Fibre Reinforced Ceramic Composites

In recent times, calcium phosphate (CaP) based materials have been applied for the augmentation of bone defects. They are available as allogenic, sintered or cementitious materials. Unfortunately these materials have very poor tensile and shear properties [59]. Calcium phosphate cements (CPCs) strength is less than that of bone, teeth, or sintered calcium orthophosphate bioceramics [60] due to their inherent brittleness, which restricts their use non-load bearing defects [61]. To overcome this problem, many researchers developed new CaP based materials to improve mechanical properties of composites using novel methods, including the addition of additives to the CaP composites either by using polymers that interpenetrate the porous matrix or via fibrous reinforcement. Interpenetration of polymer into porous matrix has been shown to improve the mechanical properties - however some limitations have been demonstrated, e.g. lack of biodegradability, rigidity, ductility [61, 64, 65]. The other major problem is the sterilisation requirement for biomaterials and medical devices, which may affect the polymer properties. Fibre reinforcement with ceramics overcomes these limitations [63]. The recent rise in the number of research publications clearly shows an increasing interest in fibre reinforcement of calcium phosphate cements (FRCPCs) as a viable alternative for bone tissue engineering applications. In this section, we will focus on mechanical properties of FRCPCs. They are classified into two types: (i) CPC fibres with non-resorbable fibres and (ii) CPC fibres with resorbable/biodegradable fibres (Fig. 3.3). The incorporation of the non-resorbable fibres provides mechanical stability to the cement. Whereas in the latter classification, the addition of the resorbable fibres provides two roles: (i) provision of mechanical reinforcement and (ii) the development of

Schematic diagram showing different classifications of fibre reinforced calcium phosphate cements porosity within the cement microstructure following degradation of the fibres

Fig. 3.3 Schematic diagram showing different classifications of fibre reinforced calcium phosphate cements porosity within the cement microstructure following degradation of the fibres. Care should be taken when selecting the most appropriate type of resorbable fibres - as the rate of degradation should be closely match the rate of bone remodeling in order to maintain mechanical stability of the scaffold.

Fibres processed from polyamide (linear polymers), aramide (amide groups separated by phenylene groups) and glass fibres are typical non-resorbable fibres that have been used in CPC based systems. Most of polyesters such as polylactide (PLA), polyglycolide (PGA) and poly-e-caprolactone (PCL) have been used as resorbable/biodegradable fibres. Polyester based polymers are largely insoluble in water but they can degrade via hydrolysis of ester bond under physiological conditions.

 
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