Dynamic redistribution and phase transition of solid particles in emulsion droplets

The dynamics of solid particles in emulsions play a fundamental role in designing delivery systems yet the mechanisms governing their confinement and redistribution remain unclear. Microfluidic droplet generation was used to load solid particles into oil droplets and to investigate how particles behave in a biphasic system. Chlorophyllin was used as a model and we found that droplet microfluidics enabled particle incorporation and reduced leaching when compared to using high-shear homogenizer to incorporate solid particles into a biphasic system. The distribution of particles within droplets whether at interface or in the core is governed by particle hydrophobicity. At the droplet surface, gum arabic stitches a barrier, capturing the particles from escaping, while polysorbate surfactant led to rapid dissolution. The polymer network anchored to the droplet surface remained intact during dilution or storage preventing release. A spontaneous transition from particle-loaded emulsion to double emulsion occurs during storage, where water diffuses from outside into the oil. The structure of particle-loaded emulsions protected chlorophyllin from degradation caused by light and heat. These polymer-coated emulsions retained particles in oral and gastric digestion, with a responsive release observed in the intestine, where bile salts perforate the interface and provide paths for pigment diffusion. This study highlights the potential of microfluidic techniques as a platform for trapping solid particles into emulsions and provides a fundamental understanding on the fate of particles in the system. The platform can potentially be adapted to deliver versatile bioactive compounds across different fields.