Optimization of the Coupling Coefficient of the Inductive Link for Wireless Power Transfer to Biomedical Implants

This work focuses on the optimization of coupling coefficient (k) of the inductive link for the wireless power transfer (WPT) system to be used in implantable medical devices (IMDs) of centimeter size. The analytic expression of k is presented. Simulations are conducted by using the high-frequency structure simulator (HFSS). Analytic results are verified with simulations. The receiving (Rx) coil is implanted in the body and set as a circular coil with a radius of 5 millimeters for reducing the risk of tissue inflammation. The inductive link under misalignment scenarios is optimized to improve k. When the distance between the transmitting (Tx) and Rx coils is fixed at 20 mm, it is found that, to maximize k, the Tx coil in a planar spiral configuration with an average radius of 20 mm is preferred, and the Rx coil in a solenoid configuration with a wire pitch of 0.7 mm is recommended. Based on these optimization results, an inductive link WPT system is proposed; the coupling coefficient k, the power transfer efficiency (PTE), and the maximum power delivered to the load (MPDL) of the system are obtained with both simulation and experiment. Different media of air, muscle, and bone separating the Tx and Rx coils are tested. For the muscle (bone) medium, PTE is 44.14% (43.07%) and MPDL is 145.38 mW (128.13 mW), respectively.

Hybrid fibrous (PVDF-BaTiO3)/ PA-11 piezoelectric patch as an energy harvester for pacemakers

Lithium batteries have been widely used to power up implantable medical devices such as pacemakers that are often designed to treat, diagnose, and prevent different diseases. However, due to their limited capacity and lifetime, patients have to undergo a surgical procedure to replace the discharged battery. Recently, nanogenerators have been emerged and are broadly accepted since they can convert tiny biomechanical forces, such as heartbeats, into electrical energy. This study aims to manufacture a biocompatible and high-performance piezoelectric energy harvester (PEH) that is capable to be charged by the energy received from the heartbeat and store the generated voltage. In this research, a hybrid structure of poly (vinylidene fluoride) (PVDF) coupling with polyamide-11 (PA-11) was fabricated using dual electrospinning to enhance the piezoelectric properties of the intended PEH. The piezoelectric test results show an acceptable increase in nanofibers’ piezoelectric sensitivity from 62.87 mV/N to 75.75 mV/N by adding 25% (v/v) of PA-11 to PVDF, indicating the synergistic effect of PVDF and PA-11. The specimen PVDF (75% v/v)-PA-11 (25% v/v) also showed the highest mechanical strength and consequently is suggested as the optimum sample. To further enhance the efficacy and sensitivity of PEH to convert the small mechanical forces into an acceptable voltage, 15% (w/w) of barium titanate (BaTiO3) nanoparticles were added to the hybrid structure. The crystallinity and mechanical strength were noticeably increased by incorporating BaTiO3 nanoparticles into the fibrous structure, leading to a piezoelectric sensitivity of 107.52 mV/N. This result lays the groundwork for producing an effective piezoelectric patch that could be used as pacemaker batteries.

Medical Device Security

Implantable medical devices (IMDs) are miniaturized computer systems used to monitor and treat various medical conditions. Examples of IMDs include insulin pumps, artificial pacemakers, neuro-stimulators, and implantable cardiac defibrillators. These devices have adopted wireless communication to help facilitate the care they provide for patients by allowing easier transferal of data or remote control of machine operations. However, with such adoption has come exposure to various security risks and issues that must be addressed due to the close relation of patient health and IMD performance. With patient lives on the line, these security risks pose increasingly real problems. This chapter hopes to provide an overview of these security risks, their proposed solutions, and the limitations on IMD systems which make solving these issues nontrivial. Later, the chapter will analyze the security issues and the history of vulnerabilities in pacemakers to illustrate the theoretical topics by considering a specific device.

Predicting Corrosion Delamination Failure in Active Implantable Medical Devices: Analytical Model and Validation Strategy

The ingress of body fluids or their constituents is one of the main causes of failure of active implantable medical devices (AIMDs). Progressive delamination takes its origin at the junctions where exposed electrodes and conductive pathways enter the implant interior. The description of this interface is considered challenging because electrochemically-diffusively coupled processes are involved. Furthermore, standard tests and specimens, with clearly defined 3-phase boundaries (body fluid-metal-polymer), are lacking. We focus on polymers as substrate and encapsulation and present a simple method to fabricate reliable test specimens with defined boundaries. By using silicone rubber as standard material in active implant encapsulation in combination with a metal surface, a corrosion-triggered delamination process was observed that can be universalised towards typical AIMD electrode materials. Copper was used instead of medical grade platinum since surface energies are comparable but corrosion occurs faster. The finding is that two processes are superimposed there: First, diffusion-limited chemical reactions at interfaces that undermine the layer adhesion. The second process is the influx of ions and body fluid components that leave the aqueous phase and migrate through the rubber to internal interfaces. The latter observation is new for active implants. Our mathematical description with a Stefan-model coupled to volume diffusion reproduces the experimental data in good agreement and lends itself to further generalisation.