Confinement of Thermoresponsive Hydrogels in Nanostructured Porous Silicon Dioxide Templates

Abstract

A thermoresponsive hydrogel, poly(N‐isopropylacrylamide) (poly(NIPAM)), is synthesized in situ within an oxidized porous Si template, and the nanocomposite material is characterized. Infiltration of the hydrogel into the interconnecting nanoscale pores of the porous SiO2 host is confirmed by scanning electron microscopy. The optical reflectivity spectrum of the nanocomposite hybrid displays Fabry–Pérot fringes characteristic of thin film interference, enabling direct, real‐time observation of the volume phase transition of the confined poly(NIPAM) hydrogel. Reversible optical reflectivity changes are observed to correlate with the temperature‐dependent volume phase transition of the hydrogel, providing a new means of studying nanoscale confinement of responsive hydrogels. The confined hydrogel displays a swelling and shrinking response to changes in temperature that is significantly faster than that of the bulk hydrogel. The porosity and pore size of the SiO2 template, which are precisely controlled by the electrochemical synthesis parameters, strongly influence the extent and rate of changes in the reflectivity spectrum of the nanocomposite. The observed optical response is ascribed to changes in both the mechanical and the dielectric properties of the nanocomposite.

Porous silicon in drug delivery devices and materials☆

“…Thus both the weaving of a soft polymer network into the pores and the covalent attachment of this polymer to the matrix combine to provide the robust chemical and mechanical properties. Hydrosilylation can also be induced via a radical mechanism, and the radical initiators used to set a hydrogel polymer probably induce similar covalent attachment reactions between these polymers and their porous Si hosts [150].…”

“…Porous Si composites show great promise for improving the mechanical stability and control over release rates of a delivery system. Polymers that have been incorporated into porous Si include polylactide [146], polydimethylsiloxane [147], polyethylene [146], polystyrene [146], polycaprolactone [148], zein (a biopolymer derived from maize) [149], and poly(N-isopropylacrylamide) [150]. Either the composite itself or a nanostructure derived from the composite by removal of the porous Si template can be used (Fig.…”

“…The oral administration of porous Si to provide a dietary supplement of silicon [182] has also been assessed [183]. Porous Si drug delivery devices have taken the form of particles [25,184,185], films [16], chip implants [186,187], composite materials [146,150], and microneedles [188,189]. Much work has focused on microparticle systems [21,25,30,31,[106][107][108][190][191][192][193] due to their relative ease of fabrication, administration, and their compatibility with existing drug delivery concepts.…”

“…Two synthetic approaches have emerged: either the polymer is synthesized within the porous matrix [151][152][153][154], or a pre-formed polymer is infused into the matrix by melt-or solution-casting [46,47,146,147,155]. For drug delivery applications, it is important to use a biocompatible polymer, and hydrogels are of particular interest [29,150]. Hydrogels are commonly used in ophthalmologic devices, biosensors, biomembranes, and controlled drug delivery [156].Water-swollen, crosslinked polymeric networks can undergo volume phase transitions in response to environmental changes such as pH [157,158], ionic strength [159], temperature [160], or electric fields [161].…”

Simple method for measuring the porosity, thickness and refractive index of porous silicon, based on the Fabry-Pérot interference spectrum

“…1, 2 and 3 it is possible to estimate the porosity and the thickness of PSi relating two different n pore , for example, air and a known alcohol. This method for estimating the thickness and porosity of the PSi is called Spectroscopic Liquid Infiltration Method -SLIM (9) . Figure 2 shows the schematic diagram of the SLIM system mounted in the laboratory at INPE.…”