Mechanomorphological Characterization of Gelatin Based Colloidal Gels
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The emergence of regenerative medicine has led us to a paradigm shift in the design of novel biomaterials, which are now increasingly considered as (bio)active scaffolds that can induce tissue regeneration as opposed to the more traditional concept of passive implant materials. Colloidal gels have recently been identified as a promising bottom-up strategy for the design of highly functional scaffolds by employing micro- or nanometer-scale particles as building blocks to assemble into 3D matrices with defined physicochemical and mechanical morphological properties. Colloidal gels are composed of continuous network of particles aggregated in a continuous dispersed medium. Gelatin based colloidal gels are distinct in morphological and mechanical characteristics owing to the spatial organization of particles on the network structure. Attractive interactions between colloid particles over short distance leads to their aggregation forming clusters which can have a fractal structure in the form of either branched open or compact dense networks. Both gel micro structure and mechanics can be regulated from this organization of colloidal building units at the microscopic scale. In this study, gelatin based colloidal gels were developed from electrostatic interaction between positively charged gelatin colloidal particles (from cationic gelatin A) through the addition of electrolytes, anionic polyelectrolyte and negatively charged gelatin colloidal particles (from anionic gelatin B). Screening and neutralization of charge on the colloidal gelatin reduces the repulsive barrier and causes the particles to aggregate. Variation of charge screening and neutralization mechanism alters the aggregation mode of particles which yields different microstructural organization and the mechanical properties of the colloidal gels. Three modes of aggregation were utilized to regulate the organization of cationic gelatin A colloid during the colloidal gel formation. In the first mode of aggregation, sodium chloride was used to aggregate the particles into compact dense clusters with constrained and less-interconnected void, where the electrolytes can screen the electrical double layer to induce the clustering of particles. In the second mode of aggregation, sodium salt of polyacrylic acid was used to induce simultaneous neutralization and bridging of the particles into tenuous strands with unconstrained and interconnected voids. Finally, negatively charged gelatin B colloids were allowed to form a heterogeneous microstructure. We utilized this approach to develop three colloidal gels which can exhibit different microstructural morphology. By employing different approaches, we characterized the gelatin based colloidal gels to define their micro structure and mechanical characteristics and to underline the structure-function-property relationship. In summary, gelatin based colloidal gels developed through modulation of aggregation kinetics provides a versatile material engineering tool to design 3D colloidal gels with distinct microstructural morphology and mechanical characteristics.