Pickering double emulsions stabilized by acylated cellulose nanocrystals for oral co-delivery of macromolecules and permeation enhancers.

Double emulsions are potential oral delivery systems for the simultaneous administration of hydrophilic drugs and hydrophobic permeation enhancers to enable effective intestinal absorption of macromolecular drugs. Emulsions stabilized by solid particles, i.e., Pickering stabilizers, have shown potential to form gastric-stable emulsions that can protect their cargo from release under gastric conditions. Here, we use acylated cellulose nanocrystals to facilitate the formation of stable double emulsions for intestinal drug delivery. Water-in-oil-in-water double emulsions were obtained by a two-step emulsification process and found to be colloidally stable over 6 months allowing permanent encapsulation of a high molecular weight compound (4 kDa fluorescein isothiocyanate-labelled dextran, FD4) in the inner water phase at >90 % encapsulation efficiency. Exposure to simulated gastric conditions and gastric lipase did not affect the emulsion structure or trigger FD4 release. Double emulsions underwent a pronounced restructuring under simulated intestinal conditions due to the presence of bile, yet without triggering excessive FD4 release (<10 %). Digested emulsions reduced the transepithelial electrical resistance of an intestinal in vitro Caco-2 cell culture model by hydrolysis of the emulsion oil phase into medium chain fatty acids that act as intrinsic permeation enhancers. The double emulsions facilitated permeation of FD4 across the intestinal in vitro model at similar levels as non-formulated FD4 and C10. Hence, double Pickering emulsions stabilized by acylated cellulose nanocrystals comprise a novel gastric stable oral delivery system that can co-deliver large hydrophilic macromolecules and permeation enhancers to the small intestine towards effective intestinal absorption.