Use of Organic Cosolvents for Enhanced Leaching of HEMA/MAA Copolymers
Leaching processes that use solvents to shrink and swell hydrogels by ionizing constituents of the gel and/or by solvating the hydrophobic regions with organic cosolvents were explored as a means to cleanse implantable hydrogels. 336 Gels of poly(2-hydroxyethyl methacrylate/methacrylic acid) (pHEMA/MAA) were chosen because of their common use as bio-materials; a composition having 2.5 mole % MAA and a cross-linker of tetraethylene glycol dimethacrylate (TEGDMA) at 0.15 mole % was used. Leaching solutions with pH 10 and 3, which lie above and below the dissociation point of the MAA moieties on the gel network, were used either alone or as 50% volume mixtures with ethanol or isopropanol. Execution of three shrink/swell cycles shows that as much as an 4% of additional material was lost from the gel compared to simple leaching in pH 6 water baths. Sequential exposure to acidic and basic aqueous alcohol solutions was shown to be a faster, but equivalent method of leaching as compared with sequential exposure to acid and base. A method for controlled swelling and shrinking was developed to allow delicate or irregularly shaped gel structures to be leached without damage due to stress associated with rapid swelling/shrinking.
KeywordsPermeability Rubber Shrinkage Syringe Oligomer
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