Caracterización de hidrogeles de gelatina a través de ensayos de hidratación, reometría y difusión

F. A. CHIAPPINI, A. PORCARO, M. V. PIAGGIO, M. L. OTTONE, M. B. PEIROTTI Y J. A. DEIBER

Valle Hermoso, Cordoba

Congreso; II Reunion Interdisciplinaria de Tecnología y Procesos Químicos; 2010

PLAPIQUI

ABSTRACT A procedure to characterize gelatin hydrogels cross-linked covalently with glutaraldehyde and polyvinyl-alcohol is proposed. An experimental methodology involving both simple mechanical extension and equilibrium swelling tests is developed to estimate relevant microstructural parameters and electrokinetic properties of these types of hydrogels, for different cross-linker to gelatin mass ratios. The main purposes of this work are the estimations of average mesh size and toughness of swollen gelatin hydrogels, and the determination of the feasibility of polyion complexation between cross-linked gelatin chains and bioactive macromolecules to be delivered through hydrogel biodegradation. In this context one expects to evaluate the matrix shear elastic modulus, the average molecular mass of network strands comprised between two consecutive cross-links, the average matrix mesh size and the swelling ratio. In addition, relevant electrokinetic parameters are estimated, like for instance, the hydrogel electrostatic zeta-potential emerging from the Donnan-type equilibrium between the swollen and charged polypeptide matrix and the surrounding electrolyte solution. Also the average effective or excess charge numbers per chain are provided, which are defined as the difference between positive and negative charge numbers of chain ionizing groups before and after the cross-linking process, respectively. In addition experimental studies of impeded diffusion in gelatin hydrogels involving small test-molecules (urea and salicylic acid) are carried out in a lab-built diffusion cell. These results allow one to visualize the interaction between hydrogel matrix and analytes presenting capabilities to form hydrogen-bond and electrostatic interactions. The later depends, in part, on gelatin amino acid sequence determining the polypeptide isoelectric point and pH and ionic strength of the aqueous solution. Polyampholytic cross-linked matrices are studied here in the framework of the rubber elasticity and thermodynamic swelling theories as described elsewhere (Deiber et al., Polymer, 50: 6065–6075, 2009). Also rigorous balances of diffusing species are formulated to establish the mechanisms of analyte release (diffusion and/or affinity-controlling mechanisms).et al., Polymer, 50: 6065–6075, 2009). Also rigorous balances of diffusing species are formulated to establish the mechanisms of analyte release (diffusion and/or affinity-controlling mechanisms).