Assembly of Anisotropic Nanocellulose Films Stronger than the Original Tree.

Natural structural materials frequently consist of multimaterial nanocomposites with complex superstructure giving rise to exceptional mechanical properties, but also commonly preventing access to their synthetic reproduction. Here we present the spin-assisted layer-by-layer assembly of anisotropic wood-inspired films composed of anionic cellulose nanofibrils and cationic poly(vinyl amine) possessing a tensile strength that exceeds that of the wood from which the fibers originate. The degree of orientation of the nanofibrils was studied by atomic force microscopy and depends strongly on the distance from the center of the spun surface. The nanofibrils are preferentially aligned in the direction of the shear flow, and consequently, the mechanical properties of such films differ substantially when measured parallel and perpendicular to the fibril orientation direction. For enabling a diversity of bioinspired applications including sensing, packaging, electronics, or optics, the preparation of nanocomposite materials and devices with anisotropic physical properties requires an extreme level of control over the positioning and alignment of nanoscale objects within the matrix material.

Coating of polydopamine on polyurethane open cell foams to design soft structured supports for molecular catalysts.

Polydopamine-coated polyurethane open cell foams are used as structured supports for molecular catalysts through the covalent anchoring of alkoxysilyl arms by the catechol groups of the mussel-inspired layer. This strong bonding prevents their leaching. No alteration of the mechanical properties of the flexible support is observed after repeated uses of the catalytic materials.

Polydopamine-coated open cell polyurethane foams as an inexpensive, flexible yet robust catalyst support: a proof of concept.

Commercially available polyurethane open cell foams are readily coated with mussel-inspired polydopamine. The polydopamine film allows robust immobilisation of TiO2 nanoparticles at the surface of the three-dimensional material. The resulting catalyst is efficient for the photo-degradation of an azo dye, reusable and highly resistant to mechanical stress. A novel type of robust structured catalytic support, easily accessible via an inexpensive and green process, is thus described.

Bio-inspired multiproperty materials: strong, self-healing, and transparent artificial wood nanostructures.

Nanocomposite films possessing multiple interesting properties (mechanical strength, optical transparency, self-healing, and partial biodegradability) are discussed. We used Layer-by-Layer assembly to prepare micron thick wood-inspired films from anionic nanofibrillated cellulose and cationic poly(vinyl amine). The film growth was carried out at different pH values to obtain films of different chemical composition, whereby, and as expected, higher pH values led to a higher polycation content and also to 6 times higher film growth increments (from 9 to 55 nm per layer pair). In the pH range from 8 to 11, micron thick and optically transparent LbL films are obtained by automated dipping when dried regularly in a stream of air. Films with a size of 10 cm(2) or more can be peeled from flat surfaces; they show tensile strengths up to about 250 MPa and Young's moduli up to about 18 GPa as controlled by the polycation/polyanion ratio of the film. Experiments at different humidities revealed the plasticizing effect of water in the films and allowed reversible switching of their mechanical properties. Whereas dry films are strong and brittle (Young's modulus: 16 GPa, strain at break: 1.7%), wet films are soft and ductile (Young's modulus: 0.1 GPa, strain at break: 49%). Wet film surfaces even amalgamate upon contact to yield mechanically stable junctions. We attribute the switchability of the mechanical properties and the propensity for self-repair to changes in the polycation mobility that are brought about by the plastifying effect of water.

Harnessing the multifunctionality in nature: a bioactive agent release system with self-antimicrobial and immunomodulatory properties.

Major problems with biomedical devices in particular implants located in nonsterile environments concern: (i) excessive immune response to the implant, (ii) development of bacterial biofilms, and (iii) yeast and fungi infections. An original multifunctional coating that addresses all these issues concomitantly is developed. A new exponentially growing polyelectrolyte multilayer film based on polyarginine (PAR) and hyaluronic acid (HA) is designed. The films have a strong inhibitory effect on the production of inflammatory cytokines released by human primary macrophage subpopulations. This could reduce potential chronic inflammatory reaction following implantation. Next, it is shown that PAR, due to its positive charges, has an antimicrobial activity in film format against Staphylococcus aureus for 24 h. In order to have a long-term antimicrobial activity, a precursor nanoscale silver coating is deposited on the surface before adding the PAR/HA films. Moreover, the PAR/HA films can be easily further functionalized by embedding antimicrobial peptides, like catestatin (CAT), a natural host defense peptide. This PAR/HA+CAT film proves to be effective as an antimicrobial coating against yeast and fungi and its cytocompatibility is also assessed. Finally, this all-in-one system constitutes an original strategy to limit inflammation and prevents bacteria, yeast, and fungi infections.