Miguel Solivan, a global product manager for Avery Dennison Medical, discusses wearable medical device growth and design considerations to enable longer wear times.
Extended wear times are the new gold standard for many wearable medical devices. Where once 3 days or a week was the norm, now use cases call for 14, 21 and more than 30 days of continuous wear. The longer wearable devices are worn, the more uninterrupted data healthcare providers can collect and analyse. Furthermore, they enable patients to go about their daily activities without stopping to change their device or visit the doctor’s office for a new one.
Longer wear times strengthen the economics for wearables. Less frequent device replacement usually means less expense for the patient and healthcare system. Still, although extended-wear device benefits are easy to see, it’s not so easy to achieve long wear times, especially for stick-to-skin devices. But with careful planning and device design, a wearable can perform for many days or even weeks.
Wearable device growth
Global wearable medical device revenue should expand at a compounded annual growth rate of 26.8% to reach $111.9 billion in 2028, according to Grand View Research Inc. The research organisation points to drivers such as:
- Home healthcare
- Remote patient monitoring
- Sedentary lifestyles and related chronic diseases requiring continuous monitoring
- Demand for COVID-19 early symptom detection.
Wearable applications include continuous glucose monitoring (CGM), drug delivery, pulse oximetry, vital signs sensing and sleep apnoea detection. Wearable devices have both diagnostic and therapeutic capabilities. On the diagnostic side, they help healthcare providers and patients monitor vital signs, activity levels, blood sugar and respiration, for example. On the therapeutic front, they can deliver medications and help patients and providers manage asthma, addiction recovery and post-operative rehabilitation.
The pandemic has accelerated wearables growth. “COVID-19 pushed telehealth to the forefront of the healthcare market” as “caring for patients beyond the confines of the hospital became an urgent need,” said VitalConnect, maker of the VitalPatch RTM wearable monitoring device. By staying home, patients reduce their risk for hospital-acquired infections.
Wearable medical devices come in multiple forms, from wrist bracelets and strap-on headbands to skin-worn patches. This article focuses on the latter.
Extended wear hurdles
For patients and healthcare providers, extended device wear time affords greater convenience and quality of life. One example is Abbott’s FreeStyle Libre 2 CGM system. The system’s self-applied sensor is designed to stay on the back of the upper arm for 14 days. Patients with diabetes can shower, bathe, exercise and go about other daily activities while wearing the sensor.
Two other examples of extended-wear devices are from BioIntelliSense. The firm’s BioSticker is designed to be worn for 30 days, and its BioButton is designed for 60-day wear. Both devices provide continuous vital signs monitoring.
To deliver long wear times in body-worn applications, medical device manufacturers face the following challenges:
- Moisture management — Human skin contains oils and perspires. Activities such as showering, swimming and exercise add to fluid-handling hurdles. Only specially engineered medical adhesives can adhere to this complex surface for long-term wear.
- Secure hold — An adhesive material must remain secure amid skin twisting and stretching. Also, beyond moisture, human skin regularly releases dead cells. The exterior layer, the epidermis, sheds every 7–14 days. These cells can saturate the device material.
- Atraumatic removal — A wearable device eventually must come off, preferably with minimal discomfort. It is a challenge for device makers to balance reliable adherence with relatively painless release when it’s time to remove the device.
- Repositionability — Sticking a body-worn device exactly where it’s supposed to go, on the first attempt, is another challenge. This especially can be the case for patients self-applying their wearable devices. Device developers must plan for this contingency.
Figure 1
Solving the challenges
Stick-to-skin patches typically contain layers of thin, plastic materials held together and to the body by biocompatible medical adhesives (Figure 1). Compared with other options such as metal and glass, plastic materials are lightweight, flexible and relatively easy to process. They enable device developers to achieve a sleek profile, which is important for discretion and comfort. Quite often, the chosen materials to achieve the desired look and function will include one or more low surface energy (LSE) plastic materials, which pose a predicament for many adhesive formulations. Following are some considerations to keep in mind when designing wearable devices.
- Skin-contact layer — This layer must manage moisture and keep the patient’s skin comfortable for the full wear-time duration. Breathable materials contain tiny pores that allow perspiration and other fluid to evaporate. Absorbent materials are another option for handling fluid. These materials absorb moisture and hold it away from the skin. The skin-contact layer also should be soft and stretchable. Polyester and polyurethane (PU) nonwovens are popular carrier materials.
- Tie layer — The tie layer, also known as the construction layer, must be compatible with both the device and the skin-contact layer. If a device is made of an LSE material, then the tie layer adhesive must have a lower SE than the device material, or the device surface must be specially treated to allow the adhesive layer to wet out consistently across it. Differential two-sided acrylic adhesive tapes are ideal tie-layer materials and adhere well to films, foams, nonwovens and other LSE substrates.
- Overlay/cover layer — This layer, which can be optional, offers device developers a way to provide additional securement as well as another layer of protection from moisture and bacteria. Breathability and transparency are desirable, as is die cuttability, so that manufacturers can design a hole in the overlay to expose part of the device, if desired.
The wearable medical device market is growing rapidly, in tandem with telehealth’s surge. Longer device wear times will continue to play an important role in chronic disease management, medication self-administration, remote patient monitoring and other at-home care. With the right materials and design, device developers can deliver wearable solutions with optimal comfort and performance.