Collins, Nikki Jane (2011)
Ph.D. thesis, University of Birmingham.
Three dimensional scaffolds were created from a biodegradable polymer (polylactide) and the mineral silica utilising supercritical fluid (SCF) gas foaming. The effect of silica on the scaffold pore architecture was investigated through X-ray computed microtomography (microCT); the scaffolds were shown to be up to 60% porous with pore diameters in the range of 0.088-0.924 mm (0% silica) to 0.044 – 0.342 mm (33.3% silica), demonstrating that silica controlled both pore size and overall scaffold porosity; Silica was found to enhance connectivity of the pores and pore wall thickness and pore connectivity were found have an inverse relationship. Differential scanning calorimetry (DSC) was used to investigate the effect of silica on the Tm, Tg and crystallinity of the PLA pre and post SCF processing; increases in ΔHf (4J/g) Tg (1oC) and crystallinity (3%) showed that silica had a beneficial effect pre-SCF but post-SCF the PLA reverted to an amorphous state; An isothermal conditioning process was found to restore the previous levels of crystallinity. Mechanical strength testing of the scaffolds showed that silica incorporation increased the load tolerated at yield by up to 60N and the strength by up to 1.5 mPa. The scaffolds were immersed in simulated body fluid (SBF), where the presence of silica was found to enhance mineral deposition by up to 10%; they were also subjected to degradation experiments in physiological saline solution and enzyme buffer solution, where degradation was found to occur most rapidly in the amorphous regions of the polymer (0% and 9.1% silica). The formation of degradation products (lactic acid, isopropanol and lactate) were monitored through HPLC.
In conclusion, addition of silica up to a loading of 9.1-16.7% was found to have many beneficial effects on the PLA scaffolds but no observable benefit was found with additions higher than this.
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