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Fidalgo DS, Jorge RMN, Parente MPL, Louwagie EM, Malanowska E, Myers KM, Oliveira DA. Pregnancy state before the onset of labor: a holistic mechanical perspective. Biomech Model Mechanobiol 2024; 23:1531-1550. [PMID: 38758337 PMCID: PMC11436406 DOI: 10.1007/s10237-024-01853-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2024] [Accepted: 04/17/2024] [Indexed: 05/18/2024]
Abstract
Successful pregnancy highly depends on the complex interaction between the uterine body, cervix, and fetal membrane. This interaction is synchronized, usually following a specific sequence in normal vaginal deliveries: (1) cervical ripening, (2) uterine contractions, and (3) rupture of fetal membrane. The complex interaction between the cervix, fetal membrane, and uterine contractions before the onset of labor is investigated using a complete third-trimester gravid model of the uterus, cervix, fetal membrane, and abdomen. Through a series of numerical simulations, we investigate the mechanical impact of (i) initial cervical shape, (ii) cervical stiffness, (iii) cervical contractions, and (iv) intrauterine pressure. The findings of this work reveal several key observations: (i) maximum principal stress values in the cervix decrease in more dilated, shorter, and softer cervices; (ii) reduced cervical stiffness produces increased cervical dilation, larger cervical opening, and decreased cervical length; (iii) the initial cervical shape impacts final cervical dimensions; (iv) cervical contractions increase the maximum principal stress values and change the stress distributions; (v) cervical contractions potentiate cervical shortening and dilation; (vi) larger intrauterine pressure (IUP) causes considerably larger stress values and cervical opening, larger dilation, and smaller cervical length; and (vii) the biaxial strength of the fetal membrane is only surpassed in the cases of the (1) shortest and most dilated initial cervical geometry and (2) larger IUP.
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Affiliation(s)
- Daniel S Fidalgo
- Institute of Science and Innovation in Mechanical and Industrial Engineering (INEGI), R. Dr. Roberto Frias 400, 4200-465, Porto, Portugal.
- Mechanical Department (DEMec), Faculty of Engineering of University of Porto (FEUP), R. Dr. Roberto Frias, 4200-465, Porto, Portugal.
| | - Renato M Natal Jorge
- Institute of Science and Innovation in Mechanical and Industrial Engineering (INEGI), R. Dr. Roberto Frias 400, 4200-465, Porto, Portugal
- Mechanical Department (DEMec), Faculty of Engineering of University of Porto (FEUP), R. Dr. Roberto Frias, 4200-465, Porto, Portugal
| | - Marco P L Parente
- Institute of Science and Innovation in Mechanical and Industrial Engineering (INEGI), R. Dr. Roberto Frias 400, 4200-465, Porto, Portugal
- Mechanical Department (DEMec), Faculty of Engineering of University of Porto (FEUP), R. Dr. Roberto Frias, 4200-465, Porto, Portugal
| | - Erin M Louwagie
- Department of Mechanical Engineering, Columbia University, New York, NY, 10027, USA
| | - Ewelina Malanowska
- Department of Gynaecology, Endocrinology and Gynaecologic Oncology, Pomeranian Medical University, Szczecin, Poland
| | - Kristin M Myers
- Department of Mechanical Engineering, Columbia University, New York, NY, 10027, USA
| | - Dulce A Oliveira
- Institute of Science and Innovation in Mechanical and Industrial Engineering (INEGI), R. Dr. Roberto Frias 400, 4200-465, Porto, Portugal
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Sachs D, Jakob R, Restivo G, Hafner J, Lindenblatt N, Ehret AE, Mazza E. A quadriphasic mechanical model of the human dermis. Biomech Model Mechanobiol 2024; 23:1121-1136. [PMID: 38489079 DOI: 10.1007/s10237-024-01827-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2023] [Accepted: 02/09/2024] [Indexed: 03/17/2024]
Abstract
The present study investigates the multiphasic nature of the mechanical behavior of human dermis. Motivated by experimental observations and by consideration of its composition, a quadriphasic model of the dermis is proposed, distinguishing solid matrix components, interstitial fluid and charged constituents moving within the fluid, i.e., anions and cations. Compression and tensile experiments with and without change of osmolarity of the bath are performed to characterize the chemo-mechanical coupling in the dermis. Model parameters are determined through inverse analysis. The computations predict a dominant role of the permeability in the determination of the temporal evolution of the mechanical response of the tissue. In line with the previous studies on other tissues, the analysis shows that an ideal model based on Donnan's equilibrium overestimates the osmotic pressure in skin for the case of very dilute solutions. The quadriphasic model is applied to predict changes in dermal cell environment and therefore alterations in what is called the "mechanome," associated with skin stretch. The simulations indicate that skin deformation causes a variation in several local variables, including in particular the electric field associated with a deformation-induced non-homogeneous distribution of fixed charges.
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Affiliation(s)
- David Sachs
- Institute for Mechanical Systems, ETH Zürich, Zurich, Switzerland.
| | - Raphael Jakob
- Institute for Mechanical Systems, ETH Zürich, Zurich, Switzerland
| | - Gaetana Restivo
- Department of Dermatology, University Hospital Zürich, Zurich, Switzerland
| | - Jürg Hafner
- Department of Dermatology, University Hospital Zürich, Zurich, Switzerland
| | - Nicole Lindenblatt
- Department of Plastic Surgery and Hand Surgery, University Hospital Zürich, Zurich, Switzerland
| | - Alexander E Ehret
- Institute for Mechanical Systems, ETH Zürich, Zurich, Switzerland
- Swiss Federal Laboratories for Materials Science and Technology, Experimental Continuum Mechanics, Dübendorf, Switzerland
| | - Edoardo Mazza
- Institute for Mechanical Systems, ETH Zürich, Zurich, Switzerland.
- Swiss Federal Laboratories for Materials Science and Technology, Experimental Continuum Mechanics, Dübendorf, Switzerland.
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3
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Fidalgo DS, Samimi K, Oyen ML, Skala MC, Jorge RMN, Parente MPL, Malanowska E, Oliveira DA, Myers KM. Development of a multilayer fetal membrane material model calibrated using bulge inflation mechanical tests. J Mech Behav Biomed Mater 2024; 150:106344. [PMID: 38160642 DOI: 10.1016/j.jmbbm.2023.106344] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2023] [Revised: 12/15/2023] [Accepted: 12/22/2023] [Indexed: 01/03/2024]
Abstract
The fetal membranes are an essential mechanical structure for pregnancy, protecting the developing fetus in an amniotic fluid environment and rupturing before birth. In cooperation with the cervix and the uterus, the fetal membranes support the mechanical loads of pregnancy. Structurally, the fetal membranes comprise two main layers: the amnion and the chorion. The mechanical characterization of each layer is crucial to understanding how each layer contributes to the structural performance of the whole membrane. The in-vivo mechanical loading of the fetal membranes and the amount of tissue stress generated in each layer throughout gestation remains poorly understood, as it is difficult to perform direct measurements on pregnant patients. Finite element analysis of pregnancy offers a computational method to explore how anatomical and tissue remodeling factors influence the load-sharing of the uterus, cervix, and fetal membranes. To aid in the formulation of such computational models of pregnancy, this work develops a fiber-based multilayer fetal membrane model that captures its response to previously published bulge inflation loading data. First, material models for the amnion, chorion, and maternal decidua are formulated, informed, and validated by published data. Then, the behavior of the fetal membrane as a layered structure was analyzed, focusing on the respective stress distribution and thickness variation in each layer. The layered computational model captures the overall behavior of the fetal membranes, with the amnion being the mechanically dominant layer. The inclusion of fibers in the amnion material model is an important factor in obtaining reliable fetal membrane behavior according to the experimental dataset. These results highlight the potential of this layered model to be integrated into larger biomechanical models of the gravid uterus and cervix to study the mechanical mechanisms of preterm birth.
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Affiliation(s)
- Daniel S Fidalgo
- Institute of Science and Innovation in Mechanical and Industrial Engineering (INEGI), R. Dr. Roberto Frias 400, 4200-465, Porto, Portugal; Mechanical Department (DEMec), Faculty of Engineering of University of Porto (FEUP), Rua Dr. Roberto Frias, 4200-465, Porto, Portugal.
| | | | - Michelle L Oyen
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - Melissa C Skala
- Morgridge Institute for Research, Madison, WI, USA; Department of Biomedical Engineering, University of Wisconsin, Madison, WI, USA
| | - Renato M N Jorge
- Institute of Science and Innovation in Mechanical and Industrial Engineering (INEGI), R. Dr. Roberto Frias 400, 4200-465, Porto, Portugal; Mechanical Department (DEMec), Faculty of Engineering of University of Porto (FEUP), Rua Dr. Roberto Frias, 4200-465, Porto, Portugal
| | - Marco P L Parente
- Institute of Science and Innovation in Mechanical and Industrial Engineering (INEGI), R. Dr. Roberto Frias 400, 4200-465, Porto, Portugal; Mechanical Department (DEMec), Faculty of Engineering of University of Porto (FEUP), Rua Dr. Roberto Frias, 4200-465, Porto, Portugal
| | - Ewelina Malanowska
- Department of Gynaecology, Endocrinology and Gynaecologic Oncology, Pomeranian Medical University, Szczecin, Poland
| | - Dulce A Oliveira
- Institute of Science and Innovation in Mechanical and Industrial Engineering (INEGI), R. Dr. Roberto Frias 400, 4200-465, Porto, Portugal
| | - Kristin M Myers
- Department of Mechanical Engineering - Columbia University, New York, NY 10027, USA
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Hu Y, Du S, Xu T, Lei Y. A novel computational fracture toughness model for soft tissue in needle insertion. J Mech Behav Biomed Mater 2023; 147:106129. [PMID: 37774443 DOI: 10.1016/j.jmbbm.2023.106129] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2023] [Revised: 09/13/2023] [Accepted: 09/13/2023] [Indexed: 10/01/2023]
Abstract
During the process of percutaneous puncture vascular intervention operation in endoscopic liver surgery, high precision needle manipulation requires the accurate needle tissue interaction model where the tissue fracture toughness is an important parameter to describe the tissue crack propagation, as well as to estimate tissue deformation and target displacement. However, the existing studies on fracture toughness estimation did not consider Young's modulus and the organ capsule structure. In this paper, a novel computational fracture toughness model is proposed considering insertion velocity, needle diameter and Young's modulus in insertion process, where the fracture toughness is determined by the tissue surface deformation, which was estimated through energy modeling using integrated shell element and three-dimensional solid element. The testbed is built to study the effect of different insertion velocities, needle diameters and Young's modulus on fracture toughness. The experiment result shows that the estimated result of computational fracture toughness model agrees well with the physical experimental data. In addition, the sensitivity analysis of different factors is conducted. Meanwhile, the model robustness analysis is investigated with different observation noises of Young's modulus and puncture displacement.
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Affiliation(s)
- Yingda Hu
- State Key Laboratory of Fluid Power and Mechatronic Systems, Zhejiang University, Hangzhou, 310027, Zhejiang, China
| | - Shilun Du
- State Key Laboratory of Fluid Power and Mechatronic Systems, Zhejiang University, Hangzhou, 310027, Zhejiang, China
| | - Tian Xu
- State Key Laboratory of Fluid Power and Mechatronic Systems, Zhejiang University, Hangzhou, 310027, Zhejiang, China
| | - Yong Lei
- State Key Laboratory of Fluid Power and Mechatronic Systems, Zhejiang University, Hangzhou, 310027, Zhejiang, China.
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Wahlsten A, Stracuzzi A, Lüchtefeld I, Restivo G, Lindenblatt N, Giampietro C, Ehret AE, Mazza E. Multiscale mechanical analysis of the elastic modulus of skin. Acta Biomater 2023; 170:155-168. [PMID: 37598792 DOI: 10.1016/j.actbio.2023.08.030] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2023] [Revised: 07/27/2023] [Accepted: 08/15/2023] [Indexed: 08/22/2023]
Abstract
The mechanical properties of the skin determine tissue function and regulate dermal cell behavior. Yet measuring these properties remains challenging, as evidenced by the large range of elastic moduli reported in the literature-from below one kPa to hundreds of MPa. Here, we reconcile these disparate results by dedicated experiments at both tissue and cellular length scales and by computational models considering the multiscale and multiphasic tissue structure. At the macroscopic tissue length scale, the collective behavior of the collagen fiber network under tension provides functional tissue stiffness, and its properties determine the corresponding elastic modulus (100-200 kPa). The compliant microscale environment (0.1-10 kPa), probed by atomic force microscopy, arises from the ground matrix without engaging the collagen fiber network. Our analysis indicates that indentation-based elasticity measurements, although probing tissue properties at the cell-relevant length scale, do not assess the deformation mechanisms activated by dermal cells when exerting traction forces on the extracellular matrix. Using dermal-equivalent collagen hydrogels, we demonstrate that indentation measurements of tissue stiffness do not correlate with the behavior of embedded dermal fibroblasts. These results provide a deeper understanding of tissue mechanics across length scales with important implications for skin mechanobiology and tissue engineering. STATEMENT OF SIGNIFICANCE: Measuring the mechanical properties of the skin is essential for understanding dermal cell mechanobiology and designing tissue-engineered skin substitutes. However, previous results reported for the elastic modulus of skin vary by six orders of magnitude. We show that two distinct deformation mechanisms, related to the tension-compression nonlinearity of the collagen fiber network, can explain the large variations in elastic moduli. Furthermore, we show that microscale indentation, which is frequently used to assess the stiffness perceived by cells, fails to engage the fiber network, and therefore cannot predict the behavior of dermal fibroblasts in stiffness-tunable fibrous hydrogels. This has important implications for how to measure and interpret the mechanical properties of soft tissues across length scales.
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Affiliation(s)
- Adam Wahlsten
- Institute for Mechanical Systems, Department of Mechanical and Process Engineering, ETH Zurich, Leonhardstrasse 21, Zurich 8092, Switzerland
| | - Alberto Stracuzzi
- Institute for Mechanical Systems, Department of Mechanical and Process Engineering, ETH Zurich, Leonhardstrasse 21, Zurich 8092, Switzerland; Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, Dübendorf 8600, Switzerland
| | - Ines Lüchtefeld
- Institute for Biomedical Engineering, Department of Information Technology and Electrical Engineering, ETH Zurich, Gloriastrasse 35, Zurich 8092, Switzerland
| | - Gaetana Restivo
- Department of Dermatology, University Hospital Zurich, Zurich 8091, Switzerland
| | - Nicole Lindenblatt
- Department of Plastic and Hand Surgery, University Hospital Zurich, Zurich 8091, Switzerland
| | - Costanza Giampietro
- Institute for Mechanical Systems, Department of Mechanical and Process Engineering, ETH Zurich, Leonhardstrasse 21, Zurich 8092, Switzerland; Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, Dübendorf 8600, Switzerland
| | - Alexander E Ehret
- Institute for Mechanical Systems, Department of Mechanical and Process Engineering, ETH Zurich, Leonhardstrasse 21, Zurich 8092, Switzerland; Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, Dübendorf 8600, Switzerland
| | - Edoardo Mazza
- Institute for Mechanical Systems, Department of Mechanical and Process Engineering, ETH Zurich, Leonhardstrasse 21, Zurich 8092, Switzerland; Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, Dübendorf 8600, Switzerland.
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6
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Poro-viscoelastic behaviour of the zona pellucida: Impact of three-dimensional modelling on material characterisation. J Mech Behav Biomed Mater 2022; 131:105211. [DOI: 10.1016/j.jmbbm.2022.105211] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2021] [Revised: 03/07/2022] [Accepted: 03/26/2022] [Indexed: 11/21/2022]
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Stracuzzi A, Dittmann J, Böl M, Ehret AE. Visco- and poroelastic contributions of the zona pellucida to the mechanical response of oocytes. Biomech Model Mechanobiol 2021; 20:751-765. [PMID: 33533999 PMCID: PMC7979617 DOI: 10.1007/s10237-020-01414-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Accepted: 12/19/2020] [Indexed: 12/22/2022]
Abstract
Probing mechanical properties of cells has been identified as a means to infer information on their current state, e.g. with respect to diseases or differentiation. Oocytes have gained particular interest, since mechanical parameters are considered potential indicators of the success of in vitro fertilisation procedures. Established tests provide the structural response of the oocyte resulting from the material properties of the cell's components and their disposition. Based on dedicated experiments and numerical simulations, we here provide novel insights on the origin of this response. In particular, polarised light microscopy is used to characterise the anisotropy of the zona pellucida, the outermost layer of the oocyte composed of glycoproteins. This information is combined with data on volumetric changes and the force measured in relaxation/cyclic, compression/indentation experiments to calibrate a multi-phasic hyper-viscoelastic model through inverse finite element analysis. These simulations capture the oocyte's overall force response, the distinct volume changes observed in the zona pellucida, and the structural alterations interpreted as a realignment of the glycoproteins with applied load. The analysis reveals the presence of two distinct timescales, roughly separated by three orders of magnitude, and associated with a rapid outflow of fluid across the external boundaries and a long-term, progressive relaxation of the glycoproteins, respectively. The new results allow breaking the overall response down into the contributions from fluid transport and the mechanical properties of the zona pellucida and ooplasm. In addition to the gain in fundamental knowledge, the outcome of this study may therefore serve an improved interpretation of the data obtained with current methods for mechanical oocyte characterisation.
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Affiliation(s)
- Alberto Stracuzzi
- Institute for Mechanical Systems, ETH Zurich, 8092, Zurich, Switzerland
- Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600, Dübendorf, Switzerland
| | - Johannes Dittmann
- Institute of Mechanics and Adaptronics, Technische Universität Braunschweig, Braunschweig, 38106, Germany
| | - Markus Böl
- Institute of Mechanics and Adaptronics, Technische Universität Braunschweig, Braunschweig, 38106, Germany.
| | - Alexander E Ehret
- Institute for Mechanical Systems, ETH Zurich, 8092, Zurich, Switzerland.
- Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600, Dübendorf, Switzerland.
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Kohn S, Leichsenring K, Kuravi R, Ehret AE, Böl M. Direct measurement of the direction-dependent mechanical behaviour of skeletal muscle extracellular matrix. Acta Biomater 2021; 122:249-262. [PMID: 33444799 DOI: 10.1016/j.actbio.2020.12.050] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2020] [Revised: 12/22/2020] [Accepted: 12/28/2020] [Indexed: 12/19/2022]
Abstract
This paper reports the first comprehensive data set on the anisotropic mechanical properties of isolated endo- and perimysial extracellular matrix of skeletal muscle, and presents the corresponding protocols for preparing and testing the samples. In particular, decellularisation of porcine skeletal muscle is achieved with caustic soda solution, and mechanical parameters are defined based on compressive and tensile testing in order to identify the optimal treatment time such that muscle fibres are dissolved whereas the extracellular matrix remains largely intact and mechanically functional. At around 18 h, a time window was found and confirmed by histology, in which axial tensile experiments were performed to characterise the direction-dependent mechanical response of the extracellular matrix samples, and the effect of lateral pre-compression was studied. The typical, large variability in the experimental stress response could be largely reduced by varying a single scalar factor, which was attributed to the variation of the fraction of extracellular matrix within the tissue. While experimental results on the mechanical properties of intact muscle tissue and single muscle fibres are increasingly available in literature, there is a lack of information on the properties of the collagenous components of skeletal muscle. The present work aims at closing this gap and thus contributes to an improved understanding of the mechanics of skeletal muscle tissue and provides a missing piece of information for the development of corresponding constitutive and computational models.
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Affiliation(s)
- Stephan Kohn
- Institute of Mechanics and Adaptronics, Technische Universität Braunschweig, Braunschweig D-38106, Germany
| | - Kay Leichsenring
- Institute of Mechanics and Adaptronics, Technische Universität Braunschweig, Braunschweig D-38106, Germany
| | - Ramachandra Kuravi
- Empa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf CH-8600, Switzerland; Institute for Mechanical Systems, ETH Zurich, Zürich CH-8092, Switzerland
| | - Alexander E Ehret
- Empa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf CH-8600, Switzerland; Institute for Mechanical Systems, ETH Zurich, Zürich CH-8092, Switzerland
| | - Markus Böl
- Institute of Mechanics and Adaptronics, Technische Universität Braunschweig, Braunschweig D-38106, Germany.
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Bircher K, Ehret AE, Spiess D, Ehrbar M, Simões-Wüst AP, Ochsenbein-Kölble N, Zimmermann R, Mazza E. On the defect tolerance of fetal membranes. Interface Focus 2019; 9:20190010. [PMID: 31485307 DOI: 10.1098/rsfs.2019.0010] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/15/2019] [Indexed: 11/12/2022] Open
Abstract
A series of mechanical experiments were performed to quantify the strength and fracture toughness of human amnion and chorion. The experiments were complemented with computational investigations using a 'hybrid' model that includes an explicit representation of the collagen fibre network of amnion. Despite its much smaller thickness, amnion is shown to be stiffer, stronger and tougher than chorion, and thus to determine the mechanical response of fetal membranes, with respect to both, deformation and fracture behaviour. Data from uniaxial tension and fracture tests were used to inform and validate the computational model, which was then applied to rationalize measurements of the tear resistance of tissue samples containing crack-like defects. Experiments and computations show that the strength of amnion is not significantly reduced by defects smaller than 1 mm, but the crack size induced by perforations for amniocentesis and fetal membrane suturing during fetal surgery might be larger than this value. In line with previous experimental observations, the computational model predicts a very narrow near field at the crack tip of amnion, due to localized fibre alignment and collagen compaction. This mechanism shields the tissue from the defect and strongly reduces the interaction of multiple adjacent cracks. These findings were confirmed through corresponding experiments, showing that no interaction is expected for multiple sutures for an inter-suture distance larger than 1 mm and 3 mm for amnion and chorion, respectively. The experimental procedures and numerical models applied in the present study might be used to optimize needle and/or staple dimensions and inter-suture distance, and thus to reduce the risk of iatrogenic preterm premature rupture of the membranes from amniocentesis, fetoscopic and open prenatal surgery.
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Affiliation(s)
- Kevin Bircher
- ETH Zurich, Institute for Mechanical Systems, 8092 Zurich, Switzerland
| | - Alexander E Ehret
- ETH Zurich, Institute for Mechanical Systems, 8092 Zurich, Switzerland.,Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland
| | - Deborah Spiess
- Department of Obstetrics, University Hospital Zurich, 8091 Zurich, Switzerland
| | - Martin Ehrbar
- Department of Obstetrics, University Hospital Zurich, 8091 Zurich, Switzerland
| | | | | | - Roland Zimmermann
- Department of Obstetrics, University Hospital Zurich, 8091 Zurich, Switzerland
| | - Edoardo Mazza
- ETH Zurich, Institute for Mechanical Systems, 8092 Zurich, Switzerland.,Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland
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10
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Wahlsten A, Pensalfini M, Stracuzzi A, Restivo G, Hopf R, Mazza E. On the compressibility and poroelasticity of human and murine skin. Biomech Model Mechanobiol 2019; 18:1079-1093. [PMID: 30806838 DOI: 10.1007/s10237-019-01129-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2018] [Accepted: 02/09/2019] [Indexed: 01/09/2023]
Abstract
A total of 37 human and 33 murine skin samples were subjected to uniaxial monotonic, cyclic, and relaxation experiments. Detailed analysis of the three-dimensional kinematic response showed that skin volume is significantly reduced as a consequence of a tensile elongation. This behavior is most pronounced in monotonic but persists in cyclic tests. The dehydration associated with volume loss depends on the osmolarity of the environment, so that tension relaxation changes as a consequence of modifying the ionic strength of the environmental bath. Similar to ex vivo observations, complementary in vivo stretching experiments on human volar forearms showed strong in-plane lateral contraction. A biphasic homogenized model is proposed which allows representing all relevant features of the observed mechanical response.
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Affiliation(s)
- Adam Wahlsten
- Department of Mechanical and Process Engineering, Institute for Mechanical Systems, ETH Zurich, 8092, Zurich, Switzerland.
| | - Marco Pensalfini
- Department of Mechanical and Process Engineering, Institute for Mechanical Systems, ETH Zurich, 8092, Zurich, Switzerland
| | - Alberto Stracuzzi
- Department of Mechanical and Process Engineering, Institute for Mechanical Systems, ETH Zurich, 8092, Zurich, Switzerland
| | - Gaetana Restivo
- Department of Dermatology, University Hospital Zurich, 8091, Zurich, Switzerland
| | - Raoul Hopf
- Department of Mechanical and Process Engineering, Institute for Mechanical Systems, ETH Zurich, 8092, Zurich, Switzerland.,Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600, Dübendorf, Switzerland
| | - Edoardo Mazza
- Department of Mechanical and Process Engineering, Institute for Mechanical Systems, ETH Zurich, 8092, Zurich, Switzerland. .,Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600, Dübendorf, Switzerland.
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Abstract
Fracture toughness characterizes the ability of a material to maintain a certain level of strength despite the presence of a macroscopic crack. Understanding this tolerance for defects in soft collagenous tissues (SCT) has high relevance for assessing the risks of fracture after cutting, perforation or suturing. Here we investigate the peculiar toughening mechanisms of SCT through dedicated experiments and multi-scale simulations, showing that classical concepts of fracture mechanics are inadequate to quantify and explain the high defect tolerance of these materials. Our results demonstrate that SCT strength is only modestly reduced by defects as large as several millimeters. This defect tolerance is achieved despite a very narrow process zone at the crack tip and even for a network of brittle fibrils. The fracture mechanics concept of tearing energy fails in predicting failure at such defects, and its magnitude is shown to depend on the chemical potential of the liquid environment.
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12
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Ehret AE, Bircher K, Stracuzzi A, Marina V, Zündel M, Mazza E. Inverse poroelasticity as a fundamental mechanism in biomechanics and mechanobiology. Nat Commun 2017; 8:1002. [PMID: 29042539 PMCID: PMC5714996 DOI: 10.1038/s41467-017-00801-3] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2017] [Accepted: 07/28/2017] [Indexed: 01/14/2023] Open
Abstract
Understanding the mechanisms of deformation of biological materials is important for improved diagnosis and therapy, fundamental investigations in mechanobiology, and applications in tissue engineering. Here we demonstrate the essential role of interstitial fluid mobility in determining the mechanical properties of soft tissues. Opposite to the behavior expected for a poroelastic material, the tissue volume of different collagenous membranes is observed to strongly decrease with tensile loading. Inverse poroelasticity governs monotonic and cyclic responses of soft biomembranes, and induces chemo-mechanical coupling, such that tensile forces are modulated by the chemical potential of the interstitial fluid. Correspondingly, the osmotic pressure varies with mechanical loads, thus providing an effective mechanism for mechanotransduction. Water mobility determines the tissue's ability to adapt to deformation through compaction and dilation of the collagen fiber network. In the near field of defects this mechanism activates the reversible formation of reinforcing collagen structures which effectively avoid propagation of cracks.How soft tissues respond to mechanical load is essential to their biological function. Here, the authors discover that - contrary to predictions of poroelasticity - fluid mobility in collagenous tissues induces drastic volume decrease with tensile loading and pronounced chemo-mechanical coupling.
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Affiliation(s)
- Alexander E Ehret
- ETH Zurich, Institute for Mechanical Systems, Leonhardstrasse 21, 8092, Zurich, Switzerland. .,Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600, Dübendorf, Switzerland.
| | - Kevin Bircher
- ETH Zurich, Institute for Mechanical Systems, Leonhardstrasse 21, 8092, Zurich, Switzerland
| | - Alberto Stracuzzi
- ETH Zurich, Institute for Mechanical Systems, Leonhardstrasse 21, 8092, Zurich, Switzerland
| | - Vita Marina
- ETH Zurich, Institute for Mechanical Systems, Leonhardstrasse 21, 8092, Zurich, Switzerland
| | - Manuel Zündel
- ETH Zurich, Institute for Mechanical Systems, Leonhardstrasse 21, 8092, Zurich, Switzerland
| | - Edoardo Mazza
- ETH Zurich, Institute for Mechanical Systems, Leonhardstrasse 21, 8092, Zurich, Switzerland. .,Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600, Dübendorf, Switzerland.
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Linka K, Itskov M, Truhn D, Nebelung S, Thüring J. T2 MR imaging vs. computational modeling of human articular cartilage tissue functionality. J Mech Behav Biomed Mater 2017; 74:477-487. [PMID: 28760354 DOI: 10.1016/j.jmbbm.2017.07.023] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2017] [Revised: 07/10/2017] [Accepted: 07/18/2017] [Indexed: 12/31/2022]
Abstract
The detection of early stages of cartilage degeneration remains diagnostically challenging. One promising non-invasive approach is to functionally assess the tissue response to loading by serial magnetic resonance (MR) imaging in terms of T2 mapping under simultaneous mechanical loading. As yet, however, it is not clear which cartilage component contributes to the tissue functionality as assessed by quantitative T2 mapping. To this end, quantitative T2 maps of histologically intact cartilage samples (n=8) were generated using a clinical 3.0-T MR imaging system. Using displacement-controlled quasi-static indentation loading, serial T2 mapping was performed at three defined strain levels and loading-induced relative changes were determined in distinct regions-of-interest. Samples underwent conventional biomechanical testing (by unconfined compression) as well as histological assessment (by Mankin scoring) for reference purposes. Moreover, an anisotropic hyperelastic constitutive model of cartilage was implemented into a finite element (FE) code for cross-referencing. In efforts to simulate the evolution of compositional and structural intra-tissue changes under quasi-static loading, the indentation-induced changes in quantitative T2 maps were referenced to underlying changes in cartilage composition and structure. These changes were parameterized as cartilage fluid, proteoglycan and collagen content as well as collagen orientation. On a pixel-wise basis, each individual component correlation with T2 relaxation times was determined by Spearman's ρs and significant correlations were found between T2 relaxation times and all four tissue parameters for all indentation strain levels. Thus, the biological changes in functional MR Imaging parameters such as T2 can further be characterized to strengthen the scientific basis of functional MRI techniques with regards to their perspective clinical applications.
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Affiliation(s)
- Kevin Linka
- Department of Continuum Mechanics, RWTH Aachen University, Kackertstr. 9, 52072 Aachen, Germany.
| | - Mikhail Itskov
- Department of Continuum Mechanics, RWTH Aachen University, Kackertstr. 9, 52072 Aachen, Germany
| | - Daniel Truhn
- Department of Diagnostic and Interventional Radiology, Aachen University Hospital, Pauwelsstr. 30, 52074 Aachen, Germany
| | - Sven Nebelung
- Department of Diagnostic and Interventional Radiology, Aachen University Hospital, Pauwelsstr. 30, 52074 Aachen, Germany
| | - Johannes Thüring
- Department of Diagnostic and Interventional Radiology, Aachen University Hospital, Pauwelsstr. 30, 52074 Aachen, Germany
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Palacio-Torralba J, Good DW, McNeill SA, Reuben RL, Chen Y. Histology-based homogenization analysis of soft tissue: application to prostate cancer. J R Soc Interface 2017; 14:rsif.2017.0088. [PMID: 28404869 PMCID: PMC5414912 DOI: 10.1098/rsif.2017.0088] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2017] [Accepted: 03/16/2017] [Indexed: 12/21/2022] Open
Abstract
It is well known that the changes in tissue microstructure associated with certain pathophysiological conditions can influence its mechanical properties. Quantitatively relating the tissue microstructure to the macroscopic mechanical properties could lead to significant improvements in clinical diagnosis, especially when the mechanical properties of the tissue are used as diagnostic indices such as in digital rectal examination and elastography. In this study, a novel method of imposing periodic boundary conditions in non-periodic finite-element meshes is presented. This method is used to develop quantitative relationships between tissue microstructure and its apparent mechanical properties for benign and malignant tissue at various length scales. Finally, the inter-patient variation in the tissue properties is also investigated. Results show significant changes in the statistical distribution of the mechanical properties at different length scales. More importantly the loss of the normal differentiation of glandular structure of cancerous tissue has been demonstrated to lead to changes in mechanical properties and anisotropy. The proposed methodology is not limited to a particular tissue or material and the example used could help better understand how changes in the tissue microstructure caused by pathological conditions influence the mechanical properties, ultimately leading to more sensitive and accurate diagnostic technologies.
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Affiliation(s)
- Javier Palacio-Torralba
- Institute of Mechanical, Process and Energy Engineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK
| | - Daniel W Good
- Edinburgh Urological Cancer Group, Division of Pathology Laboratories, Institute of Genetics and Molecular Medicine, University of Edinburgh, Western General Hospital, Crewe Road South, Edinburgh EH4 2XU, UK.,Department of Urology, NHS Lothian, Western General Hospital, Crewe Road South, Edinburgh EH4 2XU, UK
| | - S Alan McNeill
- Edinburgh Urological Cancer Group, Division of Pathology Laboratories, Institute of Genetics and Molecular Medicine, University of Edinburgh, Western General Hospital, Crewe Road South, Edinburgh EH4 2XU, UK.,Department of Urology, NHS Lothian, Western General Hospital, Crewe Road South, Edinburgh EH4 2XU, UK
| | - Robert L Reuben
- Institute of Mechanical, Process and Energy Engineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK
| | - Yuhang Chen
- Institute of Mechanical, Process and Energy Engineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK
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Stracuzzi A, Ehret AE. Bi-phasic theory vs. volumetric viscoelasticity for modelling the behaviour of thin collagenous membranes. ACTA ACUST UNITED AC 2016. [DOI: 10.1002/pamm.201610042] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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16
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Bircher K, Ehret AE, Mazza E. Mechanical Characteristics of Bovine Glisson's Capsule as a Model Tissue for Soft Collagenous Membranes. J Biomech Eng 2016; 138:2530163. [DOI: 10.1115/1.4033917] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Indexed: 01/19/2023]
Abstract
An extensive multiaxial experimental campaign on the monotonic, time- and history-dependent mechanical response of bovine Glisson's capsule (GC) is presented. Reproducible characteristics were observed such as J-shaped curves in uniaxial and biaxial configurations, large lateral contraction, cyclic tension softening, large tension relaxation, and moderate creep strain accumulation. The substantial influence of the reference state selection on the kinematic response and the tension versus stretch curves is demonstrated and discussed. The parameters of a large-strain viscoelastic constitutive model were determined based on the data of uniaxial tension relaxation experiments. The model is shown to well predict the uniaxial and biaxial viscoelastic responses in all other configurations. GC, the corresponding model, and the experimental protocols are proposed as a useful basis for future studies on the relation between microstructure and tissue functionality and on the factors influencing the mechanical response of soft collagenous membranes.
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Affiliation(s)
- Kevin Bircher
- Institute for Mechanical Systems, ETH Zurich, Zurich 8092, Switzerland e-mail:
| | - Alexander E. Ehret
- Institute for Mechanical Systems, ETH Zurich, Zurich 8092, Switzerland; Empa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf 8600, Switzerland e-mail:
| | - Edoardo Mazza
- Institute for Mechanical Systems, ETH Zurich, Zurich 8092, Switzerland; Empa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf 8600, Switzerland e-mail:
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