Redox-controlled molecular permeability of composite-wall microcapsules

Abstract

Many smart materials in bioengineering, nanotechnology and medicine allow the storage and release of encapsulated drugs on demand at a specific location by an external stimulus. Owing to their versatility in material selection, polyelectrolyte multilayers are very promising systems in the development of microencapsulation technologies with permeation control governed by variations in the environmental conditions. Here, organometallic polyelectrolyte multilayer capsules, composed of polyanions and polycations of poly(ferrocenylsilane) (PFS), are introduced. Their preparation involved layer-by-layer self-assembly onto colloidal templates followed by core removal. PFS polyelectrolytes feature redox-active ferrocene units in the main chain. Incorporation of PFS into the capsule walls allowed us to explore the effects of a new stimulus, that is, changing the redox state, on capsule wall permeability. The permeability of these capsules could be sensitively tuned via chemical oxidation, resulting in a fast capsule expansion accompanied by a drastic permeability increase in response to a very small trigger. The substantial swelling could be suppressed by the application of an additional coating bearing common redox-inert species of poly(styrene sulfonate) (PSS(-)) and poly(allylamine hydrochloride) (PAH(+)) on the outer wall of the capsules. Hence, we obtained a unique capsule system with redox-controlled permeability and swellability with a high application potential in materials as well as in bioscience.

Electrostatic Assembly with Poly(ferrocenylsilanes)

“…The fitting gave a thickness value of 0.4 nm for the contribution of a single bilayer. Thicker films (with bilayer thicknesses up to $5 nm) were also prepared by varying the ionic strength of the polyelectrolyte solutions from which the layers were deposited [34,36,[41][42][43]. Very recently, we carried out a systematic study on PFS multilayer deposition from aqueous solutions with varying ionic strength and polymer concentrations.…”

Synthesis and Solution Self‐Assembly of Polyisoprene‐block‐poly(ferrocenylmethylsilane): A Diblock Copolymer with an Atactic but Semicrystalline Core‐Forming Metalloblock

“…193 Once the capsules were assembled, the ferrocene units were chemically oxidised, which triggered capsule swelling, thus increasing shell wall permeability, consistent with the electrostatic repulsion within the polyelectrolyte shell due to the excess positive charge on the chains, which would increase the distance between segments. The substantial swelling could be suppressed by the application of an additional coating bearing common redox-inert species of PSS − and PAH + on the outer wall of the capsules.…”

“…The substantial swelling could be suppressed by the application of an additional coating bearing common redox-inert species of PSS − and PAH + on the outer wall of the capsules. 193 …”

Ferrocene-Modified Block Copolymers for the Preparation of Smart Porous Membranes

“…Within this approach, successful redox-mediated ion permselectivity in mesoporous membranes was shown. As another example, Vancso et al took advantage of redox-switchable poly(ferrocenylsilanes) (PFS) in polyelectrolyte multilayer capsules for changing the permeability [30]. In general, one major drawback of the porous membrane postmodification route is the subsequent (at least one) synthetic step for introducing the redox-active moieties.…”