An evaluation of hyaluronic acid and poly-L-lysine polyelectrolyte layers on alginate microspheres for use in protein-triggered drug release
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Age-related macular degeneration (AMD) is the leading cause of vision loss in developed countries in those 50 years of age and older. Increased expression of the protein vascular endothelial growth factor (VEGF) plays a large role in the onset and progression of the advanced, wet form of AMD. To deliver drugs to the posterior chamber of the eye to treat diseases such as AMD, intravitreal injections are performed. Due to the side effects associated with intravitreal injections, such as retinal detachment and hemorrhage, it is advantageous to reduce the frequency of injections required for treatment. This thesis investigates sustaining the release of drug through encapsulation in polymer microspheres coated with polyelectrolyte layers of poly-L-lysine (PLL) and hyaluronic acid (HA) with the potential for protein-triggered release using aptamers. In this research, the feasibility of crosslinking HA with aptamer-containing DNA oligomers for protein-triggered release (for example, in response to VEGF in AMD) was evaluated and the crosslinking of HA layers by methods of click chemistry and through a carbodiimide reaction were compared. The lysozyme aptamer (used for proof-of-concept) in the DNA crosslinker retained its affinity for lysozyme, although lower binding occurred when incubated in phosphate buffered saline (PBS). The lysozyme aptamer showed moderate specificity when incubated with bovine serum albumin (BSA) or chymotrypsin as the aptamer did not bind BSA, however there was slight binding when incubated with chymotrypsin. The properties of the PLL/HA layers on calcium alginate microspheres affected the in vitro release of encapsulated model drug FITC-dextran (MW 10 kDa) into PBS. Coating microspheres with 3 polyelectrolyte layers consisting of PLL, HA crosslinked with poly(ethylene glycol) diamine at a 1:5 molar ratio of amine groups to HA carboxyl groups, and a final layer of PLL did not change the release profile of FITC-dextran in comparison to release from microspheres coated with un-crosslinked layers. Increasing the number of layers on the microspheres from 3 to 5 layers significantly decreased the amount of encapsulated FITC-dextran released. However, increasing the number of layers to 7 layers did not further sustain the release of FITC-dextran.