Arabinoxylan/Cellulose Nanocrystal Hydrogels with Tunable Mechanical Properties

Bioinspired pullulan-starch nanoplatelets nanocomposite films with enhanced mechanical properties

Inspired by the leaf-vein network structure, the pullulan-starch nanoplatelets (SNPs) bioinspired films with enhanced strength and toughness were successfully fabricated through a water evaporation-induced self-assembly technique. SNPs (SNP200 and SNP600) of two sizes were separated by differential centrifugation. Interactions between SNPs and pullulan during drying resulted in the vein-like network structure in both nanocomposite films when the appropriate amounts of SNP200 or SNP600 were added to pullulan, respectively. The TS and toughness values of pullulan with 1 % w/w SNP200 films reached up to 51.05 MPa and 69.65 MJ·m-3, which were 86 % and 223 % higher than those of the neat pullulan films, respectively. Moreover, the TS and toughness values of pullulan-SNP200 were significantly higher than those of pullulan-SNP600 films, when SNP content exceeded the 1 % w/w level. By applying a graph theory, the network structures were found to correlate with the mechanical properties of the pullulan-SNPs bioinspired films. The new strategy for designing starch nanoplatelets-based edible films that combine mechanical strength and toughness holds promises for the development of novel biobased composite materials for food packaging application.

Arabinoxylan in Water through SANS: Single-Chain Conformation, Chain Overlap, and Clustering

Using small-angle neutron scattering (SANS), we examine the structure and conformational behavior of wheat arabinoxylan (AX) prepared at various concentrations in a sodium phosphate aqueous buffer. As for another major hemicellulose, xyloglucan, we observe a small number of large clusters surrounded by AX chains that behave exactly as a polymer in good solvent with a Flory exponent ν = 0.588. The fit of the data at high q-values to a standard worm-like chain model gives the persistence length lp = 45 Å and cross section of the chains 2Rc = 11-12 Å. In addition, using a dedicated modeling approach, we extract from the SANS data at the intermediate q-range the correlation length ξ of the solutions in the semidilute regime. The decay of ξ with concentration follows a scaling law that further confirms the self-avoiding statistical behavior of the AX chains. This first comprehensive study about the properties of water-soluble AX at different length scales may help in the development of products and processes involving AX as a substitute for fossil carbon molecules.

Understanding Nanocellulose-Water Interactions: Turning a Detriment into an Asset

Modern technology has enabled the isolation of nanocellulose from plant-based fibers, and the current trend focuses on utilizing nanocellulose in a broad range of sustainable materials applications. Water is generally seen as a detrimental component when in contact with nanocellulose-based materials, just like it is harmful for traditional cellulosic materials such as paper or cardboard. However, water is an integral component in plants, and many applications of nanocellulose already accept the presence of water or make use of it. This review gives a comprehensive account of nanocellulose-water interactions and their repercussions in all key areas of contemporary research: fundamental physical chemistry, chemical modification of nanocellulose, materials applications, and analytical methods to map the water interactions and the effect of water on a nanocellulose matrix.

Advanced Functional Materials Based on Nanocellulose for Pharmaceutical/Medical Applications

Nanocelluloses (NCs), with their remarkable characteristics, have proven to be one of the most promising "green" materials of our times and have received special attention from researchers in nanomaterials. A diversity of new functional materials with a wide range of biomedical applications has been designed based on the most desirable properties of NCs, such as biocompatibility, biodegradability, and their special physicochemical properties. In this context and under the pressure of rapid development of this field, it is imperative to synthesize the successes and the new requirements in a comprehensive review. The first part of this work provides a brief review of the characteristics of the NCs (cellulose nanocrystals-CNC, cellulose nanofibrils-CNF, and bacterial nanocellulose-BNC), as well as of the main functional materials based on NCs (hydrogels, nanogels, and nanocomposites). The second part presents an extensive review of research over the past five years on promising pharmaceutical and medical applications of nanocellulose-based materials, which have been discussed in three important areas: drug-delivery systems, materials for wound-healing applications, as well as tissue engineering. Finally, an in-depth assessment of the in vitro and in vivo cytotoxicity of NCs-based materials, as well as the challenges related to their biodegradability, is performed.

Chronicle of Nanocelluloses (NCs) for Catalytic Applications: Key Advances

Nanocellulose (NC) is a biomaterial with growing interest in the field of nanocomposites and sustainable materials. NC has various applications including biodegradable materials, reinforcing agents, packaging films, transpiring membranes and medical devices. Among the many applications, the use of NC functionalized with organic and inorganic groups has found wide use as a catalyst in chemical transformations. The goal of this review is to collect the current knowledge on its catalytic applications for chemical groups conversion. We have chosen to organize the manuscript according to subdivision of NC into Bacterial Nanocellulose (BNC), Cellulose Nanocrystals (CNCs), and Cellulose Nanofibers (CNFs) and their role as inorganic- and organic-functionalized NC-catalysts in organic synthesis. However, in consideration of the fact that the literature on this field is very extensive, we have decided to focus our attention on the scientific productions of the last five years.

Bioinspired Thermoresponsive Xyloglucan-Cellulose Nanocrystal Hydrogels

Thermoresponsive hydrogels present unique properties, such as tunable mechanical performance or changes in volume, which make them attractive for applications including wound healing dressings, drug delivery vehicles, and implants, among others. This work reports the implementation of bioinspired thermoresponsive hydrogels composed of xyloglucan (XG) and cellulose nanocrystals (CNCs). Starting from tamarind seed XG (XGt), thermoresponsive XG was obtained by enzymatic degalactosylation (DG-XG), which reduced the galactose residue content by ∼50% and imparted a reversible thermal transition. XG with native composition and comparable molar mass to DG-XG was produced by an ultrasonication treatment (XGu) for a direct comparison of behavior. The hydrogels were prepared by simple mixing of DG-XG or XGu with CNCs in water. Phase diagrams were established to identify the ratios of DG-XG or XGu to CNCs that yielded a viscous liquid, a phase-separated mixture, a simple gel, or a thermoresponsive gel. Gelation occurred at a DG-XG or XGu to CNC ratio higher than that needed for the full surface coverage of CNCs and required relatively high overall concentrations of both components (tested concentrations up to 20 g/L XG and 30 g/L CNCs). This is likely a result of the increase in effective hydrodynamic volume of CNCs due to the formation of XG-CNC complexes. Investigation of the adsorption behavior indicated that DG-XG formed a more rigid layer on CNCs compared to XGu. Rheological properties of the hydrogels were characterized, and a reversible thermal transition was found for DG-XG/CNC gels at 35 °C. This thermoresponsive behavior provides opportunities to apply this system widely, especially in the biomedical field, where the mechanical properties could be further tuned by adjusting the CNC content.

Influence of arabinoxylan on the drying of cellulose nanocrystals suspension: From coffee ring to Maltese cross pattern and application to enzymatic detection

Evaporation of sessile droplet containing suspension of cellulose nanocrystals (CNC) results on birefringent coffee ring pattern (CR), due to the concentration increase and self-assembly of CNC carried by the flow at the edge of evaporating droplet. In this work, we studied the apparition of Maltese cross pattern, (MC) after addition of an hydrosoluble biopolymer belonging to the hemicellulose family, i.e. arabinoxylan (AX). To investigate the mechanisms that control MC pattern apparition, distribution of the two components inside the dried droplet was investigated using FTIR. CNC and AX were found to be homogenously deposited and CNC self-assembly induces nanoparticles orientation in the CR deposit. We demonstrate that the increase of concentration during drying induces gelation of CNC/AX mixture leading to MC pattern apparition. We take advantage of the apparition of MC pattern to develop a novel catalytic activity detection assay based on the variation of viscosity. Indeed, addition of Endo-1,4-β-Xylanase (Xyl) addition to a suspension containing CNC/AX complex leads to hydrolysis of AX that decrease in droplet viscosity leading to MC disappearance. The enzymatic detection assay is thus simple, easy to handle, fast, sensitive and do not require complex analytical devices.