Mesoporous Silica Coatings Research Articles

Mesoporous silica coatings for controlled release of the antibiotic ciprofloxacin from implants

To generate bioactive coatings for medical implants, a novel procedure has been developed using a coating of mesoporous silica for controlled drug delivery. Plain glass slides were used as substrates. The mesoporous coatings were then loaded with the antibacterial drug ciprofloxacin. The drug release kinetics were investigated in a physiological buffered solution. The drug loading capacity of the unmodified mesoporous coatings was low but could be increased nearly ten-fold (to about 2 µg cm−2 of the macroscopic surface) by functionalizing the mesoporous surface with sulfonic acid groups. To achieve a controlled drug release over an extended time period, further coatings were added. Covering the surface of the drug loaded mesoporous silica layer by dip-coating with bis(trimethoxysilyl)hexane resulted in an organosiloxane layer which retarded the release for up to 30 days. By an additional evaporation coating with dioctyltetramethyldisilazane, the release of ciprofloxacin was prolonged for up to 60 days. The biocompatibility of the different coatings was tested in cell culture assays. The presence of the additional silane-derived hydrophobic coatings somewhat reduced the biocompatibility. The antibacterial efficacy of the materials was demonstrated by using clinically relevant biofilm-forming pathogenic bacteria. A test where the sequential release of ciprofloxacin (in 2 days intervals) and the bacterial viability were tested in parallel showed good concordance in the results. The material where a sulfonate-functionalized mesoporous silica layer is loaded with ciprofloxacin and then coated by an organosiloxane layer derived from bis(trimethoxysilyl)hexane showed the best results with regard to antibacterial efficacy and will further be tested in animal experiments.

Immobilization of alkaline phosphatase on modified silica coatings

The immobilization of a model enzyme, alkaline phosphatase (ALP), onto differently modified silica surfaces and coatings was investigated as a test case for the biofunctionalization of implant surfaces. In this context, the influence of silica surface structures and various silane linker molecules on the capacity to bind active proteins were studied. For this purpose, microscope glass slides were coated with unstructured or mesoporous silica films. The binding of the protein to the surface was mediated by trialkoxysilanes with different functional groups like amino, epoxy, and urea functions. The model protein ALP was chosen due to its robustness and the availability of a simple activity assay. This assay showed that all the functionalized trialkoxysilanes tested were able to immobilize active ALP on silica surfaces. Using the 3-aminopropylsilyl modification resulted in the highest activity of bound ALP, especially in combination with a mesoporous surface coating. Interestingly, unstructured silica sol–gel films had only low capacity to immobilize active enzyme whereas both mesoporous silica coatings and plain glass bound higher amounts of active ALP. By using mesoporous coatings functionalized with 3-aminopropylsilyl residues, maximal binding capacities for active ALP were achieved. This combination appears most promising for the further development of bioactive surfaces for practical applications such as surgical implant functionalization.

Influence of Water on the Preparation of Thick Mesoporous Silica Coatings by the Electrophoretic Deposition Method

Ordered mesoporous silica (MPS) is expected to be used as an adsorbent for energy-efficient desiccant cooling systems. For practical use, it is important to be able to fabricate thick MPS coatings on metal supports. As we reported previously, MPS coatings on metal substrates can be formed using the electrophoretic deposition (EPD) method. Since MPS adsorbs a certain amount of water depending on the relative humidity, the amount of water adsorbed in MPS influences electrification, dispersion stability, and EPD behavior. In this study, we investigated the influence of water on the formation of thick MPS coatings by using an acetone bath. MPS powder was placed in a humidity-controlled vessel prior to EPD to adsorb water. The deposited amount tended to increase when dry MPS powder was used and when the water content of the acetone was reduced. In addition, the deposited amount was constant for 24 hours or more when the MPS powder was immersed in acetone containing 0.15 vol% of water. We found that dried MPS powder and acetone containing less than 0.45 vol% water were suitable for the stable preparation of thick MPS coatings. Consequently, 100 m-thick MPS coatings were successfully fabricated with the EPD method using dried MPS powder and an acetone bath containing 0.15 vol% water

Fabrication of Mesoporous Silica Coating by Electrophoretic Deposition

The technological feasibility of applying electrophoretic deposition (EPD) to ordered mesoporous silicate (MPS) powder has been studied. The EPD technique was investigated for the fabrication of an MPS thick film using MPS synthesized by the spray-drying method. It was found that the MPS powder deposition rate was low with an alcohol EPD bath and very high with an acetone EPD bath. The deposition amount could be easily controlled by changing the MPS powder concentration, the applied dc voltage, and the deposition time. An MPS particle/acetone suspension in which the particles were negatively charged showed the highest deposition rate among the tested organic solvents. MPS powder was deposited by EPD at 50 V for 10 min onto a tubular stainless steel substrate, and a uniform coating approximately 250 μm in thickness was obtained. After heat treatment at 573 K, the MPS powder could be fixed on the substrate without the addition of binders. The obtained MPS thick film had the same porous structure and nitrogen and water vapor adsorption properties as the parent MPS powder.

Temperature Responsive Solution Partition of Organic–Inorganic Hybrid Poly(N‐isopropylacrylamide)‐Coated Mesoporous Silica Nanospheres

AbstractA series of poly(N‐isopropylacrylamide)‐coated mesoporous silica nanoparticle materials (PNiPAm‐MSNs) has been synthesized by a surface‐initiated living radical polymerization with a reversible addition–fragmentation chain transfer (RAFT) reaction. The structure and the degree of polymerization of the PNiPAm‐MSNs has been characterized by a variety of techniques, including nitrogen sorption analysis, 29Si and 13C solid‐state NMR spectroscopy, transmission electron microscopy (TEM), and powder X‐ray diffraction (XRD). The thermally induced changes of the surface properties of these polymer‐coated core–shell nanoparticles have been determined by examining their partition activities in a biphasic solution (water/toluene) at different temperatures.

Engineering porosity in polymer-derived ceramics

By employing carefully controlled processing methods, a large amount of porosity (>70 vol%) was introduced in ceramic materials derived from preceramic polymers (silicone resins) after pyrolysis at 1000–1200 °C in inert atmosphere. The resulting components have a bulk density ranging from ∼250 to 950 kg/m 3. Three main fabrication methods have here been employed: (1) direct foaming of a solution of a thermosetting silicone resin in a suitable solvent (with or without the addition of polyurethane precursors), acting also as a blowing agent; (2) the use of sacrificial fillers that decompose during pyrolysis, consisting in polymeric microbeads; (3) the mixing of preceramic polymers possessing different characteristics, in particular ceramic yield, depending on their molecular structure. In addition to that, several methods for developing micro- or meso-pores within the resulting SiOC macro-porous ceramics were explored, with the aim of fabricating components with hierarchical porosity. These include a controlled thermal treatment, the addition of fillers with a high specific surface area (SSA), the deposition of zeolites or meso-porous silica coatings, the infiltration with aerogels, selective etching of the SiOC material and the in situ formation of C-based nanostructures. Depending on the fabrication procedure adopted, cells with an average size ranging from the micrometer to the millimeter were obtained. All these processes are simple, economical and versatile, and large bodies with various shapes (tubes, plates, blocks) can be produced, possessing a wide range of morphologies and properties. Compression strength, flexural strength and Young's modulus vary with the morphology and density of the porous components. It is also possible to add to the preceramic polymers some filler powders, for instance possessing electrical conductivity or magnetic properties, leading to the production of functional cellular ceramics.

Engineering and characterization of mesoporous silica-coated magnetic particles for mercury removal from industrial effluents

Mesoporous silica coatings were synthesized on dense liquid silica-coated magnetite particles using cetyl-trimethyl-ammonium chloride (CTAC) as molecular templates, followed by sol–gel process. A specific surface area of the synthesized particles as high as 150 m 2/g was obtained. After functionalization with mercapto-propyl-trimethoxy-silane (MPTS) through silanation reaction, the particles exhibited high affinity of mercury in aqueous solutions. Atomic force microscopy (AFM), zeta potential measurement, thermal gravimetric analysis (TGA), analytical transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and atomic absorption spectroscopy (AAS) were used to characterize the synthesis processes, surface functionalization, and mercury adsorption on the synthesized magnetite particles. The loading capacity of the particles for mercury was determined to be as high as 14 mg/g at pH 2. A unique feature of strong magnetism of the synthesized nanocomposite particles makes the subsequent separation of the magnetic sorbents from complex multiphase suspensions convenient and effective.

Supra-amphiphilic transparent mesoporous silica coating

Transparent mesoporous silica coatings were achieved by conventional sol-gel process. The obtained coatings display permanent supra- amphiphilicity, transparent appearance and good wetting property with very fast spread rate. Incorpo- ration of functional materials such as crystalline tita- nia nanoparticles into the coatings was also carried out without affecting the transparency and supra- amphiphilicity.

Template‐Assisted Synthesis of Mesoporous Magnetic Nanocomposite Particles

AbstractA new concept is proposed to synthesize mesoporous magnetic nanocomposite particles of great scientific and technological importance. Mesoporous silica coatings were created on micrometer‐sized magnetite (Fe3O4) particles using cetyltrimethylammonium chloride micelles as molecular templates. The characterization by transmission electron microscopy (TEM), nitrogen adsorption–desorption, diffuse‐reflectance Fourier‐transform infrared spectroscopy, and zeta‐potential measurements confirmed the deposition of mesoporous silica thin layers on the magnetite particles. The synthesized particles showed a drastic increase in specific surface area with an average pore size of 2.5 nm. The coating material showed a negligible effect on the saturation magnetization of the original particles that were fully protected by silica coatings. The synthesized mesoporous magnetic nanocomposite particles have a wide range of applications in toxin removal, waste remediation, catalysis, reactive sorbents, and biological cell separations.

Spin casted mesoporous silica coatings for medical applications

Self-assembling organic/inorganic sol–gel systems were used to prepare mesoporous silica coatings that can qualify for medical applications. The cationic surfactant cetyltrimethyl ammonium chloride (CTAC) or an amphiphilic triblock copolymer were utilized as templates or structure-directing agents, and tetraethylorthosilicate (TEOS) as the silica precursor. Thin films could be applied on different substrates (glass, silicon, and titanium) by spin casting of the sol–gels. X-Ray diffraction analyses indicated that well ordered hexagonally packed mesostructures with unit cells of 3 and 13 nm, when CTAC and triblock copolymer were used, respectively, could be fabricated. Parameters such as CTAC/TEOS molar ratio and gel formation time highly affected the resulting structure, so the optimum values were established. A competition occurs between the formation of cylindrical mesochannels on the substrate and homogeneous nucleation of the silica in the sol–gel solution to form spherical particles. Therefore, a growing presence of silica particles on the spin casted coatings happens as the gel formation time is increased above ∼60 s, which results in poorer mesoporous films. When a triblock copolymer was used as template, a preferred alignment of the mesostructure was observed independently of the substrate. The removal of the organic template to hollow the pores was accomplished by photocalcination (selective ultraviolet irradiation). The resulting mesoporous silica coatings were able to induce apatite formation after 1 week of immersion in a simulated body fluid in physiological conditions, which is a sound indication of a bioactive behavior when tested in vivo. These results indicate that the coatings prepared by the methodology described in this work may be valid candidates to be used on implants.

Aligned bioactive mesoporous silica coatings for implants.

Ongoing research is reported aimed at preparing mesoporous silica coatings on various substrates for medical applications by a biomimetic approach (self-assembling of organic/inorganic sol-gel systems into ordered structures). Tetraethylorthosilicate (TEOS) was selected as the silica precursor, and amphiphilic triblock copolymers poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), and the cationic surfactant cetyltrimethyl ammonium chloride (CTAC), as structure-directing agents. The mesochannels diameter could be adjusted by changing the directing agent, and a preferred alignment of the mesostructure was observed independently of the used substrate (glass, silicon, Ti or Ti6Al4V). Three different treatments (thermocalcination, photocalcination, and solvent extraction) have been also studied to remove the organic templates, of which photocalcination showed to be the most versatile. When soaked in a simulated body fluid, mesoporous silica coatings induced apatite formation after seven days.

Synthesis of direct templated aligned mesoporous silica coatings within capillaries

Download options Please wait... Article information DOI https://doi.org/10.1039/A703964F Article type Paper Download Citation Chem. Commun., 1997, 1843-1844 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Synthesis of direct templated aligned mesoporous silica coatings within capillaries M. E. Raimondi, R. H. Templer, J. M. Seddon and T. Maschmeyer, Chem. Commun., 1997, 1843 DOI: 10.1039/A703964F To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Maria E. Raimondi Richard H. Templer John M. Seddon Thomas Maschmeyer