Electrospining: Highly conductive and sensitive alginate hydrogel strain sensors fabricated using near-field electrohydrodynamic direct-writing process

Abstract

The EHD printing method is used to manufacture the hydrogel strain sensor, which has excellent mechanical properties (tensile strength, high sensitivity, high conductivity). In addition, the EHD printing hydrogel strain sensor method has important potential in wearable devices and human-computer interaction applications.

Research background/challenges

Hydrogel flexible sensors have attracted much attention due to their wearability, biocompatibility and precise signal transmission capability. However, the mechanical strength and sensing characteristics of the hydrogel strain sensor prepared by traditional printing or manual injection method are difficult to balance, which limits the application of the hydrogel strain sensor.

Research methods/techniques

Loosely crosslink polyvinyl alcohol and polyacrylamide with sodium alginate through chemical crosslinking. Subsequently, MXene nano sheet doping was introduced to construct cross-linked hydrogel conductive network, and the hydrogel strain sensor was prepared by electrohydrodynamic (EHD) printing method. The relevant characteristics of the sensor were verified through experiments.

Research Highlights/Research Focus

1. High conductivity:

The ions in the hydrogel printed by EHD move directionally under the external enhanced electric field, which makes the hydrogel form a more uniform and dense porous conductive network inside, obtaining a high conductivity (0.49 S m ^{− 1}), which is 0.29Sm ^{− 1} higher than the conductivity of the hydrogel membrane prepared by manual injection method.

2. High sensitivity:

The addition of MXene material improves the compactness of the sensor conductive network. The EHD printing process basically eliminates the void defects in the hydrogel, making the porous network structure more uniform, dense and stable, thus improving the sensitivity of the sensor. (Measurement coefficient: 1.54, 0-100% strain).

3. Good stability:

The sensor underwent long-term stability tests under 50% strain during loading and unloading. The results showed that the stability time of the sensor was as long as 2000 s (500 cycles), indicating that the sensor has good stability.

4. Excellent mechanical properties:

The cross-linking between MXene nanosheets and the hydrogel network forms more hydrogen bonds. The high-voltage electric field applied during the printing process helps to improve the distribution uniformity and orientation uniformity of the printing materials to a certain extent, which is conducive to improving the mechanical properties of the hydrogel. M3-S3PB hydrogel has the highest tensile strength and elongation at break, respectively 0.17 MPa and 787%.

5. Excellent adhesion:

Sensors prepared using EHD printing method have strong physical affinity, making them easy to achieve effective adhesion to different object surfaces with the assistance of electrostatic forces. These excellent adhesion properties can meet the requirements of strain sensors and achieve high-quality signal acquisition.

Conclusion

The flexible hydrogel strain sensor with high stability, high conductivity and high sensitivity was prepared by EHD printing technology. The interaction between SA and MXene nanosheets and polymer networks significantly improved the electrical and mechanical properties of hydrogels. During the sensor manufacturing process, the orientation of the external high-voltage electric field on the internal material components of the hydrogel leads to the formation of a dense porous network structure, which makes the M₃-S₃PB hydrogel flexible strain sensor.It has excellent mechanical properties, high sensitivity, low detection limit, and good sensing stability within the strain range of 1-500%.

Paper Link: https://doi.org/10.1016/j.ijbiomac.2024.136802