Soft Wearable Piezoresistive Sensors Based on Natural Rubber Fabricated with a Customized Vat-Based Additive Manufacturing Process

Abstract

Piezoresistive sensors for monitoring human motions are essential for the prevention and treatment of injury. Natural rubber is a material of renewable origin that can be used for the development of soft wearable sensors. In this study, natural rubber was combined with acetylene black to develop a soft piezoresistive sensing composite for monitoring the motion of human joints. An additive manufacturing technique based on stereolithography was used, and it was seen that the sensors produced with the method could detect even small strains (<10%) successfully. With the same sensor composite fabricated by mold casting, it was not possible to detect low strains reliably. TEM microscopy revealed that the distribution of the filler was not homogeneous for the cast samples, suggesting a directionality of the conductive filler network. For the sensors fabricated through the stereolithography-based method, a homogeneous distribution could be achieved. Based on mechano-electrical characterization, it was seen that the samples produced with AM combined the ability to endure large elongations with a monotonic sensor response. Under dynamic conditions, the sensor response of the samples produced by 3D printing showed lower drift and lower signal relaxation. The piezoresistive sensors were examined for monitoring the motion of the human finger joints. By increasing the bending angle of the sensor, it was possible to increase the sensitivity of the response. With the renewable origin of natural rubber and manufacturing method, the featured sensors can expand the applicability of soft flexible electronics in biomedical applications and devices.

Recent developments in stretchable and flexible tactile sensors towards piezoresistive systems: A review

“…Apart from these synthetic polymers, a few materials also showed the ability to work as flexible substrates, such as NR, 40,183–185 paper, 186 and napkin, 65 which are readily available, eco‐friendly, non‐toxic, inert, light in weight, low cost, and have good enough flexibility. Eco‐friendly materials such as silk fiber are the other alternatives in the category of biomaterials that can sustain large deformation and have mechanical properties enough to behave as flexible sensors 187 …”

“…Apart from these synthetic polymers, a few materials also showed the ability to work as flexible substrates, such as NR, 40,[183][184][185] paper, 186 and napkin, 65 which are readily available, eco-friendly, nontoxic, inert, light in weight, low cost, and have good enough flexibility.…”

Closed‐Loop Optimization of Soft Sensor Morphology Using 3D Printing of Electrically Conductive Hydrogel

“…Natural rubber þ acetylene black [59] %0. phase suggests an initial sensor shape, which is printed onto the user's hand in the real-world phase.…”

Drift‐Aware Feature Learning Based on Autoencoder Preprocessing for Soft Sensors

“…Such biases result in a narrow mapping of the predicted detection range and accumulate overtime, potentially causing the malfunction of the subsequent controller. While the pre-straining method has been shown to mitigate signal drift to a certain extent, [2,11,12] it introduces a trade-off as it may result in a nonreproducible sensor response characterized by sensitivity fluctuations.…”