Microfluidic enabled flexible sensors based on self-diffusion MWCNTs dispersion

Flexible microfluidic pressure sensors have recently attracted a lot of attention due to its revolutionary potential in the field of healthcare. These sensors provide non-invasive, highly sensitive, and adaptable options for tracking various aspects of human movement and health. Nevertheless, there are a number of limitations that affect the effectiveness of microfluidic pressure sensors, including material selection, sensor packaging techniques, sensitivity, and stability. The research outlined in this paper, which aims to address these issues head-on and significantly improve the functionality of microfluidic pressure sensors in order to increase their usefulness in the fields of medical and biomedical applications.


Materials and Methods
In this study, we propose a novel flexible microfluidic pressure sensor based on MWCNTs-PDMS for measuring stress and pressure.MWCNTs are dispersed in 100% ethanol using ultrasound to create pressure-sensitive inks.The microfluidic channel template is created using 3D light curing printing technology, and the PDMS is then plasma blasted to accomplish surface modification after being hardened in a mold.The piezoresistors are formed using a novel directional liquid spreading method to deliver a conductive nanocomposite ink into micro-channels.Compared to direct printing methods, directional liquid spreading method is a much more facile and high-speed approach to form well-defined sensors with complicated structures.To complete the encapsulation, a PDMS and n-hexane combination is spun on the surface (Fig. 1).

Experiment Results
By improving material selection for self-diffusion piezoresistive ink and refining sensor packaging techniques, we successfully enhanced the sensor's consistency and increased its sensitivity by tenfold (Fig. 3a-b), a remarkable feat that enhances the sensor's ability to detect even subtle pressure changes accurately.This sensor exhibits remarkable characteristics, including high sensitivity (4.895 kPa-1), a relatively high gauge factor (GF) of 15.68(Fig.2d-e), excellent response time (5ms), outstanding stabilities (1200 cycles) (Fig. 3c-d) and stability in all-liquid immersion environment (Fig. 2f).We also model the stress and pressure force scenarios and contrast them with the real experimental results to further understand the force response principle of the microfluidic sensor.The simulation results of the linear and serpentine runner designs are in perfect accord with the experimental findings, as can be shown by applying stresses in two perpendicular directions on the plane (Fig. 4a-d).The ultimate design of the microchannel for the sensor is a serpentine shape since the response of the rectilinear microfluid in the two directions exhibits an opposite trend, interfering with the sensor's capacity to detect human movement.These features enhance the sensor's usability in medical and biomedical applications.Testing the sensor's response in a variety of application scenarios, including contact detection of pulse signals at the fingertip and wrist surfaces, flexion and rotation of the bowl joint and knuckle joints, and testing of dynamic micro-pressures from falling water droplets, revealed that the sensor functions well in applications involving both stress and pressure measurements (Fig. 5), and has potential for applications in the direction of human movement recognition.Our research represents a significant step forward in the development of flexible microfluidic pressure sensors with applications that span the medical and biomedical fields.With continued refinement and integration into medical devices, this technology holds the potential to transform healthcare and improve the quality of life for countless individuals.

Figure 1 .
Figure 1.Schematic diagram of the sensor manufacturing process

Figure 2 .
Figure 2. Sensor's performance.(a) (b) SEM before and after packaging in the microfluid;(c) SEM of conductive ink;(d) GF at different densities;(e) Sensitivity at different densities; (f) Underwater

Figure 3
Figure 3 Sensitivity and hysteresis at 2% density and other static characteristics.(a) Sensitivity and hysteresis after improved;(b) Before improved;(c) Stability ;(d) Minimum and response time.

Figure 4 .
Figure 4. Directional stretching response to different runner shapes of sensors.(a)Simulation results of serpentine and linear microfluid in Y-direction stretching;(b) Actual response of tensile testing in the X-direction;(c) Actual response of tensile testing in the Y-direction;(d) Simulation results in Y-direction stretching;(e) Simulation results of sensor surface response to pressure.