University of Missouri engineers have demonstrated that pencils and paper can be used to create on-skin electronic devices.

‘On-skin electronics are usually fabricated by patterning conventional inorganic materials, novel organic materials, or emerging nanomaterials on flexible polymer substrates,’ say the researchers, ‘consequently, the state-of-the-art on-skin electronics usually suffer from expensive precursor materials, costly fabrication facilities, complex fabrication processes, and limited disposability.’

’By using widely accessible pencils and papers as tools, we have developed a variety of cost-effective and disposable on-skin electronic devices, ranging from biophysical sensors and sweat biochemical sensors to thermal stimulators, humidity energy harvesters, and transdermal drug-delivery systems.’

’Also, pencil–paper-based antennas, two-dimensional and three-dimensional circuits, and reconfigurable structures are demonstrated,’ say the researcher, ‘the enabled devices can find wide applications particularly in low-resource environments and home-centered personal healthcare owing to their low-cost resources, handy operation, time-saving fabrication, and abundant potential designs.’
 
The researchers discovered that pencils containing more than 90% graphite are able to conduct a high amount of energy created from the friction between paper and pencil caused by drawing or writing.

Specifically, the researchers found pencils with 93% graphite were the best for creating a variety of on-skin bioelectronic devices drawn on commercial office copy paper.

Devices created include  biophysical (temperature, biopotential) sensors, sweat biochemical (pH, uric acid, glucose) sensors, thermal stimulators, and humidity energy harvesters.

Among these devices, pencil-drawn graphite patterns (or combined with other compounds) serve as conductive traces and sensing electrodes, and office-copy papers work as flexible supporting substrates.

The enabled devices can perform real-time, continuous, and high-fidelity monitoring of a range of vital biophysical and biochemical signals from human bodies, including skin temperatures, electrocardiograms, electromyograms, alpha, beta, and theta rhythms, instantaneous heart rates, respiratory rates, and sweat pH, uric acid, and glucose, as well as deliver programmed thermal stimulations.

Notably, the qualities of recorded signals are comparable to those measured with conventional methods.

Humidity energy harvesters are prepared by creating a gradient distribution of oxygen-containing groups on office-copy papers between pencil-drawn electrodes. One single-unit device (0.87 cm2) can generate a sustained voltage of up to 480 mV for over 2 h from ambient humidity.

A self-powered on-skin iontophoretic transdermal drug-delivery system was developed as an on-skin chemical intervention example.

Pencil–paper-based antennas, two-dimensional (2D) and three-dimensional (3D) circuits with light-emitting diodes (LEDs) and batteries, reconfigurable assembly and biodegradable electronics (based on water-soluble papers) are being explored.