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Soft, Stretchable Laser-Induced Graphene Sensor for Wearable Electronics

A team of researchers recently published a paper in the journal npj Flexible Electronics that demonstrated a new way to successfully fabricate stretchable and soft LIG-based devices for wearable applications.

Soft, Stretchable Laser-Induced Graphene Sensor for Wearable Electronics​​​​​​​

​​​​​​​Study: A soft and stretchable electronics using laser-induced graphene on polyimide/PDMS composite substrate. Image Credit: metamorworks/

Significance of LIG-fabrication Procedure

The photothermal conversion of the organic films into continuous three-dimensional (3D) porous graphene structures under air by pulsed laser irradiation is the most common procedure used to fabricate laser-induced graphene (LIG). The fabrication process represents a simple, direct, and one-step way to achieve the controllable formation of highly sensitive piezoresistive sensors and flexible electronics with different geometries. This approach is suitable for different applications such as wearable sensors and nanogenerators in an affordable manner.

Limitations of Existing Substrates for the Fabrication of Stretchable LIG Devices

LIG can be fabricated on different types of synthetic and natural materials with adequate carbon sources, such as commercial polyimide (PI) and woods. The commercial PI film is often used as a substrate during the formation of high-quality LIG due to its high carbon concentration and thermo-mechanical stability. However, the in-plane robustness of commercial PI films limits their application in devices that need a high stretchability.

Stretchable devices and substrates obtained through structural and material design are critical for wearable electronics. The maximum strain of LIG-based sensors fabricated on PI films is less than three percent, which is much lower compared to the maximum strain of the human skin at more than 13 percent. Thus, LIG-based electronics with a stretchability of more than 15 percent must be fabricated for wearable applications.

New Way Proposed to Fabricate LIG with High Stretchability  

The high stretchability in LIG-based devices can be achieved using sticky and stretchable polydimethylsiloxane (PDMS) as an ideal elastic substrate. The LIG can be transferred from the PI substrate to the PDMS substrate to significantly enlarge the stretchability of the fabricated LIG-based device. Thus, a PI/PDMS composite can be utilized as a stretchable and soft substrate to fabricate flexible devices such as supercapacitors and sensors.

In this study, researchers used a PI/PDMS composite substrate to fabricate a highly stretchable LIG under infrared laser beam irradiation. The addition of PI particles to the PDMS solution provided the carbon source required to form porous graphene under infrared laser beam irradiation. A 30 watts laser cutting machine with a carbon dioxide laser generator was used to fabricate the porous LIG on the PI/PDMS composite substrate.

Different manufacturing parameters, including the laser scanning procedure conditions and material composition that can significantly influence the mechanical and electrical performance of the fabricated LIG-based system were analyzed and measured through scanning electron microscopy (SEM) images and mechanical tension experiments.

The laser fluence was theoretically and experimentally determined to characterize the conductive LIG formation on PI/PDMS composite substrate, facilitating the selection of laser scanning parameters such as laser dots per inch (DPI) and frequency.

Evaluation of the Fabricated Samples

The application of the fabricated LIG-based system as a remote controller and wearable sensor was demonstrated by three examples, including an electrophysiological activity sensor, finger motion monitor, and real-time actuator control tool.

The stretchable and soft LIG-based sensors were fabricated and attached to the throat and wrist of the volunteer to monitor head motion and pronunciation and pulse wave rate, respectively. Similarly, a LIG-based soft glove was fabricated for the hand to monitor the hand gestures and evaluate its effectiveness as a wearable tool for remote control of LIG actuators.

Bending and tensile experiments were performed using a universal mechanical testing machine. Digital multimeters with a sampling rate of two hertz and one hertz were employed for the throat and pulse motion monitor experiments and gesture and finger motion monitor experiments, respectively.

Significance of the Study

LIG was fabricated successfully on the PI/PDMS composite substrate using infrared laser irradiation. LIG-based sensors with complex 3D shapes were effectively synthesized through this fabrication process. Additionally, the fabricated sensors demonstrated the capability to bear more than 15 percent mechanical tension, which is higher than the elasticity of the human skin, without impacting the stability of their electrical performances.

The good cyclability and 470 percent linear increase of the normalized resistance for a tensile strain of 15 percent in the fabricated LIG-based sensors demonstrated the feasibility of using these sensors for human motion monitoring applications.

The reasonable range of laser fluence determined theoretically and experimentally to achieve the LIG-based sensor with desired electrical performance was between 35.4 joules per square centimeter and 70.8 joules per centimeter. Observations from the demonstration examples displayed the LIG-based electrical systems' inherent stretchability, exceptional sensitivity, and good cyclability.

A high-quality and stable pulse rate signal, such as a diastolic wave and tidal wave, was recorded immediately by the LIG-based sensor after it was attached to the wrist of the volunteer. The pulse wave of 71 beats per minute indicated the healthy condition of the volunteer.

The left index finger motions were timely monitored and accurately predicted by attaching the LIG sensors to the distal interphalangeal point (DIP), proximal interphalangeal point (PIP), and metacarpophalangeal point (MP) from the fingertip to the palm.

The LIG-based sensor attached to the throat detected the words banana and apple and recognized the swallowing activity of the volunteer. The soft glove with separate LIG sensors effectively monitored the finger motion and gestures by analyzing the collective motions of five fingers. Additionally, the functional glove was used successfully as a wearable remote controller of actuators, which indicates its potential in soft robots.

Taken together, the findings of this study demonstrated that the stretchable and soft LIG-based systems fabricated using PI/PDMS as a substrate could be used effectively as a critically functional component in wearable and flexible electronics.


Guo, X., Liu, P., Wang, H. et al. (2022) A soft and stretchable electronics using laser-induced graphene on polyimide/PDMS composite substrate. npj Flexible Electronics.

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Samudrapom Dam

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Samudrapom Dam

Samudrapom Dam is a freelance scientific and business writer based in Kolkata, India. He has been writing articles related to business and scientific topics for more than one and a half years. He has extensive experience in writing about advanced technologies, information technology, machinery, metals and metal products, clean technologies, finance and banking, automotive, household products, and the aerospace industry. He is passionate about the latest developments in advanced technologies, the ways these developments can be implemented in a real-world situation, and how these developments can positively impact common people.


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