Researchers have developed a new wearable sensor that can detect potential signs of serious conditions like organ failure and sepsis in patients who have low rates of perspiration.
The small sensor monitors for the presence of a lactate, a molecule the body uses to break down sugars. Lactate is a useful biomarker for athletes and patients as it can indicate oxygen starvation is occurring in the body’s tissues.
The device only requires a small amount of sweat, making it a potential solution for critically ill patients who can’t build up enough sweat to provide a sample for current analysis techniques.
“Sweat offers a source of biomarkers we can monitor via non-invasive systems in near-real time for how the body is performing during exercise or to monitor or manage various health conditions,” says Farnaz Lorestani, co-first author of the study and an assistant research professor of engineering science and mechanics at Pennsylvania State University in the US.
When compared to other body fluids such as saliva, tears and urine, sweat is easily accessible for researchers or health care professionals to analyse at any time
“The challenge is figuring out how to collect sweat when the person isn’t sweating that much,” says Lorestani.
For example, when people undertake low-intensity activities like lying down, most will perspire 10 to 100 nanolitres per minute per centimetre of skin. This amount is significantly less than the liquid in one teardrop.
Most sweat monitoring devices use hydrogel – a matrix polymers combined with water – to take up sweat samples and process it through a laser-induced graphene (LIG) sensor, which identifies the presence of lactate.
The problem is that small sweat samples get lost during the uptake process and can’t be accurately analysed.
“We solved that challenge by engineering a platform with granular hydrogels, developed by Professor Amir Sheikhi’s research group, capable of collecting sweat even in low-intensity conditions, like checking emails or laying down,” says Lorestani.
Sheikhi, who is co-corresponding author of the paper, used this technique in previous work on protein-based granular biomaterials for tissue regeneration.
The researchers also changed where the hydrogel is located in the monitor.
In their device, the hydrogel absorbs the sweat and feeds it into a spiral-like microfluidic chamber which transports it to the sensor. This design allows the monitor to sit on the skin and increases the surface area of the sample collection to minimise sweat loss.
“We hypothesised that the porous medium in the granular hydrogel scaffold increases absorption capacity when compared with previously used hydrogel materials,” says Lorestani.
“The compact coil-shaped microfluidic channel design also contributes to accuracy and sensitivity.”
The results, published in the journal Small, show that the device can detect up to 10 times the amount of sweat from low-intensity activities compared to other wearable sweat sensors. The researchers found the device was able to absorb enough perspiration to accurately analyse the lactate within 2 hours across multiple settings.
The device is size of a standard band-aid and is made with cost-effective materials.
“The proof-of-concept demonstration features a cost-effective, sensitive and versatile flexible sensing platform for early biomarker detection, where sweat production is minimal or sporadic, such as at rest or during mild physical activities,” says Lorestani.
By ensuring their device is flexible and comfortable to wear, Lorestani and the research team hope the sensor will allow individuals to wear it across various environments like office settings or riding a bike. The fact it requires minimal sweat to produce accurate results may also be helpful for seriously ill patients who can’t move and generate as much sweat.
“Overall, our goal is to build a healthier society by making non-invasive, continuous, personalised health monitoring more accessible to everyone — and this work is a step in that direction,” says Lorestani.