Blood oxygen sensor can be 3D printed at home

Known as an oximeter, the device has been designed so that it can be easily 3D printed and assembled at home with minimal tooling. It uses widely available components to provide indicative measurements of blood oxygen and heart rate that have been widely used for triage purposes during the Covid-19 crisis.

The team said it made extensive use of open source or freely available design tools wherever possible such as PCB designer Eagle alongside FreeCAD and OpenSCAD for its body design.

Anyone with a 3D printer should be able to make their own device, which comprises a sensor, readout electronics and software, with components that cost less than £10.

The sensor is worn on a finger clip (pictured) and measures the reflection of different wavelengths of light, tracking the wearer’s heart rate and saturated percentage of oxygen.

Trial devices have already been delivered to Royal United Hospitals Bath for testing with the results shared back electronically with the team for further analysis and development.

Various options for powering the device were considered including integrating a small battery, such as a coin cell or using an external power source. One of the disadvantages of a fully integrated battery was that in a clinical setting there would be the need for frequent replacement, so the designers decided to use an external power source instead which could be either a battery or DC supply. This way the device has the potential advantage of being able to be powered perpetually using a small mains powered charger in a hospital setting, or using an off the shelf, readily available battery holder.

Professor Peter Wilson, from the University of Bath’s Department of Electronic and Electrical Engineering, said: “Monitoring blood-oxygen saturation has become a key part of patient care during the pandemic, with a particular focus on early warning of serious illness, so demand for pulse oximeters around the world is huge. We hope that, by sharing this open-source design, healthcare providers will be able to quickly produce more sensors at a reasonable cost.”

The team is now working with the University of Cambridge to develop low-cost artificial fingers, known as phantoms, that can be used to calibrate and validate oximeters.

Dr Ben Metcalfe said: “The importance of accurate measurements cannot be overstated. A recent study in the New England Journal of Medicine identified quite clearly the racial bias present in current oximeters, which worryingly over-estimate the oxygen saturation among patients who identified their race as black.”

“It is well known that calibration of pulse oximeters, especially for low levels of oxygen saturation seen in many Covid-19 patients, is technically challenging. By creating 3D printed materials with known optical properties we can develop phantoms that will enable calibration at these lower oxygen levels.”

The immediate demand for medical equipment in 2020, due to the explosion in the number of people contracting Covid-19, led to many firms developing new ideas for ventilator machines. In January, one such device was demonstrated that is less invasive than others, and allows patients to be treated away from intensive care units.