Designing Semipermeable Hydrogel Shells with Controlled Thickness through Internal Osmosis in Triple‐Emulsion Droplets

• Published in: Advanced functional materials Vol. 31; no. 42
• Main Authors: Lee, Sangmin, Che, Biao, Tai, Meiling, Li, Wanzhao, Kim, Shin‐Hyun
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.10.2021
• Subjects: Diffusion length; Droplets; Hydrogels; Materials science; microcapsules; Microfluidic devices; microfluidics; Osmosis; Penetration; Photopolymerization; Precursors; Selectivity; Stability; Thickness; triple‐emulsion droplets; Water drops
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202105477

Hydrogel shells that compartmentalize the water core from the aqueous surrounding provide molecular selectivity on size and charge in transmembrane transport. It is highly demanding to produce thin hydrogel shells to minimize diffusion length and maximize core volume. Here, internal osmosis in water‐in‐oil‐in‐water‐in‐oil (W/O/W/O) triple‐emulsion droplets is used to produce thin hydrogel shells enclosing a large water core. The triple‐emulsion droplets are prepared to have an ultrathin middle oil layer using a capillary microfluidic device. The innermost water droplet has a higher osmolarity than the outer water layer containing photopolymerizable hydrogel precursors, which pumps water from the outer layer to the core through the ultrathin oil layer by the osmosis. Therefore, the outer layer gets thinner and hydrogel precursors are enriched while the size of the triple‐emulsion droplets remains unchanged. Through photopolymerization of precursors and phase transfer from oil to water, hydrogel shells enclosing water core are produced in the water environment; the oil layer is ruptured for molecular exchange through the shells. The thickness and composition of the hydrogel shells are precisely controllable by the osmotic conditions. The shells show a high permeation rate due to the thinness as well as controlled cut‐off threshold of permeation for neutral and charged molecules. Microcapsules with a water core and thin hydrogel shell are produced by internal osmosis in water‐in‐oil‐in‐water‐in‐oil triple‐emulsion droplets. Osmotic‐pressure difference pumps water from the outer layer to the core, leading to shrinkage of the layer and enrichment of the hydrogel precursor. Thin hydrogel shells with controlled composition, designed by the internal osmosis, provide a high permeation rate and a precisely controlled cut‐off threshold.