Biomedical subjects

K H Prakash

Publications and source records attributed to K H Prakash.

4 recordsLinked to original sources

PubMed2006

Apparent solubility of hydroxyapatite in aqueous medium and its influence on the morphology of nanocrystallites with precipitation temperature.

Two differing wet-chemical synthesis routes, Ca(OH)2 + H3PO4 and CaCl2 + Na3PO4/NaOH, were used to prepare hydroxyapatite (HA) at various temperatures ranging from 30 to 95 degrees C. The electrical conductivity of the solution was measured at regular intervals of time during H3PO4 and Na3PO4 addition to the suspension/solution containing Ca2+ ions. The rate of change of conductivity is used to note the end point of the reaction. X-ray diffraction of the dried, precipitated particles revealed HA as the predominant phase, and the FTIR spectroscopy studies indicated the presence of CO3(2-) groups which substituted PO4(3-) groups in the HA lattice (B-type). FESEM observations revealed that the aspect ratio of the particles decreased with increasing precipitation reaction temperature in one system [Ca(OH)2 + H3PO4] and in the other system it increased with increasing temperature. The changes in the morphology with temperature were analyzed through conductivity measurements and the thermochemical properties of the reaction systems. Conductivity measurements showed that the concentration of dissolved ions at the end point of the reaction between Ca(OH)2 and H3PO4 increased, indicating an increased apparent solubility of HA with increasing temperature, whereas the end-point conductivity did not increase noticeably in the other reaction system.

Chemical Precipitation↗

PubMed2006

Conductometric study of precursor compound formation during wet-chemical synthesis of nanocrystalline hydroxyapatite.

Conductometry was employed to study the phase evolution of calcium phosphate compounds during the wet-chemical synthesis of hydroxyapatite (HA). Calcium hydroxide and orthophosphoric acid were used to prepare HA at various temperatures ranging from 30 to 95 degrees C. The electrical conductivity and pH of the reaction mixture were measured at regular intervals of time during acid addition, and the rate of change of conductivity was used to decipher the end point of the reaction. Our previous studies have shown that the end product of this reaction route yields mildly carbonated crystalline HA. The trend of the change in conductivity with time was similar at all temperatures. The conductivity curves were divided into three regions based on the variation in slope of the curves. The slope of the curves decreased with increasing temperatures in the first two regions, and the slope is greater in the second region than in the first. From the conductivity and pH measurement results, the possible precursor phase was identified and it had the composition Ca(3)(PO(4))(2). The kinetics of phase transformation was also analyzed and compared to previous work. The similarities between this work and the traditionally adapted experimental work for phase formation and transformation kinetics are highlighted, and the novelty in the current work is discussed.

Acids↗

PubMed2006

On the kinetics of apatite growth on substrates under physiological conditions.

Derived from reaction kinetics, a simple but useful method, based on "apatite forming capacity" or AFC of solutions mimicking blood plasma, is proposed to decipher the rate of calcium phosphate mineralization. Apatite growth rate constants were calculated using this method for a model composite surface varying the volume fraction of synthetic hydroxyapatite (HA) in a polymer matrix. Previously reported data for mineralized surfaces on Ta, Ti, and its alloys are also analyzed similarly and compared. Utilizing the growth rate constant, the bioactivity of the materials was indexed in vitro. Complementarily, semiempirical quantum mechanical calculation (ZINDO method) showed that the interaction of cations with TRIS-hydroxymethyl aminomethane molecules in the solution is stronger than that with the polymer substrate considered, but weaker than hydrated Ti and TiO(2) surfaces. This analysis then quantifies for example the extent of polymer inertness and the "bioactivity" of alkali treated Ti. The growth rate constants for the model materials prepared in this work are explained on the basis of localized dissolution of HA, the amount of which simply increases with increasing volume fraction of HA in the composite.

Apatites↗

PubMed2004

Temperature driven morphological changes of chemically precipitated hydroxyapatite nanoparticles.

Hydroxyapatite (HA) is synthesized by a wet chemical route using calcium hydroxide and ortho-phosphoric acid at various temperatures (40, 80, and 100 degrees C). X-ray diffraction of the precipitate particles revealed HA as the predominant phase (>99%) with a small amount of beta-tricalcium phosphate. Fourier transform infrared spectroscopy indicated the presence of carbonate substitution, which decreased with increasing temperature. Transmission electron microscopy observations revealed needle-shaped particles with a high aspect ratio at 40 degrees C, which changed to spheroidal when the precipitation temperature was increased to 100 degrees C. The changes in the morphology with temperature were analyzed taking into account the driving force for the HA precipitation and the supersaturation level of Ca2+ and PO4(3-) ions with respect to HA. The analysis indicated that the supersaturation level of the reactants, especially the concentration of Ca2+ ions, played a predominant role on the precipitate morphology for this classical acid-base reaction.

Chemical Precipitation↗