Endoscopic radiofrequency ablation has gained interest for treating abdominal tumors. The radiofrequency ablation electrode geometry largely determines the size and shape of the ablation zone. Mismatch between the ablation zone and tumor shapes leads to reoccurrence of the cancer. Recently, work has been published regarding a novel deployable multi-tine electrode for endoscopic radiofrequency ablation. The prior work developed a thermal ablation model to predict the ablation zone surrounding an electrode and a systematic optimization of the electrode shape to treat a specific tumor shape. The purpose of this work is to validate the thermal ablation model through experiments in a tissue phantom that changes color at ablation temperatures. The experiments highlight the importance of thermal tissue damage in finite element modeling. Thermal induced changes in tissue properties, if not accounted for in finite element modeling, can lead to significant overprediction of the expected ablation zone surrounding an electrode.

Since the early discovery in 1951 [1], shape memory alloys (SMAs) have been used in design and development of several innovative engineering systems. SMAs’ unique characteristics have introduced unconventional alternatives in design and development of advanced devices. SMA’s field of applications has covered many areas from aerospace to auto industries, and medical devices [2]. During the past couple of decades, scientists have suggested material models to predict the SMA’s shape memory effect (SME) and its superelastic behavior. The superelastic characteristic of SMAs (its capability to exhibit a large recoverable strain) has been widely used to develop innovative products including biomedical implants such as stents, artificial heart valves, orthodontic wires, frames of indestructible spectacles, etc. However, its actuation capabilities, known as SME, hasn’t been thoroughly expanded. The number of products privileging from SMA’s SME behavior has been very limited. The reason relies on the SMA’s complex material properties that depend on the stress, strain and temperature at every stage of actuation as well as the material’s processing and the thermomechanical loading history.

Colorectal surgery is widely performed to re-establish the bowel, the part of which is removed because of diverticulitis, intestinal polyps, inflammatory bowel and cancer. Stapled anastomosis is a highly standardized technique and considered the standard of care. However, complications like leakage, stenosis and postoperative bleeding cannot be completely avoided [1,2]. There is limited understanding of the impact of staplers on tissue and basic mechanics of tissue stapling. According to the previous research, compression, staple height, tissue thickness, tissue compressibility, and tissue type have an effect on the patient outcomes [3]. Hence, we conducted this prospective study to analyze the effect of staple height on tissue damage and compression pressure. An attempt was made to determine the relationship between the tissue height and the optimal closed staple height.

Fracture toughness is an important mechanical property of materials that describes the failure of material by cracking. Yet, characterizing fracture toughness in soft tissue cutting is still a challenging task as the behavior of the soft tissue may vary under different tissue, cutting and pre-crack conditions [1]. Predicting cutting force has been important to needle biopsy design, surgical planning/training, and other surgical operations. However, in order to obtain accurate predictions, understanding the fracture toughness is crucial. In this study, we present an approach to characterize the fracture toughness directly from cutting experiments of hollow needle cutting soft tissue mimicking materials. Cutting tests are carried out to obtain the dynamic force response of gelatin samples when being cut by non-rotational and rotational hollow needles. The data is used to establish a mixed-mode fracture behavior which is then used to implement a cohesive surface based finite element model. Nearly 1% difference of the axial cutting force between the simulation and experimental results showed that the approach is capable of predicting accurate cutting force in rotational needle biopsy. The approach also has the potential to be used to predict the cutting force in various types of needle biopsy.

Transcatheter closure of ventricular septal defect (VSD) has become an alternative therapy to open-chest surgery because of simple procedure, less invasion, and high safety [1–2]. The most important occluder device of the therapy is double-disc structure which occludes the VSD, with the discs of the occluder clamp the margin of VSD while the waist of the occluder supports the VSD hole (Figure 1(a)). Commercially available occluders are woven by 72 nitinol wires (Figure1(b)) and then formed by heat treatment. However, the implantation of metal occluders in perimembranous part will result in a substantial risk of complete atrioventricular block (cAVB) averaging 3.5%, because of its close proximity to the conduction system, which passes at the posterior border of defects [3]. To improve the biocompatibility, Huang [4] developed biodegradable VSD occluders (Figure 1(c)) which woven by polydioxanone (PDO) wires and can be fully absorbed within 24 weeks after implantation.

Endovascular aneurysm repair (EVAR) techniques have been widely used for the treatment of abdominal aortic aneurysm (AAA). EVAR is associated with lower postoperative morbidity and mortality than traditional surgical procedure to treat AAA [1]. However, during the patient’s follow-up, postoperative complications may occur and secondary interventions are required [2]. Stent-grafts fixation in the vessel affects the success of endovascular aneurysm repair. Researches indicate that insufficient stent-graft radial force is attributed to post-surgery complications, such as prosthesis migration and endoleak type I [3, 4]. Endoleak type I happens when there is not a complete contact between stent graft rings and vessel wall. A great radial force can prevent full obturation in the landing zone. The distal endograft fixation also has a great influence on proximal endograft migration after EVAR [5]. Therefore the radial force of the stent plays a significant role. Single stent-graft ring comprise a series of expandable Z-shaped structural elements (known as “struts”). Currently, there are series of Z-shaped stent-grafts on the market and the struts number ranges from 5 to 12. This work intends to analyze the influence of stent-graft struts number on the radial force. Finite-element analysis (FEA) and experimental method are used.

Vacuum-assisted biopsy (VAB) is a widely used technology to sample lesion tissue for breast cancer diagnosis. The technology is designed to retrieve tougher and larger breast tissue samples. The majority of VAB tools utilize a so-called rotational cutting method, in which the cutting needle simultaneously rotates and translates to produce both tangential and normal forces at the cutting surface of the tissue. The introduction of the tangential force can significantly reduce the cutting force measured in the axial direction. As a result, higher quality of tissue samples can be obtained as the samples are less deformed while being removed. The slice-push ratio, i.e. the ratio of the speed component parallel to the cutting edge to the speed component perpendicular to the cutting edge, was previously found to be the most important factor to influence the cutting force [1]. However, these studies only investigated the cases in low translational cutting speeds in a small-scale experiment. In this paper, we present a finite element (FE) model based on surface-based cohesive behavior, which simulates the rotational cutting method used in VAB to predict the progressive damage and the cutting force of soft tissue phantoms. The model is validated using the experimental data provided in the previous study [1]. The validated model will allow us to explore more cutting conditions, such as higher translational speeds, larger range of slice-push ratio, and tissue properties. The model can also be used to optimize design parameters of current VAB needles and to evaluate new VAB needle designs.

Breast lesion tissue can be extremely stiff, e.g. calcification or soft, e.g. adipose. When performing needle biopsy, too small or scanty samples can be retrieved due to the tissue is mainly compressed instead of being cut. In order to studying the tissue cutting performance in various cutting conditions, tissue-mimicking phantoms are frequently used as a surrogate of human tissue. The advantage of using tissue phantoms is that their mechanical properties can be controlled. The stiffness of a tissue phantom can be measured by an indentation test. Previous studies have demonstrated mathematic models to estimate Young’s moduli of tissue phantoms from force-displacement data with an adjustable coefficient according to the geometry of the indenter. Tissue force reactions occurred needle insertion has been largely researched [1], but few studies investigated the tissue cutting with a rotational needle, which is a cutting method largely used in the breast needle biopsy. Research has demonstrated that the influence of rotation can significantly reduce the insertion force [2], but the experiment was conducted on a specific formula of silicone-based tissue phantoms. This paper served as a pilot study of a large-scale experiment to study the effect of rotational cutting on various cutting conditions and target materials, including artificial and biological soft tissues. Two most common types of soft tissue phantoms, biopolymers (gelatin gels and agar) and chemically synthesized polymers (polydimethylsiloxane, PDMS) were investigated. Indentation tests were performed to estimate the mechanical properties of tissue phantoms which were then verified by finite element simulations. Tissue cutting tests with and without rotation were conducted to evaluate the effect of needle rotation on the tissue force reactions.

An implantable cardiac pacemaker is used to modify and treat irregular heartbeats [1] and invented in 1958 [2]. Devices have no fixation or fixed to the heart wall. No fixation leads lay in the bottom of heart cavities, while fixed leads have tines (passive) or a helix screw (active) to attach to the heart. Lead geometries and material properties vary between companies, with geometric sizing based primarily on the internal mechanics of the lead. Finite element analysis (FEA), computational fluid dynamics (CFD) and bench-top simulations are used to evaluate cardiac leads. These simulations analyze only one lead and struggle to compare and test variations in lead designs. Advanced computational resources can run many computer simulations of anatomical environments, however model complexity increases the time to run each simulation. To address this issue, we present a simplified parameterized design space for cardiac pacemaker leads in the right atrium. This information will be used to run multiple simulations of leads in blood flow, for visualization in a single virtual reality (VR) environment and allow the designer to iterate through many design variations (See Figure 1).

A Stellite 25 17mm tube valve based upon the Björk-Shiley Monostrut (BSM) valve design was developed for use in the Penn State Pediatric Ventricular Assist Device (PVAD) pump [1]. The hook of the valve was designed to hold a Delrin occluding disc in place while allowing the disc to tilt open 70 degrees from the closed position. Unlike common design constraints which remain in the elastic region, the hook experiences plastic deformation twice during the assembly process, making the material choice of Stellite 25 imperative. Stellite 25 is a cobalt-chromium-tungsten-nickel alloy (Co-20Cr-15W-10Ni) belonging to the material family of superalloys which are commonly used for wear-resistant applications exposed to heat, abrasion, and galling [2, 3]. Along with its excellent in vivo corrosion resistance [4], Stellite 25 exhibits high strength and ductility which permit the hook to be plastically deformed during disc installation while remaining below the strain to failure [3, 4]. Together these qualities make Stellite 25 an ideal material choice for the 17mm tube valve application. Predicting the resultant stresses and strains is critical for determining the safety and structural reliability of the Stellite 25 17mm tube valve for the PVAD after assembly. After performing finite element analysis (FEA), the simulation results were validated by deflection experiments and metallurgical investigations.

The Edwards SAPIEN transcatheter heart valve (Figure 1) is designed for heart valve replacement in patients with severe aortic stenosis without open-heart surgery. Physiological FEA analyses have been performed to provide an assessment of the fracture and fatigue resistance of the device during deployment and operation. The present study validates FEA frame models by comparing the crimping behavior of the FEA models with the results of crimping experiments.

A patient-specific computational finite element modeling of the abdominal wall (AW) has been developed to enable biomechanical analysis for customizing and optimizing AW surgical treatments. The methodology consisted on the identification by reverse engineering of patient-specific AW characteristics for physiological pressure settings. The approach combined in vivo experiments and numerical simulations. As a first application, a patient specific model was used to simulate mid-line incision closure technique.

Patient-specific models have been recently applied to investigate a wide range of cardiovascular problems including cardiac mechanics, hemodynamic conditions and structural interaction with devices [1]. The development of dedicated computational tools which combined the advances in the field of image elaboration, finite element (FE) and computational fluid-dynamic (CFD) analyses has greatly supported not only the understanding of human physiology and pathology, but also the improvement of specific interventions taking into account realistic conditions [2, 3]. However, the translation of these technologies into clinical applications is still a major challenge for the engineering modeling community, which has to compromise between numerical accuracy and response time in order to meet the clinical needs [4]. Hence, the validation of in silico against in vivo results is crucial. Finally, if the development of novel tools has recently attracted big investments [5], it has not been similarly easy to dedicate funds and time to test the developed technologies on large numbers of patient cases.

A proof of concept workflow is demonstrated to easily translate 3D medical image data into finite element (FE) simulation ready phantom models. First, novel methods are used to drastically reduce manual segmentation time for a virtual population. Next, using Simpleware software, the segmented voxel datasets are extracted into faceted 3D CAD objects for tissues, while simultaneously maintaining conformal multi-tissue interfaces. Finally, the 3D CAD geometries are demonstrated to be readily compatible in a commercial 3D electromagnetic simulator, ANSYS HFSS.

Many surgeons have come to view mitral valve (MV) repair as the treatment of choice in patients with mitral regurgitation (MR) [1]. According to recent long-term studies, the recurrence of significant MR after repair may be much higher than previously believed, particularly in patients with (ischemic mitral regurgitation) IMR [2]. We hypothesize that the restoration of homeostatic normal MV leaflet tissue stress in IMR repair techniques ultimately leads to improved repair durability. Therefore, the objective of this study is to develop a novel micro-anatomically accurate 3D finite element (FE) model that incorporates detailed collagen fiber architecture, accurate constitutive models, and micro-anatomically realistic valvular geometry to investigate the functional mitral valve and to aid in the assessment of the mitral valve repairs, especially the linking between the interstitial cellular deformations at the cellular level, the mechanobiological behaviors at the tissue level and the organ level mechanical responses as normal and repaired mitral valves maintaining their homeostatic state.

Atrial fibrillation (AF) is a cardiac rhythm disorder characterized by rapid, erratic muscle contraction without concordant chamber motion. Given the rising prevalence of AF and failures of pharmaceutical therapies, clinicians have increasingly used radiofrequency (RF) ablation to electrically isolate the abnormal tissue [1]. A typical ablation procedure (PVI) electrically isolates the pulmonary veins (PV) by encircling them with lesions and has a 60% success rate [2]. More aggressive procedures have been proposed to increase the success rate, including wide-area circumferential ablation (WACA), which add more lesions without considering the functional impact of additional scarring [3]. The objective of this study was to develop a finite element model of a healthy left atrium, capable of simulating passive filling during ventricular systole, and explore the functional impact of ablation by simulating various scar patterns.

The tibiofemoral joint is a complex structure and its overall mechanical response is dictated by its numerous substructures at both macro and micro levels. An in-depth understanding of the mechanics of the joint is necessary to develop preventative measures and treatment options for pathological conditions and common injuries. Finite element (FE) analysis is a widely used tool in joint biomechanics studies focused on understanding the underlying mechanical behavior at joint, tissue and cell levels [1]. Studies, regardless of their purpose (descriptive or predictive), when employing FE analysis, require anatomical and mechanical data at single or multiple scales. It is also critical that FE representations are validated and closely represent specifics of the joint of interest, anatomically and mechanically. This is an utmost need if these models are intended to be used to support clinical decision making (in surgery or for rehabilitation) and for the development of implants.

A comparative finite element analysis (FEA) model was developed to predict the relative stresses and strains in Zimmer NexGen ® Trabecular Metal ™ Tibial Cone components. The FEA predictions were compared to measurements obtained through physical testing. The model was validated for its ability to correctly rank the order of predicted strain in the components under applied load.

In this article we present a finite element simulation of an active steerable surgical needle. The highly maneuverable actuated needle can be utilized in many cases involving diagnostic and therapeutic percutaneous procedures; for example, in prostate brachytherapy. To make the surgical needle able to navigate through the tissue accurately, avoiding sensitive organs, external bending forces are being provided by smart actuators attached to the needle body (see Fig. 1). The shape memory alloy (SMA) wires, namely Nitinol, with unique properties of super-elasticity, shape memory effect, and biocompatibility are suitable as an actuator. The attached SMA wires contract when heated due to the phase transformation and therefore bends the needle. A 3D finite element (FE) model of the SMA actuated steerable needle was developed and validated by a prototype to show the feasibility of the design and also to study the factors influencing needle deflection.

Design of an artificial knee was developed using computer 3-D modeling, the high flexion knee was obtained by using a multi-radii design pattern, The increase of final 20 degrees in flexion was obtained by increasing the condylar radii of curvature. The model of the high flexion knee was developed and one of the models was subjected to finite element modeling and analysis. The compositions of components in the artificial knee were, femoral component and the tibial component were metal, whereas the patellar component and the meniscal insert were made using polyethylene. The metal component used for the analysis in this study was Ti6Al4V and the polyethylene used was UHMWPE. Overall biomaterials chosen were: meniscus (UHMWPE, mass = 0.0183701 kg, volume = 1.97518e-005 m3), tibial component (Ti6Al4V, mass = 0.0584655 kg, volume = 1.32013e-005 m3), femoral component (Ti6Al4V, mass = 0.153122 kg, volume = 3.45742e-005 m3), total artificial assembly (mass = 0.229958 kg, volume = 6.75e-005m3). However, in this design the load had been taken to 10 times the body weight. The weight over single knee is only half the maximum load as the load is shared between the two knee joints. Following were the loading conditions, taking average body weight to be 70Kgs and taking extreme loading conditions of up to 10 times the body weight, i.e. 700Kgs on each of the leg performed the Finite Element Analysis (FEA) over the newly designed knee. The loading was done at an increment of 100 Kgs. The loading conditions and the meshing details for the analysis of the assembly were Jacobian check: 4 points, element size: 0.40735 cm, tolerance: 0.20367 cm, quality: high, number of elements: 80909, number of nodes: 126898. A maximum load of 600 Kgs is optimum for this model. The other components observed linear elastic behavior for the applied loads. Based on these results it was determined that the load bearing capacity of the model were well within the failure levels of the materials used for the analysis. A maximum load of 600 Kgs is optimum for this model. The other components observed linear elastic behavior for the applied loads. Based on these results it was determined that the load bearing capacity of the model were well within the failure levels of the materials used for the analysis. Conclusion drawn from this is that for the first time an innovative new design of an artificial knee joint to suite a segment of some religious population has been developed. This allows them to pray, bend in different positions and squat without too much difficulty.