On the propulsion of a squirmer enclosed in a droplet: effects of heterogeneity and shape*

A squirmer enclosed in a droplet represents a minimal model for some drug delivery systems. Recent studies show that a spherical droplet always propels in the same direction as the enclosed spherical squirmer, albeit at different speeds. We expand the squirmer-droplet model to account for various squirmer and droplet' shapes and medium’s heterogeneity, two biologically relevant features. Our results reveal a configuration in which squirmer and droplet move in opposite direction.