Cellulose Nanocrystals As a Key in Wearable Sensors

Abstract

In recent years, the development of cellulose-based inks for 3D printing has received significant interest due to numerous cellulose and its derivatives properties [1], [2]. Carboxymethyl cellulose (CMC) is an anionic water-soluble cellulose derivative widely used as superabsorbent hydrogels [3]. Another cellulose derivative is cellulose nanocrystal (CNC), a rod-like nanoparticle that can be applied for the mechanical strengthening of hydrogels and also presents potential use in several applications in the biomedical field [2], [4]. Based on this, we have proposed to investigate if CMC and CNC mixtures result in cellulose-based nanocomposite gels suitable for extrusion printing of wearable sensors. Interactions between CNC and CMC resulted in physical gels, where rheological properties and extrusion printing parameters' effects were studied. A Modular Compact Rheometer (Anton Paar MCR-102, Austria) with a plate-plate geometry (50 mm diameter and 1 mm gap) at 25 °C was used to perform rheological measurements. Extrusion printing was performed on the customized 3DCloner Lab printer using a 22G nozzle tip of 25 mm in length and a diameter of 0.70 mm (Injex, Brazil). Gels presented shear-thinning, solid-like viscoelastic behavior, viscosity recovery, and continuous filaments obtained during printing. Moreover, the alignment of rod-like CNC during the printing process can be a key to improving properties. Tests with different print and extrusion speeds evidenced the influence of the wearable sensor's geometry and mechanical properties. Moreover, the low cytotoxicity of CMC/CNC crosslinked hydrogels was confirmed through an MTT assay of fibroblasts. Further testing is being conducted to evaluate the self-healing and conductive properties of the sensors by external stimuli. Moreover, low cytotoxicity to CMC/CNC crosslinked hydrogels was confirmed through an MTT assay of fibroblasts. External stimuli are being applied to evaluate the self-healing and conductive of the sensor printed.