Periodic Reporting for period 1 - ARIA (Validation of Magnet-Free Wireless Charging and Communication for Intra-body Devices)
Reporting period: 2023-04-01 to 2024-09-30
Cochlear implants (CIs), which electrically stimulate the auditory nerve to repair hearing in people with severe-to-profound hearing loss, are used for more than 40 years. However, conventional CIs have major drawbacks, one of which is the use of magnet in the implanted unit of the CI to help perfect alignment of the coils that are used for RF Link between external and implanted units. However, using magnets prevents the CI users from accessing some of the medical treatment and examination methods like MRI, and may also lead to damage on the skin. To eliminate the drawbacks of conventional CIs including the magnet utilization, we introduced FLAMENCO concept, which has demonstrated that a fully implantable cochlear implant (FICI) mimicking the natural hearing mechanism of the ear is feasible. In the ERC FLAMENCO project, we developed the FICI as a magnet-free device, which necessitated development of a novel wireless power and data transfer (WPDT) application to minimize transfer losses, thus the duration for utilization of external wireless unit to charge the implanted rechargeable battery. By introducing a unique multi-mode rectifier circuit charging the load for an extended coupling range and eliminating the requirement of alignment magnets, the efficiency loss is reduced and the charging efficiency is maximized. In the ARIA project, which stems from the developments within the ERC FLAMENCO project, we would perform technological and commercial validation of WPDT unit according to the market standards to optimize the unit for fabricating a demonstrator to be integrated to the FICI. We would also look into the potential for integration with other Active Implantable Medical Devices (AIMDs). If implemented successfully, the ARIA WPDT not only would be a major step for commercialization of our FICI which has already triggered interest of CI makers, users and investors, but also could lead to new applications of AIMDs suffering from lack of a high efficiency magnet-free wireless power and data transfer unit.
During the course of the project, MRI compatibility of the wireless power and data transfer unit is validated:
MRI-Compatibility: According to international standards ISO/TS 10974:2018, to validate MRI-compatibility, the system’s heating should be observed both under power transfer to the system (electrical heating) and when the implanted part is put through MRI exposure (MRI-induced heating).
Heating simulations were conducted using the Electromagnetic Heating Module in COMSOL Multiphysics 5.2. Critical heating points, areas expected to experience the highest temperatures, on the receiver coil were determined through these finite element method simulations.
Electrical Heating Simulations: The coils were modelled to match their real-life geometries and were placed within a simulated tissue phantom medium with physical properties matching those of the experimental phantom. The entire phantom-coil complex was modelled in air, with a boundary condition of 37°C to simulate body temperature.
Magnetic field calculations were performed across the entire geometry, then the transmitter coil was excited with a time-varying voltage corresponding to the power amplifier output. The coils were positioned some distance apart, yielding the voltage coupling factor consistent with experimental settings.
Given that the physical parameters remained constant with temperature changes, both methods produced consistent results.
MRI-induced Heating Simulations: To simulate MRI exposure in COMSOL, a birdcage MRI coil was implemented to generate the RF field, with the RF Module used for field calculations.
A head model was positioned within the MRI system, incorporating the receiver coil geometry to simulate the actual MRI scenario. The head model’s physical parameters were chosen to match those of the tissue phantom used in experiments. A continuous RF excitation was applied without imaging sequences to observe the temperature increase at critical points and spatial power dissipation.
Analytical Solutions: The Joule heating analytical solutions were done to explore the heat generation due to resistive losses in the coil during power transfer, accounting for the geometry of the coil and the electrical properties of the materials.
The RF heating analytical solutions were done to represent the temperature rise induced by the interaction of the implantable coil with external radio frequency fields.
Heating Tests: All of the electrical and MRI-induced heating tests were done with the receiver coil submerged in a human-body mimicking phantom, while the previously detected critical points being measured continuously. Developed by a third party, the phantom has been tested at RF frequencies up to 128 MHz (the RF frequency of a 3T MRI). Key parameters for the tissue phantom, such as electrical conductivity, thermal conductivity, relative permittivity, and specific heat capacity, were selected according to ISO/TS 10974:2018 to accurately replicate human tissue properties during heating assessment.
Electrical Heating Tests: The power amplifier and rectifier circuit were adjusted according to their intended operational settings. The transmitted power level was swept across four levels, ranging from 720 to 1260 mW.
During wireless power transfer, temperatures at the identified critical points and a reference location were recorded continuously.
For these experiments, the rectifier was operated in voltage mode, the most power-intensive rectification setting. Coils were aligned along their axis to maximize induced current in the receiver coil, and the voltage coupling between coils was adjusted to approximately 0.15.
MRI-Induced Heating Tests: Heating measurements during MRI exposure followed a similar approach, with the same instrumentation used to ensure consistency.
MRI-Compatibility: According to international standards ISO/TS 10974:2018, to validate MRI-compatibility, the system’s heating should be observed both under power transfer to the system (electrical heating) and when the implanted part is put through MRI exposure (MRI-induced heating).
Heating simulations were conducted using the Electromagnetic Heating Module in COMSOL Multiphysics 5.2. Critical heating points, areas expected to experience the highest temperatures, on the receiver coil were determined through these finite element method simulations.
Electrical Heating Simulations: The coils were modelled to match their real-life geometries and were placed within a simulated tissue phantom medium with physical properties matching those of the experimental phantom. The entire phantom-coil complex was modelled in air, with a boundary condition of 37°C to simulate body temperature.
Magnetic field calculations were performed across the entire geometry, then the transmitter coil was excited with a time-varying voltage corresponding to the power amplifier output. The coils were positioned some distance apart, yielding the voltage coupling factor consistent with experimental settings.
Given that the physical parameters remained constant with temperature changes, both methods produced consistent results.
MRI-induced Heating Simulations: To simulate MRI exposure in COMSOL, a birdcage MRI coil was implemented to generate the RF field, with the RF Module used for field calculations.
A head model was positioned within the MRI system, incorporating the receiver coil geometry to simulate the actual MRI scenario. The head model’s physical parameters were chosen to match those of the tissue phantom used in experiments. A continuous RF excitation was applied without imaging sequences to observe the temperature increase at critical points and spatial power dissipation.
Analytical Solutions: The Joule heating analytical solutions were done to explore the heat generation due to resistive losses in the coil during power transfer, accounting for the geometry of the coil and the electrical properties of the materials.
The RF heating analytical solutions were done to represent the temperature rise induced by the interaction of the implantable coil with external radio frequency fields.
Heating Tests: All of the electrical and MRI-induced heating tests were done with the receiver coil submerged in a human-body mimicking phantom, while the previously detected critical points being measured continuously. Developed by a third party, the phantom has been tested at RF frequencies up to 128 MHz (the RF frequency of a 3T MRI). Key parameters for the tissue phantom, such as electrical conductivity, thermal conductivity, relative permittivity, and specific heat capacity, were selected according to ISO/TS 10974:2018 to accurately replicate human tissue properties during heating assessment.
Electrical Heating Tests: The power amplifier and rectifier circuit were adjusted according to their intended operational settings. The transmitted power level was swept across four levels, ranging from 720 to 1260 mW.
During wireless power transfer, temperatures at the identified critical points and a reference location were recorded continuously.
For these experiments, the rectifier was operated in voltage mode, the most power-intensive rectification setting. Coils were aligned along their axis to maximize induced current in the receiver coil, and the voltage coupling between coils was adjusted to approximately 0.15.
MRI-Induced Heating Tests: Heating measurements during MRI exposure followed a similar approach, with the same instrumentation used to ensure consistency.
ARIA technology stems from the developments within the FLAMENCO project (development of a fully implantable cochlear implant (FICI)) where the need to deploy an efficient and safe power and data transmission system arose. Based on the results of ARIA project, wireless power and data transfer (WPDT) technology is confirmed to transfer power and data with highest efficiency through the skin without utilizing a magnet for alligning sending and receiving units. This would make the FICI a competitive technology to satisfy the stakeholders including the end-users suffering from a number of drawbacks of magnet integrated receiving units.
As the feasibility study confirms the applicability for CIs, it would not only facilitate an optimal FICI concept and improve the FLAMENCO outcomes further, but also would open a realm of business opportunities on the wide AIMD market. This may also lead to the introduction of new wireless AIMDs that could not be commercialized yet, which may be due to lack of access to high efficiency magnet-free WPDT technology.
The next steps for further uptake are: system integration, pre-clinical validation, clinical evaluation and the initiation of the product dossier in accordance with the MDR, thus creating a solid basis for the exploitation of the results. Then, there should be further validation phase (clinical) that requires significant resources. These resources can be raised through blended finance (EIC Accelerator) or private investment, and a start-up would enable private capital injection into development pipeline.
As the feasibility study confirms the applicability for CIs, it would not only facilitate an optimal FICI concept and improve the FLAMENCO outcomes further, but also would open a realm of business opportunities on the wide AIMD market. This may also lead to the introduction of new wireless AIMDs that could not be commercialized yet, which may be due to lack of access to high efficiency magnet-free WPDT technology.
The next steps for further uptake are: system integration, pre-clinical validation, clinical evaluation and the initiation of the product dossier in accordance with the MDR, thus creating a solid basis for the exploitation of the results. Then, there should be further validation phase (clinical) that requires significant resources. These resources can be raised through blended finance (EIC Accelerator) or private investment, and a start-up would enable private capital injection into development pipeline.