Nadine Nassif

A sol–gel matrix to preserve the viability of encapsulated bacteria

E. coli bacteria were encapsulated within silica gels and aged at room temperature in the absence of nutrients. Their viability was studied as a function of time using different viability tests. The plate count technique gives the number of culturable bacteria that remain able to form colonies in the presence of a culture medium. Their metabolic activity toward glycolysis was followed by 14C titration and 13C NMR spectroscopy. Several sol–gel matrices were tested in order to improve the viability of the trapped bacteria. The best results were obtained when encapsulation is performed in the presence of glycerol showing that almost 50% of the bacteria were still able to form metabolites after one month of ageing. Moreover, this study demonstrates that a wide range of viability tests can be adapted for use with cells encapsulated in mineral matrices.

Water-mediated structuring of bone apatite

It is well known that organic molecules from the vertebrate extracellular matrix of calcifying tissues are essential in structuring the apatite mineral. Here, we show that water also plays a structuring role. By using solid-state nuclear magnetic resonance, wide-angle X-ray scattering and cryogenic transmission electron microscopy to characterize the structure and organization of crystalline and biomimetic apatite nanoparticles as well as intact bone samples, we demonstrate that water orients apatite crystals through an amorphous calcium phosphate-like layer that coats the crystalline core of bone apatite. This disordered layer is reminiscent of those found around the crystalline core of calcified biominerals in various natural composite materials in vivo. This work provides an extended local model of bone biomineralization.

Silica–alginate composites for microencapsulation

Optimisation of membrane properties of alginate microcapsules is a key factor for the application of microencapsulation techniques to bioartificial organ elaboration. Coacervation and layer-by-layer processes involving additional biopolymers have been extensively studied. Recently, the use of silica as a membrane-forming agent was investigated. This approach was rendered possible by the development of biocompatible routes to silica formation. The composites exhibit enhanced mechanical and thermal stability as well as suitable diffusion properties. Moreover, encapsulated enzymes and cells retain their biological activities. Similarly, silica can be associated to many other biopolymers, opening a promising route for new biocomposites design and biotechnology applications.

A Core–Corona Hierarchical Manganese Oxide and its Formation by an Aqueous Soft Chemistry Mechanism

One of the main challenges that still needs to be overcome in the design of nanotextured materials is the synthesis of uniform complex architectures. Indeed, many properties are known to be greatly modified by the size and shape of nanostructures. Other than size and shape tailoring, however, control of the ordering between nanostructures and the resulting texture is still difficult. Synthetic routes that make use of organic solvents and templates (i.e., surfactants) often require subsequent purification procedures which significantly increase production costs. The development of environmentally friendly, low-cost, and template-free synthetic methods that produce complex architectures is therefore key to enhancing both the control of the properties and the viability of such materials. In this context, porous manganese oxide materials are attracting great interest due to their applicability in domains such as ion-exchange, catalysis, and energy storage in Li batteries and supercapacitors. Indeed, layered birnessitelike manganese oxides (LMO) are particularly relevant due to their lamellar structure, which contain layers of MnO6 octahedra between which different species can be intercalated (see Figure S1 in the Supporting Information). However, the design of ordered LMO architectures remains a significant challenge as their synthesis usually takes place in an aqueous medium by sol–gel or precipitation methods, both of which result in fast and uncontrolled solid growth that hinders the synthesis of well-ordered nanostructures. Herein we present a low-temperature aqueous precipitation of potassium-intercalated LMO with a peculiar hierarchical core–corona architecture in the absence of both a template and an organic medium. Particle formation takes place in an easy “one-pot” process involving two distinct precipitation kinetic stages. The synthesis of similar inorganic/ inorganic core–corona morphologies generally requires two steps for core formation and shell growth, and there are very few reports concerning one-pot procedures that lead to fully inorganic core–shell particles. Furthermore, these methods are generally limited to metal–oxide structures. The approach presented herein, which uses in situ seeding to control the solid growth, significantly broadens the range of strategies available for the elaboration of hierarchical inorganic structures and can be extended to the design of new functional nanostructured materials, by taking advantage of the unique oxide properties, in areas such as catalysis, energy harnessing, and information storage. The synthesis of birnessite (see the Experimental Section and the Supporting Information) is based on the redox reaction between MnSO4 and an excess of KMnO4 [4f, 5b] (total Mn concentration of 0.2 molL ) in water according to Equation (1). Mixing the acidic (pH 2) solutions of the

Bacteria quorum sensing in silica matrices

Serratia marcescens bacteria were encapsulated in silica gels containing glycerol. In agreement with previous studies on Escherichia coli, entrapped cells showed a ca. 50% viability rate after one month. Nutrients were provided to the bacteria, allowing the production of prodigiosin, a red pigment exhibiting some promising therapeutic properties. Addition of “quorum sensing” molecules involved in intercellular communication leads to an enhanced prodigiosin production after four subsequent recyclings of the bacteria-containing gels over one month. Moreover, at the end of this period, nearly 100% of the initial cell population remain viable within the gels. These results suggest that, in the presence of “quorum sensing” molecules, S. marcescens bacteria can enter a stationary state where their metabolism is modified, enhancing their resistance to the stresses induced by encapsulation.

Viability of Bacteria in Hybrid Aqueous Silica Gels

Whole E. coli bacteria have been trapped within silica gels obtained via the acidification of sodium silicate and silica nanoparticles solutions. Their β-galactosidase enzymatic activity increases with time, suggesting that their membrane is partially lysed during the encapsulation process. Such a lysis can be greatly reduced when encapsulation is performed in the presence of gelatin. The biocatalytic activity of trapped bacteria remains almost constant for more than a week. Moreover bacteria trapped in such gels remain able to incorporate glucose, showing that their viability has been preserved.

Sophorolipids: a yeast-derived glycolipid as greener structure directing agents for self-assembled nanomaterials

Sophorolipids, fully natural glycolipids, can form in water nanometre-size micelles of various geometries depending on their concentration as shown by small angle neutron scattering experiments. This property allows use of them, for the first time, as structure directing agents in the synthesis of nanostructured silica thin films via the evaporation induced self-assembly (EISA) process.

Dense fibrillar collagen matrices for tissue repair

The preparation of dense fibrillar collagen matrices, through a sol/gel transition at variable concentrations, offers routes to produce a range of simple, non toxic materials. Concentrated hydrogels entrapping cells show enhanced properties in terms of reduced contraction and enhanced cell proliferation. Dense fibrillar matrices attain tissue like mechanical properties and show ultrastructures described in connective tissues, namely liquid crystalline cholesteric geometries. Their colonization by cells and possible association with a mineral phase in a tissue like manner validate their use as biomimetic materials for regenerative medicine.

Characterization of Ca-phosphate biological materials by scanning transmission X-ray microscopy (STXM) at the Ca L 2,3 -, P L 2,3 - and C K-edges

Several naturally occurring biological materials, including bones and teeth, pathological calcifications, microbial mineral deposits formed in marine phosphogenesis areas, as well as bio-inspired cements used for bone and tooth repair are composed of Ca-phosphates. These materials are usually identified and characterized using bulk-scale analytical tools such as X-ray diffraction, Fourier transform infrared spectroscopy or nuclear magnetic resonance. However, there is a need for imaging techniques that provide information on the spatial distribution and chemical composition of the Ca-phosphate phases at the micrometer- and nanometer scales. Such analyses provide insightful indications on how the materials may have formed, e.g. through transient precursor phases that eventually remain spatially separated from the mature phase. Here, we present scanning transmission X-ray microscopy (STXM) analyses of Ca-phosphate reference compounds, showing the feasibility of fingerprinting Ca-phosphate-based materials. We calibrate methods to determine important parameters of Ca-phosphate phases, such as their Ca/P ratio and carbonate content at the ∼25nm scale, using X-ray absorption near-edge spectra at the C K-, Ca L2,3- and P L2,3-edges. As an illustrative case study, we also perform STXM analyses on hydroxyapatite precipitates formed in a dense fibrillar collagen matrix. This study paves the way for future research on Ca-phosphate biomineralization processes down to the scale of a few tens of nanometers.

Controlled collagen assembly to build dense tissue-like materials for tissue engineering

Intermediate states of matter, in the form of liquid crystals, are indirectly evidenced in the body. Hence concepts developed by the soft matter community have allowed the highlighting of original morphogenetic pathways, strongly suggesting how 3D structures arise at the tissue level. The clues proposed have opened the way to reproduce biomimetic, hierarchically ordered, assemblies of biological macromolecules. The present paper will focus on collagen and describe the process allowing to attain homogeneous fibrillar matrices, both at high concentrations and over long distances. Their characterization at scales ranging from μm to cm will demonstrate suprafibrillar arrangements similar to dense connective tissues, with aligned or helicoidal geometries depending on the protein concentrations. In addition we will show that in vitro and in vivo studies validate these tissue-like constructs as repair materials for tissue engineering applications.