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Case Study: Wearable Medical Devices

Wearable Medical Devices – Explaining When to use Printed Circuits

Johnson Medtech developed a process to allow surface mount components to be applied to the polyester substrate to create a waterproof circuit, which resulted in an extremely thin and conformable product.

When making a medical wearable with a large surface area, printed circuits are the natural choice for three reasons:

  1. The ability to print instructional graphics on the surface gives it the impression of it being a finished medical product without extensive coverings.
  2. Printed circuits are an additive process, where silver ink is applied to the polyester substrate. The subtractive process of a copper flex circuit is extremely harsh on the environment; you end up etching off a lot of expensive copper.
  3. Printed electronic substrates are ten times more cost-effective than the cost of the copper foil that is etched away.

Considering all of this, it is not surprising that most medical companies will first try to use a printed electronic circuit; however, there are limitations:

  1. The resistance of the ink is about ten times stronger than copper. Therefore, they are not very useful for high power circuits. However, most wearables are made to house a sensor and are battery operated; it is unusual to have high current coursing through the system.
  2. The polyester substrate cannot usually withstand more than 160°C; therefore, typical reflow solder is out of the question.

Recently, a customer requested a completely waterproof, high-volume wearable circuit, and Johnson Medtech was ready to accept the challenge.

Because of the advantage of the SIP, we were able to place several circuits on one panel. Then, we applied the dielectric coating and encapsulant over the conductive pads, resulting in a completely waterproof, lightweight, and easily conformable product, along with a happy customer.

Vital Signs Wearable – Challenges with Electrodes

Wearable medical devices are becoming increasingly popular, even assisting the public in monitoring their health status and fitness level. Electrocardiograms (ECGs) are among the most common diagnostic tools in healthcare; these provide real-time data on the performance and function of the heart and other vital signs.

The revolution of wearable technology provides the necessary data to clinicians for more reliable diagnoses and to make informed decisions on treatment.

Through the continuous addition of technology, many of our customers were unsatisfied with bulky results and crucial challenges in functionality.

Johnson Medtech accepted the challenge to assist customers in manufacturing thinner and more conformable wearable patches, increasing the functionality of the most current technologies available.

The two main challenges were presented with the development of ECG electrodes:

  1. Electrodes must be defibrillation proof.

Whether a single- or multi-use product, electrodes must not interfere with the defibrillation energy; nor may they prevent the doctor from shocking the patient. Since that amount of energy is generally large, the resistors used to limit this energy are also large, resulting in bulky devices and reduced functionality.

Ideally, the resistors would be situated adjacent to the electrodes, which are then attached to the skin.

If not, the creepage and clearance must be maintained throughout the circuit until the resistor is in place. Again, this causes devices to be bulkier in design.

  1. Mounting the battery to the substrate of the electrode created a bulky and less conformable product.

Because of the concern of size, weight, and bulk, many previous solutions with battery mounts made the wearable medical device less conformable and thicker.

Johnson Electric considered attaching a battery holder to the device; but because lithium-ion batteries have a temperature threshold, this solution did not work. Additionally, the size and weight of the device were still too large.

To combat both of these challenges, Johnson Medtech created special conductive adhesives; these allowed mounting the batteries to the substrate at a temperature that did not damage the cells.

Additionally, Medtech engineers developed the ability to screen print a carbon resistor next to the electrode, allowing a sleek and compact sensor.

Optimizing Performance and Cost of Surgical Handles and Devices

As more surgical handles and wearable medical devices become single-use, it’s incredibly important to be able to control the costs.

Even though Johnson Electric has a proven history of producing cost-effective drive systems, optimizing cost is not done just by assembling inexpensive components, but by maximizing the performance of the product.

Recently, we had the opportunity to provide the motor gearbox along with the circuitry and software to control the device.

This provided us with the opportunity to integrate smart features into the device. During development, an essential smart feature is an ability for a device to be able to measure its own performance.

The data was provided to the engineering team, enabling them to understand the limits of the device and the balance between the mechanical weak points and the limits of the electromechanical performance.

Providing these smart features allowed optimization of the product that was not possible through testing the products with external test equipment. Also, the smart features can be integrated for production units as well for troubleshooting, and further device optimization.

Medication Delivery Wearable

Johnson Medtech has a deep background in providing drive systems for biologic dosing devices. As these devices move toward single-use wearables, cost and quality assurance have become a significant consideration for our customers and their patients.

Consider how in the automotive industry, the fit, form, and finish of a car provides that sense of high quality or luxury. The same could be said for the motor tone of a medical device.

Through countless development cycles and data analysis, our engineers perfected a quality motor tone using unique gear profiles and precise distance tolerances.

Because of our finite element analysis capabilities, our team presented quality assurance data in weeks instead of months; this proved the products and materials used during the manufacturing process are safe, even in the most challenging circumstances.

With these capabilities, we can provide compelling cost advantages through automation, efficiency, and innovative design.

For more information, please contact us.


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