Lorenza Petrini

• Politecnico di Milano

Purpose This study aims to develop a realistic 3D printing-based simulator for the training and planning of the left atrial appendage occlusion (LAAO) to be used in the cath lab. Design/methodology/approach Starting from a pre-operative computed tomography dataset of a patient already treated with LAAO, the model was obtained, consisting in the ri...

The fatigue failure of Ni–Ti peripheral stents still represents an open issue of major concern due to the non-linear material behavior, the complex loads acting in vivo, and the manufacturing process. The fatigue assessment currently exploits total-life methodologies devoted to preventing crack nucleation. This work investigates a complementary fra...

Damage-tolerant approaches, relying on fracture mechanics, are powerful tools adopted in many engineering sectors to predict the initiation and propagation of fracture. In the last two decades, there has been a growing interest in extending these methods to shape memory alloy (SMA) components despite their greater complexities related to phase tran...

The left atrial appendage occlusion (LAAO) is a recommended treatment for atrial fibrillation (AF) patients unable to take anti-coagulation therapy. However, the occurrence of thromboembolic events after LAAO have an incidence up to 16%. In this study, computational fluid dynamics (CFD) was used to investigate the hemodynamic effects of different d...

Left atrial appendage occlusion (LAAO) is a percutaneous procedure to prevent thromboembolism in patients affected by atrial fibrillation. Despite its demonstrated efficacy, the LAA morphological complexity hinders the procedure, resulting in postprocedural drawbacks (device‐related thrombus and peri‐device leakage). Local anatomical features may c...

The evolution of information and communication technologies has affected all fields of science, including health sciences. However, the rate of technological innovation adoption by the healthcare sector has been historically slow, compared to other industrial sectors. Innovation in computer modeling and simulation approaches has changed the landsca...

Drug-Coated Balloons have shown promising results as a minimally invasive approach to treat stenotic arteries, but recent animal studies have revealed limited, non-uniform coating transfer onto the arterial lumen. In vitro data suggested that local coating transfer tracks the local Contact Pressure (CP) between the balloon and the endothelium. Ther...

Stents are tubular meshed endoprostheses implanted mini-invasively through a transcatheter intervention to guarantee the patency of body conduits, mainly in cardiovascular applications. In pediatric cardiology, stenting has become an accepted procedure in the treatment of congenital heart disease (CHD) as an alternative to open-heart surgery. CHD r...

The implant of self-expandable Ni-Ti stents for the treatment of peripheral diseases has become an established medical practice. However, the reported failure in clinics highlights the open issue of the fatigue characterization of these devices. One of the most common approaches for calculating the Ni-Ti fatigue limit (commonly defined in terms of...

Ni-Ti alloys are widely used for biomedical applications due to their superelastic properties, which are especially convenient for endovascular devices that require minimally invasive insertion and durable effects, such as peripheral/carotid stents and valve frames. After crimping and deployment, stents undergo millions of cyclic loads imposed by h...

Additive manufacturing (AM) is a promising technology for the personalized medicine industry, especially in the orthopedic field. It allows the production of prostheses that can fit complex anatomical sites and mimic bone morphology, featuring an external solid shell and an inner trabecular core. The new medical device regulation has recently outli...

Bioresorbable Vascular Scaffolds (BVS), developed to allow drug deliver and mechanical support, followed by complete resorption, have revolutionized atherosclerosis treatment. InSilc is a Cloud platform for in silico clinical trials (ISCT) used in the design, development and evaluation pipeline of stents. The platform integrates beyond the state-of...

Background and Objective Transcatheter aortic valve implantation (TAVI) has become the standard treatment for a wide range of patients with aortic stenosis. Although some of the TAVI post-operative complications are addressed in newer designs, other complications and lack of long-term and durability data on the performance of these prostheses are l...

The current interest of those dealing with medical research is the preparation of digital twins. In this frame, the first step to accomplish is the preparation of reliable numerical models. This is a challenging task since it is not common to know the exact device geometry and material properties unless in studies performed in collaboration with th...

Considering the field of application involving stent deployment simulations, the exploitation of a digital twin of coronary stenting that can reliably mimic the patient-specific clinical reality could lead to improvements in individual treatments. A starting step to pursue this goal is the development of simple, but at the same time, robust and eff...

This study presents a comprehensive evaluation of the mechanical, micro-mechanical and physical properties of Reva Medical Fantom Encore Bioresorbable Scaffolds (BRS) subjected to a thermally-accelerated degradation protocol. The Fantom Encore BRS were immersed in phosphate buffered saline solution at 50 °C for 112 days with radial compression test...

To date, there is a general lack of customizability within the selection of endovascular devices for catheter-based vascular interventions. Laser powder bed fusion (LPBF) has been flexibly exploited to produce customized implants using conventional biomedical alloys for orthopedic and dental applications. Applying LPBF for cardiovascular applicatio...

The major concern about Nickel-Titanium (Ni-Ti) stents, which are the gold standard in the treatment of occlusive peripheral disease, is fatigue and the consequent fracture in vivo. Indeed, their failure might be responsible for severe drawbacks, among which is the re-occlusion of the treated artery. Although many phenomenological approaches have b...

The introduction of Bioresorbable Vascular Scaffolds (BVS) has revolutionized the treatment of atherosclerosis. InSilc is an in silico clinical trial (ISCT) platform in a Cloud-based environment used for the design, development and evaluation of BVS. Advanced multi-disciplinary and multiscale models are integrated in the platform towards predicting...

Developing an efficient stent frame for transcatheter aortic valves (TAV) needs thorough investigation in different design and functional aspects. In recent years, most TAV studies have focused on their clinical performance, leaflet design, and durability. Although several optimization studies on peripheral stents exist, the TAV stents have differe...

This work investigates the processing of NiTi open-cell peripheral stents with variable diameter by SLM and consecutive heat treatments. The production of open-cell designs via SLM requires dedicated processing strategies to avoid the use of support structures with comparable dimensions to the stent struts. Process parameters were studied using an...

This study aims at proposing and discussing useful indications to all those who need to validate a numerical model of coronary stent deployment. The proof of the reliability of a numerical model is becoming of paramount importance in the era of in silico trials. Recently, the ASME V&V Standard Committee for medical devices prepared the V&V 40 stand...

Selective laser melting (SLM) is an established additive-manufacturing technology for the realization of custom-made implantable devices [1]. This could be an advantage in ankle replacement prostheses, where traditionally-manufactured implants are affected by a significant failure rate (50% at 5 years), especially for talus reconstruction devices [...

Recently, researchers focused their attention on the use of polymeric bioresorbable vascular scaffolds (BVSs) as alternative to permanent metallic drug-eluting stents (DESs) for the treatment of atherosclerotic coronary arteries. Due to the different mechanical properties, polymeric stents, if compared to DESs, are characterized by larger strut siz...

The purpose of this work is to propose a workflow that couples experimental and computational activities aimed at developing a credible digital twin of a commercial coronary bioresorbable vascular scaffold when direct access to data about material mechanical properties is not possible. Such a situation is be faced when the manufacturer is not invol...

The proof of the reliability of a numerical model is becoming of paramount importance in the era of in silico clinical trials. When dealing with a coronary stenting procedure, the virtual scenario should be able to replicate the real device, passing through the different stages of the procedure, which has to maintain the atherosclerotic vessel open...

Braiding technology is nowadays commonly adopted to build stent-like devices. Indeed, these endoprostheses, thanks to their typical great flexibility and kinking resistance, find several applications in mini-invasive treatments, involving but not limiting to the cardiovascular field. The design process usually involves many efforts and long trial a...

The ID Venous System is an innovative device proposed by ID NEST MEDICAL to treat venous compression disorders that involve bifurcations, such as the May-Thurner syndrome. The system consists of two components, ID Cav and ID Branch, combined through a specific connection that prevents the migration acting locally on the pathological region, thereby...

Ni–Ti stents fatigue strength assessment requires a multi-factorial complex integration of applied loads, material and design and is of increasing interest. In this work, a coupled experimental-numerical method for the multi-axial fatigue strength assessment is proposed and verified for two different stent geometries that resemble commercial produc...

Bioresorbable vascular scaffolds were considered the fourth generation of endovascular implants deemed to revolutionize cardiovascular interventions. Yet, unexpected high risk of scaffold thrombosis and post-procedural myocardial infractions quenched the early enthusiasm and highlighted the gap between benchtop predictions and clinical observations...

The interest in the design of shape memory alloy (SMA) actuators is recently broadened thanks to their high power density and versatility. In particular, snake-like Ni–Ti actuators demonstrated high potential at the mini- and micro-scales as SMA non-conventional active elements, due to their capacity to provide significant displacements in a very l...

Selective Laser Melting (SLM) is a promising technology for the manufacturing of patient-specific medical implants, due to the intrinsic potential in the realization of one of a kind parts with complex geometries. The present work analyses the production of balloon-expandable stents in cobalt-chromium alloy with a novel mesh which is realized using...

Atrial Fibrillation (AF) is a common disease that significantly increases the risk of strokes. Oral anticoagulants represent the standard preventive treatment, but they involve severe drawbacks, including intracerebral bleedings. Since in patients affected by nonvalvular AF, the Left Atrial Appendage (LAA) is the primary source of thromboembolism,...

In the recent years, Bioresorbable Vascular Scaffolds (BVS) for the treatment of atherosclerosis have been introduced. InSilc is a cloud based in silico clinical trial (ISCT) platform for drug-eluting BVS. The platform integrates multidisciplinary and multiscale models predicting the BVS performance. In this study, we present a use case scenario an...

Purpose to suggest an in silico modelling approach to estimate the fatigue failure on peripheral Nitinol stents implanted in the superficial femoral artery (SFA) and interpret the clinically observed stent fractures of a retrospective series of patients. Materials and Methods Preoperative data of 27 patients who underwent SFA Nitinol stenting were...

Braided stents are self-expandable devices widely used in many different clinical applications. In-silico methods could be a useful tool to improve the design stage and preoperative planning; however, numerical modeling of braided structures is not trivial. The geometries are often challenging, and a parametric representation is not always easily a...

The aim of this work is to set a finite element model of a Ni-Ti self-knotting suture, designed for deep neurosurgical applications, and to provide a reliable tool for evaluating its functionality before entering clinical practice. A closed shape is memorized through specific heat treatments; once implanted in the open configuration the surgeon doe...

Nowadays, shape memory alloys, in particular Nickel–Titanium alloys (NiTi), are widely adopted in many fields (biomedical, aerospace, automotive, civil ...) for producing devices exploiting pseudo-elasticity or shape memory effect. These devices are often subjected to cyclic loadings and sometimes to large deformations that modify the material resp...

The performance of biodegradable magnesium alloy stents (BMgS) requires special attention to non-uniform residual stress distribution and stress concentration, which can accelerate localized degradation after implantation. We now report on a novel concept in stent shape optimization using a finite element method (FEM) toolkit. A Mg-Nd-Zn-Zr alloy w...

Additive Manufacturing (AM) has risen great interest in biomedical applications, for its flexibility and the possibility of producing patient-customized devices. Customization has high importance to limit inflammation and rejection. Moreover, some occlusions may take place in bifurcation sites, which require the insertion of multiple stents, increa...

This work first numerically investigates on the effect of the application of cyclic remote loads on the local stress/strain response of a peripheral stent. For this purpose, three stents of identical geometry, but different material properties (linear elastic, elastic-plastic and Nitinol material), were modelled and subjected to uniaxial and multia...

Nickel-Titanium alloys (Nitinol) are widely used for biomedical applications. Peripheral stents are almost exclusively composed of Nitinol, as its superelasticity is suited for minimally-invasive insertion and durable effect. After crimping and deployment stents undergo cyclic multi-axial loads imposed by vascular and lower-limb motion (e.g. axial...

Polymeric bioresorbable scaffolds (BRS), at their early stages of invention, were considered as a promising revolution in interventional cardiology. However, they failed dramatically compared to metal stents showing substantially higher incidence of device failure and clinical events, especially thrombosis. One problem is that use of paradigms inhe...

Biodegradable magnesium alloy stents exhibit deficient corrosion period for clinic applications, making the protective polymer coating more crucial than drug-eluting stents with the permanent metal scaffold. We implemented a cohesive method based on finite element analysis method to predict the integrity of adhesive between coating and stent during...

Coronary artery disease (CAD) remains the leading cause of death in Europe and worldwide. One of the most common pathologic processes involved in CAD is atherosclerosis. Coronary stents are expandable scaffolds that are used to widen the occluded arteries and enable the blood flow restoration. To achieve an adequate delivery and placement of corona...

Peripheral Nickel–Titanium (NiTi) stents exploit super-elasticity to treat femoropopliteal artery atherosclerosis. The stent is subject to cyclic loads, which may lead to fatigue fracture and treatment failure. The complexity of the loading conditions and device geometry, coupled with the nonlinear material behavior, may induce multi-axial and non-...

Valve diseases are more and more treated with transcatheter aortic valves. This work is based on an experimental setup with the corresponding fluid–structure interaction model to show the feasibility of performing accurate simulations which is able to capture the main behavior of a transcatheter valve both from structural and fluid dynamic points o...

Nickel-Titanium (NiTinol) alloys exploit a typical super-elastic behavior which makes them suitable for many biomedical applications, among which peripheral stenting, requiring the device being subjected to the high mobility of the lower limbs. Unfortunately, this complex environment can lead to the device fatigue fracture with likely other more se...

Nickel-Titanium belongs to the shape memory alloys and it is widely used in many biomedical fields. Its temperature dependent property of pseudo-elasticity allows to design self-expandable devices, highly convenient for mini-invasive deployments. Peripheral stents are subjected in vivo to a complex state of cyclic solicitations due to blood pulsati...

Nickel–titanium alloys are commonly adopted for producing cardiovascular minimally invasive devices such as self-expandable stents, aortic valves and stent-grafts. These devices are subjected to cyclic loads (due to blood pulsatility, leg or heart movements), that can induce fatigue fracture, and may also be subjected to very large deformations (du...

A new version of the Italian design code for dams has been recently introduced, thus replacing after 30 years the previous code, which was still based on a permissible stress design philosophy. The new code follows a limit state approach, employs independent load and resistance factors and defines the earthquake actions in accordance with the new s...

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...

Nonlinear dynamic soil structure interaction of a pile-supported integral bridge structure has been reported in this paper. The open source code: OpenSeesSP (parallel processing) have been used to simulate the sequential steps of the analysis. Development of a soil-foundation-structure model was required to properly simulate seismic wave propagatio...

Nickel-Titanium (NiTi) peripheral stents are commonly used for the treatment of diseased femoropopliteal arteries (FPA). However, cyclic deformations of the vessel, induced by limb movements affect device performance and fatigue failure may occur. Stent strut fracture has been described in the literature, and is implicated as a potential causative...

Transcatheter aortic valve replacement (TAVR) represents an established recent technology in a high risk patient base. To better understand TAVR performance, a fluid-structure interaction (FSI) model of a self-expandable transcatheter aortic valve was proposed. After an in vitro durability experiment was done to test the valve, the FSI model was bu...

NiTi (nickel-titanium) stents are nowadays commonly used for the percutaneous treatment of peripheral arterial disease. However, their effectiveness is still debated in the clinical field. In fact a peculiar cyclic biomechanical environment is created before and after stent implantation, with the risk of device fatigue failure. An accurate study of...

A new trend in the treatment of atherosclerosis foresees the exploitation of bioresorbable materials for stents. Magnesium alloys are good candidates since they are completely biocorrodible in human body. To overcome the limitation of very fast degradation, the bioresorbable scaffold can be coated with a polymer having lower degradation rate and ta...

Biodegradable magnesium alloy stents (MAS) could improve the long-term clinical results of commercial bare metal or drug-eluting stents. MAS have shown a limited mechanical support for diseased vessels due to fast degradation. Protective polymer coating is a reasonable way to reduce the degradation rate of MAS. However, peeling of the coating durin...

Biodegradable cardiovascular stents in magnesium (Mg) alloys constitute a promising option for a less intrusive treatment, due to their high compatibility with the body tissue and intrinsic dissolution in body fluids. The design and fabrication aspects of this medical device require an integrated approach considering different aspects such as mecha...

A practical and readily implementable seismic assessment procedure for multi-span reinforced concrete bridges is introduced in this paper. The procedure is based on an existing direct displacement-based assessment (DDBA) approach, and accounts for nonlinear dynamic soil–structure interaction (NLSSI) effects. Several simplified bridge structures lyi...

Despite their success as primary treatment for vascular diseases, Nitinol peripheral stents are still affected by complications related to fatigue failure. Hip and knee movements during daily activities produce large and cyclic deformations of the superficial femoral artery, that concomitant to the effects of pulsatile blood pressure, may cause fat...

Biodegradable stents are attracting the attention of many researchers in biomedical and materials research fields since they can absolve their specific function for the expected period of time and then gradually disappear. This feature allows avoiding the risk of long-term complications such as restenosis or mechanical instability of the device whe...

Fatigue resistance of Nitinol stents implanted into femoro-popliteal arteries is a critical issue for the particular biomechanical environment of this district. Hip and knee joint movements due to the cyclic daily activity expose the superficial femoral artery (SFA), and therefore the implanted stents, to quite large and cyclic deformations influen...

Coronary stent fracture is still an unresolved issue in the field of minimally invasive cardiovascular interventions due to its high rate of incidence and uncertain clinical consequences. Recent studies, based on clinical data, proved that there are several factors which can be identified as independently responsible of coronary stent fracture. Amo...

Although the number of fractured stents in the femoro-popliteal district was largely reduced using second-generation devices, remarkable differences still exist among various products. In vitro testing offers a valid tool to comparatively assess the risk of fatigue fracture of different devices. However, there are no standardized methodologies for...

Fatigue resistance of Nitinol peripheral stents implanted into atheroscelorotic femoro-popliteal arteries is a critical issue due to the particular biomechanical environment of this district. Hip and knee joint movements associated with patient' daily activities expose the superficial femoral artery, and therefore the implanted stents, to large and...

Hip and knee movements during gait produce large and cyclic deformations of the superficial femoral artery (SFA), increasing the risk of fracture of implanted Nitinol peripheral stents. Although in vitro testing offers a valid tool to comparatively assess the risk of fatigue fracture of different marketed stents, there is still a lack of validated...

Fatigue resistance of Nitinol peripheral stents implanted into femoropopliteal arteries is a critical issue due to the particular biomechanical environment of this district. Hip and knee joint movements associated with patient’ daily activities expose the superficial femoral artery, and therefore the implanted stents, to large and cyclic deformatio...

Nitinol stents are nowadays widely used for the treatment of occlusions in peripheral arteries. However, the risk of stent rupture is source of concerns for Nitinol devices: in some recent clinical studies it affects 30% of the patients. The variability of the incidence of this complication suggests that it is due to many correlated aspects: materi...

An iterative linear-equivalent procedure to take into account nonlinear soil-structure interaction effects in the displacement-based seismic design is presented for the case of shallow foundations. The procedure is based on the use of empirical curves to evaluate the stiffness degradation and the increase of damping ratio as a function of foundatio...

Nitinol stents are nowadays widely used for the treatment of occlusions in peripheral arteries. However, the risk of stent fatigue rupture due to cyclic loads related with the patient daily activities [Smouse et al. 2005] is source of concerns for Nitinol devices: in some recent clinical studies it is shown that stent rupture may induce re-occlusio...

Numerical simulations are nowadays used as predictive and interpretative tools in many clinical fields related to cardiovascular diseases including aortic arch pathologies. In this chapter, the biomechanics of the femoro-popliteal artery is briefly described also when a stent is implanted. As stent fracture is one of the major factors compromising...

Biodegradable magnesium alloy stents (MAS) constitute a promising candidate which might present improved long-term clinical performances over commercial bare metal or drug eluting stents. However, MAS were found to show limited mechanical support for diseased vessels due to fast degradation. Optimizing stent designs through finite element analysis...

In Italy, as in other high seismic risk countries, many bridges, nowadays deemed ‘strategic’ for civil protection interventions after an earthquake, were built without antiseismic criteria, and therefore their seismic assessment is mandatory. Accordingly, the development of a seismic assessment procedure that gives reliable results and, at the same...

Finite element (FE) modelling can be a very resourceful tool in the field of cardiovascular devices. To ensure result reliability, FE models must be validated experimentally against physical data. Their clinical application (e.g., patients' suitability, morphological evaluation) also requires fast simulation process and access to results, while eng...

By taking into account patient-specific properties, finite element (FE) models can aid in the optimization of the devices’ mechanical performances, accelerating the time of development and reducing testing costs. Patient-specific cardiovascular modeling can also drive the development of novel devices [1], by means of anatomical elements that are mo...

Amongst other cardiovascular stent materials such as stainless steel, titanium, Ni-Ti shape memory alloys or polymers, magnesium stands out as a promising new option in terms of three essential features: biocompatibility, biodegradability, and good mechanical properties. Magnesium, as an element already present in the human body, is highly compatib...

Nitinol stents are nowadays widely used for the treatment of occlusions in peripheral arteries. However, the expansion of this indication has also highlighted some complications. In particular, the patient daily activities expose the peripheral arteries to large and cyclic deformations which may cause long-term failure of the device and consequentl...

ZM21 and AZ31B magnesium alloy tubes were hot extruded by a laboratory equipment in order to produce precursors for biodegradable stents. The microstructure and the texture evolution during the extrusion were investigated and related to the resulting mechanical properties. The tubes featured a homogeneous and refined equiaxed grain structure due to...