Effects of adding resorbable phosphate glass fibres and PLA to calcium phosphate bone cements.

BACKGROUND: Calcium phosphate cements (CPCs), due to their biocompatibility and degradation properties, are being widely investigated as a replacement to more commonly used polymethylmethacrylate (PMMA) for vertebroplasty. CPCs have shown the potential to be replaced by host bone tissue during the healing/remodelling process. However, brittleness and comparatively low strength restrict the use of CPC in load-bearing applications. Although porous CPC can integrate with bone over time, slow degradation profiles and poor interconnectivity between pores restricts osseointegration to the top layer of CPC only. METHODS: Polylactic acid (PLA) and phosphate glass fibres (PGFs) were incorporated in a CPC matrix to overcome the problem of inherent brittleness and limited osseointegration. RESULTS: Incorporation of PLA and PGFs within CPC was successful in achieving a much less brittle CPC matrix without affecting the mechanical properties of CPC. The area under the stress-strain curve showed that the total energy to failure of the CPC hybrid was significantly greater than that of the CPC control. CONCLUSIONS: The methodology adopted here to add PLA within the CPC matrix may also allow for incorporation of PLA cross-linked biochemicals. Micrographic studies revealed that it was possible to confer control over pore size, shape and interconnectivity without negatively affecting the mechanical properties of the cement. This tailorable porosity could potentially lead to better osseointegration within CPC.

Investigating the use of coupling agents to improve the interfacial properties between a resorbable phosphate glass and polylactic acid matrix.

Eight different chemicals were investigated as potential candidate coupling agents for phosphate glass fibre reinforced polylactic acid composites. Evidence of reaction of the coupling agents with phosphate glass and their effect on surface wettability and glass degradation were studied along with their principle role of improving the interface between glass reinforcement and polymer matrix. It was found that, with an optimal amount of coupling agent on the surface of the glass/polymer, interfacial shear strength improved by a factor of 5. Evidence of covalent bonding between agent and glass was found for three of the coupling agents investigated, namely: 3-aminopropyltriethoxysilane; etidronic acid and hexamethylene diisocyanate. These three coupling agents also improved the interfacial shear strength and increased the hydrophobicity of the glass surface. It is expected that this would provide an improvement in the macroscopic properties of full-scale composites fabricated from the same materials which may also help to retain these properties for the desired length of time by retarding the breakdown of the fibre/matrix interface within these composites.