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On February 28, 2024, the team of Professor Li Xinyue/Li Yingchun published their latest research paper, "Capacitive Pressure Sensor Combining Dual Dielectric Layers with Integrated Composite Electrode for Wearable Healthcare Monitoring," in ACS Applied Materials & Interfaces (Impact Factor: 8.3). They have made significant progress in the field of capacitive pressure sensors for wearable healthcare monitoring.
They developed a novel capacitive pressure sensor that introduces an optimized electrospinning network and micropillar array as a dual dielectric layer, integrating existing sensors with miniaturized instruments to design a smart insole as a wearable platform for gait monitoring and disease warning. This provides a cutting-edge solution for detecting diseases in a non-invasive manner and paves the way for future wearable devices and personalized medical technologies.
1.The team prepared a flexible capacitive pressure sensor with integrated dual dielectric layers through electrospinning and molding techniques. The combination of electrospinning networks and micropillar arrays provides the sensor with greater deformation capacity and stronger compression resistance, enhancing the sensor's working range and rebound performance.
2. The integrated flexible electrode is made from carbon nanotubes (CNT), two-dimensional titanium carbide Ti3C2TX (MXene), and polydimethylsiloxane (PDMS) composite materials using a template method, offering synergistic advantages in terms of conductivity, stability, sensitivity, and practicality.
3. They designed a smart insole that integrates existing sensors with miniaturized instruments as a wearable platform for gait monitoring and disease warning.
Dual Dielectric Layers Preparation:
1. TPU/AgNP Electrospinning Network:
TPU (thermoplastic polyurethane) pellets are dissolved in a mixed solution of DMF (N,N-dimethylformamide) and THF (tetrahydrofuran), followed by the addition of AgNP (silver nanoparticle) slurry. The resulting mixture is magnetically stirred to obtain a uniform TPU/AgNP solution, which is then electrospun to form the TPU/AgNP network.
2. PDMS Micropillar Array:
A mold of the micropillar structure is made through laser etching of a silicon wafer. PDMS (polydimethylsiloxane) precursor and curing agent are mixed in a weight ratio of 10:1 and degassed under vacuum. The PDMS solution is spin-coated onto the micropillar-patterned silicon mold, then cured at 80°C for 3 hours to form the PDMS micropillar film.
Integrated Flexible Composite Electrode Preparation:
1. PDMS Micropillar Array:
A mold of the micropillar structure is made through laser etching of a silicon wafer. PDMS (polydimethylsiloxane) precursor and curing agent are mixed in a weight ratio of 10:1 and degassed under vacuum. The PDMS solution is spin-coated onto the micropillar-patterned silicon mold, then cured at 80°C for 3 hours to form the PDMS micropillar film.
2. PDMS Micropillar Array:
A mold of the micropillar structure is made through laser etching of a silicon wafer. PDMS (polydimethylsiloxane) precursor and curing agent are mixed in a weight ratio of 10:1 and degassed under vacuum. The PDMS solution is spin-coated onto the micropillar-patterned silicon mold, then cured at 80°C for 3 hours to form the PDMS micropillar film.
1. Scanning electron microscopy（SEM）：
The SEM shows the uniform distribution of CNTs and MXene in the composite electrodes, ensuring excellent electrode conductivity. It depicts the surface and cross-sectional morphology of the TPU/AgNP network. Some nanoparticles can be observed on the micro/nanofibers in Figure 3c, indicating that AgNPs have been successfully introduced to the surface of TPU fibers via the blending electrospinning
method to enhance the dielectric constant of the upper dielectric layer.
2. X-ray Photoelectron Spectroscopy (XPS):
XPS analysis of TPU and TPU/AgNP electrospinning networks further proves the presence of Ag in the TPU/AgNP network. The XRD spectrum is obtained to demonstrate the successful preparation of MXene.
3. Observing the electrical conductivity, dielectric properties, and microstructure of electrodes and dielectric layers:
In order to optimize the performance of capacitive sensors for pressure sensing, the conductivity, dielectric properties, and microstructure of the electrodes and dielectric layers were evaluated and optimized. As the proportion of MXene in the conductive filler increased from 0 to 11.1%, the conductivity of the CNT/MXene/PDMS electrode also increased proportionally due to the bridging effect (Figure 5a). Since the saturation threshold of the bridging effect of two-dimensional materials in the one-dimensional grid was exceeded, the further increase in the proportion of MXene led to a decrease in conductivity (Figure 5b), so 11.1% is the optimal percentage of MXene in the conductive filler for preparing highly conductive electrodes.
This sensor has great application prospects in health monitoring and disease prediction, such as risk prediction of diabetic foot, diagnosis of flat feet, fall warning for the elderly, children and vulnerable groups, rehabilitation training for postoperative patients, training feedback for athletes, etc.
link：https://www.nature.com/articles/s41467-024-48751-x
