03 Sep 2008
A glove incorporating plastic optical fibre is ideal for autonomously monitoring vital health statistics such as blood oxygenation.
Researchers in Switzerland have published a proof-of-principle study demonstrating that plastic optical fibres (POFs) can be woven or sewn into textiles to create wearable health-monitoring devices. The team created a pulse oximeter in the form of a glove, where POFs were integrated into the fabric. (Optics Express 16 12973)
"POF can illuminate human tissue and receive transmitted light in a sufficient amount to integrate simple biomedical devices into fabrics or garments," Markus Rothmaier of the Laboratory for Protection and Physiology in St Gallen told optics.org. "Our textiles transport light to the area of interest and back to an analytical instrument."
Wearable devices, such as a pulse oximeter, offer the promise of continuous and autonomous monitoring of vital health indicators.
"We could monitor adults, babies or newborns 24 hours a day for example," said Rothmaier. "Our goal is to have the sensor in a textile-based fabric such as a t-shirt or headband. We are not competing with available oximeters, we are looking for new wearable applications."
POF suits these requirements thanks to its flexibility, high resistance to textile manufacturing processes and insensitivity to electromagnetic radiation. Rothmaier and his colleagues were able to use standard textile machines to integrate the POF into the fabric.
A pulse oximeter measures a person's arterial blood oxygenation, a quantity known as SpO2. Pulsing blood changes the absorbance of light at different wavelengths, which in turn allows SpO2 to be measured. The team worked at 690 and 830 nm.
According to Rothmaier, one crucial factor in measuring SpO2 is the loss of light from the finger to the detector. The aim of this proof-of-principle study was to compare woven versus embroidered textiles incorporating merchantable quality PMMA POF and evaluate their ability to measure SpO2 on a fingertip.
POFs with a diameter of around 200 microns were integrated into the forefinger position of a standard cotton glove and used to deliver and collect light. The POFs had been altered in various ways (such as roughening the fibre surface or cutting the end at an angle) to promote light collection.
Encouraged by the success of this study, Rothmaier and colleagues are now looking at several ways of improving the pulse oximeter glove.
"At the moment, all electronics and optics apart from the POF are external devices," explained Rothmaier. "In a future version, a small PCB with diodes and phototransistors could also be integrated into the textile. We also want to measure SpO2 in reflection mode. This initial experiment was transmission mode. Reflection is a more versatile modality - but you need a lot more sensitivity for similar results. Only reflection mode will be useful for textile-integration into t-shirts and headbands."
Jacqueline Hewett is editor of Optics & Laser Europe magazine.