Nanoporous Silica Nanoparticles Research Articles

Nanoporous silica nanoparticles as biomaterials: evaluation of different strategies for the functionalization with polysialic acid by step-by-step cytocompatibility testing.

Nanoporous silica materials have become a prominent novel class of biomaterials which are typically applied as nanoparticles or thin films. Their large surface area combined with the rich surface chemistry of amorphous silica affords the possibility to equip this material with variable functionalities, also with several different ones on the same particle or coating. Although many studies have shown that nanoporous silica is apparently non-toxic and basically biocompatible, any surface modification may change the surface properties considerably and, therefore, the modified materials should be checked for their biocompatibility at every step. Here we report on different silane-based functionalization strategies, firstly a conventional succinic anhydride-based linker system and, secondly, copper-catalyzed click chemistry, to bind polysialic acid, a polysaccharide important in neurogenesis, onto nanoporous silica nanoparticles (NPSNPs) of MCM-41 type. At each of the different modification steps, the materials are characterized by cell culture experiments. The results show that polysialic acid can be immobilized on the surface of NPSNPs by using different strategies. The cell culture experiments show that the kind of surface immobilization has a strong influence on the toxicity of the material versus the cells. Whereas most modifications appear inoffensive, NPSNPs modified by click reactions are toxic, probably due to residues of the Cu catalyst used in these reactions.

Synthesis of new antibacterial composite coating for titanium based on highly ordered nanoporous silica and silver nanoparticles

Infection is the most common factor that leads to dental titanium implant failure. Antibacterial implant surfaces based on nano-scale modifications of the titanium appear as an attractive strategy for control of peri-implantitis. In the present work, the preparation and antibacterial properties of a novel composite coating for titanium based on nanoporous silica and silver nanoparticles are presented. Starch-capped silver nanoparticles (AgNPs) were synthesized and then incorporated into sol–gel based solution system. The AgNP-doped nanoporous silica coatings were prepared on titanium surface using a combined sol–gel and evaporation-induced self-assembly (EISA) method. The coating nanostructure was characterized by XRD, SEM–EDX, and HR-TEM. Antibacterial activity was evaluated against Aggregatibacter actinomycetemcomitans, a representative pathogen of dental peri-implantitis. Colony-forming units (CFUs) were counted within the biofilm and at the planktonic state. Biofilm development was quantified using crystal violet staining and viability of adherent bacteria was confirmed with the Live/Dead fluorescence assay.Silica-based composite coating containing AgNPs (AgNP/NSC) was prepared on titanium surface by direct incorporation of AgNP suspension into the sol–gel system. The self-assembly technique enabled the spontaneous formation of a highly ordered nanoporosity in the coating structure, which is a desired property for osseointegration aspects of titanium implant surface. AgNP/NSC coating produces a strong antibacterial effect on titanium surface by not only killing the adherent bacteria but also reducing the extent of biofilm formation. Biofilm survival is reduced by more than 70% on the AgNP/NSC-modified titanium surface, compared to the control. This antibacterial effect was verified for up to 7days of incubation. The long-term antibacterial activity exhibited by the nanostructured AgNP/NSC-titanium surface against A. actinomycetemcomitans suggests that this type of nano-scale surface modification is a promissory strategy to control infections associated with dental implant rehabilitation.

Nanoporous silica nanoparticles with spherical and anisotropic shape as fillers in dental composite materials

AbstractThe objective of this study was to test whether nanoporous silica nanoparticles can be employed as fillers in dental composite materials to improve their mechanical properties. These nanoporous silica nanoparticles were synthesized using sol-gel methods, in part modified by silanization, and thoroughly characterized. The nanoporous nanoparticles were added to dental resins to form nanocomposites (resins impregnated with nanoparticles) and hybrid composites (containing in addition conventional microfillers). The incorporation of these nanoporous nanoparticles in dental resins or composites was characterized by investigation of the complex viscosity and double bond conversion as well as by determination of flexural strength and Young’s modulus. The dispersion of the nanofillers was examined by SEM and EDX imaging of fracture surfaces. Incorporation of small contents (1–3 wt%) of unmodified nanoporous particles leads to improved mechanical properties. However, the incorporation of larger contents results in particle agglomeration and declining mechanical properties. This effect is less pronounced when the surface of the particles is modified with methacrylate residues, resulting in a lower agglomeration tendency and a more homogeneous filler dispersion. Surface properties and, concomitantly, dispersibility of the nanoparticles have a strong influence on mechanical properties. But the incorporation of nanoporous instead of solid nanoparticles into dental composite materials is indeed a possibility to improve the mechanical behavior. However, modification of the surface is necessary and the key to achieving uniform dispersion and, thereby, improving mechanical properties.

Superhydrophilic Multilayer Silica Nanoparticle Networks on a Polymer Microchannel Using a Spray Layer-by-Layer Nanoassembly Method

Nanoporous and superhydrophilic multilayer silica nanoparticle networks have been developed on a hydrophobic cyclic olefin copolymer (COC) microchannel using a spray layer-by-layer (LbL) electrostatic nanoassembly method. This powerful and promising LbL method provides a simple, cost-effective, and high-throughput nanoporous silica multilayer selectively onto the hydrophobic polymer surfaces. These newly developed multilayer networks have also been successfully characterized by contact angle measurement, environmental scanning electron microscopy (ESEM), energy-dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM). The superhydrophilic effect, which was confirmed by the contact angle measurements, of the silica networks ensured the hydrophilic nature of the selectively constructed nanoporous silica nanoparticles onto the patterned hydrophobic COC microchannel. The capillary effect of the developed surface was characterized by measuring the length of a test liquid driven by the induced capillary forces in an on-chip capillary pumping platform with horizontal microchannels. The pumping capability achieved from the sprayed nanoporous surface for the on-chip micropump was mainly due to the strong capillary imbibition driven by the multicoated bilayers of hydrophilic silica nanoparticles. The developed networks with spray-assembled nanoparticles were also applied for an on-chip blood plasma separation platform with closed microchannels. The spray LbL method developed in this work can be a highly practical approach for the modification of various polymer microchannels because of several advantages such as an extremely simple process for the multilayer formation and flexibly controlled surface functionality at room temperature.

Nanoporous carbon-templated silica nanoparticles: Preparation, effect of different carbon precursors, and their hydrogen storage adsorption

New nanoporous carbon materials were synthesized using a nano-casting method with agglomerated porous silica nanoparticles that originated from rice husk as an inorganic template material and sucrose and glycerol as carbon precursors. The nanoporous carbon materials obtained have a specific surface area that reached 749m2/g and a pore volume of 1.44cm3/g. The type and molecular size of the carbon precursor played a significant role for the textural properties of the resulting carbon materials. The hydrogen storage capacity of the porous rice husk silica nanoparticles and the nanoporous carbon materials from the two carbon sources have been investigated at different temperature and pressure. In addition, the effect of the slit-shaped pore structure has been demonstrated. The highest excess hydrogen adsorption was found to be 2.41wt.% achieved at 77K and 7.3MPa and the total hydrogen uptake was 5.7wt.% at 77K and 7.3MPa. The isosteric heat of adsorption of the nanoporous carbon materials has been investigated and reached 7.3kJ/mol which was higher than the values reported on porous activated carbon AX-21_33 (5.53kJ/mol), Norit R0.8 (5kJ/mol), and metal–organic frameworks MOF-177 (3.7kJ/mol), MOF-5 (4kJ/mol).

BMP2-loaded nanoporous silica nanoparticles promote osteogenic differentiation of human mesenchymal stem cells

Nanoporous (or mesoporous) silica materials have been extensively investigated as a novel biomaterial in the last few years, especially with regard to bone tissue engineering. Due to their high specific surface areas, capability for chemical modification, and their large pore volumes, nanoporous silica nanoparticles (NPSNPs) are of tremendous interest as drug delivery systems. In this study, we describe the immobilization of the bone growth factor BMP2 on NPSNPs in biologically relevant amounts, using coupling via an aminosilane linker. The amount of BMP2 loaded onto NPSNPs was determined using two different methods. The biocompatibility of NPSNPs was tested with different cell lines upon exposure to different particle concentrations. Whereas standard cell types (HepG2, NIH3T3) are relatively insensitive against NPSNPs, adMSC cells (adipose-derived human mesenchymal stem cells) show a somewhat reduced viability. adMSC cells were also used to test for the osteoinductive effect of the BMP2-carrying NPSNPs. Histological staining reveals the osteogenic differentiation of the human mesenchymal stem cells. Even BMP-free amino-modified NPSNPs show a certain osteoinductive effect, which is however significantly stronger with immobilized BMP2 and can furthermore be enhanced by supplemental dexamethasone. We therefore suggest that NPSNPs carrying BMP2 are suitable for application in bone tissue engineering, e.g. in the construction of scaffolds.

Reversible Pore‐Structure Evolution in Hollow Silica Nanocapsules: Large Pores for siRNA Delivery and Nanoparticle Collecting

The effective modulation of pore sizes for nanoporous silica nanoparticles still remains a great challenge not satisfactorily solved. In this paper, the pore sizes in the shell of hollow silica nanocapsules are well-tuned by a reversible Si-O bond breakage and reformation process under mildly alkaline conditions (e.g., Na(2) CO(3) solution). The pores in nanosized hollow silica capsules can be modulated from 3.2 nm to larger than 10 nm by a novel, surfactant-directing alkaline-etching (SDAE) strategy. Interestingly, the pores can be fully filled through the regrowth of the dissoluted silicates by bonding to silanols (Si-OH) on the wall surface to generate the nonporous hollow silica nanocapsules. The large-sized pore hollow silica nanocapsules exhibit excellent siRNA-loading capabilities and intracellular transfection efficiencies in vitro. In addition, the large pores in the shell of hollow silica nanocapsules are explored as channels for collecting superparamagnetic, small-sized Fe(3) O(4) nanoparticles as contrast agents for magnetic resonance imaging, initiating a special approach towards pore-size modulation and multifunctionalization of silica-based nanostructural materials for nanobiomedical applications.

Anti-soiling effect of porous SiO2 coatings prepared by sol–gel processing

Thin films being composed of a nanoporous SiO2 network and silica nanoparticles were prepared on glass substrates by sol–gel processing. The surfaces combine anti-reflective (AR) and anti-soiling properties as demonstrated in laboratory testing and long term outdoor exposure. Films were characterized by scanning electron microscopy (SEM). It is shown that both, the structure of the nanoporous matrix as well as the particle density, contribute to this effect, the influence of relative humidity (RH) during dust exposure was investigated. Due to their generally improved solar transmittance and dust-repellant properties the coatings are believed to have a vast potential for many photovoltaic and solar thermal applications.

Applications of magnetic targeting in diagnosis and therapy--possibilities and limitations: a mini-review.

Applications of magnetic targeting in diagnosis and therapy--possibilities and limitations: a mini-review.