Laser-Induced Graphene Based Skin-Conformable Sensor for Fingers

Conformable electronic sensors have attracted significant scientific interest in recent years due to their ability to adapt to rough and non-planar surfaces, with applications in wearable electronics spanning health, robotics, and human-machine interaction1. Unlike other wearable sensors, skin-conformable sensors are well adherent to the skin and accurately record the body movements. Though there are several techniques currently being used for the fabrication of ultra-thin and wearable electronic devices, such as chemical/physical vapor deposition, and electrospinning2, they are expensive, and often involved complex manufacturing steps. <br/>In this study we present an alternative yet simple approach to fabricate conformable sensors, by employing Laser-Induced Graphene (LIG) technology. LIG is a three-dimensional material with very good conductivity and piezoresistive properties, produced with a single-step local pyrolysis of certain polymers by employing a commercially available laser engraver. In our study, we develop conformable strain/bending sensors for fingers, by laser scribing LIG on a polyimide (PI) tape using a hybrid IR laser (INS wavelength), and then transferring this LIG into thin elastomeric substrates made of thermoplastic medical grade polyurethane3 or silicone rubber. The LIG/elastomer sensors provide better adhesion to the skin with stretchability and maximum breathability. <br/>Thanks to the versatility of the laser engraver, a wide variety of shapes can be scribed and tested, from simple to complex patterns. We focused our study on three sensor designs covering three knuckles of a finger for detailed investigation. Static tensile tests were carried out to analyse the piezoresistive behaviour of the LIG/elastomer sensors. The best sensor design was chosen, based on their linearity and sensitivity properties. Since the micro/nano-scale morphology of the LIG plays a role in determining its piezoresistive behaviour, we studied the LIG structure before and after transferring to elastomer, and after the mechanical testing, by using Raman spectroscopy, Optical Microscopy and Scanning Electron Microscopy. <br/>Such novel conformable sensors open novel applications in biomonitoring and robotics. The conformable LIG/elastomer sensors have been developed with the aim of improving hand rehabilitation and teleoperation, by offering a more precise reflection of hand movements compared to traditional haptic gloves. <br/>References <br/>[1]. Parenti, Federico, et al. "Ultra-thin transistors and circuits for conformable electronics." arXiv preprint arXiv:2406.02442 (2024). <br/>[2]. Khan, Arshad, et al. "Ultra-thin and Skin-conformable Strain Sensors Fabricated by Inkjet Printing for Soft Wearable Electronics." 2022 IEEE International Symposium on Circuits and Systems (ISCAS). IEEE, 2022. <br/>[3]. Dallinger, Alexander, et al. "Stretchable and skin-conformable conductors based on polyurethane/laser-induced graphene." ACS applied materials & interfaces 12.17 (2020): 19855-19865.