Ultrasound for microimplants

Researchers are developing a new generation of microimplants which can be charged completely wirelessly using ultrasound waves.

With wireless charging towards personalised medicine

The treatment of chronic autoimmune diseases does not necessarily have to involve costly medication and adverse events. With the help of neuromodulation, diseases such as rheumatoid arthritis, chronic headaches, asthma or Parkinson's disease can be treated. To realise this, researchers at the Fraunhofer Institute for Reliability and Microintegration (Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration, Fraunhofer IZM) are developing a new generation of microimplants in the Europe-wide Moore4Medical project. The special feature of the highly miniaturised electronics is that the implants can be charged completely wirelessly using ultrasound waves.

Moore's Law has become indispensable in the field of consumer electronics. Every two years, new chip generations are supposed to be twice as powerful as their predecessors. However, the paradigm that emerged in 1965 has so far left out an important application area of electronics - medical technology.
In order to reduce hospital stays and healthcare costs through personalised solutions, new therapeutic approaches have been used for several decades. One example is electroceuticals, microimplants equipped with electronic solutions that use electricity to provide personalised and localised treatment without triggering adverse events in the body. Now researchers at Fraunhofer IZM have set themselves the task of taking a new approach and are relying on ultrasound instead of electricity.

Invasive interventions or wired charging become unnecessary thanks to ultrasound

Ultrasound waves are pressure waves that are applied from outside, penetrate the body and thus reach the microimplant. There are clear advantages compared to conventional battery-charged devices: Ultrasound can be used to charge the implants from the outside, making frequent invasive procedures or wired charging obsolete. Above all, the extreme miniaturisation of the systems is an innovation in the field and enables the microimplants to precisely stimulate nerves just 20 micrometres in size.

By using ultrasound to charge the implants, the Fraunhofer IZM team has found a solution to one of the greatest technological challenges in medical technology: efficient energy transmission. This is because built-in batteries have so far made miniaturisation difficult, with energy exhaustion being inevitable and thus requiring replacement, i.e. another surgical intervention. In addition, battery-powered implants equipped with induction coils can only be inserted close to the skin.

Ultrasound implants can be placed far under the skin

In contrast, tiny ultrasound transducers make it possible to use the microimplants of the future even far inside the body. When high-frequency sound hits them, they start to vibrate. These tiny movements are converted into electrical energy for the microimplant. The challenge is to optimally align the vibrating microstructures to avoid high losses during energy transmission. At the same time, only extremely small structures can be used, as the overall size of the implant must not exceed a few millimetres.

Ultrasound transducers, electrodes for recording neuronal activities and passive components - miniaturising all these components to a few millimetres, integrating them and building them to last is a major, but not insurmountable hurdle. The researchers are currently evaluating which materials they can use for the prototype. This is a key decision, because these must be biocompatible and at the same time suitable for encapsulation and energy transmission by sound waves. In the further course, several transducers will also be built in groups so that a combination of the electronic components and thus a more concentrated emission of the ultrasonic wave can be achieved.