Some physical properties of crosslinked gelatin–maltodextrin hydrogels

The physical properties and morphology of phase-separated gelatin–maltodextrin (MD) systems, cross-linked by non-toxic, biocompatible fixatives, were investigated as a function of pH (3, 5 or 7) and MD concentration (0–12% w/w), at a constant gelatin concentration (10% w/w). Gelatin was cross-linked by sodium tripolyphosphate (TPP), genipin (GP), a GP/TPP mixture or by glutaraldehyde (used as a standard). Confocal laser scanning microscopy of all mixed gels at pH 3 revealed the presence of a homogeneous network, except in the presence of TPP. Phase separation was likely inhibited by reduced network elasticity, increased entropic contribution of the mixture and minimal fixative-polymer interaction at this pH. Hydrogels under these conditions were weaker (i.e., lower elastic modulus) and swelled more than gels formed at higher pHs. At pH 7, phase separation was evident, where numerous MD inclusions of various diameters (<50 μm) became kinetically trapped within the gelatin-continuous network. In general, the extent of phase separation increased as MD concentration increased. Overall, GP cross-linked networks were strongest at pH 7, whereas TPP fixation gave the strongest gels at low pH. The addition of TPP to GP cross-linked hydrogels lead to a large increase in elastic modulus, especially near the isoelectric point of gelatin (∼pH 7–9). By controlling composition, pH and crosslinker, tailored hydrogel morphologies and physical properties were obtained.