Callcut, Suzanne; (2001) Production and Characterisation of Reticulated Glass Reinforced Hydroxyapatite Foams for Hard Tissue Surgery. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Hydroxyapatite is a calcium phosphate, which in its synthetic form closely resembles the apatite within the hard tissues of the body such as bone, dentine and enamel and consequently is biocompatible in vivo. Porous hydroxyapatite is of current interest, as the porosity will allow intimate ingrowth of bone leading to rapid regeneration of hard tissue. A novel route found for the preparation of porous hydroxyapatite has involved the use of reticulated foam technology. This technique has been applied in this project along with the addition of a glass to act as a sintering aid; to produce reticulated glass-reinforced hydroxyapatite foams with two different pore size distributions. To produce the porous hydroxyapatite foams, hydroxyapatite slips were firstly optimised with an anionic deflocculant, using rheological tests and zeta potential measurements. The polyurethane foams were then coated with the slip and subsequently burnt off to leave behind reticulated ceramic foams. The foams were then characterised using density measurements, XRD, SEM, Image analysis and mechanical testing. It was found through rheological and zeta potential measurements that the optimal deflocculant addition for the slips was 0.2wt%. Compression testing results showed that the materials exhibited properties typical of isotropic open cellular foams and that using a glass sintering aid improved the mechanical properties from a compressive strength of 0.01 MPa for HA only to 0.03MPa with a sintering aid. The density and compressive strength was further enhanced by the application of additional coatings such that improvements from 0.03MPa with one coat to 0.08MPa with two coats were achieved using the optimal glass addition of 2wt%, and a sintering time of 8 hours. The foams with the small distribution of pores and pore sizes also gave higher mechanical properties. Image analysis confirmed that the structure of the polyurethane template was conserved during the processing procedure and that the pore size distribution remained the same. However, the actual pore sizes decreased by approximately 0.05mm during sintering.

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