The impact of materials selection on medical wearables technologyThe impact of materials selection on medical wearables technology

Healthcare is one of the fastest growing segments of the wearables sector, valued at more than $13 billion globally in 2016, according to a report from Kalorama Information (Rockville, MD). These devices offer a convenient, cost-effective means of monitoring heart rate, respiratory activity and blood pressure, among many other functions. Therapeutic wearables that monitor disease states and track health activity, store data and deliver feedback—insulin management and pain therapy are two examples—are the next frontier in personalized medicine, adds Kalorama. Miniaturized sensors and wireless communications technology make this possible, but it’s all for naught if the user won’t wear the device because it is uncomfortable, and that is where material considerations play a considerable role. Issues such as skin irritation, or simple discomfort, and aesthetics can be the difference between adherence and non-compliance. Moreover, the materials must meet mechanical properties, such as strength, stiffness and toughness, and withstand exposure to a broad range of temperatures and resist chemicals. Keenly aware of the market potential in medical wearables, suppliers are developing materials that meet these requirements.

Although wearables has become a buzzword in recent years, when you think about it, medical wearables have been around for quite some time. Eyeglasses were invented in the late 13th century and the venerable Band-Aid was invented in 1920, notes Eric Larson in an article published in Med Device Online. “The difference is that, when we speak of medical wearables today, we usually are referring to devices with embedded electronics . . . [that also] connote some level of wireless connectivity,” writes Larson, a mechanical engineer who owns Art of Mass Production in San Diego, CA, and is a frequent contributor to PlasticsToday. That leads to a set of expectations from users.

“The primary expectation is that the device will work as intended for a reasonable amount of time,” Larson told PlasticsToday. Equally important, the device should be easy to use and difficult to misuse. “This is more of a design issue than a materials issue, but materials and design are interconnected,” adds Larson. One simple analogy is the child-resistant pill bottle. “It is easy to use, almost impossible to misuse, but provides safety to consumers.” When you add electronics to the mix, however, things get a bit more complicated.

One area involving wearables that is exceptionally complex is wireless communication, notes Larson. “What is the transmission of wireless wavelengths in different materials?” he asks. “Do the materials have any other effect on data transmission?” That is but the tip of the iceberg when sourcing materials for wearable devices.

In addition to the aforementioned structural requirements, materials used in wearable devices must be chemically resistant, and that includes water, which is often overlooked, notes Larson in his article for Med Device Online. We typically think of water as an inert material, but it can cause a chemical reaction with some materials—think raw iron. “Most thermoplastics do not chemically react with water,” writes Larson, “but some thermoplastics, such as nylon (and, to a lesser extent, ABS, acetal and polycarbonate), absorb water.” Water can also act as a solvent for other chemicals, and their presence may affect the material’s performance. It’s important to consider the water source, whether it’s rainfall, a body of water or even sweat, to predict the chemicals and minerals it may contain, writes Larson.

There are a number of tests and standards for skin exposure and all-around biocompatibility, to which materials suppliers are quite attentive, Larson told PlasticsToday, but when it comes to material selection, “there will always be a cost versus performance evaluation.” As the use of wearable devices expands, some will be low cost, with lower performance requirements, and others will be on the higher end of the cost spectrum with performance expectations to match, says Larson. 

“In the low-cost spectrum, I think polyolefins (polypropylene, polyethylene and so forth) and blends will become the go-to material family. They offer fantastic chemical resistance and reasonably good mechanical properties over a fairly decent temperature range. They do all this at an incredibly low cost. And they can be processed in many different ways—injection molding, blowmolding, thermoforming, extrusion and more—and in different forms (solid parts, foamed parts, films, fibers),” says Larson. 

In the high-performance area, there are many different variables, he adds, pointing to a number of materials, including nylons, polyesters, and various alloys and blends, that can be used.

Materials suppliers increasingly take note of the medical wearables space

Materials for wearable devices were very much in evidence at Medica, the largest medical trade show in the world and a bellwether of what’s trending in medical technology, and the co-located suppliers showcase Compamed, in Düsseldorf, Germany, earlier this month.

In particular, Dow Corning (Auburn, MI) introduced its strongest soft skin adhesive (SSA) to date at this year’s event. The MG 7-1010 Soft Skin Adhesive bridges the gap between the company’s high-adhesion, pressure-sensitive adhesives (PSAs) and gentle-adhesion SSAs, to deliver strong attachment for today’s wearable medical devices, according to the company.

To address the requirements of the emerging medical wearables market, Dow Corning “developed a strong, durable adhesive that is gentle even on sensitive skin,” said Marie Crane, Global Segment Leader for Medical Devices.

Vancive Medical Technologies (Chicago) introduced a breathable, double-coated tape designed to serve as a construction layer connecting a wearable device’s skin-contact material to its electronics casing as well as a stretchable, single-coated elastic nonwoven tape with a fabric-like feel. Also breathable, this material conforms to contoured body surfaces and has applications for use in wearables, wound dressings and other medical devices.

At the 2015 show, Covestro (Leverkusen, Germany) introduced a new polycarbonate/polyester blend developed specifically for wearable medical device applications. Makroblend M525 is impact resistant, dimensionally stable and can be molded into any shape in various shades to satisfy today's design requirements for wearable medical devices, said Covestro at the time. The material is compatible with standard manufacturing processes, such as ultrasonic welding and adhesive bonding.

As the market for medical wearables continues to expand, look for many more innovations in materials technology that combine performance with comfort.