Samir Kumar Ghosh

Efficacy of nano-hydroxyapatite prepared by an aqueous solution combustion technique in healing bone defects of goat

The present study was undertaken to evaluate porous hydroxyapatite (HAp), the powder of which was prepared by a novel aqueous solution combustion technique, as a bone substitute in healing bone defects in vivo, as assessed by radiologic and histopathologic methods, oxytetracycline labeling, and angiogenic features in Bengal goat. Bone defects were created in the diaphysis of the radius and either not filled (group I) or filled with a HAp strut (group II). The radiologic study in group II showed the presence of unabsorbed implants which acted as a scaffold for new bone growth across the defect, and the quality of healing of the bone defect was almost indistinguishable from the control group, in which the defect was more or less similar, although the newly formed bony tissue was more organized when HAp was used. Histologic methods showed complete normal ossification with development of Haversian canals and well-defined osteoblasts at the periphery in group II, whereas the control group had moderate fibro-collagenization and an adequate amount of marrow material, fat cells, and blood vessels. An oxytetracycline labeling study showed moderate activity of new bone formation with crossing-over of new bone trabeculae along with the presence of resorption cavities in group II, whereas in the control group, the process of new bone formation was active from both ends and the defect site appeared as a homogenous non-fluoroscent area. Angiograms of the animals in the control group showed uniform angiogenesis in the defect site with establishment of trans-transplant angiogenesis, whereas in group II there was complete trans-transplant shunting of blood vessel communication. Porous HAp ceramic prepared by an aqueous combustion technique promoted bone formation over the defect, confirming their biologic osteoconductive property.

Solution Combustion Synthesis of Calcium Hydroxyapatite Nanoparticles

Nanoparticles of calcium hydroxyapatite, Ca10(PO4)6(OH)2, (HA) an important material for biomedical applications and other non-medical uses were synthesized by combustion in the aqueous system Ca-nitrate—diammonium hydrogen orthophos-phate-urea. The combustion behaviour and phase evolution with respect to the Ca/P atom ratio in the starting materials were investigated. Single-phase hydroxyapatite particles were obtained when the Ca/P ratio in the starting batch was 1.75. Below this ratio the products contained mainly hydroxyapatite and tricalcium phosphate (Ca3(PO4)2, TCP), the relative abundance of these phases being dependent upon the batch composition. In all these cases, the particles were equiaxed, nanosized (60—130 nm) and occurred as easily dispersible soft agglomerates of sizes ranging from 0.1 to larger than 100 μm. The products were characterized for phase contents, particle size distribution and morphology.

Reaction Processing of Interpenetrating Phase AI2O3/AI Composite: Synthesis, Microstructure and Mechanical Properties

Dense AI2O3/AI composites containing three-dimensionally interconnected ceramic and metallic phases were fabricated by a displacement reaction between solid silica glass rods and molten aluminium. These composites consist of about 69% Al2O3 and 31% Al by volume. Their mechanical properties, namely, compressive strength, bend strength and microhardness are determined by the conventional procedures. The experimentally obtained data are compared with the theoretically derived one-point method. Elastic modulus, as determined by flexure testing, falls outside the Voigt-Reuss bounds. Although the two phases are interconnected in the composites to form an interpenetrating microstructure, the metallic phase is found to govern the modulus. Thermal treatments during fabrication and the interpenetrating microstructure strongly influence both the compressive and flexural strengths and the hardness of the final composite.

Machining of Interpenetrating Phase Alumina/Aluminium Composite by Electrical Discharge Technique

Factors influencing the behaviour of alumina/aluminium interpenetrating phase composite during wire-cut electrical discharge machining (WEDM) are studied. Machining performance in terms of material removal rate (mm1.mm−1) and surface roughness (Ra) were compared under different machining conditions. Results show that the machining process affects the surface quality of the machined composite. Under the conditions of the present study, the cutting rate and surface roughness are inter-dependent and vary between 5 and 8 mm3.min−1 and 3 and ~4 μm, respectively. WEDM cutting gives rise to the formation of a heat-affected surface layer containing pores and a few cracks. The results are analyzed using the prevailing concepts of electro-discharge machining.

Elastic constants of interpenetrating phase alumina/aluminium composites

Dense, pore-free interpenetrating phase Al2O3/Al composites were synthesized by a condensed phase displacement reaction between silica and aluminium, and their elastic costants were determined by an ultrasonic technique. Comparisons are made between the experimental data and analytical theoretical models of Voigt-Reuss (V-R) and Hashin-Shtrikman (H-S). Youngs moduius of these composites obey both the V-R and H-S bounds but is better predicted by the Hashin-Shtrikman model. The H-S bounds for the bulk and shear moduli are very narrow and the experimental values are close to the limit calculated on the basis of alumina as the matrix phase. The microstructural features of these composites, namely, a limited variation in the phase content and somewhat larger range of contiguity values seem not to have any significant influence on the elastic behaviour of the composites. Poissons ratio is essentially constant in these composites. Within a small range of phase composition used in this study, it can still be deduced from the results that the contiguity of the Al2O3, phase influences the elastic properties to an extent.