Mesoporous silica helical ribbon and nanotube-within-a-nanotube synthesized by sol-gel self-assembly

Using N-miristoyl-l-alanine sodium salt (C₁₄-l-AlaS) and 3-aminopropyltriethoxysilane (APES) as structure and co-structure-directing agents (CSDA), mesoporous silicas with the morphologies of helical ribbon and nanotube-within-a-nanotube have been fabricated just by increasing the APES/C₁₄-l-AlaS molar ratio from 1.0 to 1.15 and 1.25. The microstructures of the mesoporous silicas have been studied by electron microscopy and it was found that: 1) The mesostructure of the helical-ribbon silica materials was double-layer and the mesopores in the wall were disordered; 2) The nanotube-within-a-nanotube silica was multilayer and the mesopores in the wall were also disordered; 3) The silica materials obtained by increasing the APES/C₁₄-l-AlaS molar ratio to 1.25 maintained the nanotube-within-a-nanotube morphology, but with the existence of larger mesopores in the wall.     

Mesoporous silica nanoparticles in nanomedicine applications

In the last few years mesoporous silica nanoparticles (MSNs) have gained the attention of the nanomedicine research community, especially for the potential treatment of cancer. Although this topic has been reviewed before, periodic updates on such a hot topic are necessary due to the dynamic character of this field. The reasons that make MSNs so attractive for designing controlled drug delivery systems lie beneath their physico-chemical stability, easy functionalisation, low toxicity and their great loading capacity of many different types of therapeutic agents. The present brief overview tries to cover some of the recent findings on stimuli-responsive mesoporous silica nanocarriers together with the efforts to design targeted nanosystems using that platform. The versatility of those smart nanocarriers has promoted them as very promising candidates to be used in the clinic in the near future to overcome some of the pitfalls of conventional medicine.

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Mesoporous silica nanoparticles inhibit cellular respiration

We studied the effect of two types of mesoporous silica nanoparticles, MCM-41 and SBA-15, on mitochondrial O 2 consumption (respiration) in HL-60 (myeloid) cells, Jurkat (lymphoid) cells, and isolated mitochondria. SBA-15 inhibited cellular respiration at 25-500 microg/mL; the inhibition was concentration-dependent and time-dependent. The cellular ATP profile paralleled that of respiration. MCM-41 had no noticeable effect on respiration rate. In cells depleted of metabolic fuels, 50 microg/mL SBA-15 delayed the onset of glucose-supported respiration by 12 min and 200 microg/mL SBA-15 by 34 min; MCM-41 also delayed the onset of glucose-supported respiration. Neither SBA-15 nor MCM-41 affected cellular glutathione. Both nanoparticles inhibited respiration of isolated mitochondria and submitochondrial particles.     

Mesoporous hydroxyapatite by hard templating of silica and carbon foams for protein release

Calcium phosphates, particularly hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (HA), are widely used for bone regeneration due to their biocompatibility and good resorption properties. However, their performance upon implantation is improved when they are associated with bioactive molecules such as growth factors. Using mesoporous HA leads to improved protein adsorption and release kinetics because the diameter of the mesopores (2–50 nm) is in the same range as their size. We prepared this type of material by the nanocasting method using three different templates: a silica foam and two carbon templates derived from it using propylene or sucrose as carbon source. We investigated the influence of the template, the calcination temperature and of the conditions during template removal. We obtained HA materials with a surface area of up to 90 m² g^?1 and with an intergranular mesopore volume of up to 0.4 cm³ g^?1. In this paper, we show for the first time that the synthesis of mesoporous HA from a mesoporous silica foam template allows eliminating the template at lower temperatures (in an alkaline medium), thus preventing the sintering of the HA. These materials have interesting properties for drug delivery applications. The protein adsorption and release capacities of these HAs were tested with two model proteins, bovine serum albumin (BSA), and Cytochrome C. These materials are an important milestone for future bone regeneration systems based on HA associated with human growth factor proteins.     

Carbon nanotube/silica composites obtained by sol-gel and high-pressure techniques

The successful incorporation of functionalized single-walled carbon nanotubes (f-SWCNTs) into a silica matrix prepared by the sol-gel method is reported herein. SWCNTs produced through catalytic chemical-vapor deposition (CCVD) have been purified and functionalized with sulfuric, nitric and hydrochloric acids to ensure a good dispersion in an aqueous solution. The nanotube composites are prepared using three concentrations of f-SWCNTs (0.025, 0.050 and 0.075?wt%.) in a silica matrix, resulting in translucent monoliths after gelation. Dense, crack-free and hard compacts are obtained by high-pressure processing at 7.7?GPa and room temperature. Compared to the pure silica compact, compacts containing 0.025 and 0.050?wt% f-SWCNTs show an increased toughness of about 54% and 69%, respectively. The influence of f-SWCNTs on some microstructural aspects of the silica matrix has been studied using nitrogen adsorption/desorption isotherms. Raman spectroscopy has been applied to analyze the effect of the silica matrix and high-pressure compaction on the f-SWCNTs incorporated into the silica matrix. These measurements showed that f-SWCNTs remained in the silica matrix under pressure, suggesting an important interaction with the matrix.     

Mesoporous silica nanoparticles prepared by different methods for biomedical applications: Comparative study

In the current investigation, mesoporous silica nanoparticles were obtained by various techniques, namely sol–gel (S1), micro‐emulsion (S2) and hydrothermal synthesis (S3). The effect of those methods on the final features of the obtained mesoporous silica nanoparticles was studied. The obtained nanoparticles were investigated by TEM, BET surface area, Zetasizer, XRD and FTIR. The preparation method effect was evaluated on the drug release behaviour using doxycycline hyclate as a model drug. In addition, the degree of their compatibility against Saos‐2 cell line was also determined. The morphology and microstructure of silica nanoparticles were found to be dependent on the utilised method. Those techniques produced particles with particle sizes of 50, 30–20 and 15 nm and also surface areas of 111.04, 164 and 538.72 m²/g, respectively, for S1, S2 and S3. However, different preparation methods showed no remarkable changes for the physical and chemical integrities. The drug release test showed faster release from S2 compared with S1 and S3, which make them more applicable in cases require large doses for short periods. However, the release behaviour of S3 was satisfied for treatments which require long period with relatively highest release rate. The preparation method influenced the cell viability as S1 and S2 showed acceptable cell cytotoxicity compared with S3.     

Mesoporous silica templated biolabels with releasable fluorophores for immunoassays

A novel class of fluorescent immuno-biolabeling systems with extremely high F/P ratio (approximately 1000-6000) were prepared by combining the template method and layer-by-layer (LbL) technique. Labels were constructed by loading organic dye fluorescein diacetate (FDA) molecules onto hollow periodic mesoporous organosilica (H-PMO) particles followed by ployelectrolyte encapsulation and antibody attachment. The labeling systems were stimuli-responsive to the addition of concentrated NaOH with the loaded dye molecules being released and detected in a well-controlled manner. When applied in sandwich immunoassays, results indicated that the biolabels were immuno-active and generated an optimal signal that was approximately 50 times higher than the conventional dye labelled antibody system.     

Mesoporous silica nanoparticles deliver DNA and chemicals into plants

Surface-functionalized silica nanoparticles can deliver DNA and drugs into animal cells and tissues. However, their use in plants is limited by the cell wall present in plant cells. Here we show a honeycomb mesoporous silica nanoparticle (MSN) system with 3-nm pores that can transport DNA and chemicals into isolated plant cells and intact leaves. We loaded the MSN with the gene and its chemical inducer and capped the ends with gold nanoparticles to keep the molecules from leaching out. Uncapping the gold nanoparticles released the chemicals and triggered gene expression in the plants under controlled-release conditions. Further developments such as pore enlargement and multifunctionalization of these MSNs may offer new possibilities in target-specific delivery of proteins, nucleotides and chemicals in plant biotechnology.     

Mesoporous silica with controlled porous structure and regular morphology

A new procedure for the synthesis of mesoporous silica with controlled porous structure and regular morphology was developed. It is based on the precipitation from a homogeneous environment using cetyltrimethylammonium bromide as a structure directing agent. The decrease in pH, which causes the formation of solid particles, is achieved by the hydrolysis of ethyl acetate. The procedure enables to obtain not only the MCM-41 mesoporous molecular sieve with a very high degree of pore ordering and phase purity, but also materials of a new type, viz. bimodal silicas containing both the MCM-41 mesopore system with a pore size of about 3 nm and a system of larger mesopores with sizes ranging from 10 to 30 nm. Owing to their structural properties and regular worm-like morphology, bimodal silicas are promising materials for applications in separation processes or as supports for bulky molecules or nanoparticles.     

Mesoporous structure stability of zirconium-doped mesoporous silica at elevated temperature

In this work, the thermal stability of mesoporous structure of MCM-41 materials with different zirconium contents (Zr-MCM-41) was investigated. The results show that the obtained Zr-MCM-41 materials retain a relatively good long range order of mesopores up to 1000 °C. Increasing the calcining temperature to 1050 °C, the mesopore openings become anisotropic and a few new pores with dozens of nanometers are formed due to thermal stress effect. After calcination at 1100 °C, the mesopores structure of all the samples collapse completely and some tetragonal zirconia can be also detected in the sample with high zirconium content (15 ≤ Si/Zr ≤ 40). The synthesized Zr-MCM-41 materials with good thermal stability are expected to be used as the support of catalytic activators under process conditions.     

Mesoporous silica photoluminescence properties in samples with different pore size

Ultraviolet excited photoluminescence of porous silica under vacuum conditions is investigated in samples with different pore diameters. By exciting in the 180–300 nm range, a manifold luminescence activity in the 300–600 nm is found. The reconstructed three-dimensional photoluminescence excitation pattern shows how the distribution of the emissions changes by varying the pore size of the samples. Two different centers are singled out and their relative concentration is suggested to be a function of the pore size of the samples.     

Mesoporous silica directly modified by incorporation or impregnation of some heteropolyacids: Synthesis and structural characterization

The synthesis of heteropolyacids-mesoporous silica composites was carried out in acidic media by impregnation and/or by direct incorporation of active phase. The effect of incorporation of heteropolyacids (HPAs) species into organized mesoporous silica was studied by using non-ionic and cationic surfactants. A comparison between direct incorporation of HPAs into mesoporous silica and impregnation of HPAs on mesoporous silica was done. The structure and texture of H₃PMo₁₂O₄₀ and H₄PVMo₁₁O₄₀ included on mesoporous silica were studied by XRD, SEM-EDS, FT-IR and Raman spectroscopies and BET and pore size distribution. Thermal stability was determined by thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). FT-IR and Raman studies showed that HPAs anions preserved their Keggin structure after incorporation or impregnation on mesoporous silica support.     

PLA degradation pathway obtained from direct polycondensation of 2-hydroxypropanoic acid using different chain extenders

This work is focused on the structural, thermal and mechanical studies of direct polycondensation of poly (lactic acid) (PLA) modified with three different chain extenders (1,3-phenylene-bis-2-oxazoline, PBO; pyromellitic dianhydride, PMDA; and 1,1′-carbonyl bis caprolactam, CBC). Three concentrations of PBO, PMDA and CBC chain extenders (0.2, 0.5 and 1 wt%) were added during three stages (S): monomer dehydration (80 °C, S1), oligomer polycondensation (130 °C, S2) and melt polycondensation (160 °C, S3). FTIR, Raman and ¹H-NMR spectroscopies revealed the presence of signals produced by interactions between OH and C=O end groups of PLA and reactive functional groups of chain extenders. It was found that the interaction with the PMDA chain extender decreased the PLA crystallinity. Furthermore, data from thermal analysis revealed that the interaction between PLA and chain extenders increased the chain mobility, which represented a decrease in its T_g. Enhanced mechanical properties, hardness, elastic modulus and indentation creep were observed with the addition of chain extenders, improving the performance with the addition of 1 wt% of PBO at S3, 1 wt% of PMDA at either S2 or S3 and 0.25 wt% of CBC at either S2 or S3. Additionally to the synthesis, the degradation was mainly influenced by the interaction more than by any specific stage of chain extender addition. Finally, the thermal and structural characterizations revealed that the PLA-PBO, PLA-PMDA and PLA-CBC systems were more resistant than PLA to UV light and humidity during the accelerated weathering test.     

Mesoporous silica particles induce size dependent effects on human dendritic cells

The effects of mesoporous silica nano- (270 nm) and microparticles (2.5 microm) with surface areas above 500 m2/g were evaluated on human monocyte-derived dendritic cells (MDDC). Size- and concentration-dependent effects were seen where the smaller particles and lower concentrations affected MDDC to a minor degree compared to the larger particles and higher concentrations, both in terms of viability, uptake, and immune regulatory markers. Our findings support the further development of mesoporous silica particles in drug and vaccine delivery systems.     

Mesoporous silica nanoparticles improve magnetic labeling efficiency in human stem cells

Tumblerlike magnetic/fluorescein isothiocyanate (FITC)-labeled mesoporous silica nanoparticles, Mag-Dye@MSNs, have been developed, which are composed of silica-coated core-shell superparamagnetic iron oxide (SPIO@SiO(2)) nanoparticles co-condensed with FITC-incorporated mesoporous silica. Mag-Dye@MSNs can label human mesenchymal stem cells (hMSCs) through endocytosis efficiently for magnetic resonance imaging (MRI) in vitro and in vivo, as manifested by using a clinical 1.5-T MRI system with requirements of simultaneous low incubation dosage of iron, low detection cell numbers, and short incubation time. Labeled hMSCs are unaffected in their viability, proliferation, and differentiation capacities into adipocytes and osteocytes, which can still be readily detected by MRI. Moreover, a higher MRI signal intensity decrease is observed in Mag-Dye@MSN-treated cells than in SPIO@SiO(2)-treated cells. This is the first report that MCM-41-type MSNs are advantageous to cellular uptake, as manifested by a higher labeling efficiency of Mag-Dye@MSNs than SPIO@SiO(2).     

Organic–inorganic hybrids obtained by in situ polymerization of aniline in silica/phosphonate matrix

A method for preparing organic–inorganic hybrids containing organophosphorus compounds, silica, and polyaniline (PANI) was developed using sol–gel technique. This method allows the in situ synthesis of organic–inorganic hybrids by reacting tetraethoxysilane (TEOS), aniline, initiator, organophosphorus compound in formic acid. The formic acid has multiple functions: as solvent and acidic media for polymerization of aniline and reagent for sol–gel process. The use of an organophosphorus compound as coupling agent and the introduction of a conductive polymer in silica matrix was investigated.