Bio-based Organohydrogels For Pressure and Strain Sensor Applications
Abraham Mora1, Gaurav Khandelwal2, Xiaolong He1, Ajay Kottapalli2, Giuseppe Portale1*
1. Physical Chemistry of Polymeric and Nanostructured Materials, Zernike Institute of Advanced Materials, University of Groningen, Nijenborgh 3, 9743 AG Groningen, The Netherlands.
2. Bio-inspired MEMS and Biomedical Devices, Engineering and Technology Institute Groningen, University of Groningen, The Netherlands.
ABSTRACT
Health monitoring, motion detection, human-machine interfaces, and soft robotics are all becoming more prevalent with the use of smart wearable devices. These applications necessitate materials that are both mechanically robust and stretchable. Organohydrogels have recently gained attention as prospective candidates for flexible and durable sensor platforms as a result of their enhanced stability and hybrid water-organic solvent composition. This work presents the advancement of a bio-based organohydrogel system intended for wearable strain and pressure sensing applications.
Iota-carrageenan, a natural polysaccharide sourced from red algae, served as the hydrogel matrix and was functionalized with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) to enhance electrical conductivity. Epichlorohydrin functioned as a crosslinking agent to improve the mechanical integrity of the network. In order to enhance environmental stability and water retention, the hydrogels were transformed into organohydrogels by immersing them in glycerol for different time intervals.
The successful establishment of crosslinks was validated by Fourier-transform infrared spectroscopy (FTIR), while a mass loss analysis indicated that immersion in glycerol enhanced stability, with less than 1% weight loss observed after 7 days under open conditions at 21°C and 30% relative humidity. The mitigation of dehydration was achieved through the partial substitution of water with glycerol.
The optimal variant in this observation, designated CG_P_Gly3h (carrageenan/PEDOT: PSS immersed in glycerol for 3 hours), exhibited remarkable strength: it could elongate up to 500% prior to failure, withstand a peak stress of 325 kPa, possess a toughness of 55 kJ/m³, and demonstrate a Young’s modulus of 130 kPa. The organohydrogel demonstrated a conductivity surpassing 2.75 S/m, over five times greater than that of the pure hydrogel, and was able to power an LED bulb.
CG_P_Gly3h demonstrated consistent responsiveness across a wide strain range, exhibiting gauge factors of 1.8 for strains up to 70% and 1.3 for strains between 70% and 300%. The maximum sensitivity of 0.58 kPa⁻¹ was obtained in the 7–63 kPa range of pressure sensing. The device's exceptional durability was demonstrated by its ability to maintain a consistent signal output for 1000 loading cycles under 49 kPa pressure. The flexible matrix and homogeneous conductive pathways of PEDOT:PSS are responsible for this exceptional performance.
In conclusion, the CG/PEDOT:PSS organohydrogels are a prospective material for the development of next-generation wearable electronic sensors due to their compelling combination of flexibility, stretchability, conductivity, and stability.