Charge‐Selectively Permeable Self‐Healing Microcapsules

Abstract

Microcapsules possessing a selective permeability are well‐suited vessels for conducting cell studies or chemical reactions that require selective exchanges of reagents over a prolonged time. Most currently reported microcapsules are single‐use delivery carriers since cargo is only released in significant amounts if their shells are damaged or the release relies on passive diffusion. Stable capsules possessing a selective, rapidly interchangeable permeability, which enables their repeated loading and unloading with selected reagents remain to be shown. Here, capsules are introduced that are composed of thin, viscoelastic, charge‐selective shells made of surfactants that are functionalized with a chelator, 3‐hydroxy‐4‐pyridinonone and crosslinked with appropriate nm‐sized ion clusters, for example composed of Fe3+/Tris or Al3+/Tris ion clusters. The charge selectivity of the shell permeability can be conveniently tuned with the crosslinking ion clusters. It is demonstrated that these capsules can be repeatedly loaded and unloaded with well‐defined substances. This feature enables their application as re‐usable selectively permeable filters to remove certain pollutants from solutions. These capsules are envisaged to be well‐suited for waste water treatment and as picoliter‐sized reaction vessels to selectively conduct chemical reactions within capsule cores while continuously supplying new reagents.

Confinement-Controlled Crystallization of Guanine

“…Guanine is a hydrophobic molecule with a low solubility in neutral aqueous solutions, as indicated by its chemical structure in Figure a. To prevent precipitation of guanine during the double emulsion formation, which would hamper the robustness of the encapsulation process, we dissolve it in an aqueous solution with a pH of 1.5, where its solubility is reasonably high. ,, We form double emulsions with a diameter of 110 ± 10 μm and a shell thickness of 15 ± 5 μm using poly­(dimethylsiloxane) (PDMS)-based microfluidic flow-focusing devices . Unless stated otherwise, we employ an aqueous solution containing 3 mg/mL guanine and 0.1 N HCl that possesses a pH of 1.5 as an inner phase.…”

“…The shell is composed of HFE7100. We add 2 mM of a 3-hydroxy-4-pyridinone (HOPO)-functionalized diblock copolymer surfactant that has been shown to display exceptional pH stability to the emulsions: Emulsions stabilized with this surfactant remain intact at pHs ranging from 4 to 10 . The outermost aqueous phase contains 10% (w/w) partially hydrolyzed poly­(vinyl alcohol) (PVA, MW 13–23 kDa) and has a pH = 5.0.…”

“…The synthesis and characterization of HOPO-functionalized surfactants (HOPO-J900-FSH) has been reported before. 31 4.2. Guanine Encapsulation.…”

“…The HOPO-functionalized surfactant offers an additional advantage: It imparts the double emulsions with a charge selective permeability 31 which enables triggering the guanine crystallization exclusively within the double emulsion cores. HOPO has pK a values of 3.6 and 9.9, 32 values similar to the dissociation constants of guanine, pK a 3.3 and 9.2, 32 as shown in Figure 1a,b.…”

“…13,20,30 We form double emulsions with a diameter of 110 ± 10 μm and a shell thickness of 15 ± 5 μm using poly(dimethylsiloxane) (PDMS)-based microfluidic flow-focusing devices. 31 Unless stated otherwise, we employ an aqueous solution containing 3 mg/mL guanine and 0.1 N HCl that possesses a pH of 1.5 as an inner phase. The shell is composed of HFE7100.…”