(K-429) Wearable Ultrasound Transducers based on 3D Porous Graphene

Musculoskeletal injuries are a significant concern in various fields, particularly during dynamic tasks. Accurate evaluation of muscle function during these tasks is crucial for effective injury prevention and rehabilitation. Traditional methods for tracking and assessing muscle function, such as force plates and motion capture, present limitations in terms of cost, environmental constraints, and expertise requirements. This study proposes an innovative approach for evaluating muscle function and assessing musculoskeletal injuries using ultrasound technology. Ultrasound has emerged as a promising alternative due to its accessibility and ability to visualize musculoskeletal structures, including ligaments, tendons, and muscles. However, current ultrasound transducers face challenges when it comes to tracking muscle function during dynamic tasks. The rigidity, fragility, and lack of stability of conventional transducers restrict their applicability in capturing muscle dynamics accurately. To overcome these limitations, this study introduces a new paradigm of ultrasound sensors: a flexible adhesive transducer based on 3D porous graphene derived from polyimide film (PI-3DPG) via a direct laser scribing method integrated with piezoelectric PVDF(TrFE).

We employ a facile, rapid, and scalable laser photothermal approach to generate 3D porous graphene from thin films of polyimide (PI). By utilizing a far-infrared laser, localized photothermal irradiation causes a temperature increase within the laser's focused area. This rise in temperature breaks the covalent bonds between carbon atoms in the polyimide precursor, resulting in the formation of porous structures as the gaseous molecules in the polyimide evaporate. Subsequently, a composite piezoelectric material is created by integrating Polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) with 3D porous graphene. To complete the fabrication process, the transducer is subjected to poling conditions. This involves applying a voltage of 6kV with a distance of 2 cm and maintaining a temperature of 80 ^oC for 45 minutes. These poling conditions facilitate the alignment of the piezoelectric domains within the PVDF-TrFE composite, enhancing its overall piezoelectric properties.

The pores of PI-3DPG offer a high specific surface area of approximately 278 m² g^-1, thereby increasing the effective surface area of the PVDF(TrFE) coating. This expanded surface area allows for the accumulation of a greater number of electrons, leading to higher capacitance. Consequently, the dielectric constant of the material also increases. A higher dielectric constant indicates the material's enhanced ability to store electric charge per unit voltage, resulting in improved efficiency of the transducer for generating and receiving ultrasonic waves. This heightened charge storage capacity enables superior energy conversion between electrical and mechanical forms, leading to enhanced sensitivity and performance of the ultrasound transducer. The fabricated graphene-PVDF transducer shows an SNR of 7.22 and a center frequency of 8.807 MHz. The wearable graphene-based ultrasound technology holds potential for various applications, including musculoskeletal injury assessment, rehabilitation guidance and treatment, wound monitoring, and injury prevention.