Hydrogels are three-dimensional networks of hydro-soluble polymers containing a large amount of water that have found a wide panel of applications in many sectors. The need for eco-friendly and nontoxic materials for the elaboration of sustainable hydrogels is obvious, and materials derived from biomass can easily meet these requirements. Cellulose nanocrystals (CNC) and arabinoxylans (AX) are abundant, biobased, hydrophilic, and renewable nanoparticles and polymers that interact together. In this study, we have built fully biobased hydrogels using CNC and AX. First, as revealed by Quartz Crystal Microbalance with Dissipation (QCM-D) experiments, AX adsorbs almost instantly on cellulosic surfaces in an irreversible manner. Nevertheless, gelation kinetics is not instantaneous and shows temperature dependence. The determination of phase diagrams using the inverted tube method leads to the conclusion that high AX/CNC ratios are needed for gel formation. The mechanical properties of CNC-AX hydrogels were investigated by measuring storage and loss moduli (G′, G′′) as a function of concentrations and hydrogel reformation after submission to high shear rates. Hydrogel properties were also tuned by increasing the ionic strength and the enzymatic removal of arabinose moieties from AX. In light of the obtained results, we hypothesize that gel formation occurs in two steps, i.e., AX adsorption followed by gelation of the complexes, and is due to the formation of reversible and tunable interactions between CNC/AX complexes interacting with each other, offering a wide panel of physicochemical tools to tune and trigger the final properties of hydrogels.
Plant components are an inexhaustible source for the construction of bio-based materials. Here we report, for the first time, the elaboration of biobased cellulose nanocrystals (CNC)/xyloglucan (XG) hydrogels. XG is a hemicellulose displaying a great affinity for cellulose surface and can be thus irreversibly adsorbed on CNC. Properties of the hydrogels were investigated by varying the molar mass of XG either by enzymatic treatment with Endoglucanase (EG2) or physical fractionation by ultrasound (US). Fractions were characterised by high-performance size exclusion chromatography (HPSEC) and their monosacchari decompositions were determined. Three fractions with high, average and small molar mass, (800, 300 and 100 10 3 g/mol respectively), were selected in order to tune the properties of the hydrogel. Sol-gel transition conditions were determined for each fraction by achieving phase diagram using the inverted tube method. Mechanical properties, assessed by rheology, are improved by increasing XG molar mass since elastic modulus is higher for hydrogels formed with higher molar mass fractions as well as the strain at break. Gel formation is likely due to the adsorption of XG fractions on CNC which increases the effective hydrodynamic volume of CNC leading to steric stabilization and interactions between loops and tails of XG adsorbed.
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.
Thermo-responsive 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 bio-based thermo-responsive hydrogels comprised of xyloglucan (XG) and cellulose nanocrystals (CNCs). Thermo-responsive properties were obtained by enzymatic degalactosylation of tamarind seed XG (DG-XG), which reduced the galactose residue content by ~50%, and imparted a reversible thermal transition. XG with comparable molar mass to DG-XG was achieved by ultrasonication treatment (XGu) for 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 (from 1:300 to 20:1 by mass) that yielded a viscous liquid, a phase separated mixture, a simple gel, or a thermo-responsive 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, where the mechanical properties of the gel could be tuned by adjusting the CNC content
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