Implantable Wireless Charger: Transforming Medical Device Power

Key things to know:

• Chinese researchers have developed a groundbreaking implantable wireless charger, aiming to keep medical devices powered indefinitely.
• The charger utilises biodegradable Zn-ion hybrid supercapacitors featuring materials like MoS2 nanosheets and alginate gel for high capacitance and biodegradability.
• In rat trials, the device demonstrated its potential in controlled drug delivery, showing significant benefits in medical treatments.
• This innovation paves the way for rechargeable, permanent medical implants and highlights the need to address electromagnetic interference in medical technology.

Recently, researchers from China have developed an implantable wireless charger that can be used to keep implanted medical devices operating indefinitely. What issues do implanted devices currently face, what did the researchers demonstrate, and why is this development significant in the field of implantable devices?

What issues do implanted devices currently face?

There is no doubt that implantable medical devices have come leaps and bounds since the first pacemakers were put into practice. The ability to fit complex features onto tiny microchips has allowed for implantable RFID tags, allowing users to wirelessly interact with hardware, while the development of ingestible camera pills allows doctors to get data from inside the body without the need for invasive cameras on cables or surgery.

However, for all the benefits and brilliance that implantable electronic devices present, they are not without their challenges, which inevitably hold back their capabilities. One such issue is that anything implanted in the body must be biologically inert so as not to cause an immune response (this can lead to numerous complications). Another issue is that anything implanted in the body must not contain toxic compounds capable of causing serious harm, meaning that engineers must pick components and materials extremely carefully. 

But one major challenge that hasn’t been fully addressed is the need for power. Devices currently implanted into the body typically rely on non-rechargeable batteries for two main reasons. The first is that rechargeable batteries typically involve some type of electrolyte that itself can be harmful to the human body should it leak. The second challenge with rechargeable batteries is their need to store sufficient charge while providing an easy method for charging. 

Non-rechargeable batteries, however, can be made from biologically inert materials that can provide power for many years. Even then, surgery is needed to eventually access and replace the battery, which itself incurs numerous risks. Because of these limitations, implantable electronic devices must minimise the amount of power they consume, which, in turn, reduces their capabilities. 

Researchers create implantable wireless charging device

Recognising the major challenges faced by implanted medical devices, researchers from China have recently developed what could be the world’s first implantable wireless charging unit. 

According to the researchers, power delivery in implanted devices is one of the most important factors, and despite this fact being well established across the medical industry, little work has been done to try and power such devices for extended periods of time while offering enough power for computation-heavy tasks. Furthermore, many implantable devices are being designed to be biodegradable, thus eliminating the need for surgery to remove them, but trying to find biodegradable power sources is proving to be immensely challenging. 

Addressing the biodegradable power source challenge, researchers have innovated with Zn-ion hybrid supercapacitors. These devices, leveraging MoS2 nanosheets and alginate gel, offer high capacitance and are fully biodegradable. This aligns with the trend towards transient bioelectronics, potentially eliminating secondary surgical interventions for device removal.

As such, the researchers have decided to make progress in this field and have now demonstrated a fully biodegradable wireless charging receiver that can be implanted into living tissues without causing any negative side effects. 

The device itself integrates a small receiver coil for coupling with an external electromagnetic field, along with a rectification module interconnects and a zinc-based hybrid supercapacitor for storing energy. Once implanted into tissue, it can be used to deliver power to implanted devices, and its biodegradable nature means that it can safely dissolve inside the body.

 A wireless energy-harvesting and storage device. 

(A) A detailed exploded view illustration of the device's structure. (B) A detailed schematic representation of the power system integrated for use in implantable electronics. (C) An image showcasing the energy supply system as it is attached to muscle tissue. (D) Outcomes from finite element analysis alongside images showing the device in various twisted and bent forms. (E) A series of photographs depicting the device's stages of accelerated dissolution in 0.1 M PBS (pH 7.4, 80°C). Photo credit: H. W. Sheng, Lanzhou University.

Key to these devices is the seamless integration of wireless charging with energy storage. This not only ensures efficient energy transfer but also maintains consistent power output. Their flexible design conforms to body tissues, enhancing compatibility and reducing inflammation risks.

To demonstrate the capabilities of the new wireless charging solution, the researchers implanted the device into rats, showing full operation over a period of ten days. Afterwards, the devices broke down and dissolved naturally without having any negative effects on the rats.

But the trial with rats didn’t just demonstrate the capabilities of the wireless device; they also connected it to a drug-delivery system. During the trial, the rats were subjected to inflammation as a result of a yeast-induced fever. Those who had the implant showed a much faster recovery rate compared to those without the implant, thanks to the power source and drug delivery system being able to provide anti-inflammatories.

The rat trial's success goes beyond proving the wireless system's viability; it underscores its potential in controlled drug delivery. This capability for precise, timely medication administration could be a game-changer in treating acute medical conditions.

Why is this development critical for implantable technologies?

By far, the most important development in this research is that, for the first time, it is possible to power internal devices via an external field which itself can be electronically controlled. This means that researchers of implantable medical devices can start to worry less about what powers their devices and more time worrying about what features are needed.

If a non-biodegradable version can be developed, it would also allow the potential for permanently implanted devices (such as pacemakers) to be rechargeable. Such a development would help to eliminate the need for surgeries when replacing batteries, which itself carries tremendous benefits. 

Looking ahead, developing a non-biodegradable variant of this wireless system could revolutionise permanent medical implants like pacemakers. Imagine rechargeable devices without the need for battery replacement surgeries – a major step forward in medical device design.

While the device is still in its early days, the demonstration with the rats shows great promise, and it may not be long before we start seeing implanted medical devices with such wireless charging capabilities. Of course, we also have to be extremely careful with how electromagnetic fields interact with such devices (as wireless charging devices will pick up most EMI), and therefore, we could see those fitted with devices become more vulnerable in a world where tech drives everyday life.

However, we must tread carefully regarding electromagnetic interference (EMI). As beneficial as wireless charging is, ensuring these devices are EMI-resistant in our tech-saturated world is crucial for their safe and effective operation.