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The effect of organic solvents on sol-gel hydroxyapatite and its application as biocoating

University of British Columbia

Hydroxyapatite (HAp) is widely used by the biomedical industry due to its excellent biocdmpatibility. The sol-gel process offers a relatively low temperature procedure to produce hydroxyapatite powders and thin films (<1 μm). The focus of the present study is to investigate the effect of different organic solvents (methanol, ethanol, and propanol) on the sol-gel HAp in the system of triethyl phosphite and calcium nitrate. Xray diffraction analysis, thermal gravimetric analysis, differential thermal analysis, and scanning electron microscopy (SEM) are used to investigate the phase evolution and the morphology of the HAp produced in this sol-gel system. Our results show that different organic solvents induce different HAp formation pathway. In methanol and propanol-based systems HAp forms as a result of transformation of intermediate crystalline calcium phosphate phases (such as Ca₃(P0₄)₂ and Ca₂P₂0₇) . Formation of HAp in ethanol-based system is attributed to crystallization from an amorphous, intermediate apatite phase. Titanium substrates were coated using the HAp sol. IR spectroscopy of the coatings revealed that carbonated hydroxyapatite is present in the coating, which is similar to that of the natural bone. In-vitro bioactivity test confirmed the bioactive nature of the coatings while no apparent difference was observed in the bioactivity of the coatings obtained from different solvent systems. The type of solvent, concentration of the solution, and heat treatment time affect the quality of the coatings on stainless steel wires. The coatings obtained from low concentration (1M) methanol-based solution, heat treated at 500°C for a period of 10 minutes were the most satisfactory. Coronary stents were also coated with HAp using this sol-gel system. The coating remained on the stent after the expansion of the stent using an angioplasty balloon.

Thesis/Dissertation

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2009-08-05

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http://hdl.handle.net/2429/11744

Materials Engineering

University of British Columbia

UBCV

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