Calcium phosphate bone cements are currently used in a range of applications; however, their low compressive strength and brittle failure mechanics have limited their widespread application. The aim of this study was to improve the mechanical performance of the calcium phosphate cement by means of particle reduction of the powder components involved. alpha-Tricalcium phosphate (alpha-TCP) powder was produced and subsequently reacted with water to form a calcium-deficient hydroxyapatite in the form of a biocompatible and resorbable cement. It was postulated that the reduction of the alpha-TCP particle size would result in a faster-setting reaction and stronger cement. Three milling techniques were explored and their methods optimized. The techniques included the traditional ball-milling technique and two newer techniques, namely cryogenic and planetary milling. Particle size analysis through laser diffraction and scanning electron microscopy was conducted. Compressive strength, setting times and injectability characteristics of the curing cement were determined. It was observed that all three techniques were efficient methods of particle reduction and the mechanical, setting and injectability properties were significantly improved by the reduction in particle size of the alpha-TCP powder. However, agglomerations of alpha-tricalcium phosphate resulted in a reduction in compressive strength and injectability after prolonged milling periods, irrespective of milling technique.

Calcium phosphate cement (CPC) sets to form hydroxyapatite, a major component of mineral bone, and is gaining increasing interest in bone repair applications. However, concerns regarding its brittleness and tendency to fragment have limited its widespread use. In the present study, short-fibre reinforcement of an apatitic calcium phosphate has been investigated to improve the fracture behaviour. The fibres used were polypropylene (PP) fibres, 50 microm in diameter and reduced in length by cryogenic grinding. The compressive strength and fracture behaviour were examined. Fibre addition of up to 10 wt % had a significant effect on composite properties, with the energy absorbed during failure being significantly increased, although this tended to be accompanied with a slight drop in compressive strength. The fibre reinforcement mechanisms appeared to be crack bridging and fibre pull-out. The setting time of the CPC with fibre reinforcement was also investigated and was found to increase with fibre volume fraction.

The strategic incorporation of bioresorbable polymeric additives to calcium-deficient hydroxyapatite cement may provide short-term structural reinforcement and modify the modulus to closer match bone. The longer-term resorption properties may also be improved, creating pathways for bone in-growth. The aim of this study was to investigate the resorption process of a calcium phosphate cement system containing either in polyglycolic acid tri-methylene carbonate particles or polyglycolic acid fibres. This was achieved by in vitro aging in physiological conditions (phosphate buffered solution at 37 degrees C) over 12 weeks. The unreinforced CPC exhibited an increase in compressive strength at 12 weeks, however catastrophic failure was observed above a critical loading. The fracture behaviour of cement was improved by the incorporation of PGA fibres; the cement retained its cohesive structure after critical loading. Gravimetric analysis and scanning electron microscopy showed a large proportion of the fibres had resorbed after 12 weeks allowing for the increased cement porosity, which could facilitate cell infiltration and faster integration of natural bone. Incorporating the particulate additives in the cement did not provide any mechanism for mechanical property augmentation or did not demonstrate any appreciable level of resorption after 12 weeks.