Development of nanostructured silicones to deliver antimicrobials to treat human infected wounds

A ring opening anionic polymerisation (ROAP) has been used to synthesise varying molecular weight PDMS macromonomers. These macromonomers have then been functionalised with allyl and vinyl chloroformate to allow for free radical copolymerisation with N-vinyl pyrrolidone (NVP). Each macromonomer ('short, medium and long' chain) has been reacted at a molar ratio of 1:1, 1:3 and 3:1 with NVP respectively to produce a library of amphiphilic graft copolymers. These materials are designed to be used as additives to deliver antimicrobials and/or other hydrophilic molecules to treat human infected wounds, from a commercially available PDMS membranes used as the contact layer in current wound dressings for Scapa Healthcare™. The graft copolymers are intended by design to form micelles the morphology of which is solvent dependent. The amphiphilic graft copolymers were synthesised in two steps; firstly, hexamethyltrisiloxane (HMTS) was reacted with lithium isopropoxide (LIP) in tetrahydrofuran (THF) under a nitrogen atmosphere at room temperature (RT). Secondly, the PDMS macromonomers were functionalised with either allyl or vinyl chloroformate. Analysis by 1H NMR showed a percentage functionality of 90% and 40% respectively. Following this, the PDMS macromonomers were subsequently reacted with NVP. Zeta potential measurements produced a net result of zero which is expected, as these grafts are non-charged. Particle sizing of the graft copolymer in both aqueous and organic solutions was what was expected considering the relative size and ratio of NVP to PDMS, previously determined by ICP-MS and elemental analysis. SEM images of the modified PDMS membranes revealed changes in surface morphology with increasing roughness in tangent with increasing the concentration of graft copolymer content. Applying Fowkes adapted equation, using the contact angle measurements obtained, revealed that the % polarity of the surface increases with the graft copolymer concentration. The addition of a fluorophore (Rhodamine B) to the membrane was analysed by confocal microscopy showing a distribution throughout the entire membrane with release experiments showing release profiles of Fickian and non-Fickian behaviour dependent on composition. Loading of antimicrobials agents (silver and iodine) was also achieved with antimicrobial loaded modified PDMS membranes releasing antimicrobial agents and having good efficacy against test bacteria (Pseudomonas aeruginosa and Staphylococcus aureus). Cytotoxicity experiments (Alamar blue, pico green and lactose dehydrogenase assays) on human dermal fibroblasts (HDFs) coincided with what was already known in literature, incorporation of antimicrobials having a negative effect on cell viability. Furthermore, this effect was enhanced when cells were subjected to direct contact rather than indirect contact with modified membranes.