Designing Novel Smart Hydrogel Formulations for the Controlled Delivery of Ocular Therapies in Contact Lens Devices

The major challenge to ocular drug delivery is poor bio-availability of the delivered drug, due to the anatomy of the eye. This work presents an approach to address this problem, using novel contact lens drug delivery vehicles. Antihistamines were used as a model drug due to their physical properties and molecular weight. 15% of the world’s population suffer from allergic reactions confirming antihistamines as a relevant ocular pharmaceutical. A novel pilot scale wet cast moulding process and methods to measure critical lens parameters were developed. This facilitated comparison of the manufactured lenses to commercial lenses. The refractive index of the lenses fabricated and commercial lenses was 1.33. Equilibrium water content was 70 % for both commercial and fabricated lenses. % of light transmitted varied from 96 - 97.5 % for fabricated lenses, which compared to 98 % for commercial lenses ACUVUE©. This is significant to the field of study as the novel manufacturing system developed allowed for an accurate assessment of drug delivery from contact lenses. Other research groups have performed drug release studies on films and discs which do not have the same thickness and shape as contact lenses. Another advantage of the manufacturing system developed was that it allowed control over lens composition and drug loading via direct casting. Drug-laden polymer particles were investigated as a means of attenuating drug release. Zero order drug release from these drug-laden polymer particles was achieved. Drug loaded polymer particles were loaded onto contact lenses to create novel drug delivery vehicles which delivered 5.84 μg of cetirizine over 24 hours. The activation energy for the polymerisation of HEMA with AIBN initiator was calculated to be 70.8 kJ.mol-1. When drug-laden polymer particles were added to the HEMA monomer, the activation energy dropped to 60.7 kJ.mol-1. This result proved that the activation energy for the polymerisation of contact lens monomers could be decreased by the presence of polymer particles. This reduction in activation energy could result in lower cost hydrogel formation, as less energy would be required. Furthermore, it was observed that formulations with two monomers exhibited an increase in activation energy of up to 17.82 KJ.mol-1. Results obtained in this study determined that polymer particles can impact the polymerisation reaction of contact lens monomers and affect the polymers physical properties and this area warrants further investigation