3D Printable Strain Sensors from Deep Eutectic Solvents and Cellulose Nanocrystals

Area of Science:

• Materials Science
• Biomedical Engineering
• Polymer Chemistry

Background:

• Wearable electronics require stretchable and conductive materials for physiological monitoring.
• Fabricating robust hydrogel sensors with complex 3D structures remains a significant challenge.

Purpose of the Study:

• To design a 3D printable ink for fabricating robust, stretchable, and air-stable ionogel sensors.
• To develop a novel sensor capable of continuous and sensitive monitoring of human body motions.

Main Methods:

• Formulation of a 3D printable ionogel ink using cellulose nanocrystals (CNCs), deep eutectic solvents (DESs), and ionically cross-linked polyacrylic acid (PAA).
• Utilizing a dual cross-linking strategy: reversible physical network from CNCs and permanent ionic cross-linking via photopolymerization.
• 3D printing of an auxetic sensor with negative Poisson's ratios for conformal skin contact.

Main Results:

• The developed DES/CNC nanocomposite ionogel exhibits high strength and stretchability due to the CNC physical network.
• The ionogel sensors demonstrate superior air stability compared to traditional hydrogels, attributed to the low volatility of DESs.
• The 3D printed auxetic sensor successfully monitored and identified various human body motions through resistance changes.

Conclusions:

• A simple, rapid, and cost-effective strategy for fabricating stable and sensitive strain sensors from renewable resources has been demonstrated.
• The developed ionogel ink and 3D printing approach offer a promising platform for advanced wearable physiological monitoring devices.