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.

A comparison of neck bending and flexion measurement methods for assessment of ergonomic risk.

Head movements of workers were measured in the sagittal plane in order to establish a precise and accurate assessment method to be used in real work situations. Measurements were performed using two inclinometers connected to an embedded recording system. Two quantitative analysis methods were tested, i.e., measurement of bending with an inclinometer attached to the head, and measurement of flexion/extension by using an additional inclinometer located at C7/T1. The results were also compared with a video observation method (qualitative). The results showed that bending measurements were significantly different from those of flexion/extension for angles between 0° and 20°, and angles >45°. There were also significant differences between workers for flexion >45°, reflecting individual variability. Additionally, several limitations of observational methods were revealed by this study.