The multi-billion-dollar industry of smart wearables is becoming ubiquitous and witnessing revolutionary developments each day. From smart tattoos that track sunlight exposure to smart insoles that monitor your footsteps, smart technological advancements are clearly pushing the boundaries of innovation. As the wearable technology industry is still at a nascent stage of its development curve, the consortium of functional printing professionals including the technical printers, designers, engineers, and system integrators, are working together to investigate new processes, materials, technologies, and testing methods.
Aside from the dominant world of smart watches, there has been a significant growth and interest in smart clothing, electronics, and sensor solutions. Some of the common considerations that need to be addressed before developing a wearable solution include:
- Biocompatibility - Since most wearables come in direct or close contact with skin, biocompatibility is of paramount importance to ensure user safety. Depending on the intended use of the device, compounds in wearable substrates and construction layers can potentially be exposed to sweat, rain, humidity, sunscreens, and insect repellants. A comprehensive understanding of the interaction of various external factors is crucial towards eliminating unwanted risks such as skin sensitization, allergic reactions, and irritation. While there are no industry standards governing biocompatibility across all wearable devices, ISO 10993 provides a framework for wearable medical devices.
- Power management - Effective power management still remains a significant hurdle in developing wearable solutions. Thin and compact batteries often translate to shorter battery life and companies are continuously struggling to extend the battery life for devices to last at least one cycle of usage. While space is a huge constraint when working with small and lightweight devices, companies are harvesting energy by employing solar cells or powering batteries using the body movement and body heat of the wearer. Companies are actively trading Wi-Fi connectivity with Bluetooth communication modules for efficient power consumption and pivoting towards wireless power supplies through inductors. For most wearable garments intended for long-term use, the batteries must be easily replaceable or rechargeable.
- Flexibility and stretchability - Smart wearables, especially garments, are susceptible to a great deal of stretching. Flexibility, the basic form factor of wearables, has made flexible printed electronics be actively pursued as an alternative to costly silver threads and yarns sewn into apparels. Depending on the final application, wearable substrates need to strike the right balance between flexibility, stretchability, and stability. In addition to experimenting with new substrates, the industry is currently leveraging medical-grade materials including polyether-based thermoplastic polyurethane (TPU), polyester-based TPU, polyethylene terephthalate (PET), and fabrics such as spandex, nylon, elastane, and cotton. Functional inks are often printed on flexible substrates and as the user wears or moves with the garment, there is a certain amount of stretch that occurs. Therefore, inks need to exhibit acceptable change in resistance with repeatable stretch and recovery cycles.
- Sealing - Conductive epoxies, typically used to apply components on to circuits, are often not a feasible solution when dealing with wearable applications, as they tend to break under stress. Hence, applying additional components such as surface-mount LEDs and active PCBs can be very challenging. The ability to incorporate electronic components smoothly into apparels whilst ensuring strong adhesion during bending, creasing, and flexing is key to the success of smart wearables.
In addition, wearables intended for long-term use must be safe to submerge under water without damaging the circuitry, and physically endure multiple wash cycles. Achieving a water-tight seal and protecting the power source from environmental factors is vital for ensuring optimal performance and durability of the device. For electronic equipment, Ingress Protection (IP) rating specifies the degree of protection from solids and liquids including dust and water. Whether it is fusing stretchable materials with thermoplastic-adhesives backing or applying hot-melt adhesives to polyester circuits, thermal bonding is one of the most common sealing approaches in wearable solutions. Pressure sensitive adhesive (PSA) lamination is another approach that requires a medical-grade adhesive to apply a patch directly to the skin of the user. TPU overlaminates, printable insulators, and PET overlaminates are often used for sealing and potting.
The wearable technology industry is migrating towards a “smart system”, a world where all devices from head to toe communicate with each other to create a single ecosystem. As existing technologies and processes evolve, new norms, standards, and specifications for the industry will gradually develop. With a promising future in sight, the widespread adoption and integration of smart wearables in our daily lives is almost inevitable.