How Has and Will Microfluidics Influence the Advancement of Wearable Devices?
Author: Caitlin Ho
Over the last few decades, there had been increasing interest in both microfluidics and wearables, especially for remote, continuous monitoring and management of health and fitness. The rapid emergence of the wearables market has been influenced by big tech companies producing the likes of the Apple Watch, Fitbit and other wearable devices. The integration of microfluidic technology with multiplex capabilities into wearable devices is one of the most highly anticipated next-generation technologies. It has particular relevance in the fields of healthcare diagnostics, point-of-care (POC) testing and fitness monitoring with great potential to be applied to many more applications and market opportunities including the military.
This advancement can relieve some of the burdens on healthcare services and assist in faster diagnosis as a patient’s overall wellbeing history can be consulted during examination rather than a snapshot of the patient’s health at the time of examination or hospitalisation. The application of this technique can be used further to assist with drug treatment monitoring to evaluate the effect of medicines on patients; this would take us a step closer to personalised medicine (1,2).
Before microfluidics was introduced to wearable technology, wearable devices were typically made of stiff materials and used complex techniques such as photolithography and chemical etching to provide functionality. Due to this, wearables had many limitations, including cost and a lack of flexibility which made it difficult to position the devices close to the skin and obtain accurate measurements. Microfluidics overcomes some of these limitations as they can utilise flexible materials, be miniaturised, use 3D printing methods, are more sustainable and reduce the overall costs of wearable devices (1).
Figure 1: Brief schematic diagram of wearable technology process (3)
Microfluidic technology has the potential to further advance the properties of wearable devices to measure specific analytes or biomarkers associated with specific conditions and diseases. Most commercially available wearable technology measures the user’s heart rate, steps and sleeping patterns. They can also be connected to the user’s smartphones and provide app notifications, receive phone calls, store the user’s data and provide analysis on sleep quality and activity to boost the user’s motivation to live a healthier and more active lifestyle. To be able to measure specific analytes would open doors to monitoring the body’s pH, metabolite levels, perspiration rate and more for better analysis of the user’s activity and condition. The ability for continuous monitoring and measurement of specific analytes can increase the demand for microfluidic wearable technology. (2).
Continuous glucose monitoring (CGM) is a well-known example of a continuous monitoring wearable device. It can track your blood sugar levels daily, however, it is invasive, requires external equipment and regular maintenance and replacements. Excluding CGM, most wearable devices are not able to measure biomarkers, metabolites and/or diseases. At the point of care, blood is the most common sample used for analysis, however, this requires sample processing which would require additional reagents that could impact the sustainability of these devices. Exploration into an enzymatic and non-enzymatic microfluidic wearable that uses sweat as the sample has shown potential to overcome some of the challenges faced but current CGM devices (4,5).
Research has been leaning toward using sweat as the sample as it would provide a non-invasive solution and sweat contains many biomarkers and analytes that can be measured including metabolites, proteins, exogenous drugs and more to gather medical information (1,5).
Figure 2: Wearable multiplexed device developed by researchers at the Central Electrochemical Research Institute that can use sweat as a sample to monitor the user’s pH and analytes (6)
A project by researchers at the Central Electrochemical Research Institute had a successful proof of concept for a microfluidic multiplexed device that used sweat as the sample to monitor biomarkers during exercise activities. It took measurements from sweat and measured lactate, potassium, sodium and pH levels using amperometry and potentiometric techniques. The microfluidic wearable successfully measured monitored these analytes and ions during stationary biking. As the integrated electrical circuits were raised above the epidermis, it eliminated the risk of background noise that would interfere with the device’s monitoring. This could lead to an inexpensive solution for personalised POC and athletic monitoring (6).
Despite the technological advancements in non-invasive, wearable devices, few have been developed to report on specific biomarkers. This is largely due to difficulties in sampling and the developing knowledge of biomarkers in sweat. Wearable devices also need to meet the requirements below (7):
Highly stable
Portable
Reagentless
Continuous
Responsive in real-time
Microfluidics can be miniaturised and perform analysis on a very small amount of sample – ideal for wearables as they need to be lightweight, small and effective. The technology has had a great impact on the wearable market broadening the application potential of advanced, continuous, remote monitoring. However, much more research still needs to be done for a non-invasive, highly sensitive and specific microfluidic wearable device can be realised. The future of wearable devices is bright and as we become more familiar with the technology, we become one step closer to remote continuous monitoring for wellbeing.
References:
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https://www.mdpi.com/journal/micromachines/special_issues/Flexible_Microfluidic
Aroganam, G., Manivannan, N. and Harrison, D., 2019. Review on wearable technology sensors used in consumer sport applications. Sensors, 19(9), p.1983.
Khor SM, Choi J, Won P, Ko SH. Challenges and Strategies in Developing an Enzymatic Wearable Sweat Glucose Biosensor as a Practical Point-Of-Care Monitoring Tool for Type II Diabetes. Nanomaterials (Basel). 2022 Jan 10;12(2):221. doi: 10.3390/nano12020221. PMID: 35055239; PMCID: PMC8781831.
Bandodkar AJ, Jeang WJ, Ghaffari R, Rogers JA. Wearable Sensors for Biochemical Sweat Analysis. Annu Rev Anal Chem (Palo Alto Calif). 2019 Jun 12;12(1):1-22. doi: 10.1146/annurev-anchem-061318-114910. Epub 2019 Feb 20. PMID: 30786214.
ACS Sens.2021, 6, 3, 1174–1186 Publication Date:January 31, 2021 https://doi.org/10.1021/acssensors.0c02446
Brothers MC, DeBrosse M, Grigsby CC, Naik RR, Hussain SM, Heikenfeld J, Kim SS. Achievements and Challenges for Real-Time Sensing of Analytes in Sweat within Wearable Platforms. Acc Chem Res. 2019 Feb 19;52(2):297-306. doi: 10.1021/acs.accounts.8b00555. Epub 2019 Jan 28. PMID: 30688433