Health care is rapidly evolving from a generalized approach to focusing on individual patient conditions for personalized diagnostics and medical treatments — a trend that has demonstrated significantly improved outcomes. But personalized medicine requires ongoing, up-to-date information about the patient. This information is typically captured by costly, resource-intensive in-hospital monitoring, which can record data over long periods of time so artificial intelligence algorithms can “learn” about the patient and predict when the next issue may occur.

Luckily, a simpler solution is emerging. A new research field is studying the miniaturization of highly-complex medical equipment into wearable devices and “smart stickers” for remote personal monitoring of patients. This is part of what is being called the Internet of Medical Things, or IoMT — medical devices that connect wirelessly over the internet to personal computing devices and larger-scale health care IT systems. My research group, as an example, is developing low-cost wearable sensors that conform to the skin of the user.

We call these biosensors “electronic decals.” Through wireless communication, these electronic decals can efficiently transmit their readouts — measuring parameters like glucose levels, pulse, and muscle activity — to smart watches, cell phones and laptops, where a user-friendly app organizes the data, displays relevant information to the user, and transmits the numbers to the doctor.

Electronic decals can be applied not only to human skin but also to the surface of other objects and medical instruments. For example, our FlexiLab research team is exploring how diapers can be transformed into disposable “smart diapers” by embedding electronic decals among the diapers’ cellulose layers. The smart diapers will be able to tell parents when it is time to change a diaper; they can also help inhibit the development of rashes and urinary tract infections.

We have also demonstrated how implanting electronic decals in sanitary pads enables bacterial infections to be monitored at the point of care — which can help prevent the loss of unborn babies in developing countries when a bacterial infection occurs during pregnancy.

While the miniaturization of electronic components is commonplace in cellphones and tablets, the fabrication of wearable sensors presents added challenges. Cell phones and tablets don’t need to bend to operate, but wearable sensors must both bend and stretch with the wearer’s natural motions. With on-skin wearable sensors, the electronic components need to withstand stretching of at least 30 percent — the maximum stretch of human skin. Mounting and embedding these electronics into stretchable, polymer substrate materials also requires a paradigm shift in fabrication technology and new, scalable manufacturing processes.

Because many wearable sensors will be embedded in our clothes or adhered to our skin, it is also vital to address issues that compromise the performance of electronic devices. This means the wearable devices must be water-resistant so they can be washed multiple times. Additionally, their readouts must remain accurate independently of the motion of the wearer.

Our electronic decals are waterproof, enabling continuous monitoring of a patient’s physiological constants even under water. When mounted on top of textiles, the sensors can withstand multiple machine-washing cycles while preserving their sensing performance. The inexpensive polymers used in their fabrication also means the sensors can be disposed of after one day’s wear, keeping the patient’s skin healthy and preventing allergic reactions.
We have filed several patents on the use of these low-cost biosensors as wearable and implantable health-monitoring systems. Currently, our lab receives funding from the Indiana Clinical and Translational Sciences Institute (CTSI) to help support our work.

As industrial engineers, we need to envision and provide solutions for the scalable manufacturing of wearable biomedical sensors to make personalized medicine a reality. Current limitations in manufacturing plants require us to devise novel approaches to repurpose existing machines for the efficient manufacture of flexible electronics. As an example, our group has detailed how spray-painting technologies commonly used to paint cars can be repurposed for the large-scale printing of stretchable electrodes for on-skin electronics.

Ramses V. Martinez
Assistant Professor
School of Industrial Engineering and Weldon School of Biomedical Engineering

College of Engineering, Purdue University

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