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The biocompatibility and very high specific area of cellulose nanofibrils (CNF) are properties of high interest for the development of active substrates for new medical device development. Enzyme pretreated CNF (CNF-e) can be self-organized into nanostructured membranes that are suitable for active principle ingredients (API) encapsulation through adsorption phenomena. In addition, tunable surface chemistry of CNF-e, allow for covalent immobilization of API. In this work, ciprofloxacin is integrated to CNF-e membranes according to two different strategies. The first one relies only on adsorption mechanisms; ciprofloxacin is encapsulated in the bulk before the membrane formation by solvent casting. The influence of the membrane properties and preparation parameters such as grammage, thickness and drying technique, are assessed with water uptake measurements and API release experiments. The second strategy deals with the covalent immobilization of ciprofloxacin directly onto CNF-e membrane. The two kinds of membranes are then compared in terms of antibacterial activity, in both static and dynamic conditions. Thick CNF-e membranes loaded with adsorbed ciprofloxacin that were overdried (2 h, 150 °C) prove to be more resistant in liquid medium and present a more prolonged drug release. However, these membranes rapidly lost their antibacterial activity, while CNF-e membranes with covalently immobilized ciprofloxacin remain contact active for several days. These 100% CNF active nanostructured membranes can be used as new wound dressing for topical application.

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Cellulose nanofibrils (CNF) are renewable bio-based materials with high specific area, which makes them ideal candidates for multiple emerging applications including for instance on-demand drug release. However, in-depth chemical and structural characterization of the CNF surface chemistry is still an open challenge, especially for low weight percentage of functionalization. This currently prevents the development of efficient, cost-effective and reproducible green synthetic routes and thus the widespread development of targeted and responsive drug-delivery CNF carriers. We show in this work how we use dynamic nuclear polarization (DNP) to overcome the sensitivity limitation of conventional solid-state NMR and gain insight into the surface chemistry of drug-functionalized TEMPO-oxidized cellulose nanofibrils. The DNP enhanced-NMR data can report unambiguously on the presence of trace amounts of TEMPO moieties and depolymerized cellulosic units in the starting material, as well as coupling agents on the CNFs surface (used in the heterogeneous reaction). This enables a precise estimation of the drug loading while differentiating adsorption from covalent bonding (∼1 wt% in our case) as opposed to other analytical techniques such as elemental analysis and conductometric titration that can neither detect the presence of coupling agents, nor differentiate unambiguously between adsorption and grafting. The approach, which does not rely on the use of 13C/15N enriched compounds, will be key to further develop efficient surface chemistry routes and has direct implication for the development of drug delivery applications both in terms of safety and dosage., DNP-enhanced solid-state NMR unravels the surface chemistry of functionalized nanocellulose.

International audience; In this work, we present an innovative strategy for the grafting of an antibacterial agent onto nanocellulose materials in supercritical carbon dioxide (scCO2). Dense cellulose nanofibril (CNF) nanopapers were prepared and subsequently functionalized in supercritical carbon dioxide with an aminosilane, N-(6-aminohexyl)aminopropyltrimethoxysilane (AHA-P-TMS). Surface characterization (X-ray photoelectron spectroscopy, contact angle, ζ-potential analysis) evidenced the presence of the aminosilane. The results show that the silane conformation depends on the curing process: a nonpolycondensed conformation of grafted silane with the amino groups facing outwards was favored by curing in an oven, while the curing step performed in scCO2 yielded CNF structures with the alkyl chain facing outwards. The grafted nanopapers exhibited antibacterial activity, and no antibacterial agent was released into the media. Furthermore, these materials proved to benefit from low cytotoxicity. This study offers a proof of concept for the covalent grafting of active species on nanocellulose structures and the control of aminosilane orientation using a green and controlled approach. These newly designed materials could be used for their antibacterial activity in the biomedical field. Thus, perspectives for topical administration and design of wound dressing could be envisaged.

International audience; Green treatment of natural fibres is a major issue in paper, textile and biocomposites industries to design innovative and eco-friendly products. In this work, hierarchical structuring of flax woven fabrics by the adsorption of xyloglucan (XG) and cellulose nanocrystals (CNC) is studied. Indeed, CNC have high mechanical properties, high specific surface area and great potential for functionalization. The adsorption of XG and CNC has been investigated in terms of localization by confocal and scanning electron microscopy (SEM) and quantification through adsorption isotherms. Adhesion force measurements have also been performed by Atomic Force Microscopy (AFM). XG and CNC are homogeneously adsorbed on flax fabric and adsorption isotherms reach plateau values around 20 mg /gfibres for both. The pre-adsorption of XG on flax fabric influences the amount of adsorbed CNC in the high concentrations and also creates entanglements and strong interactions between XG and CNC with the formation of an extensible network.

Increasing consumer demand for high performance bio-based materials in order to develop microbiologically safer foods has forced the food industry to revise their packaging strategies. One of the emerging fields within this industry is active packaging which prevents an excess of antimicrobials in food formulation and, meanwhile, inhibits or reduces bacterial growth. In this study, a green process of immobilizing a peptide on bio-based carboxylated cellulose nanofibers (CNF) using a coupling agent has been proposed. Validity of the grafting reaction between nanocellulose, the coupling agent and peptide was first analyzed by Quartz crystal microbalance-dissipation (QCM-D). Efficiency of the grafting reaction was characterized with Fourier Transform Infrared spectroscopy and thermogravimetric analysis which suggest the grafting of nisin on CNF. Finally, the amount of grafted nisin was quantified on the surface of CNF by conductometric titration and nitrogen content analysis. The antimicrobial activity and release experiment demonstrated that the nisin grafted CNF displayed excellent antimicrobial activity against different Gram +ve bacteria (Bacillus subtilis and Staphylococcus aureus) with significant 3.5 log reduction. The obtained results are promising and confirm the interest in such strategy.

Chemical modifications of cellulose fibers as pretreatment for cellulose nanofibrils (CNF) production have been investigated to improve the production process and the quality of obtained cellulosic nanomaterial. In this study, phosphorylation of cellulose fibers was done in anticipation of a future nanofibrillation. Different phosphate salts, namely NH4H2PO4, (NH4)(2)HPO4, Na2HPO4, NaH2PO4 and LiH2PO4 with different constants of solubility (Ks) were used to increase the efficiency of the modification. Phosphorylated cellulose pulps were analyzed using elemental analysis, solid-state C-13 and P-31 NMR, or conductimetric titration method. No effect of Ks was observed whereas a counterion effect was pointed out. The study also reported the effect of pH, cellulose consistency, temperature and urea content in phosphorylation efficiency. Finally, chemical functionalization and penetration of phosphorylation reagents in the cellulose fibers were evaluated using XPS, SEM-EDX, ToF-SIMS and solid-state NMR.

International audience; A novel type of acetylated cellulose nanofibre (CNF) was extracted successfully from sisal fibres using chemical methods. Initially, a strong alkali treatment was used to swell the fibres, followed by a bleaching step to remove the residual lignin and finally an acetylation step to reduce the impact of the intermolecular hydrogen bonds in the nanocellulose. The result of this sequence of up-scalable chemical treatments was a pulp consisting mainly of micro-sized fibres, which allowed simpler handling through filtration and purification steps and permitted the isolation of an intermediate product with a high solids content. An aqueous dispersion of CNF could be obtained directly from this intermediate pulp by simple magnetic stirring. As a proof of concept, the dispersion was used directly for preparing a highly translucent CNF film, illustrating that there are no large aggregates in the prepared CNF dispersion. Finally, CNF films with alkali extracts were also prepared, resulting in flatter films with an increased mass yield and improved mechanical strength.

The recent study focusing on paper coated with microfibrillated cellulose (MFC) revealed the ability of such a structure to achieve a controlled release of molecules introduced into its nanoporous network. The present study examines this concept using a chlorhexidine digluconate-based (CHX) antibacterial solution. Various analyses were performed, optical microscopy, FE-SEM and AFM to underline the structure of the nanoporous MFC network. Release studies were conducted in an aqueous medium following two different protocols and antibacterial tests were done to evaluate the efficiency of the final materials obtained. MFC coating provided a slower and more progressive release of CHX. Indeed, papers impregnated with CHX were active for 18 days, whereas papers coated with CHX/MFC retained their antibacterial activity for 45 days. In parallel, similar tests were carried out using a model coating slurry, and although the rate of release of CHX was also slowed down, the quantities released were insufficient to confer any antibacterial activity. In conclusion, this study suggests that the use of MFC as a coating could be very promising since it allows a controlled and progressive release of molecules preserving long-term antibacterial activity.

Partially acetylated cellulose nanofibers (CNF) were chemically extracted from sisal fibers and the performance of those CNF as nanofillers for polylactide (PLA) for food packaging applications was evaluated. Three PLA nanocomposites; PLA/CNF (cellulose nanofibers), PLA/CNC (nanocrystalline cellulose), and PLA/C30B (CloisiteTM 30B, an organically modified montmorillonite clay) were prepared and their properties were evaluated. It was found that CNF reinforced composites showed a larger decrease on oxygen transmission rate (OTR) than the clay-based composites; (PLA/CNF 1% nanocomposite showed a 63% of reduction at 23°C and 50% RH while PLA/C30B 1% showed a 26% decrease) and similar behavior on terms of water vapor barrier properties with 46 and 43%, respectively of decrease on water vapor transmission rate at 23°C and 50% RH (relative humidity). In terms of mechanical and thermomechanical properties, CNF-based nanocomposites showed better performance than clay-based composites without affecting significantly the optical transparency. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43257.

An environmentally friendly and simple method, named SolReact, has been developed for a solvent-free esterification of cellulose nanocrystals (CNC) surface by using two nontoxic carboxylic acids (CA), phenylacetic acid and hydrocinnamic acid. In this process, the carboxylic acids do not only act as grafting agent, but also as solvent media above their melting point. Key is the in situ solvent exchange by water evaporation driving the esterification reaction without drying the CNC. Atomic force microscopy and X-ray diffraction analyses showed no significant change in the CNC dimensions and crystallinity index after this green process. The presence of the grafted carboxylic was characterized by analysis of the "bulk" CNC with elemental analysis, infrared spectroscopy, and (13)C NMR. The ability to tune the surface properties of grafted nanocrystals (CNC-g-CA) was evaluated by X-ray photoelectron spectroscopy analysis. The hydrophobicity behavior of the functionalized CNC was studied through the water contact-angle measurements and vapor adsorption. The functionalization of these bionanoparticles may offer applications in composite manufacturing, where these nanoparticles have limited dispersibility in hydrophobic polymer matrices and as nanoadsorbers due to the presence of phenolic groups attached on the surface.