Method of Fabrication of Metal Nanowire Film on Flexible Substrate for Bio-Signal Measurement
This invention describes a method for fabricating a sensor using a metal nanowire film on a flexible polymer substrate. The process involves creating a patterned mask from polyethylene terephthalate (PET), depositing metal nanowires onto the mask using vacuum filtration to form a film, and then transferring this film onto a flexible polymer substrate. The metal nanowires, preferably silver or gold, are embedded into the substrate, which could be a silicone-based elastomer, during a curing process. This ensures excellent adhesion of the conductive film to the substrate. This technology allows for the creation of sensors with low sheet resistivity, making them suitable for applications such as bio-potential sensors, strain sensors, pressure sensors, and stretchable interconnects.
This technology seeks to address the limitations of existing methods for fabricating conductive electrodes for bio-signal measurement. Conventional wet bio-potential sensors, which rely on conductive gels, suffer from issues like gel drying, skin irritation, and impedance changes. While dry bio-potential sensors based on vacuum-deposited metal films on polymer substrates offer an alternative, they are plagued by poor adhesion, high deposition temperatures, and forming patterns and circuits limitations. Conductive polymer composites, another alternative, exhibit lower conductivity. This technology further aims to overcome the challenges of poor adhesion, cytotoxicity concerns, and limited adaptability associated with conventional conductive film deposition techniques. The technical problem lies in developing a fabrication method for conductive and biocompatible electrodes that are easy to manufacture, cost-effective, highly adhesive, and suitable for long-term use across multiple applications.
The process involves first creating a patterned polyethylene terephthalate (PET) mask. Using vacuum filtration, a metal nanowire film is then deposited through this mask. While silver or gold are highlighted for the nanowires, the polymer substrate is recommended to be a silicone-based elastomer for its flexibility. A crucial step is the transfer printing of the patterned nanowire film onto the flexible polymer substrate. This method allows the nanowires to partially embed into the substrate during curing, ensuring strong adhesion. The resulting sensor demonstrates excellent conductivity, with a sheet resistivity of 0.1-0.2 Ω/sqr, even after a week of exposure to standard atmospheric conditions. This technology paves the way for bio-potential sensing, strain sensing, pressure sensing, and stretchable interconnecting applications.
- Strong adhesion between the metal nanowire film and the flexible polymer substrate: The method utilizes a technique where the polymer substrate is cured directly on a vacuum filtration setup, leading to the metal nanowires (especially silver nanowires) partially embedding themselves into the substrate during curing. This results in significantly improved adhesion compared to conventional deposition techniques, confirmed by scotch tape tests and resistance to IPA washing.
- Low sheet resistivity for enhanced conductivity: By forming the conductive film on the surface of the polymer substrate, the technology achieves a very low sheet resistivity, which remains stable even after weeks of exposure to standard atmospheric conditions. This high conductivity, coupled with a large contact area facilitated by the flexibility of the substrate, makes it particularly suitable for biopotential signal measurements with high signal-to-noise ratios.
- Biocompatibility for safe, long-term use: Cytotoxicity tests using the MTT assay on mouse fibroblast cells showed cell viability greater than 90% even after a week of exposure to the metal nanowire-polymer electrode. This high biocompatibility makes the technology suitable for long-term, continuous electrophysiological signal recordings without adverse effects on the skin.
- Versatility and multi-functionality: The fabricated metal nanowire film on a flexible polymer substrate has demonstrated applicability as a bio-potential sensor for acquiring ECG, EEG, and EMG signals.
This technology for fabricating highly conductive, biocompatible sensors on flexible substrates promises significant social impact. Its cost-effective, scalable production using common materials like silver nanowires and silicone elastomers can democratize access to advanced wearable electronics. In healthcare, these durable sensors enable continuous and long-term monitoring of electrophysiological signals, revolutionizing remote patient monitoring and personalized medicine. This could improve chronic disease management, reduce healthcare costs, and enhance quality of life. The technology's potential in strain sensors and stretchable interconnects may also drive innovations in soft robotics, prosthetics, and flexible displays, further benefiting society.
This technology describes a cost-effective, adaptable fabrication technique for metal nanowire films on flexible substrates and their application as sensors. The primary application domain is biomedical sensing for acquiring biopotential signals like ECG, EEG, and EMG. The technology addresses the limitations of conventional biopotential sensors by offering enhanced adhesion, biocompatibility, and long-term stability. Beyond medical uses, this technology holds significant potential for applications like wearable electronics, soft robotics, and structural health monitoring. The ability to fabricate sensors on flexible substrates opens avenues for strain and pressure sensing in these sectors. The technology’s adaptability to different substrates and cost-effectiveness position it as a valuable tool across multiple industries.