Knowledge of mechanical properties of living arteries is important to understand vascular function during health, disease and intervention. A mechanical model of the vascular tree would facilitate the development of (balloon-)catheters and stents.

A common technique to improve the local blood flow through stenotic arteries involves the implantation of a metallic scaffold known as a stent. These devices have shown excellent results in unbranched vessels. However, the treatment of coronary bifurcation lesions remains an enormous challenge and is generally associated with an increased complication rate. Many different techniques have been proposed in clinical literature, but all the suggested methodologies have specific limitations [1]. In many cases, a stent is deployed in the main branch (MB) and logically, this compromises the side branch (SB) patency. This is a frequently encountered situation that can be improved by balloon dilatation through the side of the MB stent (fig. 1). However, such balloon inflation may result in unwanted distortions of the stent [2].

Abdominal Aortic Aneurysm is an irreversible dilation of the abdominal aorta. If left untreated the aneurysm may rupture possibly leading to death. There are currently two surgical treatments for AAA, the traditional open surgery and the minimally invasive repair also known as the endovascular aneurysm repair procedure (EVAR) [1–2]. The endovascular technique having been introduced in 1991 is still beset by problems [3]. These problems mainly consist of graft migration, endoleaks and occlusion. It has been suggested that redesigning current stent-graft devices is the best method of remedying these problems [4]. Conventional graft design has normally revolved around a constant proximal diameter which includes a sudden large diameter reduction at the iliac bifurcation. In the naturally occurring case the aorta tapers into the iliac arteries.

Abdominal aortic aneurysm stent grafts have been reported to fracture at a rate as high as 8% [1]. Iliac artery deformation induced by cardiac pulsation or musculoskeletal motions has been hypothesized to cause these fractures, but little in vivo data has been available heretofore to test this hypothesis. We have utilized magnetic resonance angiography and image-processing methods to quantify in vivo deformation of the human iliac arteries due to maximal hip flexion.

Implantable devices in direct contact with flowing blood, for example, coronary stents, continuous flow and pulsatile flow ventricular assist devices, prosthetic heart valves, catheters and cannulae are currently being used to treat many medical conditions. However, thromboembolism and the attendant risk for ischemic stroke remains an impediment for all these devices. A prudent approach to developing these devices in a cost effective manner should include optimization for thrombogenic performance before going into expensive preclinical and clinical trials.

Mechanical characterization of the coronary arterial wall is important for several reasons. Mechanical factors play an important role in the development of atherosclerosis [1]. Atherosclerotic coronary arteries may be treated mechanically with interventions like PTCA and stent implantation, 1265000 PTCA procedures were performed in the United States in 2005 [2]. Furthermore, knowledge of the mechanical properties of the arterial wall is important for modeling of the coronary circulation and explaining its hemodynamics.

Endovascular stents are used to treat aneurysms, dissections and acute traumatic disruptions of the thoracic aorta. While stents are certainly a much less invasive treatment option, the behaviour of stents in the aorta is still not well understood. Gianturco stents ranging from 8mm to 44mm in diameter were tested and found to exhibit nonlinear force-displacement relationships. The effect of stent length and the common clinical practice of overlapping two stents were also tested. It was found that stent pressure was proportional to stent length and that a small stent overlap resulted in a doubling of the stent force.

In-vivo corrosion of endovascular stents presents two main risks; release of metallic debris and deterioration of the mechanical properties of the stents which may lead to fracture. Retrieval analysis of explanted nickel-titanium (NiTi) aortic stent grafts showed pitting corrosion and fracture of the NiTi wire component [1, 2].

Cerebral aneurysms are a mayor cause of hemorrhagic stroke which is a highly significant and devastating disease. Currently there is an increased interest in using endovascular devices for flow diversion such as stents, for treating intracranial aneurysms [1]. Several studies have proven that the geometry and position of the stent in its deployed state play a mayor role in the way the blood flow is diverted. The design of flow diverters and the selection of the most appropriate device for a given aneurysm require a computational model to study the changes in the blood flow patterns after stenting. In this paper an innovative methodology for virtual deployment of stents within patient-specific anatomical models is presented. One remarkable property of this technique is the ability to easily interchange different stent designs within the same model in order to perform fast comparative characterizations.

The purpose of this study was to understand how the side group dictates thermo-mechanical properties of shape-memory acrylate networks, specifically strain to failure and toughness. A useful parameter in assessing shape memory polymers is the strain to failure because it is critical to know how much recovery strain the material can experience. To understand how the structure is related to mechanical properties, such as strain to failure, materials of differing chain stiffness ratio, C ∞ , were compared at varying percentages of crosslinker. While the chemical and thermal properties of acrylate networks have been discussed in much detail, methods of toughening networks by the precise choice of certain acrylates have not been thoroughly examined. In order for these networks to be of practical use as biomedical devices, such as minimally invasive shape memory polymer stents, detailed structure-property relationships must be established.

Cardiovascular disease has historically been the leading cause of death in the US [1], and coronary artery disease in particular accounts for over fifty percent of these deaths [1]. Since their approval in 1994, coronary stents have become one of the leading treatments for this disease. However, problems persist in both bare metal and drug-eluting stents (DESs) with long-term restenosis and thrombosis. It is well accepted that disruptions in arterial wall shear stress (WSS), especially low WSS, are linked to alterations in the endothelial cell layer, atherosclerosis, and thrombogenesis [2], although the exact mechanisms are still uncertain, and studies have shown that stent design is closely linked to clinical outcomes [3].

Polymer trileaflet valves have been under investigation for the past 40–50 years in an attempt to produce a valve alternative that is both durable and non-thrombogenic. Most have met with limited success due to oxidative reactions and high dynamic stresses borne by the material [1]. With this knowledge, an oxidatively stable polyolefin, poly(styrene-b-isobutylene-b-styrene) (SIBS), was selected for the design of a fiber-reinforced polymer trileaflet heart valve. The hydrodynamic properties of prototype SIBS valves have been encouraging, but some valves failed prematurely as a result of insufficient durability during in vivo implantation in a sheep model or during accelerated in vitro fatigue.

Stenting is the most commonly used medical procedure to restore blood flow in stenotic arteries. During this endovascular intervention, a small tube-like structure is implanted in the narrowed section of the diseased artery. The vast majority of stents are crimped (i.e. plastically deformed) on a folded balloon (balloon expandable stents). After insertion through a small incision in the femoral or radial artery using a catheter, the balloon is inflated and the stent deploys. Following to the expansion, the balloon is deflated and retracted and from then on, the stent acts as a mechanical scaffold for the enlarged lumen.

In this paper computational simulations of stent coating debonding are presented. Finite element methods are implemented to model coating delamination during stent crimping, deployment and recoil. Gold, titanium and polymer coatings of differing thicknesses are explicitly modeled. The interfacial relationship between the stent surface and the coating during crimping and deployment is simulated using a cohesive zone model.

Today cardiac complications are the leading cause of death in the developed world [1]. Millions of people suffer from cardiovascular disease, with most of the cases caused by or related to atherosclerosis. Historically, blood flow in stenosed arteries has been restored by means of balloon angioplasty. In 1987 stents were introduced to the procedure in order to provide structural support to the diseased artery.

Arterial restenosis associated with intimal hyperplasia at stent revascularization sites remains the major cause of long-term failure. The objective of this study was to determine the effect of flow in promoting endothelial cell migration and the effect of re-endothelialization on smooth muscle cell (SMC) proliferation. This study demonstrated that re-endothelialization reduces SMC proliferation and migration and provides model systems to study approaches to increasing endothelial healing.

Cardiovascular disease has historically been the leading cause of death in the US [1], and accounts for approximately one third of all deaths worldwide [2]. Coronary artery disease in particular accounts for over fifty percent of these deaths and in 2004 was the single largest killer, affecting approximately 15 million people every year [1]. Coronary stenting was approved in 1994 by the FDA, and has become one of the leading treatments for the disease. However, problems persist in both bare metal and drug-eluting stents (DESs) with restenosis and thrombosis. It is well accepted that disruptions in arterial wall shear stress (WSS), especially low WSS, are linked to alterations in the endothelial cell layer and ultimately disease [3], although the exact mechanisms are still uncertain. Additionally, studies have shown that stent design is closely linked to clinical outcomes [4].

Abdominal aortic aneurysm (AAA) is treated with two methods — open repair and endovascular repair. The endovascular method has many advantages over open repair, such as shorter hospital stays, non-invasiveness and shorter recovery times but there have been several reported problems with these devices, including graft migration, endoleaks and limb occlusion. Graft migration occurs in approximately 10% of grafts [1] while limb occlusion occurs in 11% of cases [2]. The consequence of endoleaks and migration not being treated may be the ultimate rupture of the aneurysm. The occlusion of iliac graft limbs can lead to peripheral vascular problems such as ischemia and gangrene. Some of the influencing factors on migration, occlusion and endoleaks are fluid, drag, stent-graft angulation and flow characteristics such as Deans flow.

Intracranial aneurysms are pathological dilations of the arteries in the brain, whose rupture is often fatal. Surgery and endovascular embolization are the two most common methods of treatment. Surgery involves opening a portion of the skull and placing metallic clips at the aneurysm neck thereby preventing blood flow into the aneurysm. In the case of embolization, a catheter is used to pack platinum coils in the aneurysm reducing the inflow and promoting thrombus formation. Due to its less invasive approach endovascular embolization is preferred over surgery. Nevertheless this approach also has some serious aftereffects. Coil compaction followed by the re-growth or the formation of the secondary aneurysm is the most common problem. The endovascular embolization approach also has a serious shortcoming that the coils alone cannot be used to block every type of aneurysm. Wide neck or fusiform aneurysms are coiled with the help of stents. Recent studies show that stent, which is a hollow cylindrical mesh, can be successfully used to limit the flow of blood into the aneurysm. However these studies have been conducted using idealized in-vitro and numerical models. Studies conducted using patient-specific models generated from medical images will provide a more realistic approach to computationally investigate the effects of stents on intra-aneurysmal flow patterns. However generation of computational grids inside the parent vessel and around these stents is a challenging task. In this paper an algorithm to map the stent to a patient-specific vascular model and an adaptive unstructured embedded gridding technique to model flow around stents are presented. Finally these techniques are demonstrated on patient-specific cases to prove their feasibility.

The implantation of a balloon expandable stent induces chronic stent-induced stresses on the artery wall. These highly non-physiologic stresses can provoke inflammation and smooth muscle cell proliferation. Ultimately, this cascade of events leads to restenosis, or the development of a new blockage in the stented artery. Since the initial human implantation of balloon expandable stents, technological advances in stent design, material properties, and deliverability have expanded the application and success rate of the procedure. More recently, anti-restenotic strategies such as drug-eluting stents have aimed to counteract the restenosis process. While clinical trials have demonstrated the success of drug eluting stents in coronary arteries [1], risk of late thrombosis [2] and failure to prevent restenosis in peripheral arteries [3] has limited this technology. A further investigation into the artery wall stresses induced by stent implantation, and the pursuit of strategies to minimize them could reduce the restenosis rates for both bare metal and drug-eluting stents.