COMPUTATIONAL APPROACHES TO UNDERSTAND PHENOTYPIC STRUCTURE AND CONSTITUTIVE MECHANICS RELATIONSHIPS OF SINGLE CELLS

The goal of this work is to better understand the relationship between the structure and function of biological cells by simulating their nonlinear mechanical behavior under static and dynamic loading using image structure-based finite element modeling (FEM). Vascular smooth muscle cells (VSMCs) are chosen for this study due to the strong correlation of the geometric arrangement of their structural components on their mechanical behavior and the implications of that behavior on diseases such as atherosclerosis. VSMCs are modeled here using a linear elastic material model together with truss elements, which simulate the cytoskeletal fiber network that provides the cells with much of their internal structural support. Geometric characterization of single VSMCs of two physiologically relevant phenotypes in 2D cell culture is achieved using confocal microscopy in conjunction with novel image processing techniques. These computer vision techniques use image segmentation, 2D frequency analysis, and linear programming approaches to create representative 3D model structures consisting of the cell nucleus, cytoplasm, and actin stress fiber network of each cell. These structures are then imported into MSC Patran for structural analysis with Marc. Mechanical characterization is achieved using atomic force microscopy (AFM) indentation. Material properties for each VSMC model are input based on values individually obtained through experimentation, and the results of each model are compared against those experimental values. This study is believed to be a significant step towards the viability of finite element models in the field of cellular mechanics because the geometries of the cells in the model are based on confocal microscopy images of actual cells and thus, the results of the model can be compared against experimental data for those same cells

Application of adhesive joints on a tensegrity floor: verification of technology and mechanical performance

openIl lavoro svolto ha avuto come obiettivo la verifica l’applicabilità della tecnologia adesiva su componenti edilizi innovativi. L’impiego degli adesivi strutturali rappresenta la traduzione costruttiva del principio della “semplificazione tecnologica”, ovvero della possibilità di realizzare prodotti industrializzabili con elevate prestazioni ed un numero limitato di componenti, riducendo le emissioni ambientali nelle loro fasi di vita. In particolare, è stata verificata la fattibilità tecnico-costruttiva di un solaio tensegrale in acciaio e vetro, sviluppando l’idea brevettuale del brevetto n. 00014426973, inventore Prof. P. Munafò. L’attività di ricerca si è sviluppata con la sperimentazione di diverse tipologie di giunti adesivi con aderendi in acciaio, alluminio, vetro e adesivi sia dopo maturazione in condizioni di laboratorio che dopo invecchiamento artificiale accelerato. È stato poi definito costruttivamente il giunto adesivo tra sottostruttura in acciaio e l’impalcato in vetro per rendere strutturalmente collaborante l’impalcato con la sottostruttura tensegrale. Costruito il prototipo di solaio si è passati alla verifica delle prestazioni meccaniche con prove di carico. Parallelamente all’attività sperimentale sono state condotte analisi numeriche sull’elemento costruttivo, per verificare le ipotesi assunte. Il risultato ottenuto ha validato l’assunto alla base dell’idea brevettuale validando le previsioni dell’analisi numerica. In-fatti, dalle prove di carico si è riscontrato un significativo incremento della rigidezza del solaio grazie alla giunzione adesiva tra impalcato in vetro e sottostruttura tensegrale.The aim of the present work was to examine the applicability of adhesive bonding technology to innovative building components. The use of structural adhesives represents the constructive implementation of the principle of “technological simplification”, that is, the possibility of assembling industrially manufactured products with high performance and a limited number of components, reducing environmental emissions during their life phases. In particular, the technical-constructive feasibility of a steel and glass tensegrity floor was verified, developing the idea of Patent No. 00014426973 (inventor Prof. P. Munafò). The research activity developed with the testing of different types of adhesive joints with steel, aluminium, glass, and adherends both after curing in laboratory conditions and after artificial accelerated ageing. The adhesive joint between the steel substructure and the glass deck was then determined by design to allow the deck to structurally cooperate with the tensegrity substructure. The prototype of the floor was assembled, and the mechanical performance was verified by load tests. In parallel with the experiments, numerical analyses were performed on the structural element to verify the hypotheses adopted. The results obtained confirmed the assumption underlying the patent idea by validating the predictions of the numerical analysis. In fact, the load tests showed a significant increase in the stiffness of the floor thanks to the adhesive joint between the glass deck and the tensegrity substructure.INGEGNERIA CIVILE, AMBIENTALE, EDILE E ARCHITETTURAopenMarchione, Francesc

Design and analysis of geodesic tensegrity structures with agriculture applications.

"This report aims to promulgate and elucidate the effective application of scientific principles in the design and optimisation of tensegrity structures for practical applications. By developing the intrinsic geometry of the geodesic dome and applying tensegrity design principles, a range of efficient, lightweight, modular structures are developed and broadly classified as geodesic tensegrity structures. Novel systems for clustering domes in two dimensions are considered and the analytical geometry required to generate various dome structures is derived from first principles. Computational methods for performing the design optimisation of tensegrity structures are reviewed and explained in detail. It is shown how an efficient, unified computational framework, suitable for the analysis of tensegrity structures in general, may be developed using computations which involve the equilibrium matrix of a structure. The importance of exploiting symmetry to simplify structural computations is highlighted throughout, as this is especially relevant in the analysis of large dome structures. A novel approach to generating the global equilibrium matrix of a structure from element vectors and implementing symmetry subspace methods is presented, which relies on the choice of an appropriate coordinate system to reflect the symmetry of a structure. A new algorithm is developed for implementing symmetry subspace methods in a computer program which enables the symmetry-adapted vector basis to be generated more efficiently. Methods for analysing kinematically indeterminate tensegrities and prestressed mechanisms and performing the prestress optimisation of a tensegrity structure are briefly reviewed and explained. Efficient tensegrity modular systems are developed for constructing a range of double-layer geodesic tensegrity domes and grids, based on the pioneering work of the artist, Kenneth Snelson. Finally, the cultural significance of tensegrity technology is illustrated by focusing on a range of novel applications in agriculture and sustainable development and adopting the holistic, "design science, "approach advocated by Buckminster Fuller.

Collective Effects in Models for Interacting Molecular Motors and Motor-Microtubule Mixtures

Three problems in the statistical mechanics of models for an assembly of molecular motors interacting with cytoskeletal filaments are reviewed. First, a description of the hydrodynamical behaviour of density-density correlations in fluctuating ratchet models for interacting molecular motors is outlined. Numerical evidence indicates that the scaling properties of dynamical behavior in such models belong to the KPZ universality class. Second, the generalization of such models to include boundary injection and removal of motors is provided. In common with known results for the asymmetric exclusion processes, simulations indicate that such models exhibit sharp boundary driven phase transitions in the thermodynamic limit. In the third part of this paper, recent progress towards a continuum description of pattern formation in mixtures of motors and microtubules is described, and a non-equilibrium ``phase-diagram'' for such systems discussed.Comment: Proc. Int. Workshop on "Common Trends in Traffic Systems", Kanpur, India, Feb 2006; to be published in Physica

Computational modelling of mechanical tests of animal cell

Předkládaná diplomová práce se zabývá stavbou živých živočišných buněk a jejich odezvou na mechanické zatěžování. Zobecněným zaměřením práce je popis mechanického chování buňky nejenom ve fyziologickém, ale i v patologickém stavu. Výchozím předpokladem pro úspěšné řešení zadané úlohy je vysoce interdisciplinární přístup kombinující výpočtové přístupy mechaniky těles (v~tomto případě metodu konečných prvků) s lékařským výzkumem. Nejdůležitějším bodem při tvorbě výpočtového modelu, pomocí něhož je možné aproximovat chování živé buňky při zatížení, je zejména identifikace mechanicky významných komponent a~jejich materiálových parametrů. V tomto případě jsou jako mechanicky význačné identifikovány spojité součásti jádro, membrána a cytoplazma, které jsou nově propojeny s prvky diskrétními (mitochondriální sítí) v hybridním modelu, jehož platnost je ověřena pomocí experimentálních dat. Tento model slouží jako podklad k vyhodnocení míry vlivu mitochondrií na celkovou tuhost buňky.The presented Master's thesis deals with the structural arrangement of living animal cells and their mechanical behavior under loading. The generalized aim is to describe mechanical responses of cells under either physiological or pathological conditions. A highly interdisciplinary approach interconnecting the computational methods of solid mechanics (finite element method in particular) with medical research is an inseparable part of the problem solution. A crucial step in proposing a computational model for approximation of a living cell behavior under loading conditions is to establish mechanically significant components to be incorporated into the calculation and to identify their material parameters. A presented computational model incorporates continuum entities such as the nucleus, membrane, and cytoplasm interconnected with a discrete mitochondrial network. This results in a novel hybrid model which is validated through comparison with experimental data and serves as a means to estimate the mitochondrial impact on overall cell stiffness.

Modeling growth in biological materials

The biomechanical modeling of growing tissues has recently become an area of intense interest. In particular, the interplay between growth patterns and mechanical stress is of great importance, with possible applications to arterial mechanics, embryo morphogenesis, tumor development, and bone remodeling. This review aims to give an overview of the theories that have been used to model these phenomena, categorized according to whether the tissue is considered as a continuum object or a collection of cells. Among the continuum models discussed is the deformation gradient decomposition method, which allows a residual stress field to develop from an incompatible growth field. The cell-based models are further subdivided into cellular automata, center-dynamics, and vertex-dynamics models. Of these the second two are considered in more detail, especially with regard to their treatment of cell-cell interactions and cell division. The review concludes by assessing the prospects for reconciliation between these two fundamentally different approaches to tissue growth, and by identifying possible avenues for further research. © 2012 Society for Industrial and Applied Mathematics

Growth-Adapted Tensegrity Structures: A New Calculus for the Space Economy

We describe a novel approach to create and engineer an economically viable space habitat development technology, for deployment of a lightweight tensegrity habitat structure orbiting at Earth-Moon L2, where onboard robotic assets will use space-based materials to provide water for shielding, irrigation and life support, soil for ecosystem development, and to enable structural maintenance and enhancement. The habitat can become a tourist destination, an economic hub, and a multi-purpose research and support facility for lunar surface development and space ecosystem life sciences