Please note that the list below only shows forthcoming events, which may not include regular events that have not yet been entered for the forthcoming term. Please see the past events page for a list of all seminar series that the department has on offer.

 

Past events in this series


Thu, 05 Jun 2025

12:00 - 13:00
L3

Constitutive Modeling of the Microstructure of Arterial Walls Including Collagen Cross-Linking

Gerhard Holzapfel
(TU Graz)

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Extended Bio
Gerhard A. Holzapfel is a world-leading figure in biomechanics, currently serving as Professor and Head of the Institute of Biomechanics at Graz University of Technology (TUG), Austria. He also holds appointments as Adjunct Professor at the Norwegian University of Science and Technology (NTNU) in Trondheim and Visiting Professor at the University of Glasgow. From 2004 to 2013, he was Professor of Biomechanics at the Royal Institute of Technology (KTH) in Stockholm.

Following a PhD in Mechanical Engineering from Graz, Professor Holzapfel was awarded an Erwin Schrödinger Scholarship, enabling him to conduct research at Stanford University. He achieved his Habilitation at TU Vienna in 1996 and was the recipient of Austria’s prestigious START Award in 1997. Over subsequent decades, he has led pioneering work in computational biomechanics, including as Head of the Computational Biomechanics research group at TUG (1998–2004).

Professor Holzapfel has received numerous accolades, including the Erwin Schrödinger Prize of the Austrian Academy of Sciences (2011), listings among “The World’s Most Influential Scientific Minds” (Thomson Reuters, 2014), the William Prager Medal and Warner T. Koiter Medal (2021), an honorary doctorate from École des Mines de Saint-Étienne (2024), and election to the U.S. National Academy of Engineering (2025). In 2024, he was awarded a prestigious Synergy Grant from the European Research Council (ERC).

His research spans experimental and computational biomechanics and mechanobiology, with a particular focus on soft biological tissues and the cardiovascular system in both health and disease. His expertise includes nonlinear continuum mechanics, constitutive modelling, growth and remodeling, imaging and image-based modeling, and the mechanics of therapeutic interventions such as angioplasty and stenting.

Professor Holzapfel is the author of the widely adopted graduate textbook Nonlinear Solid Mechanics (Wiley), has co-edited seven additional books, and contributed chapters to over 30 volumes. He has published more than 300 peer-reviewed journal articles. He is also the co-founder and co-editor of the journal Biomechanics and Modeling in Mechanobiology (Springer). His work has been funded by numerous national and international agencies, including the Austrian Science Fund, NIH, the European Commission, and industry collaborators.

Abstract

Nowadays, the 3D ultrastructure of a fibrous tissue can be reconstructed in order to visualize the complex nanoscale arrangement of collagen fibrils including neighboring proteoglycans even in the stretched loaded state [1]. In particular, experimental data of collagen fibers in human artery layers have shown that the f ibers are not symmetrically dispersed [2]. In addition, it is known that collagen f ibers are cross-linked and the density of cross-links in arterial tissues has a stiffening effect on the associated mechanical response. A first attempt to characterize this effect on the elastic response is presented and the influence of the cross-link density on the mechanical behavior in uniaxial tension is shown [3]. A recently developed extension of the model that accounts for dispersed fibers connected by randomly distributed cross-links is outlined [4]. A simple shear test focusing on the sign of the normal stress perpendicular to the shear planes (Poynting effect) is analyzed. In [5] it was experimentally observed that, in contrast to rubber, semi-flexible biopolymer gels show a tendency to approach the top and bottom faces under simple shear. This so-called negative Poynting effect and its connection with the cross-links as well as the fiber and crosslink dispersion is also examined. 

References 

[1]A. Pukaluk et al.: An ultrastructural 3D reconstruction method for observing the arrangement of collagen fibrils and proteoglycans in the human aortic wall under mechanical load. Acta Biomaterialia, 141:300-314, 2022. 

 [2] G.A. Holzapfel et al.: Modelling non-symmetric collagen fibre dispersion in arterial walls. Journal of the Royal Society Interface, 12:20150188, 2015. 

 [3] G.A. Holzapfel and R.W. Ogden: An arterial constitutive model accounting for collagen content and cross-linking. Journal of the Mechanics and Physics of Solids, 136:103682, 2020. 

 [4] S. Teichtmeister and G.A. Holzapfel: A constitutive model for fibrous tissues with cross-linked collagen fibers including dispersion – with an analysis of the Poynting effect. Journal of the Mechanics and Physics of Solids, 164:104911, 2022. 

[5] P.A. Janmey et al.: Negative normal stress in semiflexible biopolymer gels. Nature Materials, 6:48–51, 2007.

 

Thu, 12 Jun 2025

12:00 - 13:00
L3

Microfluidic model of haemodynamics in complex media

Anne Juel
(University of Manchester)

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Short Bio
Anna Juel is a physicist whose research explores the complex dynamics of material systems, particularly in two-phase flows and wetting phenomena. Her group focuses on microfluidics, fluid-structure interactions, and complex fluid flows, with applications ranging from chocolate moulding to airway reopening and flexible displays. Based at the Manchester Centre for Nonlinear Dynamics, her experimental work often uncovers surprising behaviour, driving new insights through combined experimentation and modelling.

Abstract
The flow of red blood cells (RBCs) in heterogeneous biological porous tissues such as the human placenta, remains poorly understood despite the essential role the microvasculature plays in maintaining overall health and functionality of tissues, blood flow and transport mechanisms. This is in great part because the usual description of blood as a simple fluid breaks down when the size of RBCs is similar to that of the vessel. In this study, we use a bespoke suspension of ultra-soft microcapsules with a poroelastic membrane, which have been previously shown to mimic the motion and large deformations of RBCs in simple conduits [1], in order to explore soft suspension flows in planar porous media. Our planar porous devices are Hele-Shaw channels, where the capsules are slightly confined within the channel depth, and in which we increase confinement by adding regular or disordered arrays of pillars. We perform experiments that relate the global resistance of the suspension flow through the porous media to the local distributions of capsule concentration and velocity as a function of volume fraction, capillary number Ca, the ratio of viscous to elastic forces, and geometry. We find that the flow patterns in Hele-Shaw channels and ordered porous media differ significantly from those in disordered porous media, where the presence of capsules promotes preferential paths and supports anomalous capsule dispersion. In contrast, the flows in ordered geometries develop intriguing shear-banding patterns as the volume fraction increases. Despite the complex microscopic dynamics of the suspension flow, we observe the emergence of similar scaling laws for the global flow resistance in both regular and disordered porous media as a function of Ca. We find that the scaling exponent decreases with increasing volume fraction because of cooperative capsule mechanisms, which yield relative stiffening of the system for increasing Ca.
 
[1] Chen et al. Soft Matter 19, 5249- 5261.
 
Wed, 18 Jun 2025

12:00 - 13:00
L3

Structures and Stability: Battling Beams, Kirigami Computing, and Eye Morphogenesis

Douglas Holmes
(Boston University College of Engineering)

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Short Bio
Douglas Holmes is a Professor in the Department of Mechanical Engineering at Boston University. He received degrees in Chemistry from the University of New Hampshire (B.S. 2004), Polymer Science & Engineering from the University of Massachusetts, Amherst (M.S. 2005, Ph.D. 2009), and was a postdoctoral researcher in Mechanical & Aerospace Engineering at Princeton University. Prior to joining Boston University, he was an Assistant Professor of Engineering Science & Mechanics at Virginia Tech. His research group specializes in the mechanics of slender structures, with a focus on understanding and controlling how objects change shape. His work has been recognized by the NSF CAREER Award, the ASEE Ferdinand P. Beer and E. Russell Johnston Jr. Outstanding New Mechanics Educator Award, and the Theo de Winter Distinguished Faculty Fellowship.

Abstract

Structural mechanics plays a crucial role in soft matter physics, mechanobiology, metamaterials, pattern formation, active matter, and soft robotics. What unites these seemingly disparate topics is the natural balance that emerges between elasticity, geometry, and stability. This seminar will serve as a high-level overview of our work on several problems concerning the stability of structures. I will cover three topics: (1) shapeshifting shells; (2) mechanical metamaterials; and (3) elastogranular mechanics.


I will begin by discussing our development of a generalized, stimuli-responsive shell theory. (1) Non-mechanical stimuli including heat, swelling, and growth further complicate the nonlinear mechanics of shells, as simultaneously solving multiple field equations to capture multiphysics phenomena requires significant computational expense. We present a general shell theory to account for non-mechanical stimuli, in which the effects of the stimuli are
generalized into three forms: those that add mass to the shell, those that increase the area of the shell through the natural stretch, and those that change the curvature of the shell through the natural curvature. I will show how this model can capture the morphogenesis of the optic cup, the snapping of the Venus flytrap, leaf growth, and the buckling of electrically active polymer plates. (2) I will then discuss how cutting thin sheets and shells, a process
inspired by the art of kirigami, enables the design of functional mechanical metamaterials. We create linear actuators, artificial muscles, soft robotic grippers, and mechanical logic units by systematically cutting and stretching thin sheets. (3) Finally, if time permits, I will introduce our work on the interactions between elastic and granular matter, which we refer to as elastogranular mechanics. Such interactions occur across all lengths, from morphogenesis, to root growth, to stabilizing soil against erosion. We show how combining rocks and string in the absence of any adhesive we can create large, load bearing structures like columns, beams, and arches. I will finish with a general phase diagram for elastogranular behavior.