Wearable devices are utilized within the medical industries to continually monitor signals such as electrocardiograms and electroencephalograms. They are also used to monitor physical conditions during cardiac exertion such as exercise. In order to improve the collected data, many studies have been performed by directly attaching wearable instruments directly to the skin using a pressure-sensitive adhesive (PSA) sheet.
When a PSA sheet is applied for an extended time, the user’s skin becomes softened due to the moisture generated from their skin. This increases the amount of peeled stratum corneum (outer layer of the skin). PSAs used within these situations must meet several requirements, including patient/user safety, appropriate adhesion to the skin, reduction of humidity, and strong adhesiveness to the wearable device.
In response to the previously listed demands, studies have been conducted using a silicone PSA and an acrylic PSA for wearable devices. The acrylic PSA was found to have insufficient moisture permeability, as there are problems with sweating that may occur if it is applied for a long time. On the other hand, the silicone PSA can cause a reduction in humidity from sweat due to its moisture permeability caused by its elevated free volume. It is quite difficult to simultaneously accomplish both moderate adhesion to the skin and strong adhesion to the wearable device.
Historically, polyurethane PSAs have been widely used in the construction industries. The reason for this is because these types of adhesives are able to bond to many different types of substrates including but not limited to glass, plastics, wood and concrete. A common polyurethane often recognized would be two- part adhesives used for bonding ceiling rafters and drywall for example.
Most recently, a polyurethane PSA has been developed for the medical and physiological industry with the following characteristics, when compared to silicone and acrylic PSAs: high moisture permeability, appropriate adhesion to human skin and high adhesion to polycarbonate resin, and low amount of peeled stratum corneum from skin while maintaining adhesive strength to skin during exercise. The safety of the patch test was also confirmed. These initial results suggest that a polyurethane PSA is a suitable method for attaching a wearable device on the skin during exercise. With that being said, these double-sided medical grade polyurethane adhesives will make an excellent addition to medical censor and apparatus usability. This is quite an exciting discovery as the two-part bond of polyurethane is unparalleled in terms of efficiency!