Electronics have been finding their way into everything, and implantable devices are not an exception. The microelectronic implantable medical devices market, including advanced technologies like “Implantable Medical Device Charging,” is forecast to grow 30% more than medical implants for the next 5 years, reaching $60 billion by 2027. This is largely driven by the rise in cardiovascular disease, with the use of medical implants, such as pacemakers and defibrillators, steadily growing.

However, one of the key challenges facing these devices is power, and implantable medical device charging is becoming an increasingly important topic. Batteries have been the power source of choice but they come with several challenges:

• Bulky battery packs are difficult to implant in compact areas of the body. For example, many brain implants need to be implanted into the neck and connected to the target site via wires.
• The use of wires shows an increased rate of infection, dislodgement, and fracture.
• Device batteries last as little as 5 years.
• Replacement of a low battery requires surgery, adding to mortality risk as well as billions in costs to the healthcare system.

These limitations have created a clear need for a better solution to power implanted devices. Wireless charging has emerged as a next-generation innovation.

Current wireless charging mechanisms:

There are about 10 types of wireless powering mechanisms. The most common are radio frequency, magnetic induction, and magnetic resonance charging systems. Figure 1 shows how these mechanisms work, from the input power to the transfer of an alternating current signal (AC) to a direct current (DC). Then, frequencies are transferred wirelessly between transmitter coils (e.g., charging platform) and the receiver coils (e.g., smartphone), and eventually to the appropriate power for the battery.

• Radiofrequency charging is being developed to be used in smartphone charging pads and tablet charging stands. These types of devices require the transmitter to generate radio frequency waves and allow for a greater distance between the transmitter and receiver. Drawbacks include that this method is prone to interference, and often requires precise and stable alignment. Additionally, RF is in the early stages and is not yet deployed in commercial products. 
• Magnetic induction, or near-field charging, sends an electric current via a transmitter coil through a charging station to generate a magnetic field whenever the receiver coil is placed on or near the charging station. This is often used for smaller wireless devices, such as an electric toothbrush because it requires a shorter distance or direct contact between the receiver and transmitter coils. A key disadvantage is a longer charging time and requirement for precise alignment.
• Magnetic resonance charging is the fastest-growing segment in the wireless charging market. Magnetic resonance is primarily used for larger wireless devices that require greater power, such as electric vehicles. These large wireless devices use magnetic fields to transfer energy between two coupled coils when the receiver has the same generated frequency. Resonance allows for more variation in alignment but has disadvantages such as low efficiency due to flux leakage and greater circuit complexity. The high operating frequencies can also lead to potential electromagnetic interference challenges.

Recent advancements in wireless charging for implantable medical devices:

Wireless charging is not novel, but charging a small, implantable medical device is a lot harder and requires a lot more scrutiny from regulatory agencies than charging a phone. Small wireless implantable medical devices require enough power between the transmitter and receiver to penetrate through body tissue at varying distances. In addition, the charging technology must be flexible enough to move with the body, small enough to fit into the device, efficient enough to offer a long duration of power, and safe enough to prevent thermal wounds. Here are 2 recent innovations that caught our eye in this particularly exciting and active field:

• NuCurrent, a company that specializes in wireless charging technology, launched a product called NuEva HF Development Platform in 2021. This device uses inductive resonant power transfer to deliver power levels 1,000 times higher than radio frequency, and it shows the potential of high-frequency power transfer technology for implantable medical device charging.

• In 2022, researchers at the Korea Institute of Science and Technology created an electronic device based on technology commonly used underwater. The researchers developed a triboelectric generator that transmits ultrasonic waves, rather than electromagnetic waves, to convert acoustic energy into electricity through water or tissue. This charging method has the potential to wirelessly charge implantable medical devices from a greater distance between the transmitter and receiver with higher energy efficiency. 

Future perspectives:

Wireless charging is already well established in the consumer goods space and it is only a question of time before it makes the jump into medical devices. Implantable medical devices alone represent a significant untapped opportunity with an estimate of 1.4 million devices implanted every year and a battery lifespan of 6-10 years, we are looking at a burden to the healthcare system in the 10s of billions of USD annually just in surgery costs, let alone the major complications arising in 9% of replacement procedures.

While these numbers alone justify keeping a close look into promising technologies, we believe it to be simply the tip of the iceberg. Wireless charging technology will likely play a key role in the emerging field of implantable biosensors and smart implants which are set to revolutionize how we diagnose and track diseases. Whoever captures and successfully integrates implantable medical device charging technology will be one step closer to that.

Featured image courtesy of Korea Institute of Science and Technology