Monolithic gelation of chitosan solutions via enzymatic hydrolysis of urea

A novel process for the formation of physical hydrogels of chitosan from injectable aqueous solutions is investigated. Uniform neutralization of chitosan solutions with ammonia generated in situ from enzymatic hydrolysis of urea is shown to produce pH-induced hydrogels with monolithic and homogeneous coherent 3D structure. Hydrogel formation was characterized by rheology. We found that the gelation time decreases as temperature increases from 15 to 45 degrees C as a consequence of synergistic effect of increased reactant diffusion and increased urease activity (maximum activity at 37 degrees C). The effects of urea and urease concentration are also presented. (c) 2006 Elsevier Ltd. All rights reserved.