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Ananth Iyer, Rick Gallagher; Bioresorbable materials for ophthalmic devices. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1069.
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© ARVO (1962-2015); The Authors (2016-present)
We report the unique properties of novel miktoarm bioresorbable poly(ether-ester) urethane (PEEsU) accessed using commercially available α-methoxy-ω-diol poly(ethylene glycol) (Ymer N120) in comparison with linear PEEsU starting from poly(ethylene glycol) (PEG diol)with potential applications as ocular drug delivery systems, adhesives and sealants, scleral buckles, punctal plugs, and tissue engineering applications.
Candidate PEEsU having ethylene oxide to L-lactide (EO/LLA) ratios of 0.5, 2 and 4 were prepared using a one-pot two-step synthesis. In the first step, polyester diols were synthesized by the ring opening polymerization (ROP) of L-lactide with the appropriate diol using stannous octoate as the catalyst. In the second step, the resultant polyester diol was chain extended using hexamethylene diisocyanate (HDI) to yield the PEEsU. The poly(ether-ester) molecular weight buildup was verified using nuclear magnetic resonance spectroscopy (NMR). The different PEEsU were characterized by gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). Tensile properties were measured on dry films per ASTM D1708. The hydrolytic degradation of these polymers were followed in a pH=7.4 phosphate buffer solution at 37°C using protocols set in ISO10993-13.
Tensile load at break for the Ymer N120 based PEEsU ranged from 18.06N for EO/LLA of 0.5 to 0.03N for EO/LLA of 2. PEG diol (PEG 1000) based PEEsU for EO/LLA of 0.5 was brittle and film tensile properties were not measurable. The hydrolytic degradation studies were followed by GPC molecular weight drop method. Thus, during a 4 week incubation period, weight average molecular weight (Mw) of PEEsU with EO/LLA=0.5 dropped by 25% while it dropped by 70% for EO/LLA = 2 during the same time period. PEEsU with EO/LLA=4 completely degraded in three days. Additionally thermal profiles of the representative PEEsU were measured using DSC.
We demonstrate the successful synthesis of pendant MPEG based hydrolytically degradable PEEsU. Different forms of the polymer such as films, gels and viscous liquids were made by controlling the EO/LLA ratio of the polyester segments that were then chain extended with HDI. By controlling the EO/LA ratio in the PEEsU, the degradation times of the polymer was manipulated from days to weeks and may be further modified pending application requirements.
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