Events Calendar

Astani CEE Seminar

Speaker: Christian Hellmich, Ph.D., Vienna University of Technology (TU Wien), Vienna, Austria

Talk Title: Engineering Science and Mechanics as Key to the Mathematical Identification of "Universal" Patterns Pervading Mineralized Biological Tissues, and Beyond

Abstract:
According to the eminent Austro-American zoologist Rupert Riedl (1925-2005), "… the living world happens to be crowded by universal patterns of organization …”. While Riedl, as “classical” biologist, typically took a descriptive approach to this issue, we ventured, over the last decade and in particular during the last few years, into an engineering science approach of mathematical nature, where we have indeed been successful in identifying „universal“ rules/patterns in structural biology and their mechanical consequences. A majority of our investigations concerned mineralized biological tissues such as bones, for which we identified the following mathematically cast rules: (I) In extracellular bone tissues across different organs from different animals/humans at different ages, mineral (hydroxyapatite) and collagen contents are not randomly assgined to each other, but fulfill astonishingly precise bilinear relations1, which follow from rigorous evaluation of dehydration, demineralization, ashing, and de-organifying test data collected over a time period of more than 80 years of experimental research. Furthermore, (II) the distribution of mineral throughout the extracellular bone matrix or ultrastructure, i.e. its partitioning into the fibrillar and extrafibrillar spaces is governed by the on-average uniformity of hydroxyapatite concentration in the extracollageneous space2, as was evidenced from chemical tests like the ones mentioned before, in combination with transmission electron micrographs. Before mineralization (as well as in unmineralized collageneous tissues such as tendon or cartilage), the fibrillar and extrafibrillar spaces again obey another general rule: (III) Upon hydration, the extrafibrillar space grows propertional to the fibrillar volume gain due to accomodation of water in the intermolecular spaces3, as evidenced from dehydration and neutron diffraction tests. Finally, (IV) mineralization of such tissues is driven by fluid-to-solid phase transformations in the extracollageneous space under closed thermodynamic conditions4, predicting precisely the volume losses which the tissues undergo during mineralization. All these compositional and structural rules may serve as ideal input for multiscale mechanics models for the elasticity5, strength6, and creep7 of bone tissues; enabling various clinical applications, such as Computed Tomography (CT)-based Finite Element (FE) analysis for biomaterial design8.
The knowledge we gained in studying biological tissue, was also instrumental in driving forward the multiscale mechanics of wood9, ceramics10, and concrete11, materials that share quite some microstructural, chemical, and mechanical features with bone.

Biography: Dr. Christian Hellmich is Full Professor for Strength of Materials and Computational Mechanics in the Department of Civil Engineering at the Vienna University of Technology (TU Wien). At this university, he received his engineering degree in 1995, his Ph.D. Degree in 1999, and his Habilitation degree in 2004. Between 2000 and 2002, he was a Max Kade Postdoctoral Fellow in the Department of Civil and Environmental Engineering at the Massachusetts Institute of Technology. His work is strongly focussed on well-validated material and (micro)structural models, both for materials such as concrete, soil, rock, wood, or bone as well as man-made biomaterials, and for structures such as tunnels, pipelines, bridges, or the vertebrate skeleton including implants and tissue engineering scaffolds - with complementary experimental activities if necessary. He has held several leadership positions in projects with the tunnel and pipeline industry, as well as in the interdisciplinary and international material research activities sponsored by the European Commission, including his role as the coordinator of the mixed industry-academia consortium “BIO-CT-EXPLOIT”, merging computer tomography with continuum micromechanics. He has published 85 papers in international refereed scientific journals in the fields of engineering mechanics, materials science, and theoretical biology, 19 book chapters, and more than 100 papers in refereed conference proceedings. Dr. Hellmich has served as the Chairman of both the Properties of Materials Committee of the Engineering Mechanics Division of the American Society of Civil Engineers and the Poromechanics Committee of the Engineering Mechanics Institute, as associate editor of the Journal of Engineering Mechanics (ASCE), and in the editorial board for six other journals. As community service, he has (co-)chaired and/or supported more than 50 international conferences, and reviewed for 71 scientific journals and 11 science foundations. He was awarded the Kardinal Innitzer Science Award of the Archbishopry of Vienna in 2004 (for his habilitation thesis), the Science Award of the State of Lower Austria in 2005 (for his achievements in the micromechanics of hierarchical composites), and he was the recipient of the 2008 Zienkiewicz Award for Young Scientists in Computational Engineering Sciences, sponsored by the European Community on Computational Methods in Applied Sciences (ECCOMAS). For further activities in the multiscale poro-micromechanics of bone materials, he received one of the highly prestigious ERC Grants of the European Research Council in 2010: and he was elected member the Young Academy of the Austrian Academy of Sciences in 2011. In 2012, he was rewarded the prestigious Walter L. Huber Research Prize of the ASCE, for his contributions to the microporomechanics of hierarchical geomaterials and biomaterials.


Host: Prof. Roger Ghanem

Location: Kaprielian Hall (KAP) - 209 Conference Room

Audiences: Everyone Is Invited

Contact: Evangeline Reyes