Jammed Microgels in Deep Eutectic Solvents as a Green and Low-Cost Ink for 3D Printing of Reliable Auxetic Strain Sensors

Abstract

Additive manufacturing is a promising technique for offering novel functionality to various materials by creating three-dimensional (3D) structures. However, the development of sustainable synthesis processes for 3D printing inks or 3D-printed materials remains a major challenge. In this work, a simple two-step mixing approach is developed to prepare a 3D printing ink from green, low-cost, and low-toxicity materials [commercial Carbopol and deep eutectic solvents (DESs)]. A small weight fraction of Carbopol can impart desired rheological properties to the DES used in the 3D printing ink and also can significantly enhance the stretchability of eutectogels up to 2500% strain. The 3D-printed auxetic structure shows a negative Poisson’s ratio (within 100% strain), high stretchability (300%), high sensitivity (gauge factor of 3.1), good moisture resistance, and sufficient transparency. It can detect human motion with high skin comfort and breathability. The results of this work highlight a green, low-cost, and energy-saving strategy to fabricate conductive microgel-based inks for 3D printing of wearable devices.

Recent progress in the development of conductive hydrogels and the application in 3D printed wearable sensors

“…Vo et al . 186 proposed a green, low-cost, and energy-saving strategy to manufacture conductive ink for the 3D printing of wearable devices based on green and low-cost Carbopol and DES. Combined with DIW 3D printing, the ink could manufacture several structures, including auxetic structures, woodpile shapes, and letters.…”

A Flexible and Stretchable MXene/Waterborne Polyurethane Composite-Coated Fiber Strain Sensor for Wearable Motion and Healthcare Monitoring

“…Moreover, abundant polar functional groups generated during the liquid phase etching process endow MXene with excellent hydrophilicity, enabling and facilitating their solution-based employment approaches [ 39 , 40 , 41 ]. In addition, with the rise of environmental awareness and the use of non-pollution and low-toxicity polymers has become another trend for CPCs [ 42 , 43 , 44 , 45 ]. Waterborne polyurethane (WPU), a new type of PU system that uses water instead of organic solvents as a dispersion medium, has abundant hydrophilic functional groups, so it can form a strong bond to various substrates through hydrogen bonding, showing excellent film-forming properties and processability and thus attracting much attention [ 46 , 47 , 48 ].…”

Natural Oleanolic Acid-Tailored Eutectogels Featuring Multienvironment Shape Memory Performance

“…Deep eutectic solvents (DESs) consisting of hydrogen bond donors and acceptors have melting points lower than for each component and are regarded as alternatives to ionic liquids considering their conductivity, weak volatility, thermal stability, and antifreezing properties. − In contrast to ionic liquids, DESs offer many distinct advantages, such as low cost, nontoxicity, biodegradability, and green fabrication . As a result, eutectogels composed of polymer networks and DESs inherit these merits and have been applied to electronics, − catalytic systems, adhesives, and drug delivery systems . In 2023, Liu and co-workers first reported a thermoresponsive shape memory eutectogel by polymerization of DESs ( N -ayanomethyl cerylamide/lithium bis­(trifluoromethane)), which showed complete shape fixation/recovery and fast recovery (<6 s).…”