Brown, Helen C.
(2016)
Extractables and leachables from poly-ε-caprolactone/phosphate based glass composites.
MPhil thesis, University of Nottingham.
Abstract
In this study poly-ε-caprolactone and iron containing phosphate based glass composites have been investigated in terms of their degradability, structural changes and potential for fracture fixation devices. Any material being used within the body requires Regulary acceptance. A key aspect of this is safety and a toxicological assessment of any extracted or leached species. As a crucial part of the project, PBG fibres were assessed for extractables and leachables. Weight loss was also investigated in order to assess the durability with increasing iron content. The following glass fibre compositions were studied: 50P45Ca5Na, 50P35Ca5Na5Fe and 50P30Ca5Na10Fe. They were then fabricated into composites, with PCL, by compression moulding and stored in pH4 and pH7 buffer, krebs solution, saline solution and water for 78 weeks at 37oC. The resulting composites, and their corresponding solutions, were assessed for extractables and leachables, weight change, pH shifts, porosity and pore size, thermal properties and structural changes.
It was demonstrated that the addition of 10%w/w iron into the PBG structure increased the durability by an order of magnitude due to the iron acting as a network former within the P-O-P backbone. The order of leaching was phosphate> sodium> calcium> iron. This was explained by the amount of the oxides originally present in the PBG structure, breakage of the phosphate backbone within the PBG, divalent calcium ions forming chelate cross links which decreases the dissolution rate compared to sodium and Fe-O-P bonds being more resistant to hydration than P-O-P bonds. The weight loss for 50P35Ca5Na10Fe was a third less than the other two PBGs and the weight loss for the equivalent composite was half of the non-iron containing composite. The leaching rate of the 10%w/w iron containing composite was approximately half that of the non-iron containing composite. Unpolymerised caprolactone was observed, alongside 2 oligomers, for the organic leachables from the PCL component of the composites. The density of the PCL/PBG composite was greater than for PCL alone. As iron was added to the PBG, within the composite, it further increased due to the Fe-O-P bonds within the PBG structure which have a dual nature of tetrahedral and octahedral coordination. Differential Scanning Calorimetry (DSC) showed a decrease in crystallinity and glass transition (Tg) when PBG was added to PCL but an increase in melting point due to cross linked density of the PBG network. After storage in aqueous media the crystallinity and Tg increased which could partially be attributed to realignment of the polymer chains within the PCL under storage in aqueous media at 37oC.
The amount of iron in the glass structure extended the time for dissolution. Elemental analysis showed that the presence of iron within the composite reduced the leachables rate. Hence, the accumulation of the ions in a local area is lowered due to fewer ions being released over the same time period for iron containing PBG. The leachables were within acceptable toxicological limits and the amount of calcium present (within the PBG) is beneficial for the bone healing process. Hence, this material is suitable for use in a bone fixation device.
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