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Water-soluble drug partitioning and adsorption in HEMA/MAA hydrogels

机译：HEMA / MAA水凝胶中的水溶性药物分配和吸附

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Two-photon confocal microscopy and back extraction with UV/Vis-absorption spectrophotometry quantify equilibrium partition coefficients, k, for six prototypical drugs in five soft-contact-lens-material hydrogels over a range of water contents from 40 to 92%. Partition coefficients were obtained for acetazolamide, caffeine, hydrocortisone, Oregon Green 488, sodium fluorescein, and theophylline in 2-hydroxyethyl methacrylate/methacrylic acid (HEMA/MAA, pKa≈5.2) copolymer hydrogels as functions of composition, aqueous pH (2 and 7.4), and salinity. At pH 2, the hydrogels are nonionic, whereas at pH 7.4, hydrogels are anionic due to MAA ionization. Solute adsorption on and nonspecific electrostatic interaction with the polymer matrix are pronounced. To express deviation from ideal partitioning, we define an enhancement or exclusion factor, E≡k/φ1, where φ1 is hydrogel water volume fraction. All solutes exhibit E1 in 100wt % HEMA hydrogels owing to strong specific adsorption to HEMA strands. For all solutes, E significantly decreases upon incorporation of anionic MAA into the hydrogel due to lack of adsorption onto charged MAA moieties. For dianionic sodium fluorescein and Oregon Green 488, and partially ionized monoanionic acetazolamide at pH 7.4, however, the decrease in E is more severe than that for similar-sized nonionic solutes. Conversely, at pH 2, E generally increases with addition of the nonionic MAA copolymer due to strong preferential adsorption to the uncharged carboxylic-acid group of MAA. For all cases, we quantitatively predict enhancement factors for the six drugs using only independently obtained parameters. In dilute solution for solute i, Ei is conveniently expressed as a product of individual enhancement factors for size exclusion (Eiex), electrostatic interaction (Eiel), and specific adsorption (Eiad):Ei≡EiexEielEiad. To obtain the individual enhancement factors, we employ an extended Ogston mesh-size distribution for Eiex; Donnan equilibrium for Eiel; and Henry's law characterizing specific adsorption to the polymer chains for Eiad. Predicted enhancement factors are in excellent agreement with experiment.
机译：双光子共聚焦显微镜和紫外/可见光吸收分光光度计反萃取可量化水含量从40％到92％范围内的五种软接触镜片材料水凝胶中六种原型药物的平衡分配系数k。获得了乙酰唑胺，咖啡因，氢化可的松，俄勒冈绿色488，荧光素钠和茶碱在甲基丙烯酸2-羟乙酯/甲基丙烯酸（HEMA / MAA，pKa≈5.2）共聚物水凝胶中的分配系数，作为组成，水溶液pH（2和7.4）的函数）和盐度。在pH值为2时，水凝胶为非离子型，而在pH 7.4时，由于MAA离子化，水凝胶为阴离子型。溶质在聚合物基质上的吸附和与聚合物基质的非特异性静电相互作用是明显的。为了表示与理想分配的偏差，我们定义一个增强因子或排除因子E≡k/φ1，其中φ1是水凝胶水体积分数。由于对HEMA链的强烈比吸附，所有溶质在100wt％HEMA水凝胶中均显示E> 1。对于所有溶质，由于缺乏对带电荷的MAA部分的吸附，在将阴离子型MAA掺入水凝胶后，E显着降低。对于双阴离子荧光素钠和俄勒冈绿488，以及在pH 7.4下部分离子化的单阴离子乙酰唑酰胺，E的下降比类似尺寸的非离子溶质的下降更为严重。相反，在pH 2时，由于强烈优先吸附到MAA的不带电荷的羧酸基团上，E通常随非离子MAA共聚物的添加而增加。对于所有情况，我们仅使用独立获得的参数来定量预测六种药物的增强因子。在溶质i的稀溶液中，Ei方便地表示为尺寸增强（Eiex），静电相互作用（Eiel）和比吸附（Eiad）：Ei≡EiexEielEiad各个增强因子的乘积。为了获得单独的增强因子，我们为Eiex采用了扩展的Ogston网格大小分布。埃南的唐南均衡;亨利定律表征了Eiad对聚合物链的特异性吸附。预测的增强因子与实验非常吻合。

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