The technology behind wearable sensors has dramatically changed how human health is monitored, particularly in terms of disease progression and its response to treatments. Furthermore, wearable health sensors are considered both time- and cost-efficient treatment options that can be particularly useful for monitoring the health of individuals residing in remote and rural areas.
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Another advantage of wearable sensors when applied for medical purposes is that these devices can often collect body signals over prolonged periods of time, which would not otherwise be practical in a clinical setting.
To date, the global market for wearable medical devices has an estimated value of $8.9 billion USD, which is expected to reach $29.9 billion USD by the year 2023. This rapid market growth is primarily due to advancements made in various sensing technologies, including microfabrication, microelectronics, flexible electronics, nanomaterials, wireless communication devices, and data analyses.
Advancements in these technologies have not only improved the sensitivity of these sensing devices but it has also reduced their size, weight, and cost.
Wearable sensors can be used to monitor a wide range of physiological signals, including heart rate, heart rhythm, blood oxygen levels, respiration, hydration, temperature, and sleep patterns.
Various new wearable sensors are also being developed to diagnose and monitor the development of certain health conditions. For example, one recent study discussed the ability of a wearable sensor to detect Alzheimer’s disease early on in its development by tracking changes in the walking characteristics of elderly adults over a period of several weeks.
The Need to Monitor Chronic Wound Healing
As the largest organ in the human body, the skin plays a crucial role in the body’s first defense against external environmental hazards. Unfortunately, the skin can also be susceptible to various injuries, including cuts, abrasions, blisters, and burns, to name a few.
If any of these skin wounds arise, the wound must be immediately protected against infection from potentially invading pathogens. Typically, the health of a wound is assessed visually by various factors, including the color and whether any exudate is being released.
Despite the widespread utility of this approach to wound monitoring, visual inspections can lead to inconsistencies. This is due to changes in illumination and the angles at which these wounds are being studied. Furthermore, this type of consistent monitoring often requires the healthcare provider to frequently remove wound dressings, which can waste clinical resources and interrupt the normal wound healing process.
Thus, various adverse outcomes can result from the ineffective treatment of wounds, including delayed healing and an increased risk of infection and scarring.
Recent Advances in Wearable Sensors for Wound Healing
In an effort to improve the efficacy of wound monitoring, several smart devices have been developed. Rather than relying on visual characteristics, these devices can instead assess the physiological environment of the wound characterized by several variables ranging from the local temperature, pH, alkalization, volatile organic compounds (VOCs), the abnormal release of metabolites, as well as the presence of growth factors, bacteria, and specific metabolic by-products.
Wearable Sensors to Monitor pH
For example, normal skin will typically have a more acidic pH between 4 and 6, which promotes angiogenesis, epithelization, the release of oxygen, and a healthy environment for commensal bacteria. Comparatively, a wound is known to become more alkaline and instead exhibit a pH within the range of 7 to 9. Thus, several wearable pH sensors and systems have been developed for wound healing devices.
Wearable sensors for pH monitoring of wounds can be based on optical technology that changes colors in response to different pH levels. Although this type of sensor does not require electronics, it is limited due to the need for tight adhesion that could cause the dyes within the sensor to leak into the wound.
Comparatively, electrochemical sensors that instead rely upon certain sophisticated materials to detect target analytes can also be used to monitor pH levels during the wound healing process. Some of the different materials used for these electrochemical pH sensors include polyaniline (PANI), graphite, poly-L-tryptophan, copper oxide nanorods, and several others.
Smart sensor bandage for chronic wounds
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Wearable Temperature Sensors
Aside from this biochemical approach to wound healing, physical markers such as temperature and pressure can also be easily monitored through smart wearable devices. Typically, wound inflammation is accompanied by several different chemical and enzymatic processes that increase the temperature in the affected area.
These processes can also be accompanied by local vascular expansion geared towards increasing the availability of oxygen and nutrients to the injured site.
In addition to a rise in local temperatures, a decrease in local temperature at the wound site could also indicate that the wound is at risk of suffering from local ischemia. This type of reduction in local temperature could threaten wound rehabilitation, thus increasing the risk for wound deterioration. Therefore, monitoring the local temperature during wound healing is essential in assessing the status of the wound in real-time.
Several different types of optical sensors, many of which are based on infrared technology, have been developed to monitor the temperature of wounds. Additionally, several multifunctional wearable electronic devices have also been developed to continuously monitor the wound and periwound area temperature.
Additional mechanisms that have been proposed to monitor the temperature of wounds include capacitance, impedance, and thermomagnetic-based technologies.
Continue reading: Improving Fetal Health Monitoring with Multiple Dry Electrodes.
References and Further Reading
Tang, N., Zheng, Y., Jiang, X., et al. (2021) Wearable Sensors and Systems for Wound Healing-Related pH and Temperature Detection. Micromachines, 12(4).Available at: www.mdpi.com/2072-666X/12/4/430/htm
Khoshmanesh, F., Thurgood, P., Pirogova, E., et al. (2021) Wearable sensors: At the frontier of personalized health monitoring, smart prosthetics, and assistive technologies. Biosensors and Bioelectronics, 176. https://doi.org/10.1016/j.bios.2020.112946
RoyChoudhury, S., Umasankar, Y., Jaller, J., et al. (2018). Continuous Monitoring of Wound Healing Using a Wearable Enzymatic Uric Acid Biosensor. Journal of the Electrochemical Society, 165(8). https://doi.org/10.1149/2.0231808jes