Capsules with Concentric Biopolymer-Nylon Shells Imaged by Cryo-FIB/SEM

Capsules can be easily formed by contacting droplets of a cationic biopolymer (such as chitosan) with a solution of an anionic polymer or surfactant. These capsules have a thin shell of polymer hydrogel encompassing an aqueous interior. Such capsules can be loaded with drugs and proteins for applications in pharmaceuticals, consumer products, drug delivery, and tissue engineering. However, the capsules tend to allow the encapsulated solutes to leak out because of their large pore sizes when compared to solute sizes. Accordingly, to contain solutes for longer periods, researchers have looked at encasing the above capsules with synthetic polymers formed by chain-growth polymerization or by waxes. Here, we introduce a new method by which a biopolymer capsule can be covered by an outer layer formed by step-growth polymerization. Examples of synthetic polymers created by step-growth polymerization include polyamides such as nylon. Our approach yields capsules with an aqueous core, surrounded first by a biopolymer shell and thereafter by a concentric nylon (polyamide) layer. To our knowledge, such a multilayered capsule has never been created before. This paper presents a novel approach to investigate the internal microstructure of capsules with biopolymer-nylon shells by Cryo-FIB/SEM method.