Thermoresponsive Coatings on Hollow Particles with Mesoporous Shells Serve as Stimuli-Responsive Gates to Species Encapsulation and Release

Abstract

Nanoscale capsule-type particles with stimuli-respondent transport of chemical species into and out of the capsule are of significant technological interest. We describe the facile synthesis, properties, and applications of a temperature-responsive silica-poly(N-isopropylacrylamide) (PNIPAM) composite consisting of hollow silica particles with ordered mesoporous shells and a complete PNIPAM coating layer. These composites start with highly monodisperse, hollow mesoporous silica particles fabricated with precision using a template-driven approach. The particles possess a high specific surface area (1771 m 2 /g) and large interior voids that are accessible to the exterior environment through pore channels of the silica shell. An exterior PNIPAM coating provides thermoresponsiveness to the composite, acting as a gate to regulate the uptake and release of functional molecules. Uptake and release of a model compound (rhodamine B) occurs at temperatures below the lower critical solution temperature (LCST) of 32 °C, while the dehydrated hydrophobic polymer layer collapses over the particle at temperatures above the LCST, leading to a shutoff of uptake and release. These transitions are also manifest at an oil−water interface, where the polymer-coated hollow particles stabilize oil-in-water emulsions at temperatures below the LCST and destabilize the emulsions at temperatures above the LCST. Cryogenic scanning electron microscopy indicates patchlike particle structures at the oil−water interface of the stabilized emulsions. The silica-PNIPAM composite therefore couples advantages from both the hollow mesoporous silica structure and the thermoresponsive polymer.

Constrained thermoresponsive polymers – new insights into fundamentals and applications

“…PNIPAAm-preparation/analysis [186] PDMAAm@Fe 3 O 4 preparation/analysis [187] PNIPAAm-PNHMA@ Fe 3 O 4 drug release, preparation [188][189][190][191] PNIPAAm@SiO 2 molecule delivery, preparation [191][192][193][194] PNIPAAm@Fe 3 O 4 microfluidic separation and assay; sensing; drug release, preparation [195][196][197][198][199][200][201] PNIPAAm@Au fundamental investigation, preparation, cell up-take control [200,202] PNIPAAm-PAm@Au PNIPAAm-PNVP@Fe 3 O 4 cell up-take control drug delivery/cell separation, preparation [203] PNIPAAm-PDMAEMA@Fe 3 O 4 /Au catalysis, preparation [204] PNIPAAm-PAA@UCNP sensing, preparation [205] PNIPAAm-PMAA-PVP@Fe 2 O 3 drug delivery, preparation [206] POX-based grafted nanoparticles [207] PIPOX@Fe 3 O 4 preparation/analysis [208] PIPOX-PEtOX@SPION cell up-take control [209] PEtOX/PPropOX-PVIm/P4VP@Ag preparation/analysis [210] PEG or PEG derivates-based grafted nanoparticles [211] PEG-PDMAEMA@Au preparation/analysis [212] PEGMA@Au preparation/analysis [151,213] PMEO…”

Influence of the Surface Functionalization on the Fate and Performance of Mesoporous Silica Nanoparticles

“…With regard to p(NIPAM), it can be directly engineered as gatekeeper for MSNs, although its coil-to-globule transition taking place at ca. 32 • C complicates its use in patients [399,400]. The LCST can be tuned by introducing different types of monomers.…”

Preprogrammed Dynamic Microstructured Polymer Interfaces

“…A similar concept is realized using capsules with gating properties of a thermoresponsive shell, [46] as well as shells responsive to redox reactions [47] and near-infrared laser light [48] . In fact, stimuli-responsive capsules can be engineered to provide different mechanisms for cargo release [49] based on capsules degrading mechanically, chemically, using catalyst, and by other mechanisms.…”