Abstract:
Hydroxyapatite (HAP) coatings are used in orthopaedic surgery for bone regeneration.
Current methods of phase quantification of HAP coatings suffer from drawbacks. A
novel methodology of quantitative phase analysis of HAP coatings has been devised and
validated. This method, based on whole pattern fitting with a fundamental parameters
approach, incorporates amorphous calcium phosphate (ACP) and apatite phases into
structural refinements.
A comparison of the structural and chemical properties of plasma sprayed (PS) and novel
electrodeposited (ED) HAP coatings has been conducted. ED coatings contained less
ACP and more preferred orientation than the PS coatings, although the stoichiometry was
similar.
In vitro investigations of PS and ED coatings in simulated body fluid and foetal calf
serum revealed that both are bioactive. A carbonated apatite layer produced on the ED
coatings was -0.7μm thick with a stoichiometry and chemical constituents similar to that
of natural bone apatite.
PS coatings produced a nanocrystalline carbonated apatite layer (-4μm). For the first
time it has been possible to model crystalline HAP and nanocrystalline apatite as
independent phases and obtain accurate lattice parameters for each.
A positive linear correlation has been made between microstrain and the solubility of
HAP and carbonated apatites. Dissolution studies have shown that the behaviour of HAP
and carbonated apatite is dominated by crystallite size at low undersaturation and by
crystallite size and microstrain at high undersaturation for crystallites between -30OA-
1000A. Metastable equilibrium occurred for crystallites <_400A at low undersaturation.
Carbonate content did not affect the solubility or dissolution behaviour.
A novel technology for coating polymeric tape with HAP for potential use in anterior
cruciate ligament reconstruction has been devised. Mechanical tests have demonstrated
that no adverse properties are induced by the coating technology. Cell culture studies
have shown that the HAP layer is capable of enhanced attachment, proliferation and
differentiation of osteoblast cells compared to uncoated tape.
