title: Immobilization and release of the redox mediator ferrocene monocarboxylic acid from within cross-linked p(HEMA-co-PEGMA-co-HMMA) hydrogels.
abstract: 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.
authors: Center for Bioelectronics, Biosensors and Biochips (C3B), Clemson University Advanced Materials Center, Anderson, South Carolina 29625, USA.
authors: Ali Ozgur
authors: AO
authors: Boztas
authors: Anthony
authors: A
authors: Guiseppi-Elie
mesh_terms: D003432:Cross-Linking Reagents / Q000737:chemistry; D004337:Drug Carriers / Q000138:chemical synthesis / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry* / Q000378:metabolism*; D020100:Hydrogels / Q000138:chemical synthesis / Q000737:chemistry*; D000075163:Metallocenes; D008689:Methacrylates / Q000737:chemistry*; D008768:Methylmethacrylates / Q000737:chemistry*; D010084:Oxidation-Reduction; D011102:Polyhydroxyethyl Methacrylate / Q000031:analogs & derivatives* / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D003432:Cross-Linking Reagents; D004337:Drug Carriers; D005296:Ferrous Compounds; D020100:Hydrogels; D000075163:Metallocenes; D008689:Methacrylates; D008768:Methylmethacrylates; C515720:poly(hydroxyethyl methacrylate-co-glycerol methacrylate); D014867:Water; C021302:hydroxymethylmethacrylate; D011102:Polyhydroxyethyl Methacrylate; C004998:ferrocene