IN P WER: How micro batteries enable miniaturisation of implantable devices

Denis Pasero, product commercialisation manager at Ilika, outlines the role micro batteries will have on implantable medical devices going forward.

It is no exaggeration to say that we are set to experience change in the design of implantable medical devices. Over the course of the next decade, a wave of new products will alter how we look at implants, as a range of miniature devices become available that can be implanted close to the target organs.

The ability to manufacture smaller devices also creates new opportunities. For example, a device can be designed into a replacement joint to provide realtime information on the condition of the joint itself, the patient’s overall health and irregularities such as misalignment and abnormal bone growth. This means that remedial treatment is possible sooner, while the issue is less serious. In the future, data gained from techniques like this will allow the design of better joint replacements. Similar techniques could be applied to orthodontics, where devices will be embedded in dental wearables to monitor the patient’s saliva for diagnostic purposes, while simultaneously observing the wearable for effectiveness and usage data. Smart contact lenses could measure patient metrics such as glucose levels and intra-ocular pressure. They could one day be used to implement sight correction, and even further integrate AR/VR features.

In the short term at least, the area that offers the greatest impact for these new devices is neuromodulation, where electrical impulses are used to provide targeted stimulus to the nervous system of the patient. The treatment is well understood and very effective for many ailments, including chronic neuropathic pain, epilepsy, pelvic disorders, gastrointestinal disorders, and angina. At present, the downside of neuromodulation is the actual provision of the treatment. In some cases, treatment is performed in medical facilities, in others it is provided through relatively bulky implants. Tomorrow’s medical devices will improve the implantation process by providing less complex surgery with a quicker recovery time, fewer complications for the patient and easier battery replacement, while expanding the range of treatments available. As the devices are implanted close to the targeted organs (nerves, near the brain or spinal cord), there will be further benefits for patients, such as lower doses of medicine required and greater control over treatments.

Most of the ingredients that will enable this new wave of implantable medical devices have been in place for some time. A sophisticated microcontroller takes only a few square millimetres on a Printed Circuit Board, is less than a millimetre high, uses negligible power in standby and only a little more in operation. Other components, such as the communications chip and sensors, have similar dimensions and power requirements.

The only component that has so far resisted real miniaturisation is the power source - normally a battery - 75% of life-critical implanted devices use large, nonrechargeable batteries. Some non-life critical applications use rechargeable batteries, such as lithium-ion (LiB), which are similar to households batteries but with thicker casing making them ultrasafe so there’s no leakage. Even if made smaller, the need for a casing means it is almost impossible to get their height under 2mm. Reducing the size of LiB batteries means that they may not be able to supply the necessary peak current to power the circuit during operation.

Smaller, safer, and more powerful batteries are key to new implantable medical devices, and these are now becoming available in the form of solid-state batteries. In addition to their small size, solid-state batteries use a solid electrolyte that can’t leak.

Practical examples of solid-state batteries for medical applications can be found in Ilika’s Stereax range. The Stereax M300 battery has a capacity of 0.3 mAh and comes in a 3.6 mm x 5.6 mm x 1 mm package. It has a pulse rating of 3 mA, which is sufficient for most medical applications and communications. A manufacturing and commercialisation partnership with Cirtec Medical will bring the Stereax battery technology to market enabling medical implantable devices to have micro battery power that has low leakage and can be used with energy harvesting circuits. In the future, wireless charging from outside the patient’s body will also be possible, meaning that they will last almost indefinitely inside the human body in many use cases.