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Fratzl P, Fischer FD, Zickler GA, Dunlop JWC. On shape forming by contractile filaments in the surface of growing tissues. PNAS Nexus 2023; 2:pgac292. [PMID: 36712928 PMCID: PMC9832972 DOI: 10.1093/pnasnexus/pgac292] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2022] [Accepted: 12/11/2022] [Indexed: 12/15/2022]
Abstract
Growing tissues are highly dynamic, and flow on sufficiently long timescales due to cell proliferation, migration, and tissue remodeling. As a consequence, growing tissues can often be approximated as viscous fluids. This means that the shape of microtissues growing in vitro is governed by their surface stress state, as in fluid droplets. Recent work showed that cells in the near-surface region of fibroblastic or osteoblastic microtissues contract with highly oriented actin filaments, thus making the surface properties highly anisotropic, in contrast to what is expected for an isotropic fluid. Here, we develop a model that includes mechanical anisotropy of the surface generated by contractile fibers and we show that mechanical equilibrium requires contractile filaments to follow geodesic lines on the surface. Constant pressure in the fluid forces these contractile filaments to be along geodesics with a constant normal curvature. We then take this into account to determine equilibrium shapes of rotationally symmetric bodies subjected to anisotropic surface stress states and derive a family of surfaces of revolution. A comparison with recently published shapes of microtissues shows that this theory accurately predicts both the surface shape and the direction of the actin filaments on the surface.
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Affiliation(s)
- Peter Fratzl
- Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, Potsdam Science Park, 14476 Potsdam-Golm, Germany
| | - F Dieter Fischer
- Institute of Mechanics, Montanuniversität Leoben, 8700 Leoben, Austria
| | - Gerald A Zickler
- Institute of Mechanics, Montanuniversität Leoben, 8700 Leoben, Austria
| | - John W C Dunlop
- Morphophysics Group, Department of the Chemistry and Physics of Materials, University of Salzburg, 5020 Salzburg, Austria
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Clemens H, Boeck B, Wallgram W, Schmoelzer T, Droessler LM, Zickler GA, Leitner H, Otto A. Experimental Studies and Thermodynamic Simulations of Phase Transformations in Ti-(41-45)Al-4Nb-1Mo-0.1B Alloys. ACTA ACUST UNITED AC 2018. [DOI: 10.1557/proc-1128-u03-06] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
AbstractTNM™ alloys are novel γ-TiAl based alloys which exhibit a high concentration of β-stabilizing elements such as Nb and Mo. Due to the high volume fraction of disordered β-phase these alloys can be hot-die forged under near conventional conditions. In this study, solid-state phase transformations and phase transition temperatures in Ti-(41-45)Al-4Nb-1Mo-0.1B (in at%) alloys were analyzed experimentally and compared to thermodynamic calculations. Results from scanning electron microscopy, conventional and high-energy X-ray diffraction as well as differential scanning calorimetry were used for the characterization of the prevailing phases and phase transformations. For the prediction of phase stabilities and phase transition temperatures thermodynamic calculations were conducted. ThermoCalc® was applied using a commercially available TiAl database. Combining all results a stable as well as a metastable phase diagram for Ti-(41-45)Al-4Nb-1Mo-0.1B alloys is proposed.
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Stoeckel D, Wallacher D, Zickler GA, Thommes M, Smarsly BM. Elucidating the Sorption Mechanism of Dibromomethane in Disordered Mesoporous Silica Adsorbents. Langmuir 2015; 31:6332-6342. [PMID: 25989514 DOI: 10.1021/acs.langmuir.5b00705] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The mechanism of dibromomethane (DBM) sorption in mesoporous silica was investigated by in situ small-angle X-ray scattering (SAXS). Six different samples of commercial porous silica particles used for liquid chromatography were studied, featuring a disordered mesoporous structure, with some of the samples being functionalized with alkyl chains. SAXS curves were recorded at room temperature at various relative pressures P/P0 during adsorption of DBM. The in situ SAXS experiment is based on contrast matching between silica and condensed DBM with regard to X-ray scattering. One alkyl-modified silica sample was evaluated in detail by extraction of the chord-length distribution (CLD) from SAXS data obtained for several P/P0. On the basis of this analytical approach and by comparison with ex situ obtained data of nitrogen and DBM adsorption, the mechanism of DBM uptake was studied. Results of average mesopore sizes obtained with the CLD method were compared with pore size analysis using nitrogen physisorption (77 K) with advanced state-of-the-art nonlocal density functional theory (NLDFT) evaluation. The dual SAXS/physisorption study indicates that microporosity is negligible in all silica samples and that surface functionalization with a hydrophobic ligand has a major influence upon the process of DBM adsorption. Also, all of the mesopores are accessible as evidenced by in situ SAXS. The data suggest that no multilayer adsorption occurs on C18-(octadecyl-)modified silica surfaces using DBM as adsorptive, and it is possibly also negligible on bare silica surfaces.
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Affiliation(s)
- Daniela Stoeckel
- †Institute of Physical Chemistry, Justus-Liebig-Universität Gießen, Heinrich-Buff-Ring 58, 35392 Gießen, Germany
| | - Dirk Wallacher
- ‡Helmholtz Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109 Berlin, Germany
| | - Gerald A Zickler
- §Institute of Mechanics, Montanuniversität Leoben, Franz-Josef-Strasse 18, 8700 Leoben, Austria
| | - Matthias Thommes
- ∥Quantachrome Instruments, 1900 Corporate Drive, Boynton Beach, Florida 33426, United States
| | - Bernd M Smarsly
- †Institute of Physical Chemistry, Justus-Liebig-Universität Gießen, Heinrich-Buff-Ring 58, 35392 Gießen, Germany
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Fischer FD, Zickler GA, Dunlop JWC, Fratzl P. Tissue growth controlled by geometric boundary conditions: a simple model recapitulating aspects of callus formation and bone healing. J R Soc Interface 2015; 12:rsif.2015.0108. [PMID: 26018964 DOI: 10.1098/rsif.2015.0108] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The shape of tissues arises from a subtle interplay between biochemical driving forces, leading to cell growth, division and extracellular matrix formation, and the physical constraints of the surrounding environment, giving rise to mechanical signals for the cells. Despite the inherent complexity of such systems, much can still be learnt by treating tissues that constantly remodel as simple fluids. In this approach, remodelling relaxes all internal stresses except for the pressure which is counterbalanced by the surface stress. Our model is used to investigate how wettable substrates influence the stability of tissue nodules. It turns out for a growing tissue nodule in free space, the model predicts only two states: either the tissue shrinks and disappears, or it keeps growing indefinitely. However, as soon as the tissue wets a substrate, stable equilibrium configurations become possible. Furthermore, by investigating more complex substrate geometries, such as tissue growing at the end of a hollow cylinder, we see features reminiscent of healing processes in long bones, such as the existence of a critical gap size above which healing does not occur. Despite its simplicity, the model may be useful in describing various aspects related to tissue growth, including biofilm formation and cancer metastases.
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Affiliation(s)
- F Dieter Fischer
- Montanuniversität Leoben, Institute of Mechanics, Leoben 8700, Austria
| | - Gerald A Zickler
- Montanuniversität Leoben, Institute of Mechanics, Leoben 8700, Austria
| | - John W C Dunlop
- Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, Potsdam 14476, Germany
| | - Peter Fratzl
- Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, Potsdam 14476, Germany
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Stoeckel D, Wallacher D, Zickler GA, Perlich J, Tallarek U, Smarsly BM. Coherent analysis of disordered mesoporous adsorbents using small angle X-ray scattering and physisorption experiments. Phys Chem Chem Phys 2014; 16:6583-92. [DOI: 10.1039/c3cp55072a] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Zickler GA, Ruffoni D, Dunlop JWC, Elbaum R, Weinkamer R, Fratzl P, Antretter T. Finite element modeling of the cyclic wetting mechanism in the active part of wheat awns. Biointerphases 2012; 7:42. [PMID: 22791359 DOI: 10.1007/s13758-012-0042-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2012] [Accepted: 06/15/2012] [Indexed: 11/28/2022] Open
Abstract
Many plant tissues and organs are capable of moving due to changes in the humidity of the environment, such as the opening of the seed capsule of the ice plant and the opening of the pine cone. These are fascinating examples for the materials engineer, as these tissues are non-living and move solely through the differential swelling of anisotropic tissues and in principle may serve as examples for the bio-inspired design of artificial actuators. In this paper, we model the microstructure of the wild wheat awn (Triticum turgidum ssp. dicoccoides) by finite elements, especially focusing on the specific microscopic features of the active part of the awn. Based on earlier experimental findings, cell walls are modeled as multilayered cylindrical tubes with alternating cellulose fiber orientation in successive layers. It is shown that swelling upon hydration of this system leads to the formation of gaps between the layers, which could act as valves, thus enabling the entry of water into the cell wall. This supports the hypothesis that this plywood-like arrangement of cellulose fibrils enhances the effect of ambient humidity by accelerated water or vapor diffusion along the gaps. The finite element model shows that a certain distribution of axially and tangentially oriented fibers is necessary to generate sufficient tensile stresses within the cell wall to open nanometer-sized gaps between cell wall layers.
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Affiliation(s)
- Gerald A Zickler
- Institute for Mechanics, Montanuniversitaet Leoben, Leoben, Austria.
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Mascotto S, Wallacher D, Kuschel A, Polarz S, Zickler GA, Timmann A, Smarsly BM. Adsorption in periodically ordered mesoporous organosilica materials studied by in situ small-angle X-ray scattering and small-angle neutron scattering. Langmuir 2010; 26:6583-6592. [PMID: 20201568 DOI: 10.1021/la903934r] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Modified periodically ordered mesoporous organosilica materials were prepared starting from a recently introduced type of sol-gel precursor, containing both organic moieties and hydrolyzable Si-OR groups. In order to thoroughly characterize the mesoporosity and its accessibility, different probe gases were used in conventional gas adsorption experiments. Furthermore, in situ small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) were applied to study the mesoporosity and the sorption processes, taking advantage of scattering contrast matching conditions. Thereby, the materials were characterized not only by different probe molecules but also at different temperatures (nitrogen at 77 K, dibromomethane at 290 K and perfluoropentane at 276 K). The comparison between the standard and in situ SAXS/SANS adsorption experiments revealed valuable information about the porosity and microstructure of the materials. It is demonstrated that the organic moieties are homogeneously distributed; that is, they do not phase-separate from silica on the nanometer scale.
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Affiliation(s)
- Simone Mascotto
- Physical Chemistry Department, University of Giessen, 35392 Giessen, Germany
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Mascotto S, Wallacher D, Brandt A, Hauss T, Thommes M, Zickler GA, Funari SS, Timmann A, Smarsly BM. Analysis of microporosity in ordered mesoporous hierarchically structured silica by combining physisorption with in situ small-angle scattering (SAXS and SANS). Langmuir 2009; 25:12670-12681. [PMID: 19821588 DOI: 10.1021/la9013619] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The combination of physisorption experiments with simultaneous in situ small-angle X-ray and neutron scattering (SAXS/SANS) was used to elucidate the porosity in mesoporous silica with a trimodal pore structure. The material ("KLE-IL") contains spherical mesopores of 14 nm in diameter, worm-like mesopores (2-3 nm), and micropores, templated by a block copolymer and an ionic liquid surfactant, while the micropores originate from the hydrophilic block of the block copolymer. The main objective of the study was the quantification of the microporosity and the small mesopores and to find out if they are indeed located between the larger, spherical mesopores. Our in situ SAXS/SANS experiments took advantage of contrast matching of nitrogen (SANS, T = 77 K) and dibromomethane (SAXS, T = 290 K). By using the latter gas with a slightly larger kinetic diameter, it was possible to judge the accessibility of the pores under ambient conditions. The in situ experiments were supported by high-precision ex situ physisorption. Using suitable approaches for the SAXS/SANS analysis, it was possible to separate the content of the micropores and small mesopores.
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Affiliation(s)
- Simone Mascotto
- Institute of Physical Chemistry, University of Giessen, Heinrich-Buff-Ring 58, D-35392 Giessen, Germany
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Zickler GA, Jähnert S, Funari SS, Findenegg GH, Paris O. Pore lattice deformation in ordered mesoporous silica studied by in situ small-angle X-ray diffraction. J Appl Crystallogr 2007. [DOI: 10.1107/s0021889806055968] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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Gupta HS, Wagermaier W, Zickler GA, Raz-Ben Aroush D, Funari SS, Roschger P, Wagner HD, Fratzl P. Nanoscale deformation mechanisms in bone. Nano Lett 2005; 5:2108-11. [PMID: 16218747 DOI: 10.1021/nl051584b] [Citation(s) in RCA: 187] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Deformation mechanisms in bone matrix at the nanoscale control its exceptional mechanical properties, but the detailed nature of these processes is as yet unknown. In situ tensile testing with synchrotron X-ray scattering allowed us to study directly and quantitatively the deformation mechanisms at the nanometer level. We find that bone deformation is not homogeneous but distributed between a tensile deformation of the fibrils and a shearing in the interfibrillar matrix between them.
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Affiliation(s)
- Himadri S Gupta
- Max Planck Institute of Colloids and Interfaces, MPI-KG Golm, D-14424 Potsdam, Germany.
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