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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: Optimisation of degradable bioactive polymer composites

Author: BLEACH, Nicola

Year: 2001

Supervisor(s): Liz Tanner

A triphasic self-reinforced polylactide (SR-PLA)/calcium phosphate (CaP) composite was manufactured by forming a prepreg and compression moulding the layers into a plate. To optimise the prepregging process, PLA films, containing 0 - 25 vol. % biphasic calcium phosphate (BCP), were tested in tension, both statistically and dynamically, and the thermal properties were assessed by dynamic scanning calorimetry. Calcining the BCP changed the surface morphology and particle size and the highest mechanical properties were found with BCP particles calcined at 900°C. The effect of compression moulding temperature was considered by measuring the flexural properties of the SR-PLA composite after moulding at temperatures below the onset of melting of the PLA fibres (130°C), at the onset of melting (140°C) and in the melting range of the fibres (150°C). There was a trend for increasing flexural properties with increasing moulding temperature.

Composites containing uncalcined BCP moulded at 130°C, 140°C or 150°C or containing different calcium phosphates (hydroxyapatite (HA), tricalcium phosphate (TCP) or no filler) and moulded at 150°C were degraded by immersion in simulated body fluid (SBF) for up to 24 weeks. Samples moulded at 130°C showed a faster decrease in flexural properties with degradation time. Unfilled samples absorbed more fluid, showed greater decreases in mass and flexural properties than CaP filled samples. A CaP precipitate was formed on the filled composites after 12-24 weeks of degradation, but not on the unfilled composites.

Biocompatibility was assessed by the culture of human osteosarcoma (HOS) cells on the HA filled, TCP filled or unfilled composites. None of the samples released toxic substances, as determined by MTT tests. Metabolic activity, as measured by Alamar Blue assay, of cells cultured on the filled samples was greater or comparable to that of cells cultured on Thermanox control. Cells retained their phenotype, as confirmed by Alkaline Phosphatase assay and SEM.