© Fraunhofer IZM

Ultrasound: With wireless charging to personalized medicine

In order to reduce hospital stays and healthcare costs through personalized solutions, new therapeutic approaches have been used for several decades. One example is so-called electroceuticals, i.e. microimplants equipped with electronic solutions that use electricity to provide personalized and localized treatment without triggering side effects in the body. Researchers at Fraunhofer IZM have now set themselves the task of taking a new approach and are using ultrasound instead of electricity.

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

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

In contrast, the smallest 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 in order to avoid high losses during energy transfer. At the same time, only extremely small structures can be used, as the overall size of the implant must not exceed a few millimetres.

Ultrasonic transducers, electrodes for recording neuronal activity and passive components – miniaturizing all these components down to a few millimeters, integrating them and assembling them in a durable manner 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 they must be biocompatible and at the same time suitable for encapsulation and energy transmission by sound waves. In the further course, several transducers are also built up in groups, so that a combination of the electronic components and thus a more concentrated radiation of the ultrasonic wave is achieved.

The Fraunhofer Institute for Reliability and Microintegration IZM is one of 66 companies involved in the EU-funded Moore4Medical project. The Institute is responsible for the coordination and implementation of the work package “Implantable Devices”. At the end of the project in June 2023, an open technology platform is to be created in a kind of toolbox that will enable faster, more cost-effective and more efficient medical technology. Future research could further develop these basic building blocks developed in the project for specialized applications in the areas of wireless microimplants, organ-on-chip, 3D ultrasound, permanent monitoring using sensors, drug adherence through intelligent delivery, and X-ray-free surgery with optical detection, thus advancing medical technology in a powerful way.