Immobilization and release of the redox mediator ferrocene monocarboxylic acid from within cross-linked p(HEMA-co-PEGMA-co-HMMA) hydrogels.
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.
Boztas
Ali Ozgur
AO
Center for Bioelectronics, Biosensors and Biochips (C3B), Clemson University Advanced Materials Center, Anderson, South Carolina 29625, USA.
Guiseppi-Elie
Anthony
A
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
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