New advances in gated materials of mesoporous silica for drug controlled release

Drug delivery systems (DDS) are used to deliver therapeutic drugs to improve selectivity and reduce side effects. With the development of nanotechnology, many nanocarriers have been developed and applied to drug delivery, including mesoporous silica. Mesoporous silica nanoparticles (MSNs) have attracted a lot of attention for simple synthesis, biocompatibility, high surface area and pore volume. Based on the pore system and surface modification, gated mesoporous silica nanoparticles can be designed to realize on-command drug release, which provides a new approach for selective delivery of antitumor drugs. Herein, this review mainly focuses on the “gate keepers” of mesoporous silica for drug controlled release in nearly few years (2017–2020). We summarize the mechanism of drug controlled release in gated MSNs and different gated materials: inorganic gated materials, organic gated materials, self-gated drug molecules, and biological membranes. The facing challenges and future prospects of gated MSNs are discussed rationally in the end.     

Design of fluorescent materials for chemical sensing

There is an enormous demand for chemical sensors for many areas and disciplines. High sensitivity and ease of operation are two main issues for sensor development. Fluorescence techniques can easily fulfill these requirements and therefore fluorescent-based sensors appear as one of the most promising candidates for chemical sensing. However, the development of sensors is not trivial; material science, molecular recognition and device implementation are some of the aspects that play a role in the design of sensors. The development of fluorescent sensing materials is increasingly captivating the attention of the scientists because its implementation as a truly sensory system is straightforward. This critical review shows the use of polymers, sol-gels, mesoporous materials, surfactant aggregates, quantum dots, and glass or gold surfaces, combined with different chemical approaches for the development of fluorescent sensing materials. Representative examples have been selected and they are commented here.     

Mesoporous MCM-41 as Drug Host System

Among the large number of applications of mesoporous MCM-41 materials, we have recently developed their new use as drug delivery system. Since this kind of materials consist on a disordered network of siloxane bridges and free silanol groups, these latter could be the reacting sites against appropriate guest chemical species.In this work, this application of mesoporous MCM-41 as drug delivery system has been studied from the host-guest interaction point of view. Two factors could affect that interaction: the structure of pore wall surface, and the functional groups present in the organic molecule. Hence, two approaches have been performed: functionalising pore wall groups and changing the drug.     

Tuning stability of mesoporous silica films under biologically relevant conditions through processing with supercritical CO2

Mesoporous materials have been proposed for use in numerous biological environments such as substrates for cell culture and controlled release for drug delivery. Although mesoporous silica synthesis is facile, recent reports (Dunphy et al. Langmuir 2003, 19, 10403; Bass et al. Chem. Mater. 2007, 19, 4349) have demonstrated instability (dissolution) of pure mesoporous silica films under biologically relevant conditions. In this work, we demonstrate a simple processing handle (pressure) to control the dissolution of mesoporous silica films that are synthesized using preformed template films and supercritical CO 2. Spectroscopic ellipsometry is utilized to quantify changes in both the film thickness and porosity; these properties provide insight into the dissolution mechanism. The pore size increases as the films are exposed to phosphate-buffered saline (PBS) through preferential dissolution at the pore wall in comparison to the film surface; a mechanism reminiscent of bulk erosion of scaffolds for drug delivery. Thin mesoporous silica film lifetimes can be extended from several hours using traditional sol-gel approaches to days by using CO 2 processing for identical film thickness. Osteoblast attachment and viability on these films was found to correlate with their increased stability. This enhanced stability opens new possibilities for the utilization of mesoporous silica for biological applications, including drug delivery and tissue engineering.     

Influence of mesoporous structure type on the controlled delivery of drugs: release of ibuprofen from MCM-48, SBA-15 and functionalized SBA-15

Ordered mesoporous materials exhibit potential features to be used as controlled drug delivery systems, including their wide range of chemical compositions and their outstanding textural and structural properties. Therefore, it is possible to control the drug release kinetics by tailoring such parameters. In this paper, mesoporous materials such as MCM-48 and SBA-15, which present different pore sizes (3.7 and 8.8 nm) and structural characteristics (3D-bicontinuous cubic and 2D-hexagonal, respectively) have been synthesized to evaluate their application as drug delivery system and to determine their influence on release kinetic of ibuprofen. Moreover, a chemical modification of the SBA-15 mesoporous material with octadecyltrimethoxysilane has also been performed to study its influence on the release rate of ibuprofen. The structural characteristics (3D cubic and 2D hexagonal pore system) do not affect the release kinetic profiles of ibuprofen. On the contrary, the pore size affects highly to the release kinetic profiles from first-order kinetic to zero-order kinetic for MCM-48 and SBA-15, respectively. Moreover, the importance of surface functionalization was demonstrate through the very fast delivery of ibuprofen from SBA-15 mesoporous materials functionalized with octadecyl chains.     

Ordered mesoporous metal oxides: synthesis and applications

Great progress has been made in the preparation and application of ordered mesoporous metal oxides during the past decade. However, the applications of these novel and interesting materials have not been reviewed comprehensively in the literature. In the current review we first describe different methods for the preparation of ordered mesoporous metal oxides; we then review their applications in energy conversion and storage, catalysis, sensing, adsorption and separation. The correlations between the textural properties of ordered mesoporous metal oxides and their specific performance are highlighted in different examples, including the rate of Li intercalation, sensing, and the magnetic properties. These results demonstrate that the mesoporosity has a direct impact on the properties and potential applications of such materials. Although the scope of the current review is limited to ordered mesoporous metal oxides, we believe that the information may be useful for those working in a number of fields.     

Chemodosimeters and 3D inorganic functionalised hosts for the fluoro-chromogenic sensing of anions

We report here recent examples developed in our research group on the development of novel chemodosimeters for fluoro-chromogenic anion sensing. For instance, squaridine, pyrylium and pent-2-en-1,5-dione dye scaffoldings have been used to obtain highly specific chromo-fluorogenic responses for anions such as cyanide, sulfide or certain carboxylates in water or mixed aqueous solutions. We will also report new examples on the use of “smart sensory materials” based on nanoscopic inorganic structures as bio-mimetic hosts for anion sensing. These systems combine molecular ideas and 3D solid pre-organised features as new design concepts for the development of organic/inorganic hybrid materials for recognition/sensing protocols. For instance, the functionalisation of siliceous mesoporous materials with ureas, thioureas, guanidinium groups or saccharides and suitable dyes has resulted in enhanced fluoro-chromogenic sensing of anionic species such as fatty acids, citrate or borate.     

Amphiphilic block copolymers directed synthesis of mesoporous nickel-based oxides with bimodal mesopores and nanocrystal-assembled walls

Mesoporous late-transition metal oxides have great potential in applications of energy,catalysis and chemical sensing due to their unique physical and chemical properties.However,their synthesis via the flexible and scalable soft-template method remain a great challenge,due to the weak organic-inorganic interaction between the frequently used surfactants(e.g.,Pluronic-type block copolymers) and metal oxide precursors,and the low crystallization temperature of metal oxides.In this study,ordered mesoporous NiO with dual mesopores,high surface area and well-interconnected crystalline porous frameworks have been successfully synthesized via the facile solvent evaporation-induced co-assembly(EICA) method,by using lab-made amphiphilic diblock copolymer polystyrene-b-poly(4-vinylpyridine)(PS-b-P4 VP) as both the structure-directing agent(the soft template) and macromolecular chelating agents for nickel species,THF as the solvent,and nickel acetylacetonate(Ni(acac)2) as inorganic precursor.Similarly,by using Ni(acac)2 and Fe(acac)3 as the binary precursors,ordered mesoporous Fedoped NiO materials can be obtained,which have bimodal mesopores of large mesopores(32.5 nm) and secondary mesopores(4.0-11.5 nm) in the nanocrystal-assembled walls,high specific surface areas(～74.8 m~2/g) and large pore value(～0.167 cm~3/g).The obtained mesoporous Fe-doped NiO based gas sensor showed superior ethanol sensing performances with good sensitivity,high selectivity and fast response-recovery dynamics.     

Enzyme-inspired controlled release of cucurbit[7]uril nanovalves by using magnetic mesoporous silica

The controlled release of drugs by biostimuli is highly desirable under physiological conditions for their potential use in advanced applications. The enzyme-inspired controlled release of cucurbituril nanovalves by using magnetic mesoporous silica nanoparticles (MSNs) in near-neutral aqueous solutions is reported for the first time. The encirclement of cucurbit[7]uril (CB[7]) onto the protonated 1,4-butanediamine stalks tethered to the external surfaces of superparamagnetic Fe(3) O(4) -embedded mesoporous silica particles leads to tight blocking of the nanopores. The supramolecular nanovalves are activated by the enzymatic decarboxylation products of lysine, cadaverine (in the protonated form), which has a high affinity for CB[7], so that the encapsulated guest molecules, calcein, in the nanopores are released into the bulk solution. The release of calcein can be controlled in small portions on command by alternating changes in enzymatic decarboxylation products and CB[7]. The amino acid derived polyamines have long been associated with cell growth and cancers. The guest molecules released from the delivery system of magnetic MSNs can act not only on sensing probes for levels of decarboxylases and polyamines, but also on efficacious drugs to specific tissues and cells for regulation of polyamine synthesis.     

Incorporation of chemical functionalities in the framework of mesoporous silica

Mesoporous silica, which shows well-defined pore systems, tunable pore diameters (2-30 nm), narrow pore size distributions and high surface areas (>600 m(2) g(-1)), is frequently modified using different methodologies (including in situ and post-synthetic strategies) to introduce various chemical functionalities useful in applications like catalysis, separation, drug delivery, and sensing. This contribution aims to provide a critical overview of the various strategies to incorporate chemical functionalities in mesoporous silica highlighting the advantages of the in situ methods based on the bottom-up construction of mesoporous silica containing various chemical functionalities in its structure.     

Confinement and controlled release of bisphosphonates on ordered mesoporous silica-based materials

Bisphosphonates have been confined in siliceous ordered mesoporous materials, and the drug release rate of these systems has been investigated. The bisphosphonate adsorption rate has been increased from 1% in oral administration to around 40% locally delivered. Drug dosage can be modulated through amine modification of the material surface, leading to a bisphosphonate adsorption in the ordered mesoporous matrices 3 times larger than that for unmodified materials. The use of these drug delivery systems opens new fields with new possibilities for tissue engineering.     

Mesoporous materials in sensing: morphology and functionality at the meso-interface

Mesoporous materials are finding increasing utility in sensing applications. These applications can benefit from a surface area that may exceed 1,000 m² g⁻¹ and fast diffusion of analytes through a porous structure. This article reviews recent developments in mesoporous materials-based sensing and provides examples of the impact of different surface functionality, pore structure, and macro-morphology in an attempt to illustrate the contribution of these factors to the selectivity and sensitivity of a sensor response. The materials discussed include ordered mesoporous silicates synthesized with surfactants, hard templated ordered mesoporous carbons, and metal oxides with porous textures which have been applied to advantage in various detection schemes. Chemical functionalization of mesoporous materials through silane grafting, co-condensation, and adsorption are also addressed.     

Toward the development of ionically controlled nanoscopic molecular gates

An ionically controlled nanoscopic molecular gate has been developed by using functionalized mesoporous materials. The system shows that control of mass transport at nanometric scale can be achieved by using suitable rigid solids and pH-active molecules. The design principle suggests new perspectives in the search of ionically tuned tailored materials and devices with a fine control of mass transport for new applications in fields such as drug delivery, selective removal of toxic species, sensing, or catalysis.     

Ultrasmall Sub-10 nm Near-Infrared Fluorescent Mesoporous Silica Nanoparticles

Ultrasmall sub-10 nm nanoprobes and carriers are of significant interest due to their favorable biodistribution characteristics in in vivo experiments. Here we describe the one-pot synthesis of PEGylated mesoporous silica nanoparticles with a single pore, tunable sizes around 9 nm and narrow size distributions that can be labeled with near-infrared dye Cy5.5. Particles are characterized by a combination of transmission electron microscopy, dynamic light scattering, fluorescence correlation spectroscopy, optical spectroscopy, nuclear magnetic resonance spectroscopy, and nitrogen sorption/desorption measurements. The possibility to distinguish an "inside" and "outside" may render these particles an interesting subject for further studies in sensing, drug delivery, and theranostics applications.     

Mesoporous Hybrid Materials Containing Nanoscopic “Binding Pockets” for Colorimetric Anion Signaling in Water by using Displacement Assays

Mesoporous solids functionalized with anion‐binding groups have proved to be suitable anion hosts and have been used in selective colorimetric displacement assays. The material UVM‐7, a mesoporous MCM41‐type support characterized by the presence of nanometric mesoporous particle conglomerates, was selected as inorganic scaffolding. Reaction of the template‐free UVM‐7 solid with 3‐aminopropyltriethoxysilane ( 1 ) yielded solid S1 , from which the derivatives S2 and S3 were obtained by reaction with 2‐methylthio‐2‐imidazoline hydroiodide ( 2 ) and butyl isocyanate ( 3 ), respectively. Solids S4 and S5 were prepared by reaction of the starting mesoporous UVM‐7 scaffolding with N‐methyl‐N′‐propyltrimethoxysilyl imidazolium chloride ( 4 ) and with 3‐(trimethoxysilyl)propyl‐N,N,N‐trimethylammonium chloride ( 5 ), respectively. The solids synthesized contain mesoporous binding pockets that can interact with anions through electrostatic attractive forces ( S1 , S2 , S4 , S5 ) and hydrogen‐bonding interactions ( S1 , S2 , S3 , S4 ). These functionalized solids were loaded with a dye ( d ) capable of interacting coordinatively with the anchored binding sites, in our case 5‐carboxyfluorescein, to yield the hybrid materials S1d, S2d , S3d , S4d and S5d . These dye‐containing solids are the signaling reporters. Their sensing ability towards a family of carboxylates, namely acetate, citrate, lactate, succinate, oxalate, tartrate, malate, mandelate, glutamate and certain nucleotides, has been studied in pure water at pH 7.5 (Hepes, 0.01 mol dm^?3). In the sensing protocol, a particular analyte may be bonded preferentially by the nanoscopic functionalized pocket, leading to delivery of the dye to the solution and resulting in colorimetric detection of the guest. The response to a given anion depends on the characteristics of the binding pockets and the specific interaction of the anion with the binding groups in the mesopores. We believe that the possibility of using a wide variety of mesoporous supports that can easily be functionalized with anion‐binding sites, combined with suitable dyes as indicators, make this approach significant for opening new perspectives in the design of chromogenic assays for anion detection in pure water.     

Amphiphilic block copolymers directed synthesis of mesoporous nickel-based oxides with bimodal mesopores and nanocrystal-assembled walls

Ordered mesoporous Fe-doped NiO with dual mesopores, high surface area and well-interconnected crystalline porous frameworks have been synthesized via solvent evaporation-induced co-assembly (EICA) method, by using PS-b-P4VP as structure-directing agent, Ni(acac)₂ and Fe (acac)₃ as binary inorganic precursor, and showed superior ethanol sensing performances with good sensitivity, high selectivity and fast response-recovery dynamics.     

Enzyme‐Controlled Sensing–Actuating Nanomachine Based on Janus Au–Mesoporous Silica Nanoparticles

Novel Janus nanoparticles with Au and mesoporous silica faces on opposite sides were prepared using a Pickering emulsion template with paraffin wax as the oil phase. These anisotropic colloids were employed as integrated sensing–actuating nanomachines for enzyme‐controlled stimuli‐responsive cargo delivery. As a proof of concept, we demonstrated the successful use of the Janus colloids for controlled delivery of tris(2,2’‐bipyridyl) ruthenium(II) chloride from the mesoporous silica face, which was grafted with pH‐sensitive gatelike scaffoldings. The release was mediated by the on‐demand catalytic decomposition of urea by urease, which was covalently immobilized on the Au face.     

Electrochemical Characteristics of Discrete,Uniform, and Monodispersed Hollow Mesoporous Carbon Spheres in Double‐Layered Supercapacitors

Core–shell‐structured mesoporous silica spheres were prepared by using n‐octadecyltrimethoxysilane (C18TMS) as the surfactant. Hollow mesoporous carbon spheres with controllable diameters were fabricated from core–shell‐structured mesoporous silica sphere templates by chemical vapor deposition (CVD). By controlling the thickness of the silica shell, hollow carbon spheres (HCSs) with different diameters can be obtained. The use of ethylene as the carbon precursor in the CVD process produces the materials in a single step without the need to remove the surfactant. The mechanism of formation and the role played by the surfactant, C18TMS, are investigated. The materials have large potential in double‐layer supercapacitors, and their electrochemical properties were determined. HCSs with thicker mesoporous shells possess a larger surface area, which in turn increases their electrochemical capacitance. The samples prepared at a lower temperature also exhibit increased capacitance as a result of the Brunauer–Emmett–Teller (BET) area and larger pore size.     

Responsive Mesoporous Photonic Cellulose Films by Supramolecular Cotemplating

Cellulose‐based materials have been and continue to be exceptionally important for humankind. Considering the bioavailability and societal relevance of cellulose, turning this renewable resource into an active material is a vital step towards sustainability. Herein we report a new form of cellulose‐derived material that combines tunable photonic properties with a unique mesoporous structure resulting from a new supramolecular cotemplating method. A composite of cellulose nanocrystals and a urea–formaldehyde resin organizes into a chiral nematic assembly, which yields a chiral nematic mesoporous continuum of desulfated cellulose nanocrystals after alkaline treatment. The mesoporous photonic cellulose (MPC) films undergo rapid and reversible changes in color upon swelling, and can be used for pressure sensing. These new active mesoporous cellulosic materials have potential applications in biosensing, optics, functional membranes, chiral separation, and tissue engineering.     

Acoustic Wave Mass Sensors

The application of acoustic wave microsensors for mass sensing will be reviewed with focus on the quartz crystal microbalance (QCM) and surface acoustic wave (SAW) devices. The use of QCM and SAW devices in chemical sensing as well as in the determination of solid and liquid properties will be described. In chemical sensing, it is unlikely that a single sensor with a single coating will display a selective and reversible response to a given analyte in a mixture. Alternative strategies such as the use of sensor arrays and the use of sampling devices can be used to improve performance. QCM sensors (QCMs) will oscillate under liquids; their use in under-liquid sensing will be discussed. This revised version was published online in July 2006 with corrections to the Cover Date.