Dual functional ionic liquids as plasticizers and antimicrobial agents for medical polymers

• Main Author: Choi, Seong Ying
• Published: Queen's University Belfast 2012
• Subjects: 610.28
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.579684

PVC accounts for more than 25% of the plastics used in medical devices, with medical tubing, such as that used in catheters and endotraechal the major applications. PVC is often plasticized using phthalate esters, but this group of plasticizers is environmentally contentious and there is evidence to suggest they are dangerous to human health. Furthermore, medical device-related infections and biofilm formation have been major challenges associated with PVC medical devices. Therefore, a dual functional novel additive having both plasticizing and antimicrobial properties could be a solution to address these problems. Two ionic liquids(ILs, organic liquid salts in room temperature), l-ethylpyridiniurn docusate(IL 1) and tributyJ(2-hydroxyethyl)phosphonium docusate(IL2), were designed and synthesized in the hope they would act as both plasticizer and antimicrobial agent for PVc. The plasticization of these composites was assessed based on a reduction in the glass transition temperature(T g), determined from dynamic mechanical thermal analysis(DMTA), changes in torque data during processing, and static mechanical tensile tests. The antimicrobial efficacy of the ILs and their precursors were evaluated with time-kill assay. The antimicrobial activity of PVC-IL composites were assessed by disc diffusion tests, biofilm formation tests, and examination of biofilm growth on PVC samples using scanning electron microscopy(SEM). The leaching of ILs from PVC was also examined from leaching tests, via a combination of gravimetric measurements, UV - Vis spectrophotometry, FTIR-ATR and DMTA. The results indicated that both ILs exhibited a plasticizing effect on both sets of PVC formulations manifest by reduction in Tg, storage modulus, and torque during processing, but enhanced flexibility measured by increased elongation at break from static tensile tests was only observed for the rigid PVC-IL2 samples. Both ILs, both rigid PVC-IL samples and non-rigid PVC-ILl samples were antimicrobially active against most Gram-positive bacteria, and displayed excellent antibiofilm forming properties. Overall, IL2 was a better plasticizer for PVC than IL 1, and IL 1 was a better antimicrobial agent than IL2. The enhanced antimicrobial effectiveness of IL 1 was related to the greater release of IL 1 from the PVC matrix, observed during leaching tests, and increased surface hydrophilicity, evident from contact angle measurements. FTIR-ATR studies on PVC-IL samples during leaching tests revealed a potential interaction between the docusate anion with the surrounding immersant(PBS). The effect of PVC molecular weight on the release behaviour of ILs was also evident from leaching tests carried out on non-rigid PVC-IL samples containing PVC resins with different molecular weight. The addition of these ILs to PVC also reduced the thermal stability of both rigid and non-rigid PVC. Comparing both ILs with conventional PVC plasticizer, di- octylphthalate(DOP) in both PVC formulations, it was found that although DOP has a slightly higher plasticizing efficiency, the ILs have the advantage of dual functionality, as both plasticizers and antimicrobial agents.