitution of 1.3 wt% by both solid state synthesis and aqueous precipitation synthesis, although the latter was the result of a design composition with a higher silicate substitution (3 wt%). The silicate substitution resulted in small changes in the unit cell parameters of the alpha-TCP. More importantly, this small level of silicate substitution had a strong effect on the thermal stability of the alpha-TCP phase, with the silicate substitution stabilising the alpha-polymorph to lower temperatures. This has an immediate advantage in that the quenching conditions are not as critical for the production of silicate-substituted alpha-TCP compositions compared to silicate-free alpha- TCP.

Abstract: Micrometer-sized hydroxyapatite (HA) with rod-shape was prepared to investigate protein adsorption onto its crystal face, through hydrothermal processing. Adsorption of Bovine serum albumin (BSA) and Lysozyme from chicken egg white (LSZ) on rod-shaped HA crystals with approximately 50 μm in length and 1 μm thickness was examined in phosphate buffer solution. The amount of adsorbed BSA was decreased with increasing phosphate concentration in the examined solution. Adsorption of LSZ was increased with increasing phosphate concentration in the buffer solution up to 50 mmol/L (mM), while it was remarkably decreased when the phosphate concentration reached approximately 100 mM. These phenomena lead to understanding of chromatographic characters of HA for separation of acidic and basic proteins.

Abstract: The infrared and Raman spectra of Na substituted β-TCP are presented for various levels of substitution. The influence of Na content on main vibrational modes appears significant and among them the ν1 symmetric stretching band is very sensitive to PO4 3- tetrahedrons environment. Thus, this mode was particularly investigated and has been decomposed using Lorentzian shapes components. We assigned the calculated components to the different types of PO4 3- tetrahedrons present in the crystalline structure.

Abstract: The interaction of calcium phosphates with biological molecules under controlled conditions permits the formulation of meaningful conclusions concerning the driving forces. The uptake and release at the material-solution interface is the result of the various interactions between and within the system components which include the solid surface, the adsorbate, the solvent and other solutes present. The understanding of adsorption and desorption mechanisms with respect to active molecules can be exploited for the development of drug delivery applications.

Abstract: The present study examined the possibility of using spherical porous granules of hydroxyapatite (HA, Ca10(PO4)6(OH)2) composed of rod-shaped particles as the drug delivery system. The granules composed of rod-shaped HA were successfully prepared by an emulsion method and a hydrothermal treatment. When the rod-shaped granules were soaked in phosphate buffer salines containing lysozyme chloride or albumin, the granules of rod-shaped HA adsorbed more albumin than lysozyme. On the other hand, the HA granules prepared by a normal sintering method adsorbed little lysozyme chloride or albumin. The HA granules composed of rod-shaped particles are expected to be useful as carriers of negatively charged substances.

Abstract: In this work, we studied the surface/water interaction properties of a pure calcium hydroxyapatite (HA) and their modifications as a consequence of the partial Ca2+/Mg2+ (MHA) substitution by means of IR spectroscopy and microcalorimetry of adsorbed water. IR data indicated that water molecules in direct contact with the surface of HA are coordinated to surface cations and experience H-bond significantly stronger than in liquid water. The heats of adsorption associated to such interactions are very high, being twice-triple the heat of liquefaction of water. Interestingly, water experiences H-bond higher than in its bulk liquid state also in the second layer. Finally the entering in the material of Mg2+ ions was shown to significantly affect the affinity of the material toward water and the properties of its hydration layers.

Abstract: Two-step sintering was performed to prepare hydroxyapatite (HAp) with a high density and a fine microstructure utilizing hydrothermally synthesized nano powders. Its effectiveness was dependent on starting chemicals for precursors of HAp, powder processing condition, initial temperature in the two-step sintering, heating rate to the initial temperature, and holding time at final temperature. HAp powder, hydrothermally treated after aging of precipitate of Ca(OH)2 and H3PO4 for 48 h, led to HAp having a high phase stability at elevated temperatures, a high density, and a fine microstructure after two-step sintering with heating rate of 10°C/min to 1275°C.

Abstract: Both biochemical cell functional test and animal implantation test were done to investigate the reaction to fine particles. Particles cause nonspecifically phagocytosis to cells and inflammation to tissue for the size below 10m. With the size below 50nm particles may invade into the internal body through the respiratory or digestive system and diffuse inside body. Ti mapping by XSAM after the compulsory exposure test to the respiratory system showed the internal diffusion of 30nm TiO2 particles. They diffused with time course to lung, liver and spleen after injection from caudal vein. Nanoparticles might be the objects whose existence has not been assumed by the biophylactic system.

Abstract: Hydroxyapatite (HA) and barium titanate (BT) powders were mixed and sintered to form hydroxyapatite – barium titanate (HABT) ceramics. These materials were then poled and their piezoelectric properties were measured. The microstructure of unpoled samples was examined using scanning electron microscopy (SEM).The piezoelectric constants (d33 and d31) of the ceramics were found to be dependent on the proportion of BT in the ceramic In materials containing less than 70% BT, no piezoelectric effect was found. Above this value, the piezoelectric constant increased with the addition of BT up to a value of 108pCN-1 for pure BT. Values of d33 for ceramics containing more than 80% BT are above values previously shown to have a positive influence on bone growth in vivo. SEM analysis indicated that the grain size within the materials decreased as the proportion of BT in the material was reduced. Examination of the microstructure of the ceramics indicated the presence of electrical domains in the 100% BT and 95% BT ceramics. Domains were not visible below 95% BT. The reduction in grain size may influence the reduction in piezoelectric activity within the materials but cannot be considered to be the only cause.

Abstract: Dense bioceramics made of pure hydroxyapatite (HA) was prepared and characterized. The cylindrical samples were compacted from HA powders of diverse pretreatments; namely, from spray-dried HA, calcined HA and mixtures thereof. The samples were prepared by a hydraulic press under different compaction loads both with and without auxiliary compounds (a binder and a lubricant). Both the total mass and geometrical dimensions of the prepared cylinders were measured. Then, the cylindrical samples were sintered at 1200 °C for 4 hours. After cooling down to ambient temperature, the sintered cylinders were weighed and their geometrical dimensions were measured once again. Mass decreasing and the shrinkage degree were calculated as a result. Afterwards, the compression strength of the sintered cylinders was measured by an Instron 5587 machine. Preparation of dense HA bioceramics possessing the highest possible compression strength was the purpose of this study. The necessary processing parameters were discovered.