In a simple world, medical consumables are made of plastic and plastic only. Electronic components would remain separate in the durable device.
In the real world, though, that’s rarely the case. You might want to install fluid pumping mechanisms in a plastic tubing set, or design a diagnostic cartridge that uses power to manipulate samples, or integrate motion-tracking sensors in the disposable, for example.
Whatever the scenario, when your disposable device needs electronic components, the design process has to accommodate a slew of important considerations.
One of our recent projects shows how these issues arise and overlap. We designed a device in which a patient sample is injected into the consumable cartridge, where it was mixed with a fluid. Originally, the consumable did not include electronic components. The client later brought us in to incorporate a small memory chip that identified the disposable — which meant it had to be installed in the disposable.
We worked with our client to determine the requirements of the memory chip and to estimate the cost and timeline of the project. Once we were confident that we had the same expectations, the design process began.
That experience demonstrates the most important issues that show up when you’re trying to incorporate electronics into a disposable, including:
- Cost. Cost is often the most important driving factor. A plastic cartridge isn’t expensive, but adding electronics is like tossing a rock in a pond. Just as ripples cover the entire pond, the cost of installing a small device in a consumable adds up quickly and can drive up the project cost.
- Manufacturing. Our client needed a small amount of memory in a small package. We selected a chip that could be mounted on a printed circuit board that could be integrated into the existing device without too much disruption. That choice, however, meant that we added a step — attaching the chip — to the assembly process.
- Storage. Companies inexperienced in integrating electronics into disposables may be unaware that storage conditions, including temperature and humidity, can have a negative impact on the functioning of embedded electronics. Storage conditions for electronics are often more conservative than plastic alone. This may require the consumable to be stored in a package with a desiccant packet.
- Electromagnetic interference. Electronic connections can act like antennas that emit or receive energy. In our case, we knew that electrostatic discharge from other nearby devices could interfere with the memory chip. At the same time, we knew that the connections from the instrument to the memory chip may release enough energy to affect other devices. To address that interference, you may need to add shielding or other ways to prevent energy from entering or escaping.
- Connections. How you design the interface between the consumable and the durable will depend on the device’s function, required reliability, and the cost. We installed pogo pins on the device itself and designed mating metal pads on the printed circuit board in the cartridge. (Pogo pins move vertically up and down as you install or remove the cartridge.) That meant we had to pay close attention to the precise alignment of those connections and consider whether the metal would oxidize in the operating environment. Pogo pin connections added some time and cost to our design process, but they were the most appropriate and cost-efficient solution.
- Power. Our consumable didn’t need an internal power source, but that’s not always the case. If you need a battery to power the consumable, it’s important to make sure that the battery is durable enough to survive storage conditions as well as sterilization, if required. Battery packaging is a related consideration: How can you connect the power source where it needs to go while still protecting it from wearing down too early, or from degrading?
These six issues are the most critical that come up when putting electronics in consumables — but they’re not the only ones. Depending on the device, you may also need to consider factors like the user interface (who will be using it?) and whether or not the device needs to be programmed before assembly.