Andreea Pasc

Dynamic hybrid materials for constitutional self-instructed membranes.

Constitutional self-instructed membranes were developed and used for mimicking the adaptive structural functionality of natural ion-channel systems. These membranes are based on dynamic hybrid materials in which the functional self-organized macrocycles are reversibly connected with the inorganic silica through hydrophobic noncovalent interactions. Supramolecular columnar ion-channel architectures can be generated by reversible confinement within scaffolding hydrophobic silica mesopores. They can be structurally determined by using X-ray diffraction and morphologically tuned by alkali-salts templating. From the conceptual point of view, these membranes express a synergistic adaptive behavior: the simultaneous binding of the fittest cation and its anion would be a case of “homotropic allosteric interactions,” because in time it increases the transport efficiency of the pore-contained superstructures by a selective evolving process toward the fittest ion channel. The hybrid membranes presented here represent dynamic constitutional systems evolving over time to form the fittest ion channels from a library of molecular and supramolecular components, or selecting the fittest ion pairs from a mixture of salts demonstrating flexible adaptation.

Hollow carbon spheres, synthesis and applications – a review

Hollow carbon spheres (HCSs), also sometimes called carbon capsules, refer to hollow structured carbon particles of millimetre, micron or even nanometre size and correspondingly thin shells. These materials are presently attracting great attention due to their unique properties such as encapsulation ability, controllable permeability, surface functionality, high surface-to-volume ratios, and excellent chemical and thermal stabilities. In many aspects, carbon capsules are therefore superior to their polymer- or metal-based counterparts. In the present review, two main synthetic strategies, hard-templating and soft-templating routes, but also far more uncommon preparation ways are reported and concisely described. The main features of the resultant HCSs are also briefly given. Recent progress in the main application aspects of HCSs, such as adsorption, energy storage and catalysis, among others, is next discussed. Finally, an outlook of their prospects and challenges in terms of controlled synthesis and applications is presented.

pH-controlled delivery of curcumin from a compartmentalized solid lipid nanoparticle@mesostructured silica matrix

Silicalization of curcumin-loaded solid lipid nanoparticle (SLN)/micelle dispersions afforded a compartmentalized nanovector, with both macro- and mesostructured domains. SLNs act as reservoirs of curcumin (CU), while mesopores act as pathways to control drug release. Moreover, the release sustainability depends on the nature of the solid lipid (cetyl palmitate vs. stearic acid) and on the pH of the receiving phase. The meso-macrostructured silica matrix templated by SLNs appears thus as a promising drug delivery system for pH-responsive controlled release.

Tuning the morphology and the structure of hierarchical meso–macroporous silica by dual templating with micelles and solid lipid nanoparticles (SLN)

Solid lipid nanoparticles (SLN) stabilized by nonionic polysorbate or block copolymer surfactants were used for the preparation of hierarchical meso–macroporous silica through a co-templated approach combining a cooperative templating mechanism (CTM) with micelles and spherical soft matter particles imprinting. Depending on the reaction conditions, the morphology of the final material can be tuned to capsules or to block matter. The size of the mesopores is strongly dependent on the nature of the surfactant in excess: 3 nm (Tween 20), 5 nm (Tween 40) or 9 nm (Pluronic® P123), whereas the size of the macropores depends only on the size of SLN (250 ± 150 nm). The macroporous texture was clearly evidenced by TEM. The organization degree of the silica wall depends on the surfactant: only wormlike mesoporous capsules were obtained with Tween 20, and hexagonally ordered microdomains embedded in wormlike mesoporous silica capsules were obtained with Tween 40. Hexagonally ordered silica with circularly ordered mesoporosity could be achieved with Pluronic block copolymer P123. Combining mesoporous silica with solid lipid nanoparticles is a straightforward approach for the design of advanced formulations in drug delivery or food chemistry.

pH- and glutathione-responsive release of curcumin from mesoporous silica nanoparticles coated using tannic acid–Fe(III) complex

A novel pH- and glutathione-responsive drug delivery system has been developed by deposition of tannic acid (TA)–Fe(III) complex on the surface of mesoporous silica nanoparticles (MSN). The coating was easily accomplished within 30 seconds by successive addition of iron chloride (FeCl3) and tannic acid in aqueous dispersion of MSN (e.g. MCM-41). A hydrophobic model drug, curcumin, showed sustainable drug release under physiological condition (pH 7.4), while a rapid curcumin release was triggered by lowering the pH to 6.0 or 4.5. Moreover, curcumin release could be controlled by adjusting the glutathione level, which accelerate the decomposition of TA–Fe(III) complex by competitive liganding. Therefore, these results would allow developing novel and simple pH- and glutathione-responsive drug delivery systems with potential applications such as in biomedicine.

Easy and eco-friendly synthesis of ordered mesoporous carbons by self-assembly of tannin with a block copolymer

Ordered mesoporous carbons were prepared by the self-assembly of Mimosa tannin, a natural polyphenolic molecule, and a micellar solution of Pluronic® F127, used as soft template. The synthesis was carried out at 20 °C using water as the only solvent and without crosslinker agent (i.e., formaldehyde). When tannin, at any pH lower than 4.2, and Pluronic solutions were mixed, a phase separation mechanism immediately occurred due to the strong interaction between both polymers. The precipitated resin was recovered, dried and pyrolysed at 400, 700 and 900 °C. Ordered mesoporous carbon materials were obtained, having both high pore volume and surface areas, up to 0.64 cm3 g−1 or 720 m2 g−1, respectively.

Core-shell microcapsules of solid lipid nanoparticles and mesoporous silica for enhanced oral delivery of curcumin.

Newly designed microcapsules (MC) combining a core of solid lipid nanoparticle (SLN) and a mesoporous silica shell have been developed and explored as oral delivery system of curcumin (CU). CU-loaded MC (MC-CU) are 2 μm sized and have a mesoporous silica shell of 0.3 μm thickness with a wormlike structure as characterized by small angle X-ray scattering (SAXS), nitrogen adsorption/desorption and transmission electron microscopy (TEM) measurements. It was found that SLN acts as reservoir of curcumin while the mesoporous shell insures the protection and the controlled release of the drug. MC-CU displayed a pH-dependent in vitro release profile with marked drug retention at pH 2.8. Neutral red uptake assay together with confocal laser scanning microscopy (CLSM) showed a good cell tolerance to MC-CU at relatively high concentration of inert materials. Besides, the cell-uptake test revealed that fluorescent-MC were well internalized into Caco-2 cells, confirming the possibility to use MC for gut cells targeting. These findings suggest that organic core-silica shell microcapsules are promising drug delivery systems with enhanced bioavailability for poorly soluble drugs.

Hollow carbon spheres in microwaves: Bio inspired absorbing coating

The electromagnetic response of a heterostructure based on a monolayer of hollow glassy carbon spheres packed in 2D was experimentally surveyed with respect to its response to microwaves, namely, the Ka-band (26–37 GHz) frequency range. Such an ordered monolayer of spheres mimics the well-known “moth-eye”-like coating structures, which are widely used for designing anti-reflective surfaces, and was modelled with the long-wave approximation. Based on the experimental and modelling results, we demonstrate that carbon hollow spheres may be used for building an extremely lightweight, almost perfectly absorbing, coating for Ka-band applications.

Metallo-solid lipid nanoparticles as colloidal tools for meso-macroporous supported catalysts.

Meso-macroporous silica containing iron oxide nanoparticles (15-20 nm) was synthesized by formulating solid lipid nanoparticles and metallosurfactant as both template and metal source. Because of the high active surface area of the catalyst, the material exhibits an excellent performance in a Fenton-like reaction for methylene blue (MB) degradation, even at low amount of iron oxide (5% TOC after 14 h).

Silica-based systems for oral delivery of drugs, macromolecules and cells

According to the US Food and Drug Administration and the European Food Safety Authority, amorphous forms of silica and silicates are generally recognized to be safe as oral delivery ingredients in amounts up to 1500mg per day. Silica is used in the formulation of solid dosage forms, e.g. tablets, as glidant or lubricant. The synthesis of silica-based materials depends on the payload nature, drug, macromolecule or cell, and on the target release (active or passive). In the literature, most of the examples deal with the encapsulation of drugs in mesoporous silica nanoparticles. Still to date limited reports concerning the delivery of encapsulated macromolecules and cells have been reported in the field of oral delivery, despite the multiple promising examples demonstrating the compatibility of the sol-gel route with biological entities, likewise the interest of silica as an oral carrier. Silica diatoms appear as an elegant, cost-effective and promising alternative to synthetic sol-gel-based materials. This review reports the latest advances silica-based systems and discusses the potential benefits and drawbacks of using silica for oral delivery of drugs, macromolecules or cells.