Sure, your firm has designed and developed a lot of medical equipment. You’ve developed a solid understanding of the requirements and pitfalls of designing medical equipment that will be used in a hospital, in an ambulance, and maybe even in a patient’s home. But while you were busy, a confluence of technical breakthroughs and regulatory updates have awakened the wearable medical device industry. It’s not just about hearing aids and Holter monitors any more, and now your Marketing people have asked your Engineering group to specify and design your company’s first product to be worn by a patient directly on their body. Now what are you going to do? The following is an attempt to illustrate how several hardware-focused electrical and mechanical considerations are prompting developers to adopt an approach to wearables design that may differ greatly from that of desktop or portable medical devices, along with suggestions on how to adapt the wearable product development process.
- Consider your intended user population. Is there a certain patient age, weight or size that represents your typical user? Ideally your product could be designed so that one model of the device - perhaps with an adjustable feature - could work for your entire end-user population. Should it appear that two or more versions/sizes of the device are required to satisfy your user population, you’ll need to consider the trade-offs between excluding users at the extremes of the target population versus the complexity and sales/support implications of releasing multiple devices. A program of usability testing can often reveal problems with early prototypes and help the product developer arrive at the most effective solution for the target end-user.
- Another important consideration is the user’s ability to operate small electronic devices. Some patient populations may not have the experience, eyesight, or hearing acuity required to operate small controls or react appropriately to status indicators or alarms. For wearable devices, giving the patient a simple user interface is always preferable. Leave the complex device setups and interactions to the medical professional who is caring for the patient. If the patient is required to use a smartphone, tablet PC, or custom device to interact with the wearable device despite your best attempts to avoid it, be sure that the user interface is clear, simple and intuitive. This is another aspect of product development that can benefit from usability testing.
- Avoid small, easily-removable parts if possible. Your device will be exposed to all of the activities and chaos of daily life. Any small parts that can intentionally or unintentionally become disconnected from your device will get dislodged and lost, and possibly render your device useless. If a small, easily-removable part is required for the functionality of the product, consider providing the healthcare professional and/or the user with spare parts as appropriate to allow your wearable device to continue functioning.
- Biocompatibility evaluation according to ISO 10993 - Biological evaluation of medical devices may be new to you if this is your first wearable product. The acceptability of materials intended for patient contact is classified based on the amount of time that the material is expected to remain in contact with the patient. Ideally, a material that has already been validated for biocompatibility by the manufacturer can be located for use in the patient-contacting areas of your device. If not, ISO 10993 requires the manufacturer of the device to perform biocompatibility testing on the material in question, generally using the services of a third-party vendor.
- Since the wearable device will be used in the patient’s home, two guidance documents apply; the IEC standard 60601-1-11 - Requirements for Medical Electrical Equipment and Medical Electrical Systems Used in Home Care Applications and the FDA document Draft Guidance for Industry and Food and Drug Administration Staff, Design Considerations for Devices Intended for Home Use. These address many of the safety and usability requirements that a wearable device or a system that includes a wearable device will need to meet.
- Regarding electromagnetic compatibility (EMC), wearable medical devices fall into the same category as other devices intended for use at home, and are generally subject to tighter EMC regulations than equipment intended for use in a healthcare facility. The governing standard is IEC 60601-1-2 - General requirements for basic safety and essential performance - Collateral standard: Electromagnetic compatibility - Requirements and tests.
- If there is an IEC particular standard (IEC 60601-2-X) for the type of device you are planning, you may find that there are clauses of the standard that cannot be applied to a wearable version of the device. Be aware of these details before claiming that your device meets the particular standard. Discuss the implications with your Marketing department if you find that you will be unable to claim compliance to the particular standard.
- If your company has already released non-wearable devices with functions and features similar to your planned wearable device, take advantage of the product history and records available to you. You may find areas where problems or failure modes will be exacerbated when the device becomes a wearable. Similarly, opportunities may arise to further mitigate failures, improve performance or reduce costs. An example might be an electrode cable for an Electrocardiogram (ECG) device. Much effort is spent ensuring acceptability of ECG cables for a particular application, for example flexibility, triboelectric effects, and EMC. If the ECG electrode can be integrated into the device itself, the ECG cable and its associated functional requirements, failure modes and costs no longer need to be considered.
- If at all possible, your wearable design should be wireless and self-contained within a single housing. Device components that are wired together to create a system when the device is worn will inevitably cause patient discomfort or disconnect as the wires tug on the device components or become tangled in the patient’s clothing. The connections between components also create possible failure points.
- Consider the environment in which your wearable device will be expected to operate, as well as environments where a failure to operate under a specific condition is acceptable. As a wearable product, the device will be exposed to sweat regularly, and perhaps to other bodily fluids or rain. The device will be squeezed, dropped, and mechanically shocked constantly. Where a failure to operate in a specific environment is found to be acceptable, ensure that the device fails in a safe manner.
- Have a clear understanding of how the patient will be expected to deal with the wearable device during showering or bathing. Ensure that this information is clearly communicated to the patient.
- If necessary, consider how the wearable device will be cleaned by the patient or healthcare professional. In the event that the device or part of the device is to be washed by the user or healthcare professional, ensure that the instructions for use are clear regarding device preparation, water temperatures, detergent or cleaner types, and drying methods. Should disassembly and re-assembly of the device be required for cleaning, simplify these actions as much as possible.
- Carefully consider the scheme that will be used to provide power to the wearable device. To optimize your patient’s experience, consider how to best integrate the charging or replacing of batteries into the workflow, use requirements, and allowable “down-time” of your particular device’s functionality. This information will help to optimize design trade-offs such as device size/weight vs. battery run-time. Ideally, this familiarity with your target patient’s abilities or limitations, the requirements of the device, and the optimum use scenario will allow you to determine if your device is best designed with the battery permanently enclosed within the device or user-replaceable. Consider the use of wireless charging methods, as this technology has the potential to greatly simplify ease of use. Of course, battery safety and regulatory requirements must be strictly followed in all cases.
- Your wearable device may require active accessories to provide for data display, data storage, communications, or recharging. Carefully consider how best to allow for the transfer of data or power between system components, while minimizing the quantity and complexity of the tasks your user is required to perform. Ideally these connections and communication between system components should be implemented using wireless technology and occur automatically, with no patient involvement.
The medical device industry is entering a “Golden Age” of wearable product development that is being supported by both regulatory progress and significant innovation in battery technology, materials science, and wireless communication. This article has touched on a few of the many critical issues to be considered in the design and production of a safe, usable, and successful wearable medical device.
