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Rinku Baid, Sachin Bhaladhare, Nathan Ravi, PH; Hydrogels for cell-based intra-vitreal drug delivery. Invest. Ophthalmol. Vis. Sci. 2014;55(13):475.
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We are developing an intra-vitreal cell based drug delivery system. In such a system it is required that the drugs synthesized by the cells easily diffuses out of the system while blocking the immunoglobulins from destroying the cells. Here we optimize the hydrogel parameters for cell-encapsulation that would facilitate differential diffusion of molecules.
Hyaluronic acid (HA) and Gellan (GA) were two polymers that were amidated to contain thiol groups. Six reaction conditions were evaluated : 1) carbodiimide, 2) N-hydroxy succinimide, 3) pH, 4) time, 5) temperature, and 6) cystamine to optimize the thiol content of the polymers. Thereafter, sixteen combinations of thiol containing polymers (22 % thiolated HA (HA-22) and 3 % thiolated GA (GA-3)) were mixed in varying weight ratios, using the response surface methodology design, to form in situ hydrogel. Model proteins including insulin (5.8 kDa), bovine serum albumin (60 kDa), and aldolase (150 kDa) were incorporated into the gels during their preparation. The in vitro release of these proteins from the gels was investigated over a 24 hour duration in phosphate buffered saline pH 7.4. at 37°C.
Amidation of carboxyl group ranged from 1 to 22 % depending upon the reaction conditions with the order of influence of the reaction being: 1) mole ratio of amine, 2) mole ratio of carbo-diimide and 3) time. In vitro release of proteins from all gel compositions showed an initial burst effect followed by steady release of the proteins. Hydrogels with no GA indicated high burst release for all proteins (Fig1A). With an increase in GA there was decrease in burst release (Fig 1B). Hydrogels composed of 1 % HA-22 and 0.2 % GA-3 showed an acceptable release rate of proteins: minimum release of aldolase (post-burst) while having a continued release of insulin and BSA. The burst release was 22, 30, and, 8 % for insulin, BSA, and aldolase, respectively. While there was negligible release of aldolase over the period of 24 hrs, the cumulative % release of insulin and BSA was 37, and 63 %, respectively.
We successfully optimized the derivatization reaction using response surface methodology design. We identified an optimal hydrogel that will allow diffusion of the small molecular weight proteins and nutrients to sustain the cell viability while prevent the cells from getting destroyed by immunoglubulins.
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