Thomas Christian Gasser

• Phd
• Professor at KTH Royal Institute of Technology

Shear-induced migration of red blood cells (RBCs) is a well-known phenomenon characterizing blood flow in the small vessels (micrometre to millimetre size) of the cardiovascular system. In large vessels, like the abdominal aorta and the carotid artery (millimetre to centimetre size), the extent of this migration and its interaction with secondary f...

To translate the individual abdominal aortic aneurysm (AAA) patient's biomechanical rupture risk profile to risk-equivalent diameters, and to retrospectively test their predictability in ruptured and non-ruptured aneurysms. Biomechanical parameters of ruptured and non-ruptured AAAs were retrospectively evaluated in a multicenter study. General pati...

Aneurysm rupture is a life-threatening event, yet its underlying mechanisms remain largely unclear. This study investigated the fracture properties of the thoracic aneurysmatic aorta (TAA) using the symmetry-constraint Compact Tension (symconCT) test and compared results to native and enzymatic-treated porcine aortas' tests. With age, the aortic st...

Objective: We aimed to predict patient-specific rupture risks and growth behaviors in abdominal aortic aneurysm (AAA) patients using biomechanical evaluation with finite element analysis to establish an additional AAA repair threshold besides diameter and sex. Methods: A total of 1219 patients treated between 2005 and 2024 (conservative and repaire...

White matter (WM) tract-related strains are increasingly used to quantify brain mechanical responses, but their dynamics in live human brains during in vivo impact conditions remain largely unknown. Existing research primarily looked into the normal strain along the WM fiber tracts (i.e., tract-oriented normal strain), but it is rarely the case tha...

Background Information on the predictive determinants of abdominal aortic aneurysm rupture from CT angiography are scarce. The aim of this study was to investigate biomechanical parameters in abdominal aortic aneurysms and their association with risk of subsequent rupture. Methods In this retrospective study, the digital radiological archive was s...

This work outlines an efficient deep learning approach for analyzing vascular wall fractures using experimental data with openly accessible source codes (https://doi.org/10.25835/weuhha72) for reproduction. Vascular disease remains the primary cause of death globally to this day. Tissue damage in these vascular disorders is closely tied to how the...

White matter (WM) tract-related strains are increasingly used to quantify brain mechanical responses, but their dynamics in live human brains during in vivo impact conditions remain largely unknown. Existing research primarily looked into the normal strain along the WM fiber tracts (i.e., tract-oriented normal strain), but it is rarely the case in...

The identification of carotid atherosclerotic lesion at risk for plaque rupture, eventually resulting in cerebral embolism and stroke, is of paramount clinical importance. High stress in the fibrous plaque cap has been proposed as risk factor. However, among others, residual strains influence said stress predictions, but quantitative and qualitativ...

The fracture of vascular tissue, and load-bearing soft tissue in general, is relevant to various biomechanical and clinical applications, from the study of traumatic injury and disease to the design of medical devices and the optimisation of patient treatment outcomes. The fundamental mechanisms associated with the inception and development of dama...

The mechanics of vascular tissue, particularly its fracture properties, are crucial in the onset and progression of vascular diseases. Vascular tissue properties are complex, and the identification of fracture mechanical properties relies on robust and efficient numerical tools. In this study, we propose a parameter identification pipeline to extra...

Growth of abdominal aortic aneurysms (AAAs) is often described as erratic and discontinuous. This study aimed at describing growth patterns of AAAs with respect to maximal aneurysm diameter (Dmax) and aneurysm volume, and to characterize changes in the intraluminal thrombus (ILT) and biomechanical indices as AAAs grow. 384 computed tomography angio...

Tissue failure and damage are inherent parts of vascular diseases and tightly linked to clinical events. Additionally, experimental set-ups designed to study classical engineering materials are suboptimal in the exploration of vessel wall fracture properties. The classical Compact Tension (CT) test was augmented to enable stable fracture propagatio...

We introduce a three-dimensional geometrically nonlinear Reissner beam theory with embedded strong discontinuities for the modeling of failure in structures and discuss its finite element implementation. Existing embedded beam theories are geometrically linear or two-dimensional, motivating the need for the present work. We propose a geometrically...

Objective: The aim of this study was to assess whether aortic peak wall stress (PWS) and peak wall rupture index (PWRI) were associated with the risk of abdominal aortic aneurysm (AAA) rupture or repair (defined as AAA events) among participants with small AAAs. Methods: PWS and PWRI were estimated from computed tomography angiography (CTA) scan...

Background: Sac regression after endovascular aneurysm repair (EVAR) of abdominal aortic aneurysms (AAA) is regarded as a marker of successful response to treatment. Several factors influence sac behavior after EVAR, yet little is known about the value of preoperative biomechanics. The aim of this study was to investigate the difference in aortic...

Understanding the damage and failure of load-carrying soft biological tissue is critical in the effectual treatment of injury and disease. The difficulty in experimentally identifying the intrinsic mechanisms by which damage initiates and accumulates, and how this ultimately leads to tissue rupture, has motivated the constitutive modeling of soft t...

We investigate the compressive failure mechanisms in flax fiber composites, a promising eco-friendly alternative to synthetic composite materials, both numerically and experimentally, and explain their low compressive-compared-to-tensile strength, the compressive-to-tensile strength ratio being 0.28−0.6. We present a novel thermodynamically consist...

Objective: The indication for abdominal aortic aneurysm (AAA) repair is based on a diameter threshold. However, mechanical properties, such as peak wall stress (PWS) and peak wall rupture index (PWRI), influence the individual rupture risk. This study aims to correlate biomechanical and geometrical AAA characteristics during aneurysm growth applyi...

Intimal calcification and vascular stiffening are predominant features of end-stage atherosclerosis. However, their role in atherosclerotic plaque instability and how the extent and spatial distribution of calcification influence plaque biology remain unclear. We recently showed that extensive macro calcification can be a stabilizing feature of lat...

Aims This study was an unplanned exploratory analysis of a subset of participants from the Telmisartan in the Management of Abdominal Aortic Aneurysm (TEDY) trial, and aimed to assess the efficacy of the angiotensin 1 receptor blocker telmisartan in reducing abdominal aortic aneurysm (AAA) peak wall stress (PWS) and peak wall rupture index (PWRI) a...

Background Rupture of unstable atherosclerotic plaques with a large lipid-rich necrotic core and a thin fibrous cap cause myocardial infarction and stroke. Yet it has not been possible to assess this for individual patients. Clinical guidelines still rely on use of luminal narrowing, a poor indicator but one that persists for lack of effective mean...

The computational analysis of fiber network fracture is an emerging field with application to paper, rubber-like materials, hydrogels, soft biological tissue, and composites. Fiber networks are often described as probabilistic structures of interacting one-dimensional elements, such as truss-bars and beams. Failure may then be modeled as strong dis...

Objective: The role of atherosclerosis in abdominal aortic aneurysm (AAA) pathogenesis is controversial. The aim of this study was to compare AAA growth in patients who did and did not have concurrent athero-occlusive disease (AOD). Methods: Patients with an AAA measuring 35 - 49 mm in maximum diameter were recruited as part of the TElmisartan i...

The computational analysis of fiber network fracture is an emerging field with application to paper, rubber-like materials, hydrogels, soft biological tissue, and composites. Fiber networks are often described as probabilistic structures of interacting one-dimensional elements, such as truss-bars and beams. Failure may then be modeled as strong dis...

Abdominal aortic aneurysm (AAA) disease, the local enlargement of the infrarenal aorta, is a serious condition that causes many deaths, especially in men exceeding 65 years of age. Over the past quarter of a century, computational biomechanical models have been developed towards the assessment of AAA risk of rupture, technology that is now on the v...

To model fiber failures in random fiber networks, we have developed an elastoplastic Timoshenko beam finite element with embedded discontinuities. The method is based on the theory of strong discontinuities where the generalized displacement field is enhanced by a jump. The continuum mechanics formulation accounts for a fracture process zone and a...

It remains difficult to predict when which patients with abdominal aortic aneurysm (AAA) will require surgery. The aim was to study the accuracy of geometric and biomechanical analysis of small AAAs to predict reaching the threshold for surgery, diameter growth rate and rupture or symptomatic aneurysm. 189 patients with AAAs of diameters 40–50 mm w...

Clinical results obtained when degradable polymer-based medical devices are used in breast reconstruction following mastectomy are promising. However, it remains challenging to develop a large scaffold structure capable of providing both sufficient external mechanical support and an internal cell-like environment to support breast tissue regenerati...

A versatile constitutive model for load-carrying soft biological tissue should incorporate salient microstructural deformation mechanisms and be able to reliably predict complex non-linear viscoelastic behavior. The advancement of treatment and rehabilitation strategies for soft tissue injuries is inextricably linked to our understanding of the und...

Background Prior studies have suggested aortic peak wall stress (PWS) and peak wall rupture index (PWRI) can estimate the rupture risk of an abdominal aortic aneurysm (AAA), but whether these measurements have independent predictive ability over assessing AAA diameter alone is unclear. The aim of this systematic review was to compare PWS and PWRI i...

Objective Therapeutic advancements in atherosclerotic cardiovascular disease have improved prevention of ischemic stroke and myocardial infarction, but diagnostic methods for atherosclerotic plaque phenotyping to aid individualized therapy are lacking. In this feasibility study, we aimed to elucidate plaque biology by decoding the molecular phenoty...

This chapter concerns linear and non-linear Continuum Mechanics. We introduce the Representative Volume Element (RVE) and provide the kinematic description for the deformation of a body between its reference and spatial configuration, respectively. The presentation of strain measures is followed by the introduction of the Cauchy stress. An analysis...

This chapter introduces the linear and non-linear Finite Element Method (FEM). It begins with the spatial discretization of a continuum body, followed by the introduction of shape functions and gradient operators. We then discuss the Calculus of Variations, where problems such as diffusion, advection-diffusion, linear and non-linear solid mechanics...

This chapter addresses the active properties of blood vessels with a focus on vasoreactivity and arteriogenesis. We review the structure and function of Smooth Muscle Cells (SMC) and their interaction with Endothelium Cells (EC) in the control of blood vessels. The discussion of collagen and elastin synthesis then aims at providing a fundamental un...

This chapter discusses concepts and strategies toward the development and testing of bioengineering models. We explore the complexity of vascular bioengineering problems and then introduce the Intended Model Application (IMA), a target that determines the design of all development protocols. Following the specification of models and their developme...

This chapter analyzes the macrocirculation, the microcirculation, and the lymphatic system of the vascular apparatus. We discuss the structure of the vessel wall, the main principles of hemodynamic control, and the mechanisms of vascular exchange. We look at the circulation from a system’s perspective and introduce mechanical properties, such as pr...

This chapter concerns the analysis of conduit vessels, and given their clinical relevance in vascular disease, it mainly relates to arteries. We begin with the histology of the vessel wall, with specific emphasis placed on collagen and elastin, the main structural proteins in the ExtraCellular Matrix (ECM). Following the general description of vess...

This chapter addresses the flow of blood in conduit vessels. We review the composition of blood, a suspension of different-sized particles in plasma, and investigate the forces that act upon said particles. It results in the description of the rheological properties of blood, where single-phasic and bi-phasic models are covered. We then explore blo...

This textbook serves as a modern introduction to vascular biomechanics and provides the comprehensive overview of the entire vascular system that is needed to run successful vascular biomechanics simulations. It aims to provide the reader with a holistic analysis of the vascular system towards its biomechanical description and includes numerous ful...

Growth plate and articular cartilage constitute a single anatomical entity early in development but later separate into two distinct structures by the secondary ossification center (SOC). The reason for such separation remains unknown. We found that evolutionarily SOC appears in animals conquering the land - amniotes. Analysis of the ossification p...

Growth plate and articular cartilage constitute a single anatomical entity early in development but later separate into two distinct structures by the secondary ossification center (SOC). The reason for such separation remains unknown. We found that evolutionarily SOC appears in animals conquering the land - amniotes. Analysis of the ossification p...

Hip fractures are a major health problem with high socio-economic costs. Subject-specific finite element (FE) models have been suggested to improve the fracture risk assessment, as compared to clinical tools based on areal bone mineral density, by adding an estimate of bone strength. Typically, such FE models are limited to estimate bone strength a...

Growth plate and articular cartilage constitute a single anatomical entity early in development, but later separate into two distinct structures by the secondary ossification center (SOC). The reason for such separation remains unknown. We found that evolutionarily SOC appears in animals conquering the land - amniotes. Analysis of ossification patt...

Background: Previous studies have suggested that finite element analysis (FEA) can estimate the rupture risk of an abdominal aortic aneurysm (AAA); however, the value of biomechanical estimates over measurement of AAA diameter alone remains unclear. This study aimed to compare peak wall stress (PWS) and peak wall rupture index (PWRI) in participan...

Biologically compatible membranes are of high interest for several biological and medical applications. Tissue engineering, for example, would greatly benefit from ultrathin, yet easy‐to‐handle, biodegradable membranes that are permeable to proteins and support cell growth. In this work, nanomembranes are formed by self‐assembly of a recombinant sp...

Degradable porous polymeric structures are attractive candidates for biological tissue scaffolds, and adequate mechanical, transport, chemical and biological properties determine their functionality. Aside from the properties of polymer-based materials, the scaffold's meso-structure controls its elasticity at the organ length-scale. This study inve...

Objective: Several studies of biomechanical rupture risk assessment (BRRA) showed its advantage over the diameter criterion in rupture risk assessment of abdominal aortic aneurysm (AAA). However, BRRA studies have not investigated the predictability of biomechanical risk indices at different time points ahead of rupture, nor have they been perform...

Coronary heart disease is a major and global health care challenge, and its biomechanical analysis has been shown to be a useful complement in answering related clinical questions. Compelling evidence has been accumulated showing that two primary biomechanical factors predispose to the disease: low or oscillating wall shear stress and high wall mec...

Background: Intraluminal thrombus (ILT) is present in most abdominal aortic aneurysms (AAAs), although its role in AAA progression is controversial. Methods: A literature search was performed to identify studies that investigated the association between ILT volume and AAA rupture. A study assessment tool was developed to assess the methodologic...

Objective In a population-based cohort of ruptured abdominal aortic aneurysms (rAAAs), our aim was to investigate clinical, morphological and biomechanical features in patients with small rAAAs. Methods All patients admitted to an emergency department in Stockholm and Gotland, a region with a population of 2.1 million, between 2009–2013 with a CT-...

Tissues are built of cells integrated in an extracellular matrix (ECM) which provides a three-dimensional (3D) microfiber network with specific sites for cell anchorage. By genetic engineering, motifs from the ECM can be functionally fused to recombinant silk proteins. Such a silk protein, FN-silk, which harbours a motif from fibronectin, has the a...

The growth of long bones occurs in narrow discs of cartilage, called growth plates that provide a continuous supply of chondrocytes subsequently replaced by newly formed bone tissue. These growth plates are sandwiched between the bone shaft and a more distal bone structure called the secondary ossification center (SOC). We have recently shown that...

https://evtoday.com/2019/03/does-finite-element-analysis-enable-us-to-predict-rupture/

Purpose: To investigate how 2-dimensional geometric parameters differ between ruptured and asymptomatic abdominal aortic aneurysms (AAAs) and provide a biomechanical explanation for the findings. Methods: The computed tomography angiography (CTA) scans of 30 patients (mean age 77±10 years; 23 men) with ruptured AAAs and 60 patients (mean age 76±8 y...

Tissues are built of cells integrated in an extracellular matrix (ECM) which provides a three-dimensional (3D) fibrillar network with specific sites for cell anchorage. By genetic engineering, motifs from the ECM can be functionally fused to recombinant silk proteins. Such a silk protein, FN-silk, which harbours a motif from fibronectin, has the ab...

An Abdominal Aortic Aneurysm (AAA) is an enlargement of the infrarenal aorta, a serious condition whose clinical treatment requires assessing its risk of rupture. This chapter reviews the current state of the Biomechanical Rupture Risk Assessment (BRRA), a non-invasive diagnostic method to calculate such AAA rupture risk, and emphasizes on constitu...

Objective: Predicting which abdominal aortic aneurysms (AAA) will require surgery and which may remain stable remains a challenge. We set out to evaluate whether semi-automatic diameter measurements and finite element analysis (FEA) might predict the four-year prognosis of AAAs more precisely than standard diameter measurements. Methods: From a ret...

Introduction: Diameter is currently the only factor used to estimate rupture risk of abdominal aortic aneurysms (AAAs). Many large AAAs, however, do not rupture, and a significant portion of small AAAs do. Our aim was to investigate if simple two-dimensional geometric measurements can improve rupture risk prediction in AAAs, and relate these measur...

Biomechanics-based assessment of Abdominal Aortic Aneurysm (AAA) rupture risk has gained considerable scientific and clinical momentum. However, computation of peak wall stress (PWS) using state-of-the-art finite element models is time demanding. This study investigates which features of the constitutive description of AAA wall are decisive for ach...

Background The intraluminal thrombi (ILT) of abdominal aortic aneurysms (AAA) contain neutrophils, which can secrete elastase. We evaluated whether plasma neutrophil elastase-derived cross-linked fibrin degradation products (E-XDP) could reveal the presence, size and mechanical stress of AAAs and its ILTs. Methods E-XDP and D-dimer were measured in...

The aorta is a dynamic structure that is able to maintain conditions for optimal mechanical operation through the continuous turnover of its internal structure. The aorta's properties are critical to the entire cardiovascular system, and the study of its biomechanics may help us to better understand the role of tissue stress and strain in aortic ag...

Background An abdominal aortic aneurysm (AAA) is a focal dilation of the abdominal aorta and is associated with a risk of fatal rupture. Experimental studies suggest that myo-inositol may exert beneficial effects on AAAs through favourable changes to biological pathways implicated in AAA pathology. The aim of the Inositol in the MAnaGemENt of abdom...

The biomechanics-based Abdominal Aortic Aneurysm (AAA) rupture risk assessment has gained considerable scientific and clinical momentum. However, such studies have mainly focused on information at a single time point, and little is known about how AAA properties change over time. Consequently, the present study explored how geometry, wall stress-re...

Simple correlation analysis. Correlations amongst geometry, wall stress-related and blood flow-related biomechanical properties. ILTTmax- Maximum thickness of the Intra-Luminal Thrombus (ILT) layer; VILT–ILT volume; PWRI–Peak Wall Rupture Risk; RRED–Rupture Risk Equivalent Diameter; WSSmax—Maximal magnitude of the Wall Shear Stress (WSS) vector; WS...

(1) Background: Vascular tissue seems to adapt towards stable homeostatic mechanical conditions, however, failure of reaching homeostasis may result in pathologies. Current vascular tissue adaptation models use many ad hoc assumptions, the implications of which are far from being fully understood; (2) Methods: The present study investigates the pla...

Poster presentation

Objective: An abdominal aortic aneurysm (AAA) ruptures if the vessel wall stress exceeds its strength, with high mortality as a result. The effect of biomechanical load on AAA gene expression is currently not well understood. Methods: Aortic tissue samples from 64 patients with an AAA that had been imaged with computed tomography angiography (CTA)...

Motivated by the lack of experimental data, we investigate the influence of different growth kinematics on the abdominal aortic aneurysm growth. We model the tissue’s mechanical response by a microstructure-motivated material law. The mass changes of the constituents are governed by growth and remodeling algorithms. The tissue volume change is comp...

External (mechanical) stimuli influence cell function at the level of gene expression and thereby contribute to the overall control of Soft Biological Tissues’ (SBT) structure and function. SBT seem to adapt towards stable homeostatic mechanical conditions, and failure of reaching homeostasis may result in pathologies. SBT adaptation has to obey ba...

Objective: Finite element analysis (FEA) has been suggested to be superior to maximal diameter measurements in predicting rupture of abdominal aortic aneurysms (AAAs). Our objective was to investigate to what extent previously described rupture risk factors were associated with FEA-estimated rupture risk. Methods: One hundred forty-six patients...

The present chapter reviews vessel wall histology and summarizes relevant continuum mechanical concepts to study mechanics-induced tissue damage. As long as the accumulated damage does not trigger strain localizations, the standard non-polar continuum mechanical framework is applicable. As an example, a damage model for collagenous tissue is discus...

Introduction and Objectives: An adequate artificial bladder is still a challenge to overcome. The computational model presented here intends to assist the conception of artificial solutions for bladder replacement. The numerical model for the urinary bladder was implemented using Finite Element Method, taking into account anatomical morphometry of...

Introduction and Objectives: An adequate artificial bladder is still a challenge to overcome. The computational model presented here intends to assist the conception of artificial solutions for bladder replacement. The numerical model for the urinary bladder was implemented using Finite Element Method, taking into account anatomical morphometry of...

Introduction: The maximum diameter and its expansion over time are clinically used to predict the risk of Abdominal Aortic Aneurysm (AAA) rupture. However, both indices lack the power to describe the rupture risk of individual cases. In contrast a biomechanics-based AAA rupture risk assessment allows a highly individualized analysis [1-3]. Such bio...