Bacteria metabolic adaptation to oxidative stress: the case of silica

Although the presence of silica in many living organisms offers advanced properties including cell protection, the different in vitro attempts to build living materials in pure silica never favoured the cells viability. Thus, little attention has been paid to host-guest interactions to modify the expected biologic response. Here we report the physiological changes undergone by Escherichia coli K-12 in silica from colloidal solution to gel confinement. We show that the physiological alterations in growing cultures are not triggered by the initial oxidative Reactive Oxygen Species (ROS) response. Silica promotes the induction of alternative metabolic pathways along with an increase of growth suggesting the existence of rpoS polymorphisms. Since the functionality of hybrid materials depends on the specific biologic responses of their guests, such cell physiological adaptation opens perspectives in the design of bioactive devices attracting for a large field of sciences.

A multiscale study of bacterial proliferation modes within novel E. coli@Si(HIPE) hybrid macrocellular living foams

This multiscale study depicts the fundamentals of bacterial proliferation modes within hybrid E. coli@Si(HIPE) macrocellular living foams.

Rational design of one-dimensional vanadium(v) oxide nanocrystals: an insight into the physico-chemical parameters controlling the crystal structure, morphology and size of particles

This highlight deals with the recent advances on the synthesis in aqueous solution of one-dimensional vanadium(v) oxide nanocrystals.

Silica@proton-alginate microreactors: a versatile platform for cell encapsulation

Acid gelation of alginate allows the inclusion of living cultures within sol–gel silica hydrogels. The formed beads spontaneously revert into a liquid viable culture.

In vitro studies and preliminary in vivo evaluation of silicified concentrated collagen hydrogels

Hybrid and nanocomposite silica-collagen materials derived from concentrated collagen hydrogels were evaluated in vitro and in vivo to establish their potentialities for biological dressings. Silicification significantly improved the mechanical and thermal stability of the collagen network within the hybrid systems. Nanocomposites were found to favor the metabolic activity of immobilized human dermal fibroblasts while decreasing the hydrogel contraction. Cell adhesion experiments suggested that in vitro cell behavior was dictated by mechanical properties and surface structure of the scaffold. First-to-date in vivo implantation of bulk hydrogels in subcutaneous sites of rats was performed over the vascular inflammatory period. These materials were colonized and vascularized without inducing strong inflammatory response. These data raise reasonable hope for the future application of silica-collagen biomaterials as biological dressings.

Formation Of Spinel Iron Oxide In Solution

The alkalizing of aqueous mixtures Fe111 + xFe11 has been investigated at pH ≈ 8 for 0≤x≤0.5. Three composition zones have been observed. At x<O.l goethite was the only stable product. At 0.1≤x≤0.25 the early stage, characterized as mixed-valent protoferrihydrite, spontaneously transformed into nonstoichiometric magnetite. At x>0.25 the system, made of spinel particles, was homogeneous during all the evolution.

Synthesis, Structure And Applications Of TiO2 Gels

TiO2 gels are usually obtained through hydrolysis of titanium alkoxides. Chemical additives can however react with the precursor at a molecular level and therefore modify the hydrolysis-condensation reactions. Several examples will be described :acetic acid, acetylacetone or Cr(acac)3 The whole solgel process is followed all the way from the precursors to the gel and each step is characterized by spectroscopic experiments (Infra-red, N.M.R, E.S.R.). Some electronic properties of TiO2 gels are then described. Chemical additives allow an optimization of the sol-gel process according to each specific applications : electrochromic display devices, photoanodes or photochemical reactions.

Spectroscopic Characterization of a Pre-Ceramic Polymer For Sic/Tic System

Polytitanocarbosilane precursor for SiC/TiC ceramics was characterized by various spectroscopic techniques (29Si and 13C CP MAS NMR, Ti K-edge XANES and EXAFS) in order to follow how titanium ions are incorporated into the polycarbosilane-based polymer. This polymer has been fired in argon atmosphere, and the evolution of the local environments of Si and Ti atoms, during the pyrolysis process, have been followed using 29Si MAS-NMR and Ti K-edge X-ray absorption: this study reveals the formation of Si-O bonds above 500°C, while Ti-C bonds clearly appear around 800°C. Above 1000°C, Si-O bonds are consumed by reaction with excess carbon and the system finally crystallizes into SiC/TiC mixture above 1200°C.

Assembly of Decavanadate Polyanions by Collagen Helices: Synthesis of an Hybrid Inorganic-Bioorganic Mmaterial

Vanadium oxide-collagen hybrid nanocomposites were prepared by adding a V2O5 sol to a dilute collagen solution. 51V MAS NMR spectroscopy shows that the inorganic phase is composed of the decavanadate [H2V10O28]4− polyanion and V2O5 ribbon-like particles. The broadening of the 51V signals and the absence of Bragg peaks in the XRD pattern suggest a strong disorder concerning the organization of the V2O5 particles and of the decavanadate species in the composites. Analogous hybrid nanocomposites were obtained with a solution that contains only the decavanadate species, showing that the cohesion in the hydrid material results mainly from electrostatic interactions between decavanadate [H2V10O28]4− polyanions and positively-charged collagen helices.

Structural Investigation of the Hydrolysis-Condensation Process of a Modified Titanium Alkoxide

Titanium isopropoxide was modified with acetylacetone in order to get stable photosensitive colloids via an hydrolysis-condensation process. The various steps of this process were followed by infrared, 1H and 13C NMR and X-Ray absorption (XANES and EXAFS). The latter techniques provided some interesting structural data (coordination of titanium, Ti-O and Ti-Ti distances) on the various species, from the precursor to the colloids. A structural model is proposed for each one, with a scheme of the different reactions occuring during the process.

Ionic Properties of Hydrous Oxide Gels

The sol-gel process offers new opportunities for the synthesis of ionic materials, specially in the shape of thin films. Hydrous oxides are obtained which exhibit specific properties arising from strong interactions betwwen adsorbed water molecules and the oxide network. Sol-gel derived coatings are good candidates as electrode materials for lithium batteries or electrochromic devices. Their open structure allows easier diffusion of Li+ions in the liquid phase while electrons are delocalized through the oxide network. Moreover, water molecules favor the formation of ordered phases leading to the deposition of layers with preferred orientation. Electrochemical insertion can then be described as an intercalation process between solid particles.

Structural Characterization of Silicon Carbonitride Ceramics from Polymeric Precursors using Nuclear Magnetic Resonance

The pyrolytic conversion of a polyvinylsilazane precursor to Si-C-N ceramics is studied using solid-state NMR. 13C and 29Si magic angle spinning and 1H static NMR experiments allow us to investigate the structure of the disordered multiphased intermediates formed during the pyrolysis. The Si environments are quantitatively analyzed by 29Si MAS NMR spectra simulations. The relative abundance of SiHCN2, SiC2N2, SiN3C and SiN4 sites at different temperatures are used to calculate elemental compositions that characterize the Si-containing phase. The comparison of these compositions with those obtained from chemical analyses shows evidence of the presence of a free carbon phase.We have also determined the H and C contents in the free carbon phase.

Ionic Properties of Vanadium Pentoxide Gels

Vanadium pentoxide gels V2O5·nH2O are actually hydrous oxides. Water adsorption and dissociation occurs at the surface of the oxide leading to negatively charged oxide particles surrounded by an acid aqueous medium. Ionic conductivity is observed, arising from proton diffusion through the water molecules. This process mainly depends on the nature of adsorbed water molecules. Proton conductivity is strongly related to the water adsorption isotherm.

Ion exchange readily occurs at the oxide-solution interface when the gel is dipped into an aqueous solution of a metal chloride. New vanadium bronzes have been obtained upon heating such gels around 300° C. They exhibit interesting properties as reversible cathodes.

Electrochemical insertion of Li* into the gel phase is quite easy. This is due to the very open structure of the gel and the mixed valence behavior of the vanadium oxide.

Transition metal oxide gels could then be used as thin films or pressed pellets for making micro-ionic devices.

Structural Characterization of Gels Prepared from Co-Hydrolysis of Tetraethoxysilane and Dimethyldiethoxysilane

This work is part of a more general study on the structural characterization of organically modified silica gels that are usually prepared from tetrafunctional, trifunctional and difunctional alkoxides. The systems that were investigated in this paper are gels prepared from co-hydrolysis of dimethyldiethoxysilane (DEDMS) and tetraethoxysilane (TEOS). The condensation process was followed by 29Si and 17O liquid NMR and shows clearly evidence for co-condensation reactions. Gels with various DEDMS/TEOS ratios were studied by 29Si and 1H MAS-NMR. The results are clearly correlated to the change in physical properties of the materials, from flexible polymeric gels at high DEDMS content to crosslinked brittle networks at low DEDMS content.

Structural Investigation of Sol-Gel-Derived Hybrid Siloxane-Oxide Materials Using 29Si MAS-NMR Spectroscopy

Hybrid siloxane-oxide systems were prepared by sol-gel techniques. Siloxane precursors are either monomeric species, dimethyldiethoxysilane, or OH-terminated polydimethylsiloxanes. The oxide component is introduced via metallic alkoxides, M(OR)n (M=Si, Ti, Zr). Transparent materials from flexible to brittle gels, can be obtained over a large M/siloxane range. The structure of the various systems was investigated by 29Si MAS-NMR. The signals due to the difunctional Si units, (CH3)2SiO, depend strongly on the nature of M and on the M/siloxane ratio. Structural models are proposed, ranging from single phase systems with highly interconnected siloxane and oxide units, to nanocomposites made of polysiloxane chains crosslinked with oxide-based particles.

Vanadium Pentoxide Gels from Liquid Crystals to Lithium Batteries

Vanadium pentoxide gels V205.nH20 are formed via the condensation of vanadic acid in aqueous solutions. They exhibit both ionic and electronic conductivity and could therefore be used as cathode materials in lithium batteries or electrochromic display devices. The polymerization process leads to ribbon-like vanadium pentoxide particles. In a given range of concentration, sols and gels exhibit a homogeneous lyotropic nematic phase in which the ribbons align in the same direction. Ordered fluid phases are thus obtained leading to oriented films when deposited onto flat substrates. Moreover, mixed oxides MxV205 (M = Na+, K+,Ba2+, Al3+, Fe3+,Fe3+,...) exhibiting some preferred orientation are obtained via ion exchange.These compounds exhibit improved lectrochemical properties (specific capacity, cycling properties) compared to usual mixed oxides prepared via solid state reactions.

Structure and Properties of Vanadium Pentoxide Gels

Transition metal oxide gels can be obtained, through a polycondensation process, by acidification of aqueous solutions. Thin layers can be easily deposited onto a substrate. Their electronic and ionic properties could lead to new developments of the sol-gel process. The semiconducting properties of V2O gels can be used for antistatic coatings or electrical switching devices. These gels exhibit a lamellar structure and can be described as particle hydrates. They are fast proton conductors and could behave as a host lattice for intercalation.

Synthesis of Polyvanadates from Solutions

A wide range of polyvanadates can be synthesized from aqueous solutions. Vanadium oxide gels V2O5nH2O are formed around the point of zero charge (pH≈2). They exhibit a ribbon-like structure. Weak interactions between these ribbons lead to the formation of mesophases in which vanadium oxide gels or sols behave as nematic liquid crystals. Organic species can be easily intercalated between these oxide ribbons leading to the formation of hybrid nanocomposites made of alternative layers of organic and inorganic components. Hybrid nanophases can also be formed above the point of zero charge, in the presence of large organic ions such as [N(CH3)4]+. They often exhibit layered structures in which organic cations lie between the polyvanadate planes. Cluster shell polyvanadates have been obtained in the presence of anions such as Cl− or I−. They are made of negatively charged polyvanadate hollow spheres in which the anion is encapsulated. Organic cations then behave as counter ions for the formation of the crystal network.

Bioencapsulation in Sol-Gel Glasses

Bioencapsulation in sol-gel materials has been widely studied during the past decade. Trapped species appear to retain their bioactivity in the porous silica matrix. Small analytes can diffuse through the pores allowing bioreactions to be performed in-situ, inside the sol-gel glass. A wide range of biomolecules and micro-organisms have been encapsulated. The catalytic activity of enzymes is used for the realization of biosensors or bioreactors. Antibody-antigen recognition has been shown to be feasible within sol-gel matrices. Trapped antibodies bind specifically the corresponding haptens and can be used for the detection of traces of chemicals. Even whole cells are now encapsulated without any alteration of their cellular organization. They can be used for the production of chemicals or as antigens for immunoassays.

A Novel Route to Collagen-Silica Biohybrids

A novel synthetic pathway to obtain collagen-silica biohybrids using a co-gelation process is described. Concentration control of the inorganic and organic precursors leads to various morphologies. Of special interest is the possibility to obtain, through collagen templating, silica fibres that are maintained after protein removal.

Sol-Gel Entrapment of Enzymes

Two enzymes, lipase and β-galactosidase, have been encapsulated within sol-gel matrices. Enzymatic activity of encapsulated lipase for hydrolysis and trans-esterification reactions is maintained. Encapsulation yields depend not only on the sol-gel porous texture but also on the water amount added for the sol-gel synthesis and the hydratation history of the enzyme. When the water amount is low, the highly active enzyme conformation generated by the phase separation is frozen during gelation. Escherichia Coli have been also encapsulated. The cellular organization appears to be well preserved. Their β-galactosidase activity seems to be better in wet gels but decreases dramatically upon drying.

Influence of DNA, Alginate, Lysozyme and Bovine Serum Albumin on Sodium Silicate Condensation

The interaction of DNA, alginate, Lysozyme and Bovine Serum Albumin with diluted solutions of sodium silicate was studied using the molybdosilicate method. DNA and alginate showed very weak interactions with silica precursors whereas both proteins were able to form silica gels. Both electrostatic interactions and hydrogen bonds are suggested to arise between peptide chain and polysilicates, bringing new informations on the nature of inorganic and bio-organic species involved in the natural biosilicification processes.

From diatoms to silica-based biohybrids

Diatom inspired bio-hybrids offer new possibilities for the synthesis of nanostructured materials and the development of nanomedicine.

Silica-collagen bionanocomposites as three-dimensional scaffolds for fibroblast immobilization

Silica-collagen bionanocomposite hydrogels were obtained by addition of silica nanoparticles to a protein suspension followed by neutralization. Electron microscopy studies indicated that larger silica nanoparticles (80 nm) do not interact strongly with collagen, whereas smaller ones (12 nm) form rosaries along the protein fibers. However, the composite network structurally evolved with time due to the contraction of the cells and the dissolution of the silica nanoparticles. When compared to classical collagen hydrogels, these bionanocomposite materials showed lower surface contraction in the short term (1 week) and higher viability of entrapped cells in the long term (3 weeks). A low level of gelatinase MMP2 enzyme expression was also found after this period. Several proteins involved in the catabolic and anabolic activity of the cells could also be observed by immunodetection techniques. All these data suggest that the bionanocomposite matrices constitute a suitable environment for fibroblast adhesion, proliferation and biological activity and therefore constitute an original three-dimensional environment for in vitro cell culture and in vivo applications, in particular as biological dressings.

Photosynthetic microorganism-mediated synthesis of akaganeite (beta-FeOOH) nanorods

Common Anabaena and Calothrix cyanobacteria and Klebsormidium green algae are shown to form intracellularly akaganeite beta-FeOOH nanorods of well-controlled size and unusual morphology at room temperature. X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy X-ray energy dispersive spectrometry (SEM-EDS) analyses are used to investigate particle structure, size, and morphology. A mechanism involving iron-siderophore complex formation is proposed and compared with iron biomineralization in magnetotactic bacteria.

Influence of decavanadate clusters on the rheological properties of gelatin

The influence of polyoxovanadate clusters ([H(2)V(10)O(28)](4-)) on the thermo-reversible gelation of porcine skin gelatin solution (type A, M w approximately 40 000 g.mol (-1), pH = 3.4 << isoelectric point (IEP) approximately 8) has been investigated as a function of temperature and vanadate concentration by combining rheology and microcalorimetry. This work shows that the rheological properties of the system depend on electrostatic interactions between [H(2)V(10)O(28)](4-) and positively charged gelatin chains. In a first stage, we describe the renaturation of the gelatin triple helices in the presence of decavanadate clusters. We reveal that, when gelatin chains are in coil conformation (30 degrees C < T < 50 degrees C), the inorganic clusters act as physical cross-linkers that govern the visco-elastic properties of the mixture with an exponential dependence of the (G', G'') modulus with the vanadate concentration. Below 30 degrees C, we show that gelatin triple helix nucleation is slightly favored by the presence of vanadate, but above a helix concentration of 0.012 g.cm (-3), G' is fully governed by the helix concentration. During the melting process, we reveal the non-fully reversible behavior of the vanadate/gelatin rheological properties and the stabilization of gelatin triple helices due to vanadate species until 50 degrees C. This non-reversible character has also been observed in the same experimental conditions with collagen/vanadate solutions. This is the first time that such a stabilization of triple helices has been reported in the case of gelatin hydrogels chemically cross-linked or not. We propose to analyze these results by considering that triple helix aggregates should persist because of decavanadate bridging, that the nucleation of an extended triple helix network may induce a strong modification of the vanadate cross-linker distribution in the system, or both, thus promoting the formation of thermally stable vanadate/gelatin micro-gels in the dangling end of the triple helices.

First example of biopolymer-polyoxometalate complex coacervation in gelatin- mixtures

The first example of complex coacervation between a biopolymer and polyoxometalate clusters is identified in the gelatin-decavanadate system.