Boztas Ali Ozgur, Guiseppi-Elie Anthony
Center for Bioelectronics, Biosensors and Biochips (C3B), Clemson University Advanced Materials Center, Anderson, South Carolina 29625, USA.
Biomacromolecules. 2009 Aug 10;10(8):2135-43. doi: 10.1021/bm900299b.
Cross-linked hydrogels are synthesized from hydroxyethylmethacrylate (HEMA), polyethyleneglycol methacrylate (PEGMA), and N-[tris(hydroxymethyl)methyl]-acrylamide (HMMA) [p(HEMA-co-PEGMA-co-HMMA) hydrogels] containing 1, 3, 5, 7, 9, or 12 M % of the cross-linker tetraethyleneglycol diacrylate (TEGDA) and are loaded during synthesis with the well-known redox mediator, ferrocene monocarboxylic acid (FcCOOH). In the absence of FcCOOH, the M% TEGDA in deionized (DI) water (48%; 1 mol % TEGDA to 32%; 12 mol % TEGDA) scales with the cross-link density in accordance with Flory-Huggins-Rehner theory. The release profiles of FcCOOH from hydrogel slabs (43.0 mM) into 0.1 M HEPES/0.1 M KCl buffer are determined from the oxidation peak current of FcCOOH via cyclic voltammetry (100 mV/s) and are decidedly Fickian with overall diffusion coefficients that range from 2.64 x 10(-8) cm(2)/s (1 mol % TEGDA) to 4.87 x 10(-9) cm(2)/s (12 mol % TEGDA) and with n parameters that approximated 0.5 but nonetheless linearly declined from 0.49 (1 mol %) to 0.42 (12 mol %). Diffusion coefficients, like hydration, strongly correlate with the M% TEGDA and hence with the cross-link density or the molecular weight (MW) between cross-links. The temperature dependence of the release profiles measured at 10, 15, 20, 25, 30, 35, 40, and 45 degrees C reveal thermally activated transport with activation energies that are 30 kJ/mol (3 mol %), 36 kJ/mol (5 mol %), 45 kJ/mol (7 mol %), 47 kJ/mol (9 mol %) and 57 kJ/mol (12 mol %). Covalent tethering of the FcCOOH via the UV-polymerizable monomers ferrocene monomethacrylate (Fc-AEMA) and ferrocene polyethylene glycol monomethacrylate (Fc-PEG(3500)-AEMA) to produce pendant redox moieties is shown to eliminate or attenuate release of Fc. While, Fc-AEMA showed no evidence of release (0%) from the hydrogel, its PEG-conjugated equivalent, Fc-PEG(3500)-AEMA, shows release of 16% Fc after 5 days of immersion. These hydrogels will serve as the immobilization matrix for oxidoreductase enzymes of biosensors and the parameters obtained used in the modeling of such systems.
交联水凝胶由甲基丙烯酸羟乙酯（HEMA）、聚乙二醇甲基丙烯酸酯（PEGMA）和N-[三（羟甲基）甲基]-丙烯酰胺（HMMA）[p（HEMA-co-PEGMA-co-HMMA）水凝胶]合成，其中含有1、3、5、7、9或12 M%的交联剂四甘醇二丙烯酸酯（TEGDA），并在合成过程中负载著名的氧化还原介质二茂铁单羧酸（FcCOOH）。在没有FcCOOH的情况下，去离子（DI）水中的TEGDA的M%（48%；1 mol% TEGDA至32%；12 mol% TEGDA）根据Flory-Huggins-Rehner理论与交联密度成比例。通过循环伏安法（100 mV/s）从FcCOOH的氧化峰电流确定水凝胶板（43.0 mM）中FcCOOH向0.1 M HEPES/0.1 M KCl缓冲液中的释放曲线，其明显符合菲克定律，总扩散系数范围为2.64×10⁻⁸ cm²/s（1 mol% TEGDA）至4.87×10⁻⁹ cm²/s（12 mol% TEGDA），n参数近似为0.5，但仍从0.49（1 mol%）线性下降至0.42（12 mol%）。扩散系数与水合作用一样，与TEGDA的M%密切相关，因此与交联密度或交联之间的分子量（MW）密切相关。在10、15、20、25、30、35、40和45℃下测量的释放曲线的温度依赖性显示出热活化传输，其活化能分别为30 kJ/mol（3 mol%）、36 kJ/mol（5 mol%）、45 kJ/mol（7 mol%）、47 kJ/mol（9 mol%）和57 kJ/mol（12 mol%）。通过可紫外光聚合的单体二茂铁单甲基丙烯酸酯（Fc-AEMA）和二茂铁聚乙二醇单甲基丙烯酸酯（Fc-PEG(3500)-AEMA）将FcCOOH共价连接以产生侧链氧化还原部分，结果表明可消除或减弱Fc的释放。虽然，Fc-AEMA没有显示出从水凝胶中释放的迹象（0%），但其PEG共轭物Fc-PEG(3500)-AEMA在浸泡5天后显示出16%的Fc释放。这些水凝胶将作为生物传感器氧化还原酶的固定基质，并将所获得的参数用于此类系统的建模。
