The wearable device product category is exploding in healthcare design. Wearing these sensory devices that continuously collect, measure and report the user's physiology, exercise behavior, lifestyle activity, and health status requires three key human factors in the design. In this two-part series on robotics and wearable devices, part 1 dives into wearable designs by taking a look at the research being done now that eliminates the device altogether.

In Search of the Perfect Fit

Fig. 1 - Body somatotypes (Credit: Encyclopedia Britannica.)

The wearable product market is significantly transforming day-to-day communication between a user's body and technology. Whether the device is sharing GPS coordinates or monitoring blood glucose levels, A1c counts, heart rate, respiration, stress, steps, or caloric burn, the cloud-based apps are connecting and sharing personal information in real time.

The infatuation of continuously receiving data on personal health and performance is influencing customized health and drug plans specific to individual needs and capabilities. However, with the customization of products comes a lack of standardization, especially in the wearable device industry. As all the paths a user takes to collect and digest information aren't the same, product designers must look at several factors to streamline cacophony of digital noise. What do users do with this data? When do users need it? How do users interact with it?

All this technology is great, but if it is not designed to deliver results on how users think, feel, and behave, then the technology will not matter. A good wearable device design fits perfectly with the user's body. From intuitive controls and position for access to easy-to-read displays and material selection, all interactions between the user and the device needs to be seamless.

Size and Lifestyle Matter

Whether a user's body type is a slender ectomorphic, muscular mesomorphic, or rounded endomorphic, these differences directly affect the user's strength, reach, sightlines, and ability to move efficiently (see Figure 1).

As people move throughout the day, their body shape changes — it is never in a static stage. This is the biggest challenge in the design of wearables. Size matters because it changes how skin moves and morphs, fluctuating the landing site where the wearable device meets the skin. With this difference for each person, designers must pay attention to the wearable device's size, shape, and topology. Standard ergonomic design practice accommodates from the 5th percentile female to the 95th percentile male.

Lifestyle impacts device design as well. Clothing is always a consideration because there is a fight between the arms and shirt cuffs and a wrist wearable. Pant waistbands and belts are common interference points for people wearing continuous monitoring devices on their lower abdomen or upper arm. Designers must also consider active lifestyle users where sweat, showering, and waterproofing are must-have performance requirements.

Location, Location, Location

Fig. 2 - Yellow highlights map of all the sites where people are being typically injected, having blood drawn, or monitoring vital signs.

Not unlike real estate, location is key with wearables, but in this case its anatomic location.

Typically, the thigh and stomach areas are used for auto injections. Finger sticks are used to get small blood samples. The stomach and upper arm are used for continuous monitoring. The back of the hand, forearm, and antecubital sites are used as intravenous sites. The wrist, upper arm, chest, and earlobe are used as noninvasive sites. Each of these anatomic sites have unique surface topologies that shape and inform the design of the wearable device (see Figure 2).

People wearing continuous monitoring devices on their abdomen need a design that has a low profile, so that it does not snag clothing. The device should be a smooth, long form that lays longitudinally following the natural folds of the user's abdomen when bent forward. Its location is not precise and allows the user to find the most comfortable spot for their body size and shape, clothing choices, and lifestyle. In contrast, a wrist wearable has a small anatomic landmark, so targeting and accuracy becomes an issue when donning the device.

Regardless of the anatomic site, all skin contact surfaces of a wearable device should have large radii along all edges, so it will not dig into adjacent tissue and become irritating or painful. In general, designers should mimic anthropomorphic forms, staying away from any edges or corners on the wearable that do not fit the user's surface anatomy comfortably.

Fig. 3 - The right image shows the 3D scan of the ear foil and as far as we can see into the ear canal, overlaid by arteries and veins in the middle image, and nerve sites in the far-left image.

Scanning body parts in 3D creates databases that define sizing programs and overlay veins and arteries, designers can understand exactly how to interpret the best anatomic fit. For example, a designer who is creating an in-ear audio wearable like a hearing aid can look at the intersection between anatomy, physiology, and 3D view of the ear. Those three layers of data can be used to develop a taxonomy of ears — a classification schema for size, shape, comfort, and anatomic fit (see Figure 3).

Taking a step back from physical devices that are strapped on the wrist or stuck to the stomach, the future of wearables don't require the device itself, but instead tattoos the circuitry directly onto the user's skin.

Your Signal Says…

How can a wearable tell a user how happy or sad or exhausted or energized they may be at any moment in time, whether they want to know or not? A new class of sensing technologies called epidermal electronics are in the building and testing phases. These devices of ultrathin electrodes, electronics, sensors, wireless power, and communication systems attach to the skin and record and transmit electrophysiological measurements. Research is being done now on different ways of applying these sensors directly to the skin's surface from electronic tattoos, stamps, and bandages that force skin-sensor contact.

A few things are certain with the wearables market: users will see an increasing proliferation of them that cut across the boundaries between fitness, healthcare, and lifestyle. Regardless of how sophisticated a wearables device is, its success boils down to how well it interfaces with the user's skin and fits the user's lifestyle. So, one of the most fundamental questions in the conception of any wearable device is first to ask if it is needed. Is it technology for technology sake? If not, one must define the essential features and functionality that directly deliver value to user — the rest is noise. But what if you are beyond monitoring and need surgery? Part 2 moves the discussion from wearable devices to how robotics are changing the future of surgery.

This article was written by Dr. Bryce Rutter, founder and CEO of Metaphase Design Group Inc., St. Louis, MO. To view the company's portfolio of medical instruments, devices, surgical systems, drug-delivery devices, and disposables, visit here. For more information, click here.