Future of smart cardiovascular implants

Cardiovascular disease remains the leading cause of death in Western society. Recent technological advances have opened the opportunity of developing new and innovative smart stent devices that have advanced electrical properties that can improve diagnosis and even treatment of previously intractable conditions, such as central line access failure, atherosclerosis and reporting on vascular grafts for renal dialysis. Here we review the latest advances in the field of cardiovascular medical implants, providing a broad overview of the application of their use in the context of cardiovascular disease rather than an in-depth analysis of the current state of the art. We cover their powering, communication and the challenges faced in their fabrication. We focus specifically on those devices required to maintain vascular access such as ones used to treat arterial disease, a major source of heart attacks and strokes. We look forward to advances in these technologies in the future and their implementation to improve the human condition

Biointegrated and wirelessly powered implantable brain devices: a review

Implantable neural interfacing devices have added significantly to neural engineering by introducing the low-frequency oscillations of small populations of neurons known as local field potential as well as high-frequency action potentials of individual neurons. Regardless of the astounding progression as of late, conventional neural modulating system is still incapable to achieve the desired chronic in vivo implantation. The real constraint emerges from mechanical and physical diffierences between implants and brain tissue that initiates an inflammatory reaction and glial scar formation that reduces the recording and stimulation quality. Furthermore, traditional strategies consisting of rigid and tethered neural devices cause substantial tissue damage and impede the natural behaviour of an animal, thus hindering chronic in vivo measurements. Therefore, enabling fully implantable neural devices, requires biocompatibility, wireless power/data capability, biointegration using thin and flexible electronics, and chronic recording properties. This paper reviews biocompatibility and design approaches for developing biointegrated and wirelessly powered implantable neural devices in animals aimed at long-term neural interfacing and outlines current challenges toward developing the next generation of implantable neural devices

In silico evaluation of the thermal stress induced by MRI switched gradient fields in patients with metallic hip implant

This work focuses on the in silico evaluation of the energy deposed by MRI switched gradient fields in bulk metallic implants and the consequent temperature increase in the surrounding tissues. An original computational strategy, based on the subdivision of the gradient coil switching sequences into sub-signals and on the time-harmonic electromagnetic field solution, allows to realistically simulate the evolution of the phenomena produced by the gradient coils fed according to any MRI sequence. Then, Pennes' bioheat equation is solved through a Douglas-Gunn time split scheme to compute the time-dependent temperature increase. The procedure is validated by comparison with laboratory results, using a component of a realistic hip implant embedded within a phantom, obtaining an agreement on the temperature increase better than 5%, lower than the overall measurement uncertainty. The heating generated inside the body of a patient with a unilateral hip implant when undergoing an Echo-Planar Imaging (EPI) MRI sequence is evaluated and the role of the parameters affecting the thermal results (body position, coil performing the frequency encoding, effects of thermoregulation) is discussed. The results show that the gradient coils can generate local increases of temperature up to some kelvin when acting without radiofrequency excitation. Hence, their contribution in general should not be disregarded when evaluating patients' safety

Extending the limits of wireless power transfer to miniaturized implantable electronic devices

Implantable electronic devices have been evolving at an astonishing pace, due to the development of fabrication techniques and consequent miniaturization, and a higher efficiency of sensors, actuators, processors and packaging. Implantable devices, with sensing, communication, actuation, and wireless power are of high demand, as they pave the way for new applications and therapies. Long-term and reliable powering of such devices has been a challenge since they were first introduced. This paper presents a review of representative state of the art implantable electronic devices, with wireless power capabilities, ranging from inductive coupling to ultrasounds. The different power transmission mechanisms are compared, to show that, without new methodologies, the power that can be safely transmitted to an implant is reaching its limit. Consequently, a new approach, capable of multiplying the available power inside a brain phantom for the same specific absorption rate (SAR) value, is proposed. In this paper, a setup was implemented to quadruple the power available in the implant, without breaking the SAR limits. A brain phantom was used for concept verification, with both simulation and measurement data.This work is supported by FCT with the reference project PTDC/EEI-TEL/5250/2014, by FEDER funds through Projecto 3599-Promover a Produção Científica e Desenvolvimento Tecnológico e a Constituição de Redes Temáticas (3599-PPCDT) and by grant SFRH/BD/116554/2016.info:eu-repo/semantics/publishedVersio

Intra-Body Communications for Nervous System Applications: Current Technologies and Future Directions

The Internet of Medical Things (IoMT) paradigm will enable next generation healthcare by enhancing human abilities, supporting continuous body monitoring and restoring lost physiological functions due to serious impairments. This paper presents intra-body communication solutions that interconnect implantable devices for application to the nervous system, challenging the specific features of the complex intra-body scenario. The presented approaches include both speculative and implementative methods, ranging from neural signal transmission to testbeds, to be applied to specific neural diseases therapies. Also future directions in this research area are considered to overcome the existing technical challenges mainly associated with miniaturization, power supply, and multi-scale communications.Comment: https://www.sciencedirect.com/science/article/pii/S138912862300163

Doctor of Philosophy

dissertationMagnetic fields are permeable to the biological tissues and can induce electric field in the conductive structures. Some medical devices take advantage of this ability to transfer energy from the source to the receiving site without direct contact. Prosthetic devices such as retinal implants use time-varying magnetic field to achieve wireless power transfer to the implanted magnetic coil. However, devices such as magnetic stimulators use the induction principle to create an electric field at the stimulation site. Efficiency of these devices is primarily dependent on the design of the magnetic coils. Therefore, in this work, we designed and validated efficient magnetic coils for wireless power transfer to implanted devices and magnetic stimulation of the peripheral nerves. Typical wireless power transfer (WPT) systems uses two-coil based design to achieve contactless power transfer to the implanted electronics. These systems achieve low power transfer efficiency (< 30%) and frequency bandwidth. Moreover, efficient wireless system requires high coupling and load variation tolerance during device operation. To design an electromagnetic safe WPT system, the power absorbed by the tissue and radiated field due to the proximal magnetic coils needs to be minimized. In this work, we proposed a multi-coil power transfer system which solves some of the current challenges. The proposed multi-coil WPT system achieves more than twice the power transfer efficiency, controllable voltage gain, wider frequency bandwidth, higher tolerance to coupling and load variations, lower absorbed power in the tissue and lower radiated field from the magnetic coil than a comparable two-coil system. In this work, we have developed analytic models of the multi-coil WPT system and validated the accuracy of the solutions using experiments. Magnetic coils play an important role in controlling the distribution of induced electric field inside the nerve during magnetic stimulation. In the past, homogeneous models were used to estimate the field profile inside conductive tissue due to the time varying current in the magnetic coil. Moreover, the effect of the surrounding media and stimulation mechanisms was understudied, which limits the optimization accuracy of the magnetic coils. In this work, we developed anatomically correct tissue models to study the effect of tissue heterogeneity and the surrounding media on the induced electric field. We also developed an optimization algorithm for designing energy efficient cm-size magnetic coils, that were then used for ex-vivo magnetic stimulation of the frog's sciatic nerve