Powering and communicating with implantable medical devices using NIR light

Featured in Optics Continuum, the research outlines an approach that promises to enhance the performance and durability of IMDs while providing more secure, safer, more private, and radio interference-free communication. The published paper, authored by Syifaul Fuada, Mariella Särestöniemi, and Marcos Katz at the CWC-NS, has demonstrated research merit as it was designated an Editor's Pick, highlighting articles of excellent scientific quality and representing the work occurring in a specific field. The paper is a small part of Syifaul Fuada's doctoral research, which is funded by Infotech, University of Oulu.

“This is the initial step that could open other ideas to advance the proposed approach,” Fuada says.

“Modern IMDs typically consist of several key components, such as a sensing module, an actuation module, a communication module, a power source, and most often, a programmable component is also involved within the system that acts to control all functionalities. So it is clear that wireless communication is needed, and at the same time, wireless communication capabilities are typically power hungry, which can deplete the battery,” Katz points out.

When we think of IMDs, pacemakers, defibrillators, and neurostimulators are the most often mentioned devices used by patients worldwide. These active devices operate within the body by generating pulses. Traditional methods relying on radio communication have triggered security worries. In practice, third parties or malicious actors can interfere with radio communication links, spoof signals, and gain access to devices, issuing false commands. Indeed, it is very harmful. Recent studies have demonstrated that commercial pacemakers and defibrillators are vulnerable to hacking, leading to significant recalls of these devices. In contrast, Katz emphasizes that NIR light, as a communication modality to IMDs, has limited coverage (i.e., a local link), practically mitigating the risk of remote hacking attempts.

“It is envisioned that utilizing NIR light allows us to establish more resistance to interference and unauthorized access,” Fuada explaines.

Most implantable devices, such as pacemakers, typically use single-use or primary batteries, which need replacement after 5 to 7 years of use. Once pacemakers are implanted in a patient’s body, everything must function properly. Certainly, the patient does not wish to undergo an additional surgical procedure merely because an electronic component malfunctions or because the battery has depleted. Regular battery changes could compromise patient safety and comfort, and also require money to do that kind of surgery. Similarly, the power source of IMDs must be reliable.

“Our proposed approach not only provides safe, secure, private data transmission to IMDs but also involves a strategy on how to tackle the critical challenge of power source issues in IMDs. Using safe, private, and secure wireless charging capability is envisioned to help in reducing the healthcare costs due to frequent surgical interventions to replace batteries," Fuada tells.

The paper presents a proof-of-concept conducted on a testbed. It uses a single beam 810 nm NIR LED to transfer data and power through a 10 mm-thick optical phantom mimicking human soft tissue. The team employs a tiny commercial PV cell to harvest NIR light energy that penetrates the optical phantom. Using a testbed allows different parameters to be adjusted easily, which benefits early-stage research.

"The optical phantoms used in the experiments were created at the University of Oulu,” Katz notes.

While initial findings indicate data speeds in the tens of kbps, limited penetration depth, and limited harvested energy, there are opportunities to improve performance greatly. The human body presents unique challenges; some NIR light is reflected, refracted, absorbed, and scattered within tissue layers before reaching the receiver (photodetector and PV cell). NIR light source is typically narrowband with a single peak wavelength, e.g., 810 nm, 850 nm, 970 nm, etc. For instance, pulsed communication can increase the range of communication within the tissue. To enhance energy-harvesting efficiency, optimized PV cells can be used to convert energy from a broadband NIR light source. The MIMO scheme could be an option to improve communication speed.

“In our group, we focus on the strategy of using light to wirelessly control, monitor, and also wirelessly charge for diverse applications, including free space, biological tissue, and underwater settings. In the context of IMD, we believe each device has unique requirements for wireless communications (e.g., for actuation instructions, reprogramming, etc.). We are also exploring light, especially NIR light, for a wireless charging function dedicated to these mentioned IMDs.” Katz adds.

At present, there are no plans for in vivo experiments; however, the team adheres rigorously to regulations specifying the maximum permissible light power per square millimeter (mW/cm2) in human tissue.

“We have performed the experiments using carefully tuned optical phantoms to mimic the designated tissue. In this paper, we used soft-tissue-mimicking phantoms. We have created other optical phantom types, such as skin, skull, fat, muscle, and brain, in our university, which could then be used for further studies”, Mariella Särestöniemi says.

The paper demonstrated only the alignment case. In practice, misalignment can occur when the doctor fails to set the transmitter to an alignment position with the IMDs.

“In future studies, we will investigate how much angular and lateral misalignment affects the data and power transmission performances,” Fuada explains.

Further projects can develop NIR light-enabled external units, such as wearables, patches, or belts, worn by patients to ensure alignment with the IMDs and not disturb daily activities during wireless charging. These external units can also be used for data transmission, such as transmitting instructions, synchronizing the operation or activation of several devices, and even powering rechargeable IMDs.

About WiMeC Research group:

The scientific group focuses on diverse health-related applications, aiming to provide solutions for dependable and seamless wireless personalized care throughout our life cycle. We realize a vision of future healthcare services, which are enabled by the use of the latest wireless technology. The team pursues essentially four lines of research: wireless body area networks (WBAN), a full chain of data transfer from measurements to the patient’s electronic health record, edge-cloud continuum, and novel secure solutions for care facilities. We are also involved in ETSI standardization relating to smart body area networks.