From breathing to guiding the movement of biological cells, 3D printing of transparent, fine conductive fibers can be used to manufacture devices that can "smell, hear, and touch" - making them particularly suitable for IoT, health monitoring, and biosensing applications.

Scientists at the University of Cambridge used 3D printing (also known as additive manufacturing) methods to produce electronic fibers, each of which is 100 times thinner than a single strand of human hair, resulting in sensors that exceed the capabilities of traditional film-based devices.

Science Advances reported that fiber printing technology can be used to manufacture portable, wearable, and non-contact breath sensors. Such printed sensors are economical, highly sensitive, and can be attached to mobile phones to simultaneously acquire sound, image, and breathing pattern data.

The first author of the study, Andy Wang, is a doctoral student in the Department of Engineering at the University of Cambridge. He used fiber sensors to test the amount of respiratory moisture escaping through face coverings in response to coughing, rapid breathing, and normal breathing.

Fiber optic sensors greatly outperform similar commercial sensors, especially in tracking shortness of breath, which mimics rapid breathing.

Although fiber optic sensors capable of detecting viral particles have not yet been developed, growing scientific evidence emphasizes that viral particles such as coronaviruses can be transmitted via aerosols and respiratory droplets. Quantifying the direction and volume of respiratory moisture escaping through various masks can serve as an indicator for protecting "weak points."

Researchers found that most leakage from surgical or fabric masks comes from the front, especially when coughing, while most leakage from N95 masks comes from the sides and top even when fitted securely. Nevertheless, wearing both types of masks correctly helps reduce exhaled airflow.

Compared with traditional thin-film technology, sensors made of fine conductive fibers are particularly useful for volumetric sensing of 3D fluids and gases, but so far, printing them, integrating them into devices, and mass-producing them has remained a challenge.

Dr. Yan Yan Shery Huang, Head of Research, Department of Engineering, University of Cambridge

Huang and her collaborators 3D printed composite fibers made of silver and/or semiconductor polymers. This fiber printing method produces a core-shell fiber structure, where a high-purity conductive fiber core is covered by a thin skin of protective polymer, similar to the structure of standard electrical wires, but with a diameter of just a few micrometers.

In addition to breath sensors, the printing method can also be used to manufacture biocompatible fibers with dimensions similar to those of biological cells, enabling them to guide cell movement and "sense" this dynamic process as electrical signals.

Moreover, the fibers are so small that they are invisible to the naked eye; therefore, when used to connect tiny electronic components in a 3D manner, the electronics appear to be floating in mid-air.

Our fiber optic sensors are lightweight, inexpensive, compact, and easy to use, making it possible to transform them into home testing devices that allow the public to perform self-managed tests to obtain information about their environment.

Dr. Yan Yan Shery Huang, Head of Research, Department of Engineering, University of Cambridge

Researchers look forward to developing this fiber printing method for several multifunctional sensors that can detect more respiratory species for bio-machine interfaces or mobile health monitoring applications.