Morphology and mechanical properties of bicontinuous gels of agarose and gelatin and the effect of added lipid phase

This study examines the structural properties of binary and tertiary mixtures made of the cold-setting biopolymers agarose and gelatin and a lipid phase with solid or liquid-like viscoelasticity. The working protocol included the techniques of small-deformation dynamic oscillation on shear, modulated differential scanning calorimetry and scanning electron microscopy, and theoretical modeling that adapted ideas of relating the morphology to the elastic modulus of synthetic polyblends and block polymers. The experimental setting was designed to encourage extensive phase separation in the binary gel of agarose and gelatin whose mechanical properties were rationalized on the basis of a bicontinuous blending law. The presence of two continuous phases allowed the slower-gelling component (gelatin) to exhibit favorable relative affinity for the solvent with increasing concentrations of the protein in the system. This is an unexpected outcome that contradicts the central finding of a single value of the p factor observed in the distribution of solvent between the continuous matrix and discontinuous inclusions of deswelled binary gels reported earlier in the literature. The incorporation of a lipid phase of effectively zero elastic modulus or in excess of 108 Pa in the composite aqueous gel weakens or reinforces the matrix accordingly. The elastic moduli and morphology of the tertiary blend were related to changing the relative phase volumes of components using analytical expressions of isotropically dispersed soft or rigid filler particles in a polymeric matrix