Putting Pencil to Paper

Wearable biological signal monitoring devices have the ability to track vital signs, physiological parameters, and other health-related data in real-time. From heart rate and blood pressure to temperature, sleep patterns, and stress levels, these sensors offer a comprehensive understanding of an individual's overall health and well-being. The data collected can be utilized by both individuals and healthcare professionals to make informed decisions regarding personal health management and early intervention.

Despite the immense potential of wearable devices in transforming healthcare, their widespread adoption has been hindered by cost and manufacturing complexities. Fabricating these intricate sensing devices requires advanced technology, precise engineering, and high-quality materials. Such requirements contribute to elevated production costs, making these devices prohibitively expensive for many consumers and healthcare institutions. Additionally, the complexities of developing and maintaining these devices present challenges for manufacturers, limiting their scalability.

However, the demand and interest in wearable sensing devices continues to grow, prompting ongoing research and development efforts aimed at overcoming these barriers. Innovations in materials, manufacturing techniques, and miniaturization are gradually driving down costs and simplifying the production process. A particularly interesting advancement has recently been reported on by a team at Penn State University and Hebei University of Technology. They have developed a versatile, wearable sensor that can literally be made with paper and a pencil.

The sensors are patterned onto a soft cellulose paper, with electrodes being drawn using conductive graphite exfoliated from an 8B pencil. Paper is not normally especially well suited to be the substrate for an on-skin device, but in this case, the team laser cut kirigami structures into the paper to make it stretchable, so that it can move with the skin.

This makes for a low-cost platform that is simple to fabricate, which opens the door to population-level health monitoring. However, paper-based sensors are susceptible to inaccuracies or failures stemming from water absorption from the human body, or from the external environment. To mitigate this problem, the researchers coated their device with a hydrophobic fumed silicon dioxide layer that repels water, making it effectively waterproof. Yet this coating still allows the sensor to accurately measure a wide range of biological metrics.

The initial sensors were developed to measure gas molecules, temperature, and electrical physiological signals. This encompasses electromyography, which can diagnose Parkinson’s disease, electrocardiography, which can detect heart problems, and electroencephalography, which has applications in monitoring epilepsy. The pencil-on-paper sensors can also measure gas molecule concentrations and body temperature.

Aside from diagnostics, the team points out that the skin patches can also be used for therapeutic purposes. By applying thermal therapy and electrical stimulation, inflammation and infections can be treated, which may help to treat injuries and chronic wounds. Future applications may also arise in the area of sports medicine.

A prototype device was constructed, with the goal of detecting nitrogen dioxide gas. The sensor was found to be capable of doing so with a high degree of accuracy, with a low detection limit of several parts per billion. The device was also found to have a quick response/recovery time, and was not affected by fluctuations in either temperature or moisture levels.

The methods outlined by this team open up the possibility of trillions of low-cost, environmentally friendly sensors being placed on countless individuals, and throughout the environment, to give us new insights into human health and beyond. The versatility of the platform may help in making significant contributions to scientific understanding in the future.