Alex Hui, OD, is a Master's Candidate at the Centre for Contact Lens Research in the School of Optometry and Vision Science, University of Waterloo. His research focus is on the development of novel contact lens materials for drug delivery.
Alex Hui, Andrea Weeks, Heather Sheardown, Lyndon Jones
Centre for Contact Lens Research, School of Optometry, University of Waterloo
Department of Chemical Engineering, McMaster University
While over 90% of drug delivery to the eye is in the form of eye drops, they are far from an efficient means of drug delivery. This inefficiency of current ocular drug delivery has spurned research into alternate drug delivery paradigms such as contact lens delivery devices. Introduction of highly oxygen permeable silicone hydrogels in the late 1990s has also contributed to interest in alternative contact lens applications as safe extended wear was shown to be a clinical possibility. Unfortunately, commercially available, non-customized materials have been shown to be unsuited for drug delivery as they are unable to sustain release over time, necessitating the creation of novel materials using various strategies. One such strategy to delay the release of drugs from materials is molecular imprinting. Molecular imprinting is a technique in which “cavities” or “molecular memory” are created within a material by incorporating templates during the polymerization process. The interaction between the cavities and the drug of interest serve to slow drug movement through the material, potentially extending release times to the order of hours, days and even weeks or months in some instances.
pHEMA+tris(trimethylsiloxy) silylpropylmethacrylate (TRIS) and pHEMA+TRIS+Hyaluronic Acid (HA) materials were polymerized in the presence of dissolved Ciprofloxacin-HCl as a template for molecular imprinting. Small discs of the material were punched out, and then rinsed over several days in phosphate buffered saline to remove imprinted ciprofloxacin. Uptake of a 0.3% Ciprofloxacin solution into the discs for one week, and subsequent release into a phosphate buffered saline solution for two weeks was monitored using spectrophotometry at an excitation wavelength of 274 nm and an emission wavelength of 419 nm.
Approximately 0.2 mg and 0.1 mg of ciprofloxacin was released from pHEMA+TRIS and pHEMA+TRIS+HA materials respectively. Unlike previous studies, this release was achieved relatively linearly over the course of at least five hours, and followed by a much slower rate of release for the remaining two weeks.
Molecular imprinting techniques can be used successfully to slow and control the amount of drug released from different materials, and remains an area rife with potential for further investigation for drug delivery materials.
Alex Hui is supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada, the Canadian Optometric Education Trust Fund (COETF) and a Vistakon® Research Grant administered by the American Optometric Foundation (AOF). This study is also supported by the NSERC 20/20 Network for the Development of Advanced Ophthalmic Materials.