Parametric study of protein-encapsulated microcapsule formation and effect on self-healing efficiency of ‘green’ soy protein resin

Soy protein isolate-loaded poly (d,l-lactide-co-glycolide) (SPI-PLGA) microcapsules were prepared using a water-in-oil-in-water emulsification solvent evaporation technique. Effects of microencapsulation formulation parameters such as homogenization speed (1000 or 10,000 rpm) and PLGA and poly(vinyl alcohol) concentrations (1 or 5%) were investigated on size, size distribution, protein loading, encapsulation efficiency, and morphology of the microcapsules as well as their self-healing efficiency. SPI-PLGA microcapsules produced using homogenization speed of 10,000 rpm had an average diameter of 0.76 µm and contained smaller size of subcapsules within themselves, whereas microcapsules produced using homogenization speed of 1000 rpm were larger with an average diameter of 9.1 µm and contained diverse size of subcapsules inside. The PVA concentration did not show any significant effect on the SPI-PLGA microcapsule size. However, at higher PVA concentration of 5%, the SPI-PLGA aggregation of microcapsules resulted because of the excess residual PVA outside the microcapsules. Higher PVA also resulted in better bonding of microcapsules with the SPI resin, resulting in higher self-healing efficiency. The self-healing efficiency for various formulations studied varied between 29 and 53%. The SPI-PLGA microcapsules prepared using 1% PLGA, 5% PVA, and homogenization speed of 10,000 rpm resulted in the highest self-healing efficiency of 53%.