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Wearable Technology: Epidermal (Skin) Electronics

Epidermal wearable technology is a liquid form of sensors that is either worn on the surface of the skin or injected under the skin in the same manner as a tattoo. This technology has been listed as wearable, healable and adhesive. The sensors are usually applied to the neck or forearm but depending on what information is gathered they can be placed in many different places on the body. The sensors need to act as a second skin to the wearer. This type of technology is being developed for constant monitoring of health information. This is generally used in older patients or patients that are not hospitalized or near immediate medical attention. The benefit is that the wearer is free to move around and is not constantly attached to traditional monitors.

Tattoo style epidermal sensors are injected under the skin and generally work for a set amount of time. The first temporary tattoo sensors utilized the screen-printing technology to apply the epidermal sensors. This style of technology was developed to combine the electrochemical performance with resistance to mechanical stress such as stretching or bending all while causing minimal intrusion to the wearer. Once the crystals have worked through their life cycle the “tattoo” is no longer useable and needs to be reapplied. The sensors are designed to track the wearers health over long periods of time. This will provide necessary information immediately to the wearer or health professional. Generally, information such as pH, electrolytes, lactates, and other metabolic changes as well as temperature, heart rate, blood flow and skin hydration are tracked. The liquid crystals can change color according to the wearers skin temperature or hydration. This gives the wearer immediate feedback about their health.

One study was performed using adhesive sensors on neonatal babies in intensive care to reduce the need for cords attaching the machines to the patient. In this environment constant monitoring of the baby's vitals is a must. The technology allowed for the information to be gathered wirelessly, battery free and much less invasive. One of the major benefits is having continuous monitoring while allowing the baby the therapeutic ski-to-skin contact with the parents. In the study the subjects would wear one adhesive sensor on the chest and one on the foot to capture electrocardiograms (ECGs) and photoplethysmography (PPGs). The tests were successful on neonates from 28 weeks to full term (38-42 weeks).

Bandodkar, Amay J., et al. “Tattoo-Based Wearable Electrochemical Devices: A Review.”Electroanalysis, vol. 27, no. 3, 2015, pp. 562–572., doi:10.1002/elan.201400537.

Chung, Ha Uk, et al. “Binodal, Wireless Epidermal Electronic Systems with in-Sensor Analytics for Neonatal Intensive Care.” Science, vol. 363, no. 6430, 2019, doi:10.1126/science.aau0780.

Health-Monitoring “Tattoo.” Inside Science: American Institute of Physics,, 2015. Film. Retrieved from https://fod.infobase.com/p_ViewVideo.aspx?xtid=94794

Liao, Meihong, et al. “Wearable, Healable, and Adhesive Epidermal Sensors Assembled from Mussel-Inspired Conductive Hybrid Hydrogel Framework.” Advanced Functional Materials, vol. 27, no. 48, 2017, p. 1703852., doi:10.1002/adfm.201703852.