Correlation between cryogenic parameters and physico-chemical properties of porous gelatin cryogels

In the present work, we have performed an in-depth physico-chemical and bio-physical evaluation of a series of previously described porous gelatin scaffolds (S. VanVlierberghe, V. Cnudde, P. Dubruel, B. Masschaele, A. Cosijns, I. DePaepe, P.J.S. Jacobs, L. VanHoorebeke, J.P. Remon and E. Schacht, Biomacromolecules 8, 331 (2007)). All scaffolds were prepared by a cryogenic treatment and subsequent freeze-drying. Three types of scaffolds were prepared by using different gelatin concentrations and cooling protocols. Type-I hydrogels were composed of cone-like pores with decreasing diameter from top (330 microm) to bottom (20-30 microm). Type-II and type-III scaffolds contained spherical pores with an average diameter of 135 (type II) and 65 microm (type III), respectively. The physico-chemical and bio-physical properties studied include the water uptake capacity and kinetics, the mechanical properties and the enzyme-mediated degradation. We can conclude that the pore geometry affects the water uptake capacity, the mechanical properties and the degradation profile of the hydrogels. Type-I hydrogels possess the highest water uptake, the lowest compression modulus and the fastest enzyme mediated degradation, indicating a clear effect of the pore morphology (elongated channels for type I versus spherical pores for types II and III) on the physico-chemical and bio-physical properties of the materials. In contrast to the effect of the pore geometry (channel-like versus spherical), the pore size does not significantly affect the water uptake, the mechanical properties and the enzyme mediated degradation in the investigated pore size range (65-135 microm). To the best of our knowledge, this is the first report in which the effects of a cryogenic treatment on the hydrogel network properties are investigated in such detail.