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International audience; The effect of enzymatic modification of polysaccharides on the formed supramolecular structures was studied. Gum Arabic and chitosan were modified by covalent grafting of ferulic acid oxidation products so that they could establish new interactions such as π interactions. The stoichiometry of the interaction was studied by ITC measurements, as well as its strength and related thermodynamic parameters. These experiments were supported by Zeta potential and turbidity measurements and optical macroscopy observations. Grafting of phenolic compounds onto the polymers increased their ability to exhibit π-π stacking and π-cation interactions and led to the formation of various supramolecular structures. For native gum Arabic and chitosan assemblies, the stoichiometry value determined by ITC was consistent with optical microscopy, macroscopic observations and Zeta potential (around a molar ratio gum Arabic:chitosan of 3). The structures formed were coacervates. For the modified polymers, the optimal molar ratio determined by Zeta potential measurements (3.27) differed from the one determined by ITC (6.3). This meant the formation aggregates was not only due to electrostatic interactions but also to other type of interactions (new π-π stacking and π-cation interactions). It was concluded that by modifying the polymers, it was possible to control the supramolecular structures formed

In this study, a novel multi-scale drug encapsulation system, curcumin-Solid Lipid Nanoparticles (SLNs) loaded chitosan microparticles, has been formulated by combining biopolymer- and lipid-based drug delivery systems. Curcumin was loaded into phospholipids / Tween 80 stabilized shea butter SLNs (C-SLNs) using high shear homogenization – ultrasonication technique. Over than 99% of curcumin was entrapped into SLNs. In order to protect and to improve their stability, C-SLNs were encapsulated within chitosan microparticles (CS-C-SLNs) by ionotropic gelation using sodium tripolyphosphate (TPP) as a crosslinking agent. The final microparticles presented a thin size distribution centered on 21.6 ± 1.6 μm and were stable upon time in water. Differential scanning calorimetry and X-Ray diffraction revealed that the SLNs lipid structure was not affected by either curcumin or chitosan. These preliminary results showed that CS-SLNs microparticles can be a promising encapsulation system for hydrophobic compounds.

Curcumin interaction with micellar caseins (MC), Lactobacillus delbrueckii bulgaricus (Lb) and Streptococcus thermophilus (St) and its influence on the acid gelation were investigated. Epifluorescence microscopy evidenced the adsorption of curcumin on bacteria surfaces and its transfer from MC to bacteria. Fluorescence spectroscopy of curcumin and fluorescence quenching of caseins variations in presence of bacteria and MC were evaluated. The interaction between curcumin and St and Lb was confirmed due to the decrease of curcumin fluorescence intensity from 1.7 A.U to 1.20 A.U and to 1.40 A.U, respectively. The transfer of curcumin between MC and bacteria was confirmed. The curcumin interacted more with St than with Lb envelope with a fluorescence intensity decrease from 6.20 ± 0.02 A.U to 5.20 ± 0.08 A.U and to 4.60 ± 0.08 A.U, respectively. It also showed that St was more hydrophobic than Lb bacterial envelope leading curcumin to interact more with Streptococcus surface. Curcumin adsorption did not affect Lb and St growth nor its acidification rate of milk. The acid gelation study led to a typical gel yoghurt-like formation. For the first time, it was demonstrated that curcumin interacted with lactic bacteria without modifying its growth and milk acidic gelation property.

International audience; Despite various spectacular therapeutic properties, curcumin has low bioavailability mainly due to its poor solubility in water. In this paper, we encapsulated curcumin by nanoliposomes prepared from salmon purified phospholipid and coated with chitosan. Various techniques were used in order to study the interactions among phospholipid, chitosan and curcumin. FTIR results showed both electrostatic and hydrophobic interactions as well as hydrogen bonding between chitosan and phospholipid, while hydrophobic forces and hydrogen bonding dominated the interactions between curcumin and phospholipid as well as between curcumin and chitosan. Shear viscosity measurements demonstrated a flow behavior change from Newtonian to shear thinning after liposome coating. The increase/decrease stress ramp showed that the addition of chitosan layer decreased significantly the hysteresis loop area (thixotropic behavior) and therefore increased significantly the liposomal dispersion stability. The viscoelastic properties investigated by small-amplitude oscillatory shear rheology demonstrated improvement of mechanical stability after chitosan addition. Small-angle X-ray scattering experiments revealed that the liposome membrane structure was not affected by the chitosan layer or the encapsulated curcumin.

We report here the synthesis of mesoporous silica materials from various fluorinated-based systems using as the inorganic precursor either sodium silicate solution or silicate ions produced from the dissolution of silica under basic conditions. The properties of the materials are compared with the ones of the mesostructures prepared from tetramethoxysilane as silica source. Results show that whatever the silica source, well-ordered hexagonal materials with a narrow pore size distribution are obtained. Nevertheless, the pH has a great influence on the properties of the recovered materials since it governs the interactions between the surfactant and the inorganic precursor and the pH range for which the hexagonal mesopore ordering is obtained, depends on the silica source. Using sodium silicate, hexagonal mesostructured materials with high specific surface area (≥800 m 2 /g) and narrow pore size distribution (4 nm) are recovered for pH from 0.3 to 5. It should be noted that the formation of organized mesoporous silica under acidic conditions with this precursor is barely reported in literature. Replacing sodium silicate by silica fumed, the pH range leading to a hexagonal mesopore ordering is reduced to 0.3–1.5. When the organosilane is used the ordered mesoporous materials are recovered regardless the pH. In addition in that case a better control of the self assembly between the surfactant and the silica species allows tuning the particles’ morphology. Under acidic conditions tetramethoxysilane gives rise to gyroids or toroids and favors the formation of submicrometer particles, while irregularly shaped particles are produced with sodium silicate or silica fumed under alkaline conditions. Results also show that neither the specific surface area, nor the cell parameter strongly depend on the silica precursor as long as the hexagonal structure is kept.

Mesoporous silica materials have been prepared using aqueous solutions of hydrogenated-fluorinated surfactant mixtures. The phase behavior of the C18H35(OC2H4)10-C6F15C2H4(OC2H4)11OH [RH18(EO)10-RF6(EO)11] mixture in aqueous solution was first established at the temperature at which the silica source is added, i.e., 20 or 40 degrees C. We have delimited the different phase domains. Concerning the mesostructured silica, whatever the temperature at which the silica source is added, mesoporous material with a hexagonal array of their channel is formed via a cooperative templating mechanism (CTM), if the content of RF6(EO)11 in the surfactant mixture is lower than 50%. Moreover, when the silica source is added at 40 degrees C, the recovered materials exhibit a bimodal pore size distribution. The appearance of this bimodality has been related to the coexistence of hydrogenated micelles with fluorinated wormlike micelles. By contrast, the bimodality is not observed when the silica source is added at 20 degrees C.

International audience; In the present work, shea butter solid lipid nanoparticles (SLN) were prepared by sonication using nonionic surfactants as stabilizers without organic solvent. The mixture design methodology enabled to control particles size from 50?nm to more than 1?µm according to the mixture composition. Then, curcumin, a natural polyphenol, has been encapsulated in nanoparticles with a wide range of diameters (50–230?nm) and the encapsulation efficiency has been related to the particles sizes. The bigger the nanoparticles, the lower the encapsulation efficiency. The lipid structure at non dispersed state and under SLN form has been studied by differential scanning calorimetry and X-ray diffraction. From the obtained results, encapsulated curcumin did not affect the lipid properties at the SLN state unlike at non dispersed state. The localization of the curcumin in the outer shell of the lipid nanoparticles explained the evolution of the encapsulation efficiency according to the nanoparticles size. Practical applications: Solid lipid nanoparticles (SLN) can be used for the delivery of both hydrophobic and hydrophilic drugs. Preparing such nanovectors with natural, non-expensive materials and easily available (i.e., shea butter) will promote their potential use in several applications like oral, parenteral, dermal or ocular delivery. Controlling the particles size from the formulation composition and also the drug loading from SLN properties is of main importance to optimize the use of SLN as colloidal carrier. Mixture design of experiments methodology allowed the control of shea butter solid lipid nanoparticles size upon system composition. The influence of SLN size on the encapsulation efficiency of curcumin was studied.

International audience; Abstract The experimental design methodology has been used to study the influence of the synthesis parameters on the properties of nanostructured mesoporous materials prepared using a fluorinated surfactant based system. In a first set of experiments, the surfactant concentration, the pH of the micellar solution and the hydrothermal treatment conditions (duration and temperature) have been related to the organization of the materials pore network studied by SAXS. From the obtained results, the parameters ranges have been reduced to investigate their effect on the textural properties (specific surface area, pore diameter and pore volume) and silanol groups of well-ordered 2D-hexagonal materials. Models are proposed and validated for the prediction of the specific surface area and the pore diameter.

The formation of two-dimensional (2D)-hexagonal (p6m) silica-based hybrid materials from concentrated micellar solutions (10 wt %) of two nonionic fluorinated surfactants, R(7)(F)(EO)(8) and R(8)(F)(EO)(9), is investigated in situ using synchrotron time-resolved small angle X-ray scattering (SAXS). The two surfactants form direct micelles with different structures prior to the silica precursor addition as demonstrated by SAXS and SANS. R(8)(F)(EO)(9) gives spherical micelles and R(7)(F)(EO)(8) more complex ones, modeled here as short wormlike micelles. The in situ SAXS experiments reveal that both surfactants form well-ordered 2D-hexagonal hybrid materials after the addition of the silica precursor, in coexistence with an excess of surfactant micelles. The structures of both 2D-hexagonal phases are compared just after precipitation, and it is found that more robust and larger silica walls are formed for R(8)(F)(EO)(9) than for R(7)(F)(EO)(8). This could explain why only the material obtained with R(8)(F)(EO)(9) is stable upon washing, as observed previously. Moreover, it is proposed that in both cases, only a part of the micelles interact with the silica oligomers and undergo structural modifications before forming the 2D-hexagonal mesophase. The obtained results are finally discussed in the more general framework of the templating mechanism for nonionic surfactants.

International audience; The mechanisms of formation of organically modified (phenyl, vinyl, and methyl) silica materials with cubic Pm3̅n and hexagonal p6m periodic mesostructures obtained in one step in the presence of the cetyltrimethylammonium bromide (CTA+B) surfactant are reported in this study. Understanding the way these complex materials form is difficult but undoubtedly necessary for controlling the material structure and its properties because of the combined presence of surface organic groups and large surface areas. Here, the mechanism of formation is clarified on the basis of the modeling of time-resolved in situ small angle X-ray scattering (SAXS) experiments, with a specific focus on the micelle evolution during material formation. Their fast self-assembly is followed for the first time with a quick temporal resolution of a few seconds using a third-generation synchrotron radiation source. To better understand the behavior of the complex organic-containing mesostructure, we perform a comparative study with the corresponding organo-free, isostructural materials obtained from three different surfactants (CTA+, CTEA+, and CTPA+) having a constant chain length (C16) and an increasing polar head volume (met-, et-, and prop-). Numerical modeling of SAXS data was crucial to highlighting a systematic sphere-to-rod micellar transition, otherwise undetected, before the formation of the 2D hexagonal phase in both organo-free and organo-containing systems. Then, two different pathways were found in the formation of the cubic Pm3̅n mesostructure: either an ordering transition from concentrated flocs of spherical micelles (from CTEA+ or CTPA+) for pure TEOS systems or a structural transformation from an intermediate 2D hexagonal mesophase in organosilane systems (from CTA+). Combining the comparison between organo-free and organo-containing systems with numerical modeling, we find that the hexagonal-to-cubic phase transition in the organically modified materials seems to be strongly influenced not only by the obvious presence of the organic group but also by the quicker and more massive condensation kinetics of silicate oligomers on the CTA+ micellar surface. Finally, quite unexpectedly, we find a wormlike-to-sphere micellar transition in the CTPA+ system.

A second generation of boron nitride-based porous materials has been synthesized by a double nanocasting process via a carbonaceous template as a medium starting from a zeolite. In the multistep pr...

We report the immobilization of Rhizomucor miehei lipase (RmL) onto mesoporous silica materials, in particular the investigations concerning the effects of the level of silica condensation and of the pore size on the enzyme activity. The efficiency of the immobilization was revealed by FTIR spectroscopy. Infrared was also used to determine the quantity of adsorbed enzyme. Immobilization efficiency increased when the RmL concentration in the buffer solution was changed from 2 to 10 mg/mL. Nevertheless, while upon enzyme immobilization the mesopore ordering was sustained for the support recovered after hydrothermal treatment at 100 °C, a structure collapse occurred for the one prepared at 80 °C. The difference in behavior is attributed to the lower hydrothermal stability of this material, which reflects the lower level of silica condensation. The enzyme-containing mesostructured silica was effectively used to catalyze the model esterification reaction of lauric acid with 1-propanol, as the immobilized lipase retained its catalytic activity. A linear relationship was observed between the reaction rate and the amount of catalyst. RmL immobilized on mesoporous materials presented a satisfactory reusability, while the remaining activity of RmL after 4 months of storage was 47% of the initial one.

In this study, we have investigated the influence of the temperature during the synthesis on the hydrothermal stability of mesostructured silica prepared from a system based on nonionic fluorinated surfactant. Results obtained by SAXS, nitrogen adsorption–desorption analysis and infrared spectroscopy show that when the temperature is increased the hydrothermal stability of the recovered material is enhanced. Indeed, as soon as the treatment into boiling water begins, the structure of the sample synthesized at 80 °C is altered, while the material synthesized at 100 °C is very stable up to 24 h. This behavior has been attributed to a higher degree of silica condensation and to a decrease of both the number of silanol groups and the microporosity. A comparison of the characteristics of the materials obtained with both hydrogenated and fluorinated surfactants also evidences that the lather are more stable when treated with boiling water.

We have investigated the influence of the ratio between the volume of the hydrophilic head (VA) and the volume of the hydrophobic part (VB) of the surfactant on the mesopore ordering. To understand the difference of behavior we have performed a complete study dealing with fluorinated [Rm(F)(EO)n] and hydrogenated [Rm(H)(EO)n] surfactants. Their mixtures have also been taken into account. Here only the phase diagrams and the structural parameters of the liquid crystal phases of the mixed systems are reported. We have shown that the mutual or partial miscibility of the fluorinated and the hydrogenated surfactants depends on the number of oxyethylene units of each surfactant. To follow, various systems were used for the preparation of silica mesoporous materials via a cooperative templating mechanism (CTM). Results clearly reveal that VA/VB ratios in the range between 0.95 and 1.78 lead to the formation of well-ordered mesostructures. Wormhole-like structures are obtained for higher or lower values. Moreover, results show that from the VA/VB point of view, polyoxyethylene fluoroalkyl ether surfactants behave like their hydrogenated analogues.

In this study, we have shed some light on the relation between the position of the lower consolute boundary of various nonionic surfactants in water and the structure of the mesoporous silica materials synthesized from these surfactants-based systems. In the first part, the lower consolute boundary was shifted by adding salts. Depending on the features of the phase diagram, we have looked for either a salting out or a salting in effect. Mesoporous materials were prepared from a micellar solution of the investigated surfactants. Results clearly evidenced that the cooperative self-assembly mechanism is not favored if the lower consolute boundary is not shifted toward high temperatures. Moreover, the higher the difference between the phase separation temperature and the temperature at which the silica precursor is added to the surfactant solution, the better the mesopore ordering is. In the second part, this tendency has been confirmed by using a hydrogenated surfactant as additive.