Biocompatible whiskers with controlled morphology and stoichiometry

Abstract

Hydroxyapatite whiskers have been prepared by the hydrothermal method. The crystals had diameter, length, and aspect ratio in the range of 1–10 μm, 30–50 μm, and 5–20, respectively. Their Ca/P molar ratio varied from 1.59 to 1.62. The morphology of the crystals can easily be controlled by the concentrations of species in the starting solution, while the Ca/P ratio is almost independent of them. Through the reaction with calcite powder at 600 °C, the Ca/P ratio of the whiskers has been improved even to the stoichiometric value of 1.67. Taking into account morphology and chemical composition of the HAp whiskers, they should not be health hazardous and may find applications as substitutes for asbestos and other fibrous materials which presently have restricted use because of their carcinogenic natures.

Molten Salt Synthesis of Calcium Hydroxyapatite Whiskers

“…For the molten-salt-synthesized HA whiskers of the present study, the previously mentioned problem (for the whiskers synthesized by the hydrothermal method) [3][4][5][6] of morphologic degradation apparently was not present. The W4 whiskers retained their shapes perfectly, formed a skeleton of HA, and just fused together at the points of mutual contact.…”

“…Then, 0.090 mol of (NH 4 ) 2 HPO 4 (99.8% purity, Merck) was dissolved in that solution. Following that step, 115 mL of 24 vol% NH 4 OH was added, in its entirety, to the above-described opaque solution. The solution was heated and vigorously stirred at 60°-70°C for 3 h, on a hot plate.…”

“…[2][3][4][5][6][7][8][9] However, the whiskers synthesized by these methods 4 -6 suffer from nonstoichiometry (i.e., calcium deficiency) and have low thermal stability, i.e., they partially decompose into a ␤-TCP phase (5-35 vol% TCP), even after 1 h of heating at 1100°C. Moreover, Suchanek et al 5 have reported that, for HA composite ceramics reinforced with hydrothermally synthesized HA whiskers (ϳ30 vol% whiskers), the whiskers disappear within the HA matrixes at sintering temperatures Ն1000°C and turn themselves into large, equiaxed grains.…”

Calcium phosphate biomaterials from marine algae. Hydrothermal synthesis and characterisation

“…All the spectra shown give rise to the characteristic absorption bands of HAp [53][54][55][56][57][58][59][60][61][62][63] . The bands at 565, 602, 1045 and a shoulder at 960 cm -1 can be attributed to the PO 4 3-ions.…”

Hydrothermal technology for nanotechnology

“…Greater flexibility in tailoring HAp crystal size and morphology by the hydrothermal technique could be achieved through precipitation from homogeneous solutions containing both Ca and P. Use of chelating agents for Ca, such as lactic acid or EDTA, prevents formation of ACP upon mixing sources of Ca and P at room temperature. However, published work with these chelating agents shows that anisotropic fibers are also formed [177,178]. Thus, future work will need to identify additives that inhibit anisotropic particle growth.…”