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Processing and characterization of hydroxyapatite-based bioceramic pastes Chae, Taesik

Abstract

Repair of skeletal defects and filling fracture gaps requires bioactive, biocompatible, biodegradable and easy to handle bone grafts. Although synthetic hydroxyapatite (HAp) based pastes are very good candidates for such bone grafting applications (as they meet most of these requirements), there is a need for improved handling of such pastes. In the present research, a processing technology was developed for improving the injectability of HAp paste through surface modifications of HAp with surfactants. A novel syringe-based system for simple, practical assessment of paste's flow and injectability was developed to correlate viscosity of the modified paste with its flowability. HAp-based bioceramic pastes were prepared by combining HAp powder and surfactants in an intensive planetary ball milling in three kinds of liquid media: 1) distilled water, 2) binary solution of water and ethylene glycol (EG) and 3) poly(dimethyl siloxane) (PDMS). In order to observe the effect of tri-sodium citrate (TSC) on flowability of the pastes, it was dissolved in each of the water-containing liquids. The pastes were carefully loaded into a novel syringe-based practical viscometer for injection tests using Instron Universal Testing System. It was found that TSC was very effective in reducing viscosity of the HAp pastes. EG was also found to be helpful for homogenization of the pastes. It is hypothesized that the citrate ions from TSC induced negative surface charges on HAp particles, which resulted in homogeneously dispersed HAp in the pastes. The hydrocarbon steric layer on HAp particles produced by EG molecules also induced less agglomeration of the particles in the pastes. These two surfactants helped to achieve good flowability of the water-based HAp pastes. However, high viscosity and hydrophobicity of PDMS caused poor mixing and increased viscosity of the pastes. It was also found that the custom-developed syringe-based practical viscometer can be conveniently used to quickly assess flowability of pastes of very high viscosity.

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