Inverse Finite Element Approach to Identify the Post-Necking Hardening Behavior of Polyamide 12 under Uniaxial Tension.

Finite-element (FE) simulations that go beyond the linear elastic limit of materials can aid the development of polymeric products such as stretch blow molded angioplasty balloons. The FE model requires the input of an appropriate elastoplastic material model. Up to the onset of necking, the identification of the hardening curve is well established. Subsequently, additional information such as the cross-section and the triaxial stress state inside the specimen is required. The present study aims to inversely identify the post-necking hardening behavior of the semi-crystalline polymer polyamide 12 (PA12) at different temperatures. Our approach uses structural FE simulations of a dog-bone tensile specimen in LS-DYNA with mesh sizes of 1 mm and 2 mm, respectively. The FE simulations are coupled with an optimization routine defined in LS-OPT to identify material properties matching the experimental behavior. A Von Mises yield criterion coupled with a user-defined hardening curve (HC) were considered. Up to the beginning of necking, the Hockett−Sherby hardening law achieved the best fit to the experimental HC. To fit the entire HC until fracture, an extension of the Hockett−Sherby law with power-law functions achieved an excellent fit. Comparing the simulation and the experiment, the following coefficient of determination R2 could be achieved: Group I: R2 > 0.9743; Group II: R2 > 0.9653; Group III: R2 > 0.9927. Using an inverse approach, we were able to determine the deformation behavior of PA12 under uniaxial tension for different temperatures and mathematically describe the HC.

A Robot Mimicking Heart Motions: An Ex-Vivo Test Approach for Cardiac Devices.

PURPOSE: The pre-clinical testing of cardiovascular implants gains increasing attention due to the complexity of novel implants and new medical device regulations. It often relies on large animal experiments that are afflicted with ethical and methodical challenges. Thus, a method for simulating physiological heart motions is desired but lacking so far. METHODS: We developed a robotic platform that allows simulating the trajectory of any point of the heart (one at a time) in six degrees of freedom. It uses heart motion trajectories acquired from cardiac magnetic resonance imaging or accelero-meter data. The rotations of the six motors are calculated based on the input trajectory. A closed-loop controller drives the platform and a graphical user interface monitors the functioning and accuracy of the robot using encoder data. RESULTS: The robotic platform can mimic physiological heart motions from large animals and humans. It offers a spherical work envelope with a radius of 29 mm, maximum acceleration of 20 m/s2 and maximum deflection of ±19° along all axes. The absolute mean positioning error in x-, y- and z-direction is 0.21 ±0.06, 0.31 ±0.11 and 0.17 ±0.12 mm, respectively. The absolute mean orientation error around x-, y- and z-axis (roll, pitch and yaw) is 0.24 ±0.18°, 0.23 ±0.13° and 0.18 ±0.18°, respectively. CONCLUSION: The novel robotic approach allows reproducing heart motions with high accuracy and repeatability. This may benefit the device development process and allows re-using previously acquired heart motion data repeatedly, thus avoiding animal trials.

Implications of Wound Healing on Subcutaneous Photovoltaic Energy Harvesting.

OBJECTIVE: Cardiac pacemakers must be regularly replaced due to depleted batteries. A possible alternative is proposed by subcutaneous photovoltaic energy harvesting. The body's reaction to an implant can cause device encapsulation. Potential changes in spectral light transmission of skin can influence the performance of subcutaneous photovoltaic cells and has not yet been studied in large animal studies. METHODS: Subcutaneous implants measuring changes in the light reaching the implant were developed. Three pigs received those implants and were analyzed for seven weeks. Spectral measurements with known irradiation were performed to identify possible changes in the transparency of the tissues above the implant during the wound healing process. A histological analysis at the end of the trial investigated the skin tissue above the subcutaneous photovoltaic implants. RESULTS: The implants measured decreasing light intensity and shifts in the light's spectrum during the initial wound healing phase. In a later stage of tissue recovery, the implants measured a generally reduced light intensity compared to the healthy tissue after implantation. The spectral distribution of the measured light at the end of the trial was similar to the first measurements. The histological analysis showed subcutaneous granulation tissue formation for all devices. CONCLUSION: The varying reduction of light intensity reaching the implants means that safety margins must be sufficiently high to ensure the power. At the end of the wound healing process, the spectral distribution of the light reaching the implant is similar to healthy tissue. SIGNIFICANCE: Optimizations of spectral sensitivity of photovoltaic cells are possible.

Potential of subdermal solar energy harvesting for medical device applications based on worldwide meteorological data.

SIGNIFICANCE: Active implants require batteries as power supply. Their lifetime is limited and may require a second surgical intervention for replacement. Intracorporal energy harvesting techniques generate power within the body and supply the implant. Solar cells below the skin can be used to harvest energy from light. AIM: To investigate the potential of subdermal solar energy harvesting. APPROACH: We evaluated global radiation data for defined time slots and calculated the output power of a subdermal solar module based on skin and solar cell characteristics. We assumed solar exposure profiles based on daily habits for an implanted solar cell. The output power was calculated for skin types VI and I/II. RESULTS: We show that the yearly mean power in most locations on Earth is sufficient to power modern cardiac pacemakers if 10 min midday solar irradiation is assumed. All skin types are suitable for solar harvesting. Moreover, we provide a software tool to predict patient-specific output power. CONCLUSIONS: Subdermal solar energy harvesting is a viable alternative to primary batteries. The comparison to a human case study showed a good agreement of the results. The developed code is available open source to enable researchers to investigate further applications of subdermal solar harvesting.

Unexpected high failure rate of a specific MicroPort/LivaNova/Sorin pacing lead.

BACKGROUND: Pacing leads are the Achilles heel of pacemakers. Most manufacturers report a 3-year survival rate of >99% of their leads. We observed several failures of the Beflex/Vega leads (MicroPort, Shanghai, China; formerly Sorin/LivaNova). OBJECTIVE: The purpose of this study was to investigate failure rates of Beflex/Vega leads. METHODS: We analyzed the performance of Beflex/Vega leads implanted at our tertiary referral center. All-cause lead failures (any issues requiring reinterventions such as lead dislocations, cardiac perforations, and electrical abnormalities) were identified during follow-up. The Beflex/Vega lead was compared with a reference lead (CapSureFix Novus 5076, Medtronic, Minneapolis, MN) implanted within the same period and by the same operators. RESULTS: A total of 585 leads were analyzed (382 Beflex/Vega and 203 CapSureFix Novus 5076 leads). Cumulative failure rate estimates were 5.2%, 6.3%, and 12.4% after 1, 2, and 3 years for the Beflex/Vega lead. This was worse compared to the reference lead (1.5%, 1.5%, 3.7% after 1, 2, and 3 years; P = .001). Early failure manifestations up to 3 months occurred at a similar rate (Beflex/Vega vs CapSureFix Novus 5076 lead: 1.3% vs 0.5% for dislocations; 1.3% vs 1.0% for perforations). During follow-up, electrical abnormalities such as noise oversensing (P = .013) and increased pacing thresholds (P = .003) became more frequent in the Beflex/Vega group. Electrical abnormalities were the most common failure manifestation 3 years after implantation in this group (9.4% vs 2.2% for the CapSureFix Novus 5076). CONCLUSION: The failure rate of the Beflex/Vega lead of >10% after 3 years was higher than that of a competitor lead. This gives rise to concern since >135,000 such leads are active worldwide.

A miniaturized endocardial electromagnetic energy harvester for leadless cardiac pacemakers.

Life expectancy of contemporary cardiac pacemakers is limited due to the use of an internal primary battery. Repeated device replacement interventions are necessary, which leads to an elevated risk for patients and an increase of health care costs. The aim of our study is to investigate the feasibility of powering an endocardial pacemaker by converting a minimal amount of the heart's kinetic energy into electric energy. The intrinsic cardiac muscle activity makes it an ideal candidate as continuous source of energy for endocardial pacemakers. For this reason, we developed a prototype able to generate enough power to supply a pacing circuit at different heart rates. The prototype consists of a mass imbalance that drives an electromagnetic generator while oscillating. We developed a mathematical model to estimate the amount of energy harvested from the right ventricle. Finally, the implemented prototype was successfully tested during in-vitro and in-vivo experiments.

Intracardiac Turbines Suitable for Catheter-Based Implantation-An Approach to Power Battery and Leadless Cardiac Pacemakers?

OBJECTIVE: Cardiac pacemakers are powered by batteries, which become exhausted after a few years. This is a problem in particular for leadless pacemakers as they are difficult to explant. Thus, autonomous devices powered by energy harvesters are desired. METHODS: We developed an energy harvester for endocardial implantation. The device contains a microgenerator to convert a flexible turbine runner's rotation into electrical energy. The turbine runner is driven by the intracardiac blood flow; a magnetic coupling allows hermetical sealing. The energy harvester has a volume of 0.34 cm3 and a weight of 1.3 g. Computational simulations were performed to assess the hemodynamic impact of the implant. The device was studied on a mock circulation and an in vivo trial was performed in a domestic pig. RESULTS: In this article, we show that an energy harvester with a 2-bladed 14-mm-diameter turbine runner delivers 10.2 ± 4.8 µW under realistic conditions (heart rate 80/min, stroke volume 75 ml) on the bench. An increased output power (>80 µW) and power density (237.1 µW/cm3) can be achieved by higher stroke volumes, increased heart rates, or larger turbine runners. The device was successfully implanted in vivo. CONCLUSION: The device is the first flow-based energy harvester suitable for catheter-based implantation and provides enough energy to power a leadless pacemaker. SIGNIFICANCE: The high power density, the small volume, and the flexible turbine runner blades facilitate the integration of the energy harvester in a pacemaker. This would allow overcoming the need for batteries in leadless pacemakers.

Radiofrequency ablation lesion assessment using optical coherence tomography - a proof-of-concept study.

BACKGROUND: Radiofrequency catheter ablation (RFA) is an effective treatment for atrial fibrillation. However, ablation lesions are usually only assessed functionally. The immediate effect of RFA on the tissue is not directly visualized. Optical coherence tomography (OCT) is an imaging technique that uses light to capture high-resolution images with histology-like quality. Therefore, it might be used for high-precision imaging of ablation lesions. METHODS AND RESULTS: Radiofrequency ablation lesions (n = 25) were produced on the freshly excised left and right ventricular porcine endocardium. A Thermocool ST SF NAV ablation catheter (Biosense Webster Inc) and an EP-Shuttle ablation generator (Stockert GmbH) were used to produce ablation lesions with powers from 10 to 40 W (energies ranging from 100 Ws to 900 Ws). After ablation, the tissue was imaged with a swept source OCT system (at a wavelength of 1300 nm). Subsequently, the ablation lesions underwent the histological analysis. The ablation lesions could be visualized by OCT in all 17 samples with ablation powers ≥20 W, meanwhile, no lesion could be observed in the other eight samples with lower power (10 W). Lesion depths and lesion radiuses, as assessed by OCT, correlated well with those observed on the subsequent histological analysis (Spearman's r = 0.94, P < 0.001 and r = 0.84, P < 0.001). In addition, successful three-dimensional reconstructions of ablation lesions were performed. CONCLUSION: OCT can provide a visual high-resolution assessment of ablation lesions.

Leadless cardiac resynchronization therapy: An in vivo proof-of-concept study of wireless pacemaker synchronization.

BACKGROUND: Contemporary leadless pacemakers (PMs) only feature single-chamber ventricular pacing. However, the majority of patients require dual-chamber pacing or cardiac resynchronization therapy (CRT). Several leadless PMs implanted in the same heart would make that possible if they were able to synchronize their activity in an efficient, safe, and reliable way. Thus, a dedicated ultra-low-power wireless communication method for PM synchronization is required. OBJECTIVE: The purpose of this study was to develop a leadless CRT system and to evaluate its function in vivo. METHODS: Device synchronization was implemented using conductive intracardiac communication (CIC). Communication frequencies were optimized for intracardiac device-device communication. Energy consumption, safety, and reliability of the leadless PM system were tested in animal experiments. RESULTS: We successfully performed CRT pacing with 3 independent devices synchronizing their action using CIC. No arrhythmias were induced by the novel communication technique. Ninety-eight percent of all communication impulses were transmitted successfully. The optimal communication frequency was around 1 MHz, with a corresponding transmitted power of only 0.3 µW at a heart rate of 60 bpm. CONCLUSION: Leadless PMs are able to synchronize their action using CIC and may overcome the key limitation of contemporary leadless PMs.

An Intracardiac Flow Based Electromagnetic Energy Harvesting Mechanism for Cardiac Pacing.

Contemporary cardiac implantable electronic devices such as pacemakers or event recorders are powered by primary batteries. Device replacement due to battery depletion may cause complications and is costly. The goal of energy harvesting devices is to power the implant with energy from intracorporeal power sources such as vibrations and blood flow. By replacing primary batteries with energy harvesters, reinterventions can be avoided and the size of the total device might be reduced. This paper introduces a device with a lever, which is deflected by the blood stream within the right ventricular outflow tract (RVOT), an attractive site for cardiac pacing. The resulting torque is converted to electrical energy by an electromagnetic mechanism. The blood flow harvester weighs 6.4 g and has a volume of 2 cm3, making the harvester small enough for catheter implantation. It was tested in an experimental setup mimicking flow conditions in the RVOT. The blood flow harvester generated a mean power of 14.39 ± 8.38 µW at 60 bpm (1 Hz) and up to 82.64 ± 17.14 µW at 200 bpm (3.33 Hz) during bench experiments at 1 m/s peak flow velocity. Therefore, it presents a viable alternative to power batteryless and leadless cardiac pacemakers.

Endocardial Energy Harvesting by Electromagnetic Induction.

OBJECTIVE: cardiac pacemakers require regular medical follow-ups to ensure proper functioning. However, device replacements due to battery depletion are common and account for ∼25% of all implantation procedures. Furthermore, conventional pacemakers require pacemaker leads which are prone to fractures, dislocations or isolation defects. The ensuing surgical interventions increase risks for the patients and costs that need to be avoided. METHODS: in this study, we present a method to harvest energy from endocardial heart motions. We developed a novel generator, which converts the heart's mechanical into electrical energy by electromagnetic induction. A mathematical model has been introduced to identify design parameters strongly related to the energy conversion efficiency of heart motions and fit the geometrical constraints for a miniaturized transcatheter deployable device. The implemented final design was tested on the bench and in vivo. RESULTS: the mathematical model proved an accurate method to estimate the harvested energy. For three previously recorded heart motions, the model predicted a mean output power of 14.5, 41.9, and 16.9 µW. During an animal experiment, the implanted device harvested a mean output power of 0.78 and 1.7 µW at a heart rate of 84 and 160 bpm, respectively. CONCLUSION: harvesting kinetic energy from endocardial motions seems feasible. Implanted at an energetically favorable location, such systems might become a welcome alternative to extend the lifetime of cardiac implantable electronic device. SIGNIFICANCE: the presented endocardial energy harvesting concept has the potential to turn pacemakers into battery- and leadless systems and thereby eliminate two major drawbacks of contemporary systems.

Leadless Dual-Chamber Pacing: A Novel Communication Method for Wireless Pacemaker Synchronization.

Contemporary leadless pacemakers only feature single-chamber pacing capability. This study presents a prototype of a leadless dual-chamber pacemaker. Highly energy-efficient intrabody communication was implemented for wireless pacemaker synchronization. Optimal communication parameters were obtained by in vivo and ex vivo measurements in the heart and blood. The prototype successfully performed dual-chamber pacing in vivo. The presented wireless communication method may in the future also enable leadless cardiac resynchronization therapy.

Towards Batteryless Cardiac Implantable Electronic Devices-The Swiss Way.

Energy harvesting devices are widely discussed as an alternative power source for todays active implantable medical devices. Repeated battery replacement procedures can be avoided by extending the implants life span, which is the goal of energy harvesting concepts. This reduces the risk of complications for the patient and may even reduce device size. The continuous and powerful contractions of a human heart ideally qualify as a battery substitute. In particular, devices in close proximity to the heart such as pacemakers, defibrillators or bio signal (ECG) recorders would benefit from this alternative energy source. The clockwork of an automatic wristwatch was used to transform the hearts kinetic energy into electrical energy. In order to qualify as a continuous energy supply for the consuming device, the mechanism needs to demonstrate its harvesting capability under various conditions. Several in-vivo recorded heart motions were used as input of a mathematical model to optimize the clockworks original conversion efficiency with respect to myocardial contractions. The resulting design was implemented and tested during in-vitro and in-vivo experiments, which demonstrated the superior sensitivity of the new design for all tested heart motions.

[Future cardiac pacemakers ­ technical visions]. / Der Herzschrittmacher der Zukunft - technische Visionen.

Cardiac pacemakers are routinely used for the treatment of bradyarrhythmias. Contemporary pacemakers are reliable and allow for a patient specific programming. However, pacemaker replacements due to battery depletion are common (~25 % of all implantation procedures) and bear the risk of complications. Batteryless pacemakers may allow overcoming this limitation. To power a batteryless pacemaker, a mechanism for intracorporeal energy harvesting is required. Such a generator may consist out of subcutaneously implanted solar cells, transforming the small amount of transcutaneously available light into electrical energy. Alternatively, intravascular turbines may harvest energy from the blood flow. Energy may also be harvested from the ventricular wall motion by a dedicated mechanical clockwork converting motion into electrical energy. All these approaches have successfully been tested in vivo. Pacemaker leads constitute another Achilles heel of contemporary pacemakers. Thus, leadless devices are desired. Miniaturized pacemaker circuits and suitable energy harvesting mechanisms (incorporated in a single device) may allow catheter-based implantation of the pacemaker in the heart. Such miniaturized battery- and leadless pacemakers would combine the advantages of both approaches and overcome major limitations of today's systems.

The first batteryless, solar-powered cardiac pacemaker.

BACKGROUND: Contemporary pacemakers (PMs) are powered by primary batteries with a limited energy-storing capacity. PM replacements because of battery depletion are common and unpleasant and bear the risk of complications. Batteryless PMs that harvest energy inside the body may overcome these limitations. OBJECTIVE: The goal of this study was to develop a batteryless PM powered by a solar module that converts transcutaneous light into electrical energy. METHODS: Ex vivo measurements were performed with solar modules placed under pig skin flaps exposed to different irradiation scenarios (direct sunlight, shade outdoors, and indoors). Subsequently, 2 sunlight-powered PMs featuring a 4.6-cm(2) solar module were implanted in vivo in a pig. One prototype, equipped with an energy buffer, was run in darkness for several weeks to simulate a worst-case scenario. RESULTS: Ex vivo, median output power of the solar module was 1963 µW/cm(2) (interquartile range [IQR] 1940-2107 µW/cm(2)) under direct sunlight exposure outdoors, 206 µW/cm(2) (IQR 194-233 µW/cm(2)) in shade outdoors, and 4 µW/cm(2) (IQR 3.6-4.3 µW/cm(2)) indoors (current PMs use approximately 10-20 µW). Median skin flap thickness was 4.8 mm. In vivo, prolonged SOO pacing was performed even with short irradiation periods. Our PM was able to pace continuously at a rate of 125 bpm (3.7 V at 0.6 ms) for 1½ months in darkness. CONCLUSION: Tomorrow's PMs might be batteryless and powered by sunlight. Because of the good skin penetrance of infrared light, a significant amount of energy can be harvested by a subcutaneous solar module even indoors. The use of an energy buffer allows periods of darkness to be overcome.

Successful pacing using a batteryless sunlight-powered pacemaker.

AIMS: Today's cardiac pacemakers are powered by batteries with limited energy capacity. As the battery's lifetime ends, the pacemaker needs to be replaced. This surgical re-intervention is costly and bears the risk of complications. Thus, a pacemaker without primary batteries is desirable. The goal of this study was to test whether transcutaneous solar light could power a pacemaker. METHODS AND RESULTS: We used a three-step approach to investigate the feasibility of sunlight-powered cardiac pacing. First, the harvestable power was estimated. Theoretically, a subcutaneously implanted 1 cm(2) solar module may harvest ∼2500 µW from sunlight (3 mm implantation depth). Secondly, ex vivo measurements were performed with solar cells placed under pig skin flaps exposed to a solar simulator and real sunlight. Ex vivo measurements under real sunlight resulted in a median output power of 4941 µW/cm(2) [interquartile range (IQR) 3767-5598 µW/cm(2), median skin flap thickness 3.0 mm (IQR 2.7-3.3 mm)]. The output power strongly depended on implantation depth (ρSpearman = -0.86, P < 0.001). Finally, a batteryless single-chamber pacemaker powered by a 3.24 cm(2) solar module was implanted in vivo in a pig to measure output power and to pace. In vivo measurements showed a median output power of >3500 µW/cm(2) (skin flap thickness 2.8-3.84 mm). Successful batteryless VVI pacing using a subcutaneously implanted solar module was performed. CONCLUSION: Based on our results, we estimate that a few minutes of direct sunlight (irradiating an implanted solar module) allow powering a pacemaker for 24 h using a suitable energy storage. Thus, powering a pacemaker by sunlight is feasible and may be an alternative energy supply for tomorrow's pacemakers.

Energy harvesting from the cardiovascular system, or how to get a little help from yourself.

Human energy harvesting is envisioned as a remedy to the weight, the size, and the poor energy density of primary batteries in medical implants. The first implant to have necessarily raised the idea of a biological power supply was the pacemaker in the early 1960s. So far, review articles on human energy harvesting have been rather unspecific and no tribute has been given to the early role of the pacemaker and the cardiovascular system in triggering research in the field. The purpose of the present article is to provide an up-to-date review of research efforts targeting the cardiovascular system as an alternative energy source for active medical implants. To this end, a chronological survey of the last 14 most influential publications is proposed. They include experimental and/or theoretical studies based on electromagnetic, piezoelectric, or electrostatic transducers harnessing various forms of energy, such as heart motion, pressure gradients, and blood flow. Technical feasibility does not imply clinical applicability: although most of the reported devices were shown to harvest an interesting amount of energy from a physiological environment, none of them were tested in vivo for a longer period of time.