Propylene Glycol-Assisted Printing of Graphene Piezoresistive Sensor Array for Analytical Motion Tracking and Spinal Kinetics Monitoring.

Continuous monitoring of spinal kinematics is crucial for posture correction and rehabilitation, yet conventional approaches like radiological imaging and camera-based motion capture are limited by snapshot-only information and the reliance on specialized medical equipment. Wearable sensor arrays enable spinal monitoring by tracking the critical muscular deformation, while the inter-channel discrepancies within a sensor array usually leads to compromised accuracy in deformation mapping. Herein, we report a graphene-based piezoresistive sensor array with minimized inter-channel discrepancy (4.12% difference in baseline resistance across 8 channels) for spinal monitoring. The high inter-channel consistency is achieved through a printing-and-transfer methodology employing photo paper as the intermediate substrate, which overcome the intrinsic incompatibility between graphene dispersion and stretchable polydimethylsiloxane (PDMS) substrate for homogeneous film deposition. Moreover, propylene glycol (PG) is applied as the ink-engineering additive, which not only improve the printability of graphene dispersion, but also enable a high-yield film transfer from photo paper to PDMS substrate through forming an interim layer at the graphene-photo paper interface. For spinal kinetics monitoring, the sensor array could differentiate 6 trunk postures with a classification accuracy of 95.4% using machine learning algorithm. This work provides a scalable platform for daily spinal health tracking, enabling disease prevention and rehabilitation monitoring.