Biphasic composite of Tricalcium phosphate reinforced with Hydroxyapatite Whiskers
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Biphasic Composite of Tricalcium Phosphate Reinforced with Hydroxyapatite Whiskers B.Viswanath and N.Ravishankar Materials Research Center, Indian Institute of Science, Bangalore, India. Abstract Biphasic calcium phosphates have received considerable attention due to their optimum dissolution rate in the human body after implantation. These materials are composed of hydroxyapatite (HA) and resorbable tricalcium phosphate (TCP). In the present investigation, HA whiskers are reinforced into TCP to enhance the mechanical properties of this biphasic composite. Various amounts (30-50 wt%) HA whiskers are reinforced in TCP matrix. Microstructural characterization has been carried out using field-emission scanning electron microscope. Mechanical properties have been investigated by microindentation in a universal testing machine (UTM). As TCP is resorbable, it will dissolve in body fluid and there is a strong possibility for the faceted HA whiskers to interact with functional groups present in the body fluid surroundings. l. Introduction Biphasic calcium phosphates, comprising a mixture of stable hydroxyapatite [HA, Ca10(PO4)6(OH)2] and resorbable β-tricalcium phosphate [β-TCP, Ca3PO4], are considered better than single phase HA for implant applications. The advantage of the biphasic composite lies in the fact that the dissolution rates of the components are different (low for and high for β-TCP) [1]. Thus, the right combination of the HA and β-TCP will have the optimum dissolution rate which will have the significant impact on the rapid formation of new bone at the implant site. Different routes have been reported in the literature to prepare the biphasic composites; mechanical milling and heating of Ca-deficient apatites being the primary ones [2]. Other than the dissolution rate, the composite should have sufficient mechanical properties for application in implants, bone grafting or filling of bone defects. Especially important are the hardness to resist abrasion, toughness to withstand load and low modulus of elasticity (to avoid stress-shielding effect). There has been little effort so far to enhance the mechanical properties of HA-TCP biphasic composites. The present investigation is an attempt to enhance the mechanical properties of the biphasic composite by reinforcing well-faceted HA whiskers into tricalcium phosphate matrix. In addition to enhanced mechanical properties, the reinforced HA whiskers will have the desirable surface physico-chemical interactions with the amino acids in the biological systems [3].
ll. Experimental (a) Synthesis of HA whiskers Nanocrystalline powder of hydroxyapatite was prepared by drop-wise addition of diammonium hydrogen phosphate into a calcium nitrate solution and the pH of the mixture was adjusted to 11 with the addition of ammonium hydroxide solution. After the completion of the precipitation reaction, the precipitate was kept at room temperature for 48 hours. Then, the precipitate was washed, filtered and dried at 100°C for 12 hours. This HA powders used as a pr
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