PhD Thesis Defence Presentations - Giannokostas Konstantinos
Abstract (Περίληψη)
Blood is a complex suspension of red and white cells, and platelets in an aqueous solution, the so-called
plasma, containing dissolved proteins. In the last decades, the investigation of hemorheology has
stimulated a lot of attention to the complex mechanical behavior of blood primarily due to the direct
relevance of blood rheology to disease detection, treatment, and prevention. This work aims to the
development a robust and consistent hemorheological model, able to offer reliable predictions in various
rheometric tests such as shear or extensional flows. Additionally, it describes the blood flow in microtubes
under steady and pulsatile conditions incorporating microcirculation phenomena such as the Fåhraeus
and the Fåhraeus-Lindqvist effects. This work is extended to the overall study of microcirculation since
blood flows into microvessels in which many mechanical and biochemical phenomena are involved,
incorporating the interaction of the blood flow with the elastic walls. We introduce a fluid-structure
interaction model in a coupled manner to provide accurate results of the vessel dilation and stress field
under various intraluminal pressure conditions. We also account for smooth muscle contractility, an
internal mechanism that incorporates biochemical phenomena which lead to the development of active
stresses. Apart from the integrated modeling of blood rheological complexity, our implementation is
adequate for multi-dimensional simulations due to its tensorial formalism. To this end, blood flow in 3D
aneurysmal geometries is investigated under sinusoidal waveforms with different frequencies, amplitudes,
and patterns, providing a thorough parametric study. This work offers accurate predictions of the
instantaneous structure of blood as well as of WSS which are strongly correlated with aneurysm growth,
stabilization, and rupture.
Το αίμα είναι ένα πολύπλοκο εναιώρημα ερυθρών αιμοσφαιρίων, λευκών αιμοσφαιρίων και αιμοπεταλίων
σε ένα υδατικό διάλυμα, το λεγόμενο πλάσμα αίματος, που περιέχει κυρίως πρωτεΐνες. Τις τελευταίες
δεκαετίες, η μελέτη της ρεολογίας του αίματος έχει επικεντρωθεί στη περίπλοκη συμπεριφορά του, κυρίως
λόγω της άμεσης σχέσης της με την ανίχνευση, τη θεραπεία και την πρόληψη ασθενειών. Βασικός
σκοπός αυτής της εργασίας είναι η ανάπτυξη ενός καταστατικού μοντέλου το οποίο να προσφέρει
αξιόπιστες προβλέψεις σε διάφορα ρεομετρικά πειράματα, όπως διατμητικές ή εκτατικές ροές. Επιπλέον,
να προσφέρει τη δυνατότητα της σωστής περιγραφής της διφασικής ροής του αίματος σε μικροσωλήνες
υπό σταθερές και παλμικές συνθήκες που ενσωματώνουν τα φαινόμενα μικροκυκλοφορίας όπως ο
σχηματισμός του αμιγούς στρώματος πλάσματος καθώς και τα φαινόμενα Fåhraeus και Fåhraeus-
Lindqvist. Η εργασία επεκτείνεται στην μελέτη και των αιμοφόρων αγγείων καθώς σε αυτά εμπλέκονται
πολλά μηχανικά και βιοχημικά φαινόμενα, ενσωματώνοντας την αλληλεπίδραση της ροής του αίματος με
τα ελαστικά τοιχώματα αυτών. Εισάγουμε ένα μοντέλο αλληλεπίδρασης ρευστού-δομής ώστε να
παρέχουμε ακριβή αποτελέσματα της διαστολής και των τάσεων που αναπτύσσονται στα τοιχώματα των
αγγείων υπό διάφορες συνθήκες αρτηριακής πίεσης. Το μοντέλο μας παρέχει την δυνατότητα πρόβλεψης
της συσταλτικότητας των λείων μυών, ενσωματώνοντας βιοχημικά φαινόμενα, τις λεγόμενες ενεργές
δυνάμεις. Εκτός από την ολοκληρωμένη μοντελοποίηση της ρεολογικής πολυπλοκότητας του αίματος, η
τανυστική περιγραφή του μοντέλου δίνει την δυνατότητα υλοποίησης προσομοιώσεων πολυδιάστατων
προβλημάτων. Για το σκοπό αυτό, μελετήθηκε η ροή του αίματος σε τρισδιάστατες ανευρυσματικές
γεωμετρίες επιβάλλοντας ημιτονοειδείς κυματομορφές με διαφορετικές συχνότητες και πλάτη κύματος,
παρέχοντας μια ενδελεχή παραμετρική μελέτη. Αυτή η εργασία παρέχει ακριβείς προβλέψεις της
στιγμιαίας δομής του αίματος καθώς και της τάσης στην ανευρισματική περιοχη η οποία συσχετίζεται με
την ανάπτυξη, τη σταθεροποίηση και τη ρήξη του ανευρύσματος.
Speakers Short CV (Σύντομο Βιογραφικό Ομιλητή)
He was born and grew in Agrinio, Greece. In 2013, he obtained a B.Sc. degree in Physics from the University of Patras with a core in “Environment & Energy”. Following the completion of his B.Sc. degree, he entered the Department of Chemical Engineering to pursue a M.Sc. Degree in “Process Simulation, Optimization & Control”, from which he graduated in 2017. Hence, he has been working towards completing a Ph.D. thesis in “Multiscale modeling of hemodynamics in microvessels” by participating in the Laboratory of Fluid Mechanics & Rheology (FluidsLab), under the supervision of Associate Professor Y. Dimakopoulos, and the guidance of Professor J. Tsamopoulos. He has seven in peer-review scientific journals and eleven participations in international conferences.
Education
Ph.D. in Chemical Engineering Aug 2022
Department of Chemical Engineering, University of Patras
Thesis title: “Multiscale modeling of hemodynamics in microvessels”
Advisor: Ass. Prof. Yannis Dimakopoulos
M.Sc. in Simulation, Optimization and Control of Processes November 2017
Department of Chemical Engineering, University of Patras
Thesis title: “Hemodynamics in complex 2D and 3D microcirculation: An apparent slip law for the accurate calculation of Wall Shear Stress in blood flow”
Grade: 9.15/10
Advisor: Ass. Prof. Yannis Dimakopoulos
Bachelor in Physics June 2013
Department of Physics, University of Patras
Thesis title: “Aerodynamic simulation of an airplane wing under subsonic and supersonic flow”
Grade: 6.92/10
Advisor: Prof. Vasilios Loukopoulos
Publications
- Giannokostas, K.; Dimakopoulos, Y.; Tsamopoulos, J.
Shear Stress and Intravascular Pressure effects on Vascular Dynamics: Two-phase blood flow in elastic microvessels accounting for the passive stresses. Biomech. Model Mechanobiol. 2022, DOI: 10.1007/s10237-022-01612-2
- Giannokostas, K.; Dimakopoulos, Y.; Tsamopoulos, J.
Shear Stress and Intravascular Pressure effects on Vascular Dynamics: Two-phase blood flow in elastic microvessels accounting for the passive and active stresses. Interface focus 2022 (under review)
- Giannokostas, K.; Dimakopoulos, Y.; Tsamopoulos, J.
TEVP model predictions of the pulsatile blood flow in 3D aneurysmal geometries. J. Nonnewton. Fluid Mech. 2022 (under review)
- Psevdos, C.; Giannokostas, K.; Dimakopoulos, Y.; Tsamopoulos, J.
Monophasic Blood Flow Model with Wall Slip for Accurate and Accessible Prediction of Wall Shear Stresses in the Microcirculation. J. Nonnewton. Fluid Mech. 2022 (under review)
- Giannokostas, K.; Photeinos, D.; Dimakopoulos, Y.; Tsamopoulos, J.
Quantifying the Non-Newtonian Effects of Pulsatile Hemodynamics in Tubes. J. Nonnewton. Fluid Mech. 2021, 298, 104673.
- Giannokostas, K.; Dimakopoulos, Y.; Anayiotos, A; Tsamopoulos, J.
Advanced Constitutive Modeling of the Thixotropic Elasto-Visco-Plastic Behavior of Blood: Steady-State Blood Flow in Microtubes. Materials (Basel). 2021, 14 (2), 367.
- Giannokostas, K.; Moschopoulos, P.; Varchanis, S.; Dimakopoulos, Y.; Tsamopoulos, J. Advanced Constitutive Modeling of the Thixotropic Elasto-Visco-Plastic Behavior of Blood: Description of the Model and Rheological Predictions. Materials (Basel). 2020, 13 (18), E4184.
Presentations
- JNNF Complex Fluids Seminar Series, Virtual, March 2022
Title: “From biorheology to biofluid mechanics: Elucidating the behavior of Biofluids in complex flows”
Oral presentation
- 25th International Congress of Theoretical and Applied Mechanics (ICTAM), Milano, Italy, August 2021
Title: “Effect of blood thixotropy and viscoelasticity on the hemodynamics in large vessels: Advanced hemorheological modelling and simulation”
Oral presentation
- 18th Congress on Rheology (ICR), Rio de Janeiro, Brazil, December 2021
Title: “Hemodynamics in microvessels: Comparison of cellular level simulations and continuous advanced constitutive modeling”
Oral presentation
- Annual European Rheology Conference (AERC), Virtual, April 2021
Title: “The Thixo-Elasto-ViscoPlastic Behavior Of Blood In Pulsatile Flows”
Poster presentation
- 12th Panhellenic Scientific Conference of Chemical Engineering, Athens, Greece, May 2019
Title: “An integrated model for predicting passive and active stresses in elastic blood vessels”
Oral presentation
- 12rd Fluid Mechanics Conference (EFMC), Vienna, Austria, Sep 2018
Title: “Transient Effects of NO Production/Diffusion in Microvessels”
Oral presentation
- 8th World Congress of Biomechanics (WCB), Dublin, Ireland, Jul 2018
Title: “An integrated model of arteriole tissue dynamics accounting for passive stresses”
Oral presentation
- 23rd Congress of the European Society of Biomechanics (ESB), Seville, Spain, Jul 2017
Title: “An apparent slip law for the accurate calculation of the WSS in microcirculation”
Oral presentation
- 11th Panhellenic Scientific Conference of Chemical Engineering, Thessaloniki, Greece, May 2017
Title: “The accurate calculation of the WSS in microcirculation”
Oral presentation