Novel casein hydrogels: formation, structure and controlled drug release.

To develop biocompatible, non-toxic materials for pharmaceutical and biomedical applications, the enzyme-assisted formation and structural characteristics of novel casein hydrogels were investigated by dynamic rheology and fractal analyses. As revealed by oscillatory time sweep and stress relaxation tests, the gelation time was shortened greatly and the hydrogel strength was enhanced obviously when a natural tissue enzyme, microbial transglutaminase (MTGase), was used. For aqueous system containing 10.0 wt% casein and 0.05 wt% MTGase, temperature dependence of the gelation time could be described by an Arrhenius plot with its apparent activation energy of 95.4 kJ/mol. In particular, the resultant casein hydrogel was found to show a "weak-link" behavior with fractal character. The use of the enzyme resulted in the increase of the fractal dimension and the formation of a more "tight" network structure. By means of this enzyme-assisted gelation, Vitamin B12 as the model drug could be incorporated into the casein hydrogel matrix under mild conditions and then show a prolonged release behavior. Copyright 2010 Elsevier B.V. All rights reserved.