Protein capsules with cross-linked, semipermeable, and enzyme-degradable surface barriers for controlled release.

This paper describes a method for fabricating protein-based capsules with semipermeable and enzyme-degradable surface barriers. It involves the use of a simple fluidic device to generate water-in-oil emulsion droplets, followed by cross-linking of proteins at the water-oil interface to generate a semipermeable surface barrier. The capsules can be readily fabricated with uniform and controllable sizes and, more importantly, show selective permeability toward molecules with different molecular weights: small molecules like fluorescein sodium salt can freely diffuse through the surface barrier while macromolecules such as proteins can not. The proteins, however, can be released by digesting the surface barrier with an enzyme such as pepsin. Taken together, the capsules hold great potential for applications in controlled release, in particular, for the delivery of protein drugs.