Electrospinning Equipment: Green Chemistry in Flexible Electrodes for Wearable Technology

In recent years, flexible wearable electronic products have witnessed rapid development and are widely applied in multiple fields. Especially in the area of health monitoring, they can be attached to human skin for real - time monitoring, which is of great significance. In this field, various flexible sensors have emerged, employing multiple sensing technologies such as capacitive and piezoelectric sensing. However, current research mainly focuses on sensing mechanisms and conductive layers, with relatively less attention paid to flexible substrates. Flexible substrates are crucial for wearable electronic devices. They need to possess multiple characteristics to meet the requirements of high - precision sensing and medical monitoring. At the same time, flexible conductive electrodes are indispensable. They not only need to adapt to different surfaces but also maintain conductivity when bent or stretched, and should be biocompatible to ensure safe long - term use.

The team consisting of Vundrala Sumedha Reddy, S. Shiva, and Seeram Ramakrishna from the Institute of the Centre for Nanotechnology & Sustainability at the National University of Singapore published the latest research findings titled "Green Chemistry Innovation in Flexible Electrodes for Wearable Technology" in the journal Journal of Electronic Materials. By combining electrospinning technology with biosynthesis methods, the team used an electrospinning machine to successfully develop a piezoelectric composite nanofiber based on polyvinylidene fluoride (PVDF) and barium titanate (BTO), as well as a flexible electrode made of biosynthesized silver flakes from durian waste. This achievement provides a sustainable solution for wearable sensor technology. It not only improves the flexibility, conductivity, and biocompatibility of sensors but also significantly extends the service life of devices, offering important support for innovative applications in the fields of future health monitoring and human - machine interaction.

In the research, by combining polyvinylidene fluoride (PVDF) and barium titanate (BTO) nanoparticles, the electrospinning device was used to successfully prepare PVDF/BTO composite nanofibers. By adjusting the ratio of the polymer to the nanoparticles, the uniformity and consistency of the fibers were ensured. Mechanical tests showed that the elastic modulus of the composite nanofibers increased from 84.4 MPa for pure PVDF - HFP to 95.7 MPa, indicating that the addition of nanoparticles significantly enhanced the mechanical properties of the material. Experimental data demonstrate that this composite material not only has excellent piezoelectric properties but also good mechanical strength and flexibility, making it suitable for wearable sensor devices. (Figure 1)

Figure 1：(a) SEM image of the silver flakes; (b) energy - dispersive x - ray spectroscopy (EDX) spectra and elemental distribution in silver flakes; (c) x - ray diffraction (XRD) spectra; (d) tensile testing of electrode; (e) Fourier transform infrared (FTIR) spectra of silver flakes

Subsequently, the research team biosynthesized silver flakes from durian waste and combined them with Ecoflex material to fabricate flexible electrodes. These electrodes not only have high conductivity (20.3 S/cm) but also maintain stable performance when stretched to 561.2%. The morphology and structure of the silver flakes, analyzed by scanning electron microscopy (SEM), show an irregular flaky structure. This structure provides a large surface area, which is conducive to charge transfer. The conductivity increased from 18 S/cm to 20.3 S/cm within the elastic range.(Figure 2)

When assembling the sensor device, the research team placed the piezoelectric composite layer between two flexible Ecoflex silver - flake electrodes. The electrodes were in a stacked morphology, with the stacked layers facing the piezoelectric layer. This structure can enhance conductivity, providing multiple paths for charge transfer between the piezoelectric layer and the external circuit. It can also optimize the response time and sensitivity of the device, ensuring the efficient transmission of mechanical stimuli to the piezoelectric layer. In the pressure range of 1 - 15 kPa, the device can stably output voltage. By simulating a 10 kPa external force impact with a tensile testing machine to test its durability, it was found that it could still maintain stable performance after approximately 10,000 cycles. Compared with devices made of traditional metal electrodes (such as copper and aluminum), its service life is significantly extended, demonstrating great application potential in the field of wearable technology. (Figure 3)

Figure 3：(a) The flexibility of the fabricated electrode; (b) The assembly of the piezoelectric sensing platform device; (c) Variation in voltage output corresponding to different pressure conditions, ranging from 1 to 15 kPa; (d) The performance of the piezoelectric layer

Article source: https://doi.org/10.1007/s11664-025-11912-9