Investigating the Equivalent Plastic Strain in a Variable Ring Length and Strut Width Thin-Strut Bioresorbable Scaffold.

Purpose: The ArterioSorb[Formula: see text] bioresorbable scaffold (BRS) developed by Arterius Ltd is about to enter first in man clinical trials. Previous generations of BRS have been vulnerable to brittle fracture, when expanded via balloon inflation in-vivo, which can be extremely detrimental to patient outcome. Therefore, this study explores the effect of variable ring length and strut width (as facilitated by the ArterioSorb[Formula: see text] design) on fracture resistance via analysis of the distribution of equivalent plastic strain in the scaffold struts post expansion.

Exploring a parallel rheological framework to capture the mechanical behaviour of a thin-strut polymeric bioresorbable coronary scaffold.

Computational modelling of bioresorbable scaffolds (BRS) has employed several different material property models, ranging from those based on simple elasto-plastic theory through to anisotropic parallel network models that capture the viscoelastic-plastic behaviour observed in poly-l-lactic acid (PLLA). The increased complexity of higher fidelity material models, particularly in terms of calibration to in-vitro data, can limit their use. Consequently, their suitability for predicting the mechanical response of next-generation BRS is not well understood.

Magnetic retrieval of prosthetic heart valves for redo-TAVI.

Bioprosthetic aortic heart valves are known to degenerate within 7-15 years of implantation. Currently, the options for treating a failing valve are (a) redo surgical aortic valve replacement or, increasingly, (b) valve-in-valve transcatheter aortic valve implantation (ViV-TAVI). The ViV-TAVI procedure is referred to as redo-TAVI when the failing valve is a TAVI device.

Investigating the material modelling of a polymeric bioresorbable scaffold via in-silico and in-vitro testing.

The accurate material modelling of poly-l-lactic acid (PLLA) is vital in conducting finite element analysis of polymeric bioresorbable scaffolds (BRS) to investigate their mechanical performance and seek improved scaffold designs. To date, a large variety of material models have been utilised, ranging from simple elasto-plastic models to high fidelity parallel network models. However, no clear consensus has been reached on the appropriateness of these different models and whether simple, less computationally expensive models can serve as acceptable approximations.

A control mechanism for intra-mural peri-arterial drainage via astrocytes: How neuronal activity could improve waste clearance from the brain.

The mechanisms behind the clearance of soluble waste from deep within the parenchyma of the brain remain unclear. Experimental evidence reveals that one pathway for clearance of waste, termed intra-mural peri-arterial drainage (IPAD), is the rapid drainage of interstitial fluid along basement membranes (BM) of the smooth muscle cells of cerebral arteries; failure of IPAD is closely associated with the pathology of Alzheimer's disease (AD), but its driving mechanism remains unclear. We have previously shown that arterial pulsations generated by the heart beat are not strong enough to drive IPAD.

Arterial Pulsations cannot Drive Intramural Periarterial Drainage: Significance for β Drainage.

Alzheimer's Disease (AD) is the most common form of dementia and to date there is no cure or efficient prophylaxis. The cognitive decline correlates with the accumulation of amyloid-β (β) in the walls of capillaries and arteries. Our group has demonstrated that interstitial fluid and β are eliminated from the brain along the basement membranes of capillaries and arteries, the intramural periarterial drainage (IPAD) pathway.

The implication of the osteolysis threshold and interfacial gaps on periprosthetic osteolysis in cementless total hip replacement.

Osteolysis around joint replacements may develop due to migration of wear particles from the joint space into gaps between the interface bone and the implant where they can accumulate in high concentrations to cause tissue damage. Osteolysis may appear in various postoperative times and morphological shapes which can be generalized into linear and focal. However, there are no clear explanations on the causes of such variations.

The impact of imperfect frame deployment and rotational orientation on stress within the prosthetic leaflets during transcatheter aortic valve implantation.

TAVI devices are manufactured with cylindrical frames. However, the frames are rarely cylindrical post-deployment since deformation due to localised under expansion can be induced by calcified material on the native valve leaflets exerting irregular forces upon the frame. Consequently, the leaflets within a deformed TAVI device may undergo elevated stress during operation, which may lead to premature device failure.

Skin Microstructure is a Key Contributor to Its Friction Behaviour.

Due to its multifactorial nature, skin friction remains a multiphysics and multiscale phenomenon poorly understood despite its relevance for many biomedical and engineering applications (from superficial pressure ulcers, through shaving and cosmetics, to automotive safety and sports equipment). For example, it is unclear whether, and in which measure, the skin microscopic surface topography, internal microstructure and associated nonlinear mechanics can condition and modulate skin friction. This study addressed this question through the development of a parametric finite element contact homogenisation procedure which was used to study and quantify the effect of the skin microstructure on the skin frictional response.

A Simulation Model of Periarterial Clearance of Amyloid-β from the Brain.

The accumulation of soluble and insoluble amyloid-β (Aβ) in the brain indicates failure of elimination of Aβ from the brain with age and Alzheimer's disease (AD). There is a variety of mechanisms for elimination of Aβ from the brain. They include the action of microglia and enzymes together with receptor-mediated absorption of Aβ into the blood and periarterial lymphatic drainage of Aβ.

Multi-objective optimisation of stent dilation strategy in a patient-specific coronary artery via computational and surrogate modelling.

Although contemporary stents have been shown to improve short and long term clinical outcomes, the optimum dilation protocol is still uncertain in challenging cases characterised by long, highly calcified and tortuous anatomy. Recent clinical studies have revealed that in these cases, sub-optimal delivery can result in stent thrombosis (ST) and/or neointimal thickening as a result of stent malapposition (SM) and/or severe vessel trauma. One of the major contributors to vessel trauma is the damage caused by balloon dilation during stent deployment.

Computational fluid dynamics modelling in cardiovascular medicine.

This paper reviews the methods, benefits and challenges associated with the adoption and translation of computational fluid dynamics (CFD) modelling within cardiovascular medicine. CFD, a specialist area of mathematics and a branch of fluid mechanics, is used routinely in a diverse range of safety-critical engineering systems, which increasingly is being applied to the cardiovascular system. By facilitating rapid, economical, low-risk prototyping, CFD modelling has already revolutionised research and development of devices such as stents, valve prostheses, and ventricular assist devices.

The Computational Fluid Dynamics Rupture Challenge 2013--Phase II: Variability of Hemodynamic Simulations in Two Intracranial Aneurysms.

With the increased availability of computational resources, the past decade has seen a rise in the use of computational fluid dynamics (CFD) for medical applications. There has been an increase in the application of CFD to attempt to predict the rupture of intracranial aneurysms, however, while many hemodynamic parameters can be obtained from these computations, to date, no consistent methodology for the prediction of the rupture has been identified. One particular challenge to CFD is that many factors contribute to its accuracy; the mesh resolution and spatial/temporal discretization can alone contribute to a variation in accuracy.

Assessing the impact of including leaflets in the simulation of TAVI deployment into a patient-specific aortic root.

Computational simulation of transcatheter aortic valve implantation (TAVI) device deployment presents a significant challenge over and above similar simulations for percutaneous coronary intervention due to the presence of prosthetic leaflets. In light of the complexity of these leaflets, simulations have been performed to assess the effect of including the leaflets in a complete model of a balloon-expandable TAVI device when deployed in a patient-specific aortic root. Using an average model discrepancy metric, the average frame positions (with and without the leaflets) are shown to vary by 0.

Design Optimisation of Coronary Artery Stent Systems.

In recent years, advances in computing power and computational methods have made it possible to perform detailed simulations of the coronary artery stenting procedure and of related virtual tests of performance (including fatigue resistance, corrosion and haemodynamic disturbance). Simultaneously, there has been a growth in systematic computational optimisation studies, largely exploiting the suitability of surrogate modelling methods to time-consuming simulations. To date, systematic optimisation has focussed on stent shape optimisation and has re-affirmed the complexity of the multi-disciplinary, multi-objective problem at hand.

A mechanistic insight into the mechanical role of the stratum corneum during stretching and compression of the skin.

The study of skin biophysics has largely been driven by consumer goods, biomedical and cosmetic industries which aim to design products that efficiently interact with the skin and/or modify its biophysical properties for health or cosmetic benefits. The skin is a hierarchical biological structure featuring several layers with their own distinct geometry and mechanical properties. Up to now, no computational models of the skin have simultaneously accounted for these geometrical and material characteristics to study their complex biomechanical interactions under particular macroscopic deformation modes.

Computational Modelling of Multi-folded Balloon Delivery Systems for Coronary Artery Stenting: Insights into Patient-Specific Stent Malapposition.

Despite the clinical effectiveness of coronary artery stenting, percutaneous coronary intervention or "stenting" is not free of complications. Stent malapposition (SM) is a common feature of "stenting" particularly in challenging anatomy, such as that characterized by long, tortuous and bifurcated segments. SM is an important risk factor for stent thrombosis and recently it has been associated with longitudinal stent deformation.

Simulation of longitudinal stent deformation in a patient-specific coronary artery.

In percutaneous coronary intervention (PCI), stent malapposition is a common complication often leading to stent thrombosis (ST). More recently, it has also been associated with longitudinal stent deformation (LSD) normally occurring through contact of a post balloon catheter tip and the protruding malapposed stent struts. The aim of this study was to assess the longitudinal integrity of first and second generation drug eluting stents in a patient specific coronary artery segment and to compare the range of variation of applied loads with those reported elsewhere.

Periprosthetic wear particle migration and distribution modelling and the implication for osteolysis in cementless total hip replacement.

In total hip replacement (THR), wear particles play a significant role in osteolysis and have been observed in locations as remote as the tip of femoral stem. However, there is no clear understanding of the factors and mechanisms causing, or contributing to particle migration to the periprosthetic tissue. Interfacial gaps provide a route for particle laden joint fluid to transport wear particles to the periprosthetic tissue and cause osteolysis.

Variability of computational fluid dynamics solutions for pressure and flow in a giant aneurysm: the ASME 2012 Summer Bioengineering Conference CFD Challenge.

Stimulated by a recent controversy regarding pressure drops predicted in a giant aneurysm with a proximal stenosis, the present study sought to assess variability in the prediction of pressures and flow by a wide variety of research groups. In phase I, lumen geometry, flow rates, and fluid properties were specified, leaving each research group to choose their solver, discretization, and solution strategies. Variability was assessed by having each group interpolate their results onto a standardized mesh and centerline.

Do capsular pressure and implant motion interact to cause high pressure in the periprosthetic bone in total hip replacement?

When there is a debonding at the bone-implant interface, the difference in stiffness between the implant and the bone can result in micromotion, allowing existing gaps to open further or new gaps to be created during physiological loading. It has been suggested that periprosthetic fluid flow and high pressure may play an important role in osteolysis development in the proximity of these gaps. To explain this phenomenon, the concepts of "effective joint space" and "pumping stem" have been cited in many studies.

Multiobjective design optimisation of coronary stents.

We present here a multi-objective and multi-disciplinary coronary stent design optimization paradigm. Coronary stents are tubular, often mesh-like, structures which are deployed in diseased (stenosed) artery segments to provide a scaffolding feature that compresses atheromatus plaque, hence restoring luminal area and maintaining vessel patency. A three variable geometry parameterisation of a CYPHER (Cordis Corporation, Johnson & Johnson co.

Geometry parameterization and multidisciplinary constrained optimization of coronary stents.

Coronary stents are tubular type scaffolds that are deployed, using an inflatable balloon on a catheter, most commonly to recover the lumen size of narrowed (diseased) arterial segments. A common differentiating factor between the numerous stents used in clinical practice today is their geometric design. An ideal stent should have high radial strength to provide good arterial support post-expansion, have high flexibility for easy manoeuvrability during deployment, cause minimal injury to the artery when being expanded and, for drug eluting stents, should provide adequate drug in the arterial tissue.

Red blood cell migration in microvessels.

Red blood cell (RBC) migration effects and RBC-plasma interactions occurring in microvessel blood flow have been investigated numerically using a shear-induced particle migration model. The mathematical model is based on the momentum and continuity equations for the suspension flow and a constitutive equation accounting for the effects of shear-induced RBC migration in concentrated suspensions. The model couples a non-Newtonian stress/shear rate relationship with a shear-induced migration model of the suspended particles in which the viscosity is dependent on the haematocrit and the shear rate (Quemada model).

The influence of strut-connectors in stented vessels: a comparison of pulsatile flow through five coronary stents.

The design of coronary stents has evolved significantly over the past two decades. However, they still face the problem of in-stent restenosis, formation of neointima within 12 months of the implant. The biological response after stent implantation depends on various factors including the stent geometry which alters the hemodynamics.