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Accepted Manuscripts

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research-article  
M. Nicolas, B. Lucea, A. Laborda, E. Peña, M. A. De Gregorio, M. A. Martínez and M. Malvè
J. Med. Devices   doi: 10.1115/1.4035983
Anticoagulants are the treatment of choice for pulmonary embolism. When these fail or are contraindicated, vena cava filters are effective devices for preventing clots from the legs from migrating to the lung. Many uncertainties exist when a filter is inserted, especially during physiological activity such as normal breathing and the Valsalva manoeuvre. These activities are often connected with filter migration and vena cava damage due to the various related vein geometrical configurations. In this work we analysed the response of the vena cava during normal breathing and Valsalva manoeuvre, for a healthy vena cava and after insertion of a commercial Günther-Tulip filter. Computational fluid dynamics (CFD) and patient specific data are used for analysing blood flow inside the vena cava during these manoeuvres. While during normal breathing the vena cava flow can be considered almost stationary with a very low pressure gradient, during Valsalva the extravascular pressure compresses the vena cava resulting in a drastic reduction of the vein section, a global flow decrease through the cava but increasing the velocity magnitude. This change in section is altered by the presence of the filter which forces the section of the vena cava before the renal veins to keep open. The effect of the presence of the filter is investigated during these manoeuvres showing changes in wall shear stress and velocity patterns.
research-article  
Nathan Banka, Yau Luen Ng and Santosh Devasia
J. Med. Devices   doi: 10.1115/1.4035984
This paper introduces a new design for individually controlled magnetic artificial cilia for use in fluid devices, and specifically intended to improve the mixing in DNA microarray experiments. The design has been implemented using a low-cost prototype that can be fabricated using polydimethylsiloxane (PDMS) and off-the-shelf parts, and achieves large cilium deflections (59% of the cilium length). The device's performance is measured via a series of mixing experiments using different actuation patterns inspired by the blinking vortex theory. The experimental results, quantified using the relative standard deviation of the color when mixing two colored inks, show that exploiting the individual control leads to faster mixing (38% reduction in mixing time) than when operating the device in a simultaneous-actuation mode with the same average cilium beat frequency. Furthermore, the experimental results show an optimal beating pattern that minimizes the mixing time. The existence and character of this optimum is predicted by simulations using a blinking-vortex approach for 2D ideal flow, suggesting that the blinking-vortex model can be used to predict the effect of parameter variation on the experimental system.
Technical Brief  
Disha N. Dutta, Reshmi Das and Saurabh Pal
J. Med. Devices   doi: 10.1115/1.4035982
In this article, the design and development of a real-time heart rate (HR) and respiratory rate (RR) monitoring device is reported. The proposed device is designed to impose minimum data acquisition hazards on the subject. In standard bedside monitors, HR and RR are derived from ECG and respiration signals, respectively, and different electrodes are required for capturing the 12-lead ECG and respiration via a chest belt, which is cumbersome for patients and healthcare providers. Respiration signal has an impact on ECG due to anatomical proximity of the heart and lung, and ECG is modulated by respiration,a phenomenon known as Respiratory Sinus Arrhythmia (RSA). In the proposed method, the ECG signal is acquired using clip electrodes at the wrists and the respiration signal is extracted from the ECG using an Arduino Uno microcontroller-based real-time processing of ECG. RR is then derived from ECG-derived Respiration (EDR). The prototype is tested on healthy subjects and compared to measurements taken using a standard MP45 data acquisition device associated with a Biopac Student Lab (BSL). A mean percentage error of 5.54±8.48% was observed under normal breathing conditions and an error of -3.41 ±3.27% was observed for a single subject tested under a variety of breathing conditions, such as resting, stair-climbing, and paced breathing. The proposed algorithm can also be used in combination with standard ECG monitoring systems to measure HR and RR, without any data acquisition hazard to the subject.
research-article  
Gokce Nur Oguz, Senol Piskin, Erhan Ermek, Samir Donmazov, Naz Altekin, Ahmet Arnaz and Kerem Pekkan
J. Med. Devices   doi: 10.1115/1.4035981
Recent clinical studies showed that the hemodynamic energy loss of the surgical conduit used in 3rd-stage repair of single-ventricle heart defects (Fontan surgery) determines the post-operative exercise capacity. Still, our understanding of the Fontan pathway energy loss is based on fully-functional conduits that are acquired from patients with optimal post-operative health, while a significant portion of the patients struggle with severe complications due to their gradually failing physiology. In this study, the hemodynamics of severely deformed surgical pathways due to torsional deformation and anastomosis offset, are investigated. We designed a mock-up circuit to replicate the mechanically failed inferior vena cava (IVC) anastomosis morphologies under physiological venous pressure (9, 12, 15 mmHg), in vitro, employing the commonly used conduit materials; PTFE, Dacron and porcine pericardium. For three twist angles (0°, 30°, 60°) and caval offsets (0Diameter, 0.5D and 1D) conduit shapes are digitized in 3D and employed in computational fluid dynamic simulations to determine the corresponding hydrodynamic efficiency levels. A total of 81 deformed configurations are analyzed in which the pressure drop values increased 80 to 1070 % with respect to the uniform diameter IVC conduit. Surgical materials resulted significant variations in terms of flow separation and energy loss. The porcine pericardium and PTFE conduit resulted 8 and 3 times more pressure drop than the Dacron conduit, respectively. If anastomosis twist and/or offset cannot be avoided due to the patients anatomy, alternative materials with high structural stiffness can be considered.
research-article  
Enda L. Boland, James A. Grogan and Peter E. McHugh
J. Med. Devices   doi: 10.1115/1.4035895
Coronary stents made from degradable biomaterials such as magnesium alloy are an emerging technology in the treatment of coronary artery disease. Biodegradable stents provide mechanical support to the artery during the initial scaffolding period after which the artery will have remodelled. The subsequent resorption of the stent biomaterial by the body has potential to reduce the risk associated with long term placement of these devices such as in-stent restenosis, late stent thrombosis. Computational modelling such as finite element analysis has proven to be an extremely useful tool in the continued design and development of these medical devices. What is lacking in computational modelling literature is the representation of the active response of the arterial tissue in the weeks and months following stent implantation (neointimal remodelling). The phenomenon of neointimal remodelling is particularly interesting and significant in the case of biodegradable stents, when both stent degradation and neointimal remodelling can occur simultaneously, presenting the possibility of a mechanical interaction and transfer of load between the degrading stent and the remodelling artery. In this paper a computational modelling framework is developed that combines magnesium alloy degradation and neointimal remodelling, that is capable of simulating both uniform (best case) and localised pitting (realistic) stent corrosion in a remodelling artery. The framework is used to evaluate the effects of the neointima on the mechanics of the stent, when the stent is undergoing uniform or pitting corrosion, and to assess the effects of the neointimal formation rate relative to the overall stent degradation rate.
TOPICS: Magnesium (Metal), Corrosion, Equipment performance, Modeling, stents, Biodegradation, Biomaterials, Magnesium alloys, Stress, Design, Finite element analysis, Medical devices, Risk, Thrombosis, Coronary arteries, Diseases, Biological tissues
research-article  
Jan L Bruse, Giuliano Giusti, Catriona Baker, Elena Cervi, Tain-Yen Hsia, Andrew M Taylor and Silvia Schievano
J. Med. Devices   doi: 10.1115/1.4035865
Patients born with a single functional ventricle typically undergo three-staged surgical palliation in the first years of life, with the last stage realizing a cross-like total cavopulmonary connection (TCPC) of superior and inferior vena cavas (SVC, IVC) with both left and right pulmonary arteries, allowing all deoxygenated blood to flow passively back to the lungs (Fontan circulation). Even though within the past decades more patients survive into adulthood, the connection comes at the prize of deficiencies such as chronic systemic venous hypertension and low cardiac output, which ultimately may lead to Fontan failure. Studies have suggested that the TCPC's inherent insufficiencies might be addressed by adding a cavopulmonary assist device (CPAD) to provide the necessary pressure boost. While many device concepts are being explored, few take into account the complex cardiac anatomy typically associated with TCPCs. In this study, we focus on the extra cardiac conduit vascular graft connecting IVC and pulmonary arteries as one possible landing zone for a CPAD and describe its geometric variability in a cohort of 18 patients that had their TCPC realized with a 20mm vascular graft. We report traditional morphometric parameters and apply statistical shape modeling to determine the main contributors of graft shape variability. We further compute the anatomical mean 3D graft shape (template graft) as a representative of key shape features of our cohort and proved this template graft to be a significantly better approximation of population and individual patient's hemodynamics than a commonly used simplified tube geometry.
TOPICS: Modeling, Geometry, Hemodynamics, Shapes, Pulmonary artery, Anatomy, Lung, Pressure, Flow (Dynamics), Blood, Surgery, Approximation, Failure
Technical Brief  
Tina M. Morrison, Maureen L. Dreher, Srinidhi Nagaraja, Leonardo M. Angelone and Wolfgang Kainz
J. Med. Devices   doi: 10.1115/1.4035866
The total product life cycle (TPLC) of medical devices has been defined by four stages: discovery and ideation, regulatory decision, product launch, and post-market monitoring. Manufacturers of medical devices intended for use in the peripheral vasculature, such as stents, inferior vena cava filters and stent-grafts, mainly use computational modeling and simulation (CM&S) to aid device development and design optimization, supplement bench testing for regulatory decisions, and assess post-market changes or failures. For example, computational solid mechanics and fluid dynamics enable the investigation of design limitations in the ideation stage. To supplement bench data in regulatory submissions, manufactures can evaluate the effects of anatomical characteristics and expected in vivo loading environment on device performance. Manufacturers might also harness CM&S to aid root-cause analyses that are necessary when failures occur post-market, when the device is exposed to broad clinical use. Once identified, CM&S tools can then be used for redesign to address the failure mode, and re-establish the performance profile with the appropriate models. The Center for Devices and Radiological Health (CDRH) wants to advance the use of CM&S for medical devices and supports the development of virtual physiological patients, clinical trial simulations, and personalized medicine. Thus, the purpose of this paper is to describe specific examples of how CM&S is currently used to support regulatory submissions at different phases of the TPLC, and to present some of the stakeholder-led initiatives for advancing CM&S for regulatory decision-making.
TOPICS: Computer simulation, Simulation, Cardiovascular devices, Cycles, Medical devices, Design, Failure, stents, Physiology, Biomedicine, Root cause analysis, Filters, Decision making, Failure mechanisms, Optimization, Solid mechanics, Testing, Fluid dynamics
research-article  
Lorenza Petrini, Elena Dordoni, Dario Allegretti, Desiree Pott, Maximilian Kütting, Francesco Migliavacca and Giancarlo Pennati
J. Med. Devices   doi: 10.1115/1.4035791
Nowadays, transcatheter aortic valve (TAV) replacement is an alternative to surgical therapy in selected high risk patients for the treatment of aortic stenosis. However, left ventricular contraction determines a severe cyclic loading for the implanted stent-frame, undermining its long-term durability. Technical standards indicate in vitro tests as a suitable approach for the assessment of TAV fatigue behavior: generally, they do not specify test methods but require to test TAV in the worst loading conditions. The most critical conditions could be different according to the specific valve design, hence the compartment where deploying the valve has to be properly identified. A fast and reliable computational methodology could significantly help to face this issue. In this paper, a numerical approach to analyze Nickel-Titanium TAV stent-frame behavior during in vitro durability tests is proposed. A simplified multi-stage strategy was adopted where, in each stage, only two of the three involved components are considered. As a proof-of-concept the method was applied to a TAV prototype. Despite its simplifications, the developed computational framework gave useful insights into the stent-frame failures behaviour during a fatigue test. Numerical results agree with experimental findings. In particular, the most dangerous condition was identified among a number of experimental tests, where different compartments and pressure gradients were investigated. The specific failure location was also correctly recognized. In conclusion, the presented methodology provides a tool to support the choice of proper testing conditions for the in vitro assessment of TAV fatigue behavior.
TOPICS: Fatigue, Valves, Nickel titanium alloys, stents, Failure, Durability, Surgery, Testing, Fatigue testing, Nickel, Engineering standards, Engineering prototypes, Design, Titanium, Risk, Patient treatment, Pressure gradient
research-article  
Rosa Shine, Reyhaneh Neghabat Shirazi, William Ronan, Caoimhe A Sweeney, Nicola Kelly, Yury A Rochev and Peter E McHugh
J. Med. Devices   doi: 10.1115/1.4035723
The interest in biodegradable polymers for clinical and biomedical engineering applications has seen a dramatic increase in the last ten years. Recent innovations include bioresorbable polymeric stents (BPS); temporary vascular scaffolds designed to restore patency and provide short-term support to a blocked blood vessel. BPS offer possibilities to overcome the long-term complications often observed with permanent stents, well established in the treatment of vascular disease. From the perspective of designing next generation BPS, the bulk degradation behaviour of the polymer material adds considerable complications. Computational modelling offers an efficient framework to predict the behaviour of medical devices and implants. Current computational modelling techniques for the degradation of BPS are either phenomenologically or physically-based. In this work, a physically-based polymer degradation model is implemented into a number of computational frameworks to investigate the degradation of a number of polymeric structures. A thermal analogy is presented to implement the degradation model into the commercially available finite element code, Abaqus/Standard. This approach is then applied to the degradation of BPS, and the effects of material, boundary condition and design on the degradation rates of the stents are examined. The results indicate that there is a notable difference in the molecular weight trends predicted for the different materials and boundary condition assumptions investigated, with autocatalysis emerging as a dominant mechanism controlling the degradation behaviour. Insights into the scaffolding ability of the various BPS examined are then obtained using a suggested general relationship between Young's modulus and molecular weight.
TOPICS: Modeling, stents, Biodegradation, Polymers, Boundary-value problems, Design, Molecular weight, Young's modulus, Finite element analysis, Medical devices, Biomedical engineering, Blood vessels, Diseases
research-article  
Kent Grove, Steve M Deline, Tim F Schatz, Sarah E Howard, Deanna Porter and Mark E Smith
J. Med. Devices   doi: 10.1115/1.4035724
ISO 10993-4 in vivo thrombogenicity testing is required for regulatory approval of all blood-contacting medical devices and is often a key part of submission packages. Given the current state of in vivo thrombogenicity assays, the industry needs a more robust and reproducible assay design including in vitro models. This study describes an in vitro assay which integrates freshly-harvested ovine blood containing minimal heparin in a closed pumped loop. To confirm the reproducibility of this assay, control materials were identified which elicited either a positive or a negative thrombogenic response. These controls were used over a 13 month period, successfully demonstrating reproducibility in the resulting thrombogenicity scores, and were then used in a head-to-head comparison with an in vivo thrombogenicity study using a marketed, approved catheter as test article. Thrombogenicity scoring with the positive and negative controls was consistent over the 24 independent assays with >95% confidence (p = 1.0 for negative controls and p = 0.55 for positive controls) when in vitro results were compared to the in vivo assay. This in vitro blood loop method allows prediction of a materials' in vivo thrombogenicity, can substantially de-risk the materials or coating selection process and should replace the in vivo models currently in use.
TOPICS: Blood, Medical devices, Testing, Assaying, Catheters, Risk, Design, Coating processes, Coatings
research-article  
Anastasios Raptis, Michalis Xenos, Efstratios Georgakarakos, George Kouvelos, Athanasios Giannoukas and Miltiadis Matsagkas
J. Med. Devices   doi: 10.1115/1.4035687
Endovascular aneurysm repair (EVAR) is a clinically effective technique for treating anatomically eligible abdominal aortic aneurysms (AAAs), involving the deployment of an endograft (EG) that is designed to prevent blood leakage in the aneurysmal sac. While most EGs have equivalent operating principles, the hemodynamic environment established by different EGs is not necessarily the same. So, to unveil the post-EVAR hemodynamic properties, we need an EG-specific computational approach that currently lacks from the literature. Endurant and Excluder are two EGs with similar pre-installation designs. We assumed that the flow conditions in the particular EGs do not vary significantly. The hypothesis was tested combining image reconstructions, computational fluid dynamics (CFD) and statistics, taking into account the post-implantation position of the EGs. Ten patients with Endurant EGs and ten patients with Excluder EGs were included in the study. The two groups were matched with respect to the preoperative morphological characteristics of the AAAs. The EG models derived from image reconstructions of postoperative computed tomography scans. Wall shear stress (WSS), displacement force, velocity, and helicity were calculated in regions of interest within the EG structures, i.e. the main body, the upper and the lower part of the limbs. Excluder generated higher WSS compared to Endurant, especially on the lower part of the limbs (p=0.001)...
TOPICS: Hemodynamics, Accounting, Image reconstruction, Aneurysms, Computational fluid dynamics, Computerized tomography, Displacement, Flow (Dynamics), Maintenance, Blood, Leakage, Statistics as topic, Shear stress
Technical Brief  
Hoda Sharei, Ronald Stoute, John J van den Dobbelsteen, Maria Siebes and Jenny Dankelman
J. Med. Devices   doi: 10.1115/1.4035545
Background: As the connection at the proximal tip plays an important role for sensing guidewires, we compared various sensing guidewires with regard to their proximal connectors. The strengths and weaknesses of each are discussed and recommendations for future development are provided. Method: A literature search was carried out on the USPTO database, Espacenet and Web of Science and was limited to the English language for the time period from the 1960s to the 2010s. The results were categorized on the basis of the connector design. Results: A comprehensive overview and classification of proximal connectors for sensing guidewires used for cardiovascular interventions is presented. The classification is based on the type of connector (fixed or removable) and the type of connection (physical, wireless, or a combination). Conclusion: Considering the complexity of the currently prototyped and tested connectors, future connector development will necessitate an easy and cost effective manufacturing process that can ensure safe and robust connections.
TOPICS: Manufacturing, Design, Cardiovascular system, Databases
Design Innovation Paper  
F. Mark Payne, Tony Connell and Jacob Rice
J. Med. Devices   doi: 10.1115/1.4030812
Background: Tissue expanders are used in breast reconstruction after mastectomy to create a space for placement of permanent breast implants. The AeroForm™ Tissue Expander, developed by AirXpanders™ Inc., utilizes carbon dioxide released from an internal reservoir to inflate the expander. The released gas is contained within a high barrier material pre-formed into a breast shaped shell of the desired volume. During patient travel to higher altitude, a partially inflated expander will increase in volume proportionately to the gas fill volume. At volume levels near full, expansion is governed by the compliance of the inner gas barrier and silicone shell. Therefore, the assessment of the expander performance at altitude consists of the analysis of two operating regimes. The first regime is fill levels < 70% full where the implant, when exposed to cabin pressure, expands without significantly stressing the inner gas barrier. The second is fill levels ~>70% where the response of the inner gas barrier is important, both in terms of structural capability and determination of the volume increase. We assessed the impact of pressurized flight on expander performance in both operating regimes. Findings: The volume increase associated with altitude increase to 8000 feet (maximum cabin altitude per FAA) is typically within the range administered during post-operative fills of saline expanders. Although assessment must be conducted by a clinician, a patient can be typically expected to tolerate the increased volume with some minor discomfort, such as a feeling of tightness. At higher fill levels, the structural capability of shell has been demonstrated to withstand the additional pressure loading. At these fill levels, the expander does not expand as much, due to the structural restraint of the shell. To date, 7 subjects have flown with the expander in situ during clinical trials. All subjects were required to temporarily cease dosing up to two weeks prior. Flight travel was completed uneventfully and they reported discomfort levels ranging from none to moderate. The recommendation to cease dosing two weeks prior to flying was made to allow the expected 1 cc per day of CO2 permeation to occur, which will result in slight deflation to accommodate for the expansion of the CO2 when flying. As expected, subjects reported a sensation of pressure upon ascent which subsided on descent.
TOPICS: Biological tissues, Carbon dioxide, Shells, Pressure, Flight, Reservoirs, Silicones

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