title: Polymeric Materials for Controlled Ophthalmic Drug Delivery
Creators: name: Cauldbeck, Helen
Publisher: name: University of Liverpool Repository
Year: 2016

description: Proliferative vitreoretinopathy, a potentially blinding condition, involves excessive proliferation of retinal pigment epithelium (RPE) cells and is the main complication following retinal detachment (RD). Complicated cases of RD are treated with silicone oil (SiO) tamponades which can potentially be used as drug reservoirs. The aim of this study was to investigate different methodologies to develop a sustained and controlled drug release of anti-proliferative and anti inflammatory drugs from SiO tamponades using all-trans retinoic acid (atRA) and ibuprofen (Ibu). In detailed studies of atRA and Ibu, including atRA degradation behaviour, the drugs were found to be non-toxic to an adult RPE cell line (ARPE 19) below 10-5 M. The solubility of both drugs in SiO was assessed using radioisotope techniques. Prodrugs of atRA and Ibu were synthesised via conjugation to polyethylene oxide (PEO), and cleavage of the resulting ester bond, toxicity towards RPE cells, solubility in SiO and release into media were assessed. Prodrug cleavage was successful in vitro for Ibu but not achieved in the case of atRA due to its highly conjugated nature. Cytotoxicity assays showed PEO attachment had no effect on cytotoxicity and PEO prodrug solubility in SiO followed the expected trend of decreasing solubility with increased PEO chain length. Overall the saturation concentration of drug in SiO achieved through the use of PEO-prodrugs was too low for an effective therapy. Lipophilic prodrugs with a poly(dimethylsiloxane) (PDMS) pro-moiety were synthesised and investigated. Their cleavage was problematic due to PDMS being highly hydrophobic and cleavage could only be achieved in vitro when a small hydrophilic spacer was added between PDMS and the drug. The effects of PDMS prodrugs as additives in SiO were investigated and the presence of PDMS-atRA in SiO was shown to have a positive effect on both atRA solubility and longevity of release. The clinically-relevant release period (6-8 weeks) was independent of atRA starting concentration but dependant on the PDMS-atRA concentration within the blend. This has potential for further development into tamponade drug reservoirs for future patient benefits. A series of linear and branched amphiphilic copolymer architectures were also evaluated as additives for SiO. Monomer selection included oligoethylene oxide methacrylate (OEGMA), 2-hydroxyethyl methacrylate, PDMS-methacrylate (PDMSMA) and the brancher PDMS-dimethacrylate (PDMSDMA). SiO solubility of p(OEGMA-co-PDMSDMA) was investigated and copolymers which contained the smallest hydrophilic and largest lipophilic components only achieved small solubility (0.1 % v/v). To overcome these solubility issues, hydrophobic PDMSMA monomer was utilised. Both linear p(PDMSMA-co-OEGMA) and branched p(PDMSMA-co-OEGMA-co-PDMSDMA) were successfully synthesised and displayed high solubility within SiO, up to 40-50 % v/v. The potential for SiO tamponades as long-acting drug reservoirs has been demonstrated after inclusion of a novel end-modified PDMS additive leading to long term release of atRA. The formation of novel polymer architectures that show considerable miscibility with SiO also shows the scope of the opportunity for further additive development to tailor release profiles.