Robust voltage-controlled transcutaneous energy transfer system for artificial anal sphincter.

BACKGROUND: The artificial anal sphincter (AAS) system has gained significant attention as a solution for treating fecal incontinence (FI). It relies on transcutaneous energy transfer (TET) as its primary energy source. However, changes in posture or biological tissue can cause misalignment of the coil, resulting in unstable power reception. Inadequate power affects charging efficiency, while excessive power leads to excessive heating at the receiver side. Consequently, achieving safe and constant voltage charging for the AAS becomes a complex challenge. METHODS: To maintain a consistent charging voltage and overcome the issue of variations in load and coil coupling strength, this article proposes a wireless charging control system that utilizes an LCC-S-type resonant network and phase shift to adjust the transmitting voltage based on feedback charging voltage in real time. In particular, the PI controller and neural network are introduced to change the phase-shift angle swiftly. The dynamic performance is then evaluated under different misalignments and presented with comparative results. RESULTS: The results indicate that the multilayer perceptron control system outperforms the PI. Under the complex misalignment disturbance, the average error of receiver side load voltage is only 0.007 V, with an average settling time of 960 ms. Additionally, the average temperature at the receiver side is 40.4°C. CONCLUSION: The experiments demonstrate that the proposed system effectively addresses the misalignment issue in TET during the charging, ensuring constant voltage charging at the receiver side and thermal safety.

Design of a hybrid left ventricular assist device with a new wireless charging system.

BACKGROUND: The objective of this study was to design a new wireless left ventricular assist device (LVAD) that can be charged without using a conventional transcutaneous energy transfer system (TETS). METHODS: Our new wireless LVAD was a hybrid pump operating in two different modes: magnetic and electric modes. The pump was driven wirelessly by extracorporeal rotating magnets in magnetic mode, whereas it was driven by electricity provided by an intracorporeal battery in electric mode. A magnetic torque transmission system was introduced to wirelessly transmit torque to the pump impeller. The intracorporeal battery was charged in magnetic mode making use of electromagnetic coils as a generator, whereas the coils were used as a motor in electric mode. To demonstrate the feasibility of our system, we conducted a bench-top durability test for 1 week. RESULTS: Our hybrid pump had shown sufficient pump performance as a LVAD, with a head pressure of approximately 80 mm Hg and a flow volume of 5.0 L/min, for 1 week. The intracorporeal battery was wirelessly charged enough to power electric mode for 2.5 h a day throughout the 1-week durability test. CONCLUSIONS: Our hybrid wireless LVAD system demonstrated the possibility of a wireless LVAD and has the potential to reduce medical complications of LVAD therapy.

Thermal evaluation of a hermetic transcutaneous energy transfer system to power mechanical circulatory support devices in destination therapy.

Current generation left ventricular assist devices (LVADs) are powered by a percutaneous driveline. The high prevalence of driveline infections has motivated the development of transcutaneous energy transfer (TET) systems which eliminate driveline associated complications by wirelessly delivering power across the skin. Destination therapy (DT) requires long-term reliable operation of the TET electronics suggesting the use of hermetic packaging techniques as used in all other chronically implanted devices. TET coils dissipate heat during operation and in order for the technology to be suitable for patient use, sufficient power must be delivered while maintaining temperatures at levels deemed safe. The heating of a TET system designed for DT which uses hermetic packaging technology was evaluated in silico and in vivo. A numerical model was used to evaluate the temperature of the TET coils. The TET system was fabricated and assessed in vivo using an ovine model. The receiving coil was implanted subcutaneously in a sheep and the transmission coil placed in contact with the skin and concentric to the implanted coil. Temperatures of the system were measured using sensors fixed to the surface of the coils. Numerical modeling indicated that the maximum temperatures of the primary and secondary coil surfaces were 38.13°C and 38.41°C, respectively, when delivering 10 W continuously. Stable temperatures were observed in vivo after 70 minutes and the maximum skin and implant surface temperatures were 37.73°C and 38.31°C, respectively. This study showed that a hermetic, chronically implantable TET system is thermally safe when continuously delivering 10 W of power, sufficient to power modern LVADs.

A novel power supply system for puborectalis-like artificial anal sphincter.

Puborectalis-like artificial anal sphincter (PAAS) is an innovative new type of artificial anal sphincter (AAS). It overcomes many drawbacks and inadequacies of various previous AASs, and it has successfully been implanted in vivo for almost 3 weeks. During in vivo testing, PAAS shows its ability to retain continence with low risk of ischemia necrosis, and somehow truly helps to remodel rectal perception. However, there are still many defects that influence the long-term implantation of PAAS, especially in the power supply system (PSS). This article presents a new designed PSS which includes a new transcutaneous energy transfer (TET) system, a heat reduction system, and a safety usage system. The new PSS reduces the total size of PAAS by at least 30%. Newly designed TET system can satisfy the Qi standard, and render a power of 3W to fulfill the requirement of fast charging and normal use of PAAS at the distance of 15.5 mm when frequency of TET system is 110 kHz, which previous TET systems can hardly achieve. Heat reduction system helps to reduce the heat generated during TET charging. It can reduce heat by 40% during the same period of time of TET charging. Safety usage system helps the user control PAAS more properly which can reduce the rate of failure of PAAS system.

Adaptive Transcutaneous Power Transfer to Implantable Devices: A State of the Art Review.

Wireless energy transfer is a broad research area that has recently become applicable to implantable medical devices. Wireless powering of and communication with implanted devices is possible through wireless transcutaneous energy transfer. However, designing wireless transcutaneous systems is complicated due to the variability of the environment. The focus of this review is on strategies to sense and adapt to environmental variations in wireless transcutaneous systems. Adaptive systems provide the ability to maintain performance in the face of both unpredictability (variation from expected parameters) and variability (changes over time). Current strategies in adaptive (or tunable) systems include sensing relevant metrics to evaluate the function of the system in its environment and adjusting control parameters according to sensed values through the use of tunable components. Some challenges of applying adaptive designs to implantable devices are challenges common to all implantable devices, including size and power reduction on the implant, efficiency of power transfer and safety related to energy absorption in tissue. Challenges specifically associated with adaptation include choosing relevant and accessible parameters to sense and adjust, minimizing the tuning time and complexity of control, utilizing feedback from the implanted device and coordinating adaptation at the transmitter and receiver.

Optimal Design of Litz Wire Coils With Sandwich Structure Wirelessly Powering an Artificial Anal Sphincter System.

Transcutaneous energy transfer system (TETS) is widely used to energize implantable biomedical devices. As a key part of the TETS, a pair of applicable coils with low losses, high unloaded Q factor, and strong coupling is required to realize an efficient TETS. This article presents an optimal design methodology of planar litz wire coils sandwiched between two ferrite substrates wirelessly powering a novel mechanical artificial anal sphincter system for treating severe fecal incontinence, with focus on the main parameters of the coils such as the wire diameter, number of turns, geometry, and the properties of the ferrite substrate. The theoretical basis of optimal power transfer efficiency in an inductive link was analyzed. A set of analytical expressions are outlined to calculate the winding resistance of a litz wire coil on ferrite substrate, taking into account eddy-current losses, including conduction losses and induction losses. Expressions that describe the geometrical dimension dependence of self- and mutual inductance are derived. The influence of ferrite substrate relative permeability and dimensions is also considered. We have used this foundation to devise an applicable coil design method that starts with a set of realistic constraints and ends with the optimal coil pair geometries. All theoretical predictions are verified with measurements using different types of fabricated coils. The results indicate that the analysis is useful for optimizing the geometry design of windings and the ferrite substrate in a sandwich structure as part of which, in addition to providing design insight, allows speeding up the system efficiency-optimizing design process.

Tissue Variability and Antennas for Power Transfer to Wireless Implantable Medical Devices.

The design of effective transcutaneous systems demands the consideration of inevitable variations in tissue characteristics, which vary across body areas, among individuals, and over time. The purpose of this paper was to design and evaluate several printed antenna topologies for ultrahigh frequency (UHF) transcutaneous power transfer to implantable medical devices, and to investigate the effects of variations in tissue properties on dipole and loop topologies. Here, we show that a loop antenna topology provides the greatest achievable gain with the smallest implanted antenna, while a dipole system provides higher impedance for conjugate matching and the ability to increase gain with a larger external antenna. In comparison to the dipole system, the loop system exhibits greater sensitivity to changes in tissue structure and properties in terms of power gain, but provides higher gain when the separation is on the order of the smaller antenna dimension. The dipole system was shown to provide higher gain than the loop system at greater implant depths for the same implanted antenna area, and was less sensitive to variations in tissue properties and structure in terms of power gain at all investigated implant depths. The results show the potential of easily-fabricated, low-cost printed antenna topologies for UHF transcutaneous power, and the importance of environmental considerations in choosing the antenna topology.

In vivo demonstration of ultrasound power delivery to charge implanted medical devices via acute and survival porcine studies.

Animal studies are an important step in proving the utility and safety of an ultrasound based implanted battery recharging system. To this end an Ultrasound Electrical Recharging System (USER™) was developed and tested. Experiments in vitro demonstrated power deliveries at the battery of up to 600 mW through 10-15 mm of tissue, 50 mW of power available at tissue depths of up to 50 mm, and the feasibility of using transducers bonded to titanium as used in medical implants. Acute in vivo studies in a porcine model were used to test reliability of power delivery, temperature excursions, and cooling techniques. The culminating five-week survival study involved repeated battery charging, a total of 10.5h of ultrasound exposure of the intervening living tissue, with an average RF input to electrical charging efficiency of 20%. This study was potentially the first long term cumulative living-tissue exposure using transcutaneous ultrasound power transmission to an implanted receiver in situ. Histology of the exposed tissue showed changes attributable primarily due to surgical implantation of the prototype device, and no damage due to the ultrasound exposure. The in vivo results are indicative of the potential safe delivery of ultrasound energy for a defined set of source conditions for charging batteries within implants.

Design and assessment of novel artificial anal sphincter with adaptive transcutaneous energy transfer system.

This paper presents the in vitro assessment of a novel elastic scaling artificial anal sphincter system (ES-AASS) with an adaptive transcutaneous energy transfer system (TETS) for treatment of severe faecal incontinence (FI). The proposed adaptive TETS has a phase control, which can maintain the output voltage at ∼7 V across the full range of the coupling coefficient variation (from 0.09-0.31) during the whole process of charging with a phase shift of 177.5° to 79.1°. A maximum surface temperature of 42.2 °C was measured above the secondary coil during an energy transmission of 3.5 W in air. The specific absorption rate (SAR) and current density analysis of the biological three-layers structure, including the skin, fat and muscle) surrounding the coil pair were analysed and the results of simulation analysis showed that the value of SAR and current density were very small at any given transmission condition compared with the basic restrictions of the International Commission on Non-Ionizing Radiation Protection (ICNIRP). In conclusion, in vitro experimental results showed that the ES-AASS can control simulated faecal behaviour effectively and the performance of TETS was validated.

Power flow control of TET system for a novel artificial anal sphincter system.

This paper presents an adaptive transcutaneous energy transfer system (TETS) integrated with a novel elastic scaling artificial anal sphincter system (ES-AASS) for treating severe faecal incontinence (FI). The ES-AASS is based on a novel executive mechanism that uses a spring scalable structure to clamp the rectum. To deliver the correct amount of power (i.e. to match the load demand under variable coupling conditions or different operation stages of the implanted device) for internal battery charging and ensure safety for the human body, theoretical analysis was conducted as a control rule with respect to the relationship between the phase of driver signals and output voltage. An easy regulating procedure to stabilize output voltage with a phase shift controller is also presented. To validate the phase control rules, a prototype of the TETS was constructed and its performance was validated across the whole coupling coefficient range (0.09 ∼ 0.29) as well as load resistance (50 ∼ 120 Ω). The results show that the output voltage of the secondary side can be maintained at a constant 7 V with a phase regulation range of 78.7-178.2° and the proposed controller has reached a maximal end-to-end power efficiency of 74.2% at 1 W.

Transcutaneous Energy Transfer with Voltage Regulation for Rotary Blood Pumps.

Rotary blood pumps often require a constant operating voltage. To meet this requirement and to eliminate the need for percutaneous leads, a voltage-regulated transcutaneous energy transfer (TET) system has been developed. Voltage regulation is achieved by using a transcutaneous infrared feedback control loop operating on a 890 nanometer (nm) wavelength. In vitro testing of the system developed has shown that output voltage can be maintained to within 0.2 V of nominal (14.5 V) for delivered powers up to 50 watts (W) and coil separations of between 3 and 10 mm. Power transfer efficiencies were determined to be from 68% to 72% over the tested range of coil separations and output currents from 1.5 to 3.6 amperes (A). This system has demonstrated acceptable performance in regulating output voltage while transferring power inductively without using percutaneous connections. By integrating this type of TET system with an implanted rotary blood pump, the quality of life for the device recipient could be improved.