Publications by authors named "Philipp J Thurner"

41 Publications

Effects of Osteoporosis on Bone Morphometry and Material Properties of Individual Human Trabeculae in the Femoral Head.

JBMR Plus 2021 Jun 4;5(6):e10503. Epub 2021 May 4.

Institute of Lightweight Design and Structural Biomechanics TU Wien Gumpendorfer Straße 7 Vienna 1060 Austria.

Osteoporosis is the most common bone disease and is conventionally classified as a decrease of total bone mass. Current diagnosis of osteoporosis is based on clinical risk factors and dual energy X-ray absorptiometry (DEXA) scans, but changes in bone quantity (bone mass) and quality (trabecular structure, material properties, and tissue composition) are not distinguished. Yet, osteoporosis is known to cause a deterioration of the trabecular network, which might be related to changes at the tissue scale-the material properties. The goal of the current study was to use a previously established test method to perform a thorough characterization of the material properties of individual human trabeculae from femoral heads in cyclic tensile tests in a close to physiologic, wet environment. A previously developed rheological model was used to extract elastic, viscous, and plastic aspects of material behavior. Bone morphometry and tissue mineralization were determined with a density calibrated micro-computed tomography (μCT) set-up. Osteoporotic trabeculae neither showed a significantly changed material or mechanical behavior nor changes in tissue mineralization, compared with age-matched healthy controls. However, donors with osteopenia indicated significantly reduced apparent yield strain and elastic work with respect to osteoporosis, suggesting possible initial differences at disease onset. Bone morphometry indicated a lower bone volume to total volume for osteoporotic donors, caused by a smaller trabecular number and a larger trabecular separation. A correlation of age with tissue properties and bone morphometry revealed a similar behavior as in osteoporotic bone. In the range studied, age does affect morphometry but not material properties, except for moderately increased tissue strength in healthy donors and moderately increased hardening exponent in osteoporotic donors. Taken together, the distinct changes of trabecular bone quality in the femoral head caused by osteoporosis and aging could not be linked to suspected relevant changes in material properties or tissue mineralization. © 2021 The Authors. published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.
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http://dx.doi.org/10.1002/jbm4.10503DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8216141PMC
June 2021

Effects of anti-resorptive treatment on the material properties of individual canine trabeculae in cyclic tensile tests.

Bone 2021 09 1;150:115995. Epub 2021 May 1.

Institute of Lightweight Design and Structural Biomechanics, TU Wien, Gumpendorfer Straße 7, 1060 Vienna, Austria. Electronic address:

Osteoporosis is defined as a decrease of bone mass and strength, as well as an increase in fracture risk. It is conventionally treated with antiresorptive drugs, such as bisphosphonates (BPs) and selective estrogen receptor modulators (SERMs). Although both drug types successfully decrease the risk of bone fractures, their effect on bone mass and strength is different. For instance, BP treatment causes an increase of bone mass, stiffness and strength of whole bones, whereas SERM treatment causes only small (4%) increases of bone mass, but increased bone toughness. Such improved mechanical behavior of whole bones can be potentially related to the bone mass, bone structure or material changes. While bone mass and architecture have already been investigated previously, little is known about the mechanical behavior at the tissue/material level, especially of trabecular bone. As such, the goal of the work presented here was to fill this gap by performing cyclic tensile tests in a wet, close to physiologic environment of individual trabeculae retrieved from the vertebrae of beagle dogs treated with alendronate (a BP), raloxifene (a SERM) or without treatments. Identification of material properties was performed with a previously developed rheological model and of mechanical properties via fitting of envelope curves. Additionally, tissue mineral density (TMD) and microdamage formation were analyzed. Alendronate treatment resulted in a higher trabecular tissue stiffness and strength, associated with higher levels of TMD. In contrast, raloxifene treatment caused a higher trabecular toughness, pre-dominantly in the post-yield region. Microdamage formation during testing was not affected by either anti-resorptive treatment regimens. These findings highlight that the improved mechanical behavior of whole bones after anti-resorptive treatment is at least partly caused by improved material properties, with different mechanisms for alendronate and raloxifene. This study further shows the power of performing a mechanical characterization of trabecular bone at the level of individual trabeculae for better understanding of clinically relevant mechanical behavior of bone.
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http://dx.doi.org/10.1016/j.bone.2021.115995DOI Listing
September 2021

The role of extracellular matrix phosphorylation on energy dissipation in bone.

Elife 2020 12 9;9. Epub 2020 Dec 9.

Department of Biomedical Engineering, Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, United States.

Protein phosphorylation, critical for cellular regulatory mechanisms, is implicated in various diseases. However, it remains unknown whether heterogeneity in phosphorylation of key structural proteins alters tissue integrity and organ function. Here, osteopontin phosphorylation level declined in hypo- and hyper- phosphatemia mouse models exhibiting skeletal deformities. Phosphorylation increased cohesion between osteopontin polymers, and adhesion of osteopontin to hydroxyapatite, enhancing energy dissipation. Fracture toughness, a measure of bone's mechanical competence, increased with ex-vivo phosphorylation of wildtype mouse bones and declined with ex-vivo dephosphorylation. In osteopontin-deficient mice, global matrix phosphorylation level was not associated with toughness. Our findings suggest that phosphorylated osteopontin promotes fracture toughness in a dose-dependent manner through increased interfacial bond formation. In the absence of osteopontin, phosphorylation increases electrostatic repulsion, and likely protein alignment and interfilament distance leading to decreased fracture resistance. These mechanisms may be of importance in other connective tissues, and the key to unraveling cell-matrix interactions in diseases.
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http://dx.doi.org/10.7554/eLife.58184DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7746230PMC
December 2020

Microdamage formation in individual bovine trabeculae during fatigue testing.

J Biomech 2021 01 17;115:110131. Epub 2020 Nov 17.

Institute of Lightweight Design and Structural Biomechanics, TU Wien, Gumpendorfer Str. 7, BE02, 1060 Vienna, Austria. Electronic address:

Ageing, disease and osteoporosis treatment have been linked to accumulation of microdamage, which is caused by repetitive loading and may eventually causes fatigue failure of bones. Post-hoc investigations for in vivo loading and in vitro experiments have been developed to better understand microdamage formation. In this context, previous studies were not able to discriminate the effects caused by structural changes of the trabecular network from differences of tissue/material properties on microdamage formation. In the present study a fatigue test protocol was established to induce microdamage at a defined tensile stress state of individual trabeculae. Further, a thorough analysis of microdamage analysis was presented for 2D and 3D confocal images, enabling a comparison between the tissue and the meso-scale. Eight individual trabeculae were tested for 1500 cycles, six for 2100 cycles and seven for 3000 cycles (close to failure). Microdamage increased slowly from 1500 to 2100 cycles and showed a rapid increase at 3000 cycles. Diffuse damage was mainly present, although also linear microcracks were visible at 2100 and 3000 cycles. Average microcrack length was 93 µm and diffuse damage density was 4.4% for samples tested for 3000 cycles, comparable to previous studies on trabecular bone cores. Only one to three large microdamage sites were observed in the central region, connected to the trabecular surface with small straight cracks. The presented procedure is a first step to better understand how microdamage formation is influenced by material properties in aged and diseased bone, independently of deteriorated trabecular microarchitecture.
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http://dx.doi.org/10.1016/j.jbiomech.2020.110131DOI Listing
January 2021

Single-Molecule Force Spectroscopy Reveals Adhesion-by-Demand in Statherin at the Protein-Hydroxyapatite Interface.

Langmuir 2020 11 29;36(44):13292-13300. Epub 2020 Oct 29.

Christian Doppler Laboratory for Advanced Polymers for Biomaterials and 3D Printing, TU Wien, Vienna 1060, Austria.

Achieving strong adhesion in wet environments remains a technological challenge in biomedical applications demanding biocompatibility. Attention for adhesive motifs meeting such demands has largely been focused on marine organisms. However, bioadhesion to inorganic surfaces is also present in the human body, in the hard tissues of teeth and bones, and is mediated through serines (S). The specific amino acid sequence DpSpSEEKC has been previously suggested to be responsible for the strong binding abilities of the protein statherin to hydroxyapatite, where pS denotes phosphorylated serine. Notably, similar sequences are present in the non-collagenous bone protein osteopontin (OPN) and the mussel foot protein 5 (Mefp5). OPN has previously been shown to promote fracture toughness and physiological damage formation. Here, we investigated the adhesion strength of the motif D(pS)(pS)EEKC on substrates of hydroxyapatite, TiO, and mica using atomic force microscopy (AFM) single-molecule force spectroscopy (SMFS). Specifically, we investigated the dependence of adhesion force on phosphorylation of serines by comparing findings with the unphosphorylated variant DSSEEKC. Our results show that high adhesion forces of over 1 nN on hydroxyapatite and on TiO are only present for the phosphorylated variant D(pS)(pS)EEKC. This warrants further exploitation of this motif or similar residues in technological applications. Further, the dependence of adhesion force on phosphorylation suggests that biological systems potentially employ an adhesion-by-demand mechanism via expression of enzymes that up- or down-regulate phosphorylation, to increase or decrease adhesion forces, respectively.
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http://dx.doi.org/10.1021/acs.langmuir.0c02325DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7660943PMC
November 2020

Correction to: A two‑layer elasto‑visco‑plastic rheological model for the material parameter identification of bone tissue.

Biomech Model Mechanobiol 2020 10;19(5):1977

Division Biomechanics, Department of Anatomy and Biomechanics, Karl Landsteiner University of Health Sciences, Krems an der Donau, Austria.

In the original publication of the article.
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http://dx.doi.org/10.1007/s10237-020-01356-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7502445PMC
October 2020

A two-layer elasto-visco-plastic rheological model for the material parameter identification of bone tissue.

Biomech Model Mechanobiol 2020 Dec 6;19(6):2149-2162. Epub 2020 May 6.

Division Biomechanics, Department of Anatomy and Biomechanics, Karl Landsteiner University of Health Sciences, Krems an der Donau, Austria.

The ability to measure bone tissue material properties plays a major role in diagnosis of diseases and material modeling. Bone's response to loading is complex and shows a viscous contribution to stiffness, yield and failure. It is also ductile and damaging and exhibits plastic hardening until failure. When performing mechanical tests on bone tissue, these constitutive effects are difficult to quantify, as only their combination is visible in resulting stress-strain data. In this study, a methodology for the identification of stiffness, damping, yield stress and hardening coefficients of bone from a single cyclic tensile test is proposed. The method is based on a two-layer elasto-visco-plastic rheological model that is capable of reproducing the specimens' pre- and postyield response. The model's structure enables for capturing the viscously induced increase in stiffness, yield, and ultimate stress and for a direct computation of the loss tangent. Material parameters are obtained in an inverse approach by optimizing the model response to fit the experimental data. The proposed approach is demonstrated by identifying material properties of individual bone trabeculae that were tested under wet conditions. The mechanical tests were conducted according to an already published methodology for tensile experiments on single trabeculae. As a result, long-term and instantaneous Young's moduli were obtained, which were on average 3.64 GPa and 5.61 GPa, respectively. The found yield stress of 16.89 MPa was lower than previous studies suggest, while the loss tangent of 0.04 is in good agreement. In general, the two-layer model was able to reproduce the cyclic mechanical test data of single trabeculae with an root-mean-square error of 2.91 ± 1.77 MPa. The results show that inverse rheological modeling can be of great advantage when multiple constitutive contributions shall be quantified based on a single mechanical measurement.
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http://dx.doi.org/10.1007/s10237-020-01329-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7603462PMC
December 2020

Influence of experimental constraints on micromechanical assessment of micromachined hard-tissue samples.

J Mech Behav Biomed Mater 2020 06 24;106:103741. Epub 2020 Mar 24.

Institute of Lightweight Design and Structural Biomechanics, TU Wien, 1060, Vienna, Austria. Electronic address:

Continuing technological advancement of mechanical characterization at the microscale has enabled the isolation of micron-sized specimens and their direct mechanical characterization. Such techniques, initially developed for engineering materials and MEMS, can also be applied on hard biological materials. Bone is a material with a complex hierarchical structure ranging from the macro- all the way down to the nanoscale. To fully understand bone tissue mechanics, knowledge of the mechanics of all structural elements i.e. at every length scale is necessary. Particularly, the mechanical properties of microstructural elements, such as bone lamellae are still largely unknown. In the last decade, testing protocols have been devised to close this gap including bending and compression of micrometer-sized bone specimens. However, the precision and accuracy of results obtained have not been discussed. In this study, we aim to do exactly this: we validate microbeam bending by testing silicon microbeams with known mechanical constants, and evaluate the precision and sources of errors in both microbeam bending and micropillar compression by means of finite element (FE) modeling. Bending of Si-microbeams reproduced the expected value for the bending modulus within 17% accuracy, although the effect of geometrical uncertainties was estimated to result in relative errors of up to 50%. The deformation of constraining bulk material had a smaller influence, with relative errors of 11%, for microbeam bending and 25% for micropillar compression. For the latter this error could be sufficiently eliminated by the Sneddon correction. The tapering of micropillars had a negligible effect on overall apparent stiffness, but induced inhomogeneous stress state within micropillars may lead to superposed structural deformation mechanisms and be responsible for failure patterns observed in past studies.
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http://dx.doi.org/10.1016/j.jmbbm.2020.103741DOI Listing
June 2020

Organotypic human skin culture models constructed with senescent fibroblasts show hallmarks of skin aging.

NPJ Aging Mech Dis 2020 6;6. Epub 2020 Mar 6.

Christian Doppler Laboratory for Biotechnology of Skin Aging, Vienna, Austria.

Skin aging is driven by intrinsic and extrinsic factors impacting on skin functionality with progressive age. One factor of this multifaceted process is cellular senescence, as it has recently been identified to contribute to a declining tissue functionality in old age. In the skin, senescent cells have been found to markedly accumulate with age, and thus might impact directly on skin characteristics. Especially the switch from young, extracellular matrix-building fibroblasts to a senescence-associated secretory phenotype (SASP) could alter the microenvironment in the skin drastically and therefore promote skin aging. In order to study the influence of senescence in human skin, 3D organotypic cultures are a well-suited model system. However, only few "aged" skin- equivalent (SE) models are available, requiring complex and long-term experimental setups. Here, we adapted a previously published full-thickness SE model by seeding increasing ratios of stress-induced premature senescent versus normal fibroblasts into the collagen matrix, terming these SE "senoskin". Immunohistochemistry stainings revealed a shift in the balance between proliferation (Ki67) and differentiation (Keratin 10 and Filaggrin) of keratinocytes within our senoskin equivalents, as well as partial impairment of skin barrier function and changed surface properties. Monitoring of cytokine levels of known SASP factors confirmedly showed an upregulation in 2D cultures of senescent cells and at the time of seeding into the skin equivalent. Surprisingly, we find a blunted response of cytokines in the senoskin equivalent over time during 3D differentiation.
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http://dx.doi.org/10.1038/s41514-020-0042-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7060247PMC
March 2020

Thiol-Gelatin-Norbornene Bioink for Laser-Based High-Definition Bioprinting.

Adv Healthc Mater 2020 08 26;9(15):e1900752. Epub 2019 Jul 26.

TU Wien, 3D Printing and Biofabrication Group, Institute of Materials Science and Technology, Getreidemarkt 9, 1060, Vienna, Austria.

Two-photon polymerization (2PP) is a lithography-based 3D printing method allowing the fabrication of 3D structures with sub-micrometer resolution. This work focuses on the characterization of gelatin-norbornene (Gel-NB) bioinks which enables the embedding of cells via 2PP. The high reactivity of the thiol-ene system allows 2PP processing of cell-containing materials at remarkably high scanning speeds (1000 mm s ) placing this technology in the domain of bioprinting. Atomic force microscopy results demonstrate that the indentation moduli of the produced hydrogel constructs can be adjusted in the 0.2-0.7 kPa range by controlling the 2PP processing parameters. Using this approach gradient 3D constructs are produced and the morphology of the embedded cells is observed in the course of 3 weeks. Furthermore, it is possible to tune the enzymatic degradation of the crosslinked bioink by varying the applied laser power. The 3D printed Gel-NB hydrogel constructs show exceptional biocompatibility, supported cell adhesion, and migration. Furthermore, cells maintain their proliferation capacity demonstrated by Ki-67 immunostaining. Moreover, the results demonstrate that direct embedding of cells provides uniform distribution and high cell loading independently of the pore size of the scaffold. The investigated photosensitive bioink enables high-definition bioprinting of well-defined constructs for long-term cell culture studies.
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http://dx.doi.org/10.1002/adhm.201900752DOI Listing
August 2020

Hydration and nanomechanical changes in collagen fibrils bearing advanced glycation end-products.

Biomed Opt Express 2019 Apr 14;10(4):1841-1855. Epub 2019 Mar 14.

Insitute of Lightweight Design and Structural Biomechanics, TU Wien, Getreidemarkt 9, 1060 Vienna, Austria.

Accumulation of advanced glycation end-products (AGEs) in biological tissues occurs as a consequence of normal ageing and pathology. Most biological tissues are composed of considerable amounts of collagen, with collagen fibrils being the most abundant form. Collagen fibrils are the smallest discernible structural elements of load-bearing tissues and as such, they are of high biomechanical importance. The low turnover of collagen cause AGEs to accumulate within the collagen fibrils with normal ageing as well as in pathologies. We hypothesized that collagen fibrils bearing AGEs have altered hydration and mechanical properties. To this end, we employed atomic force and Brillouin light scattering microscopy to measure the extent of hydration as well as the transverse elastic properties of collagen fibrils treated with ribose. We find that hydration is different in collagen fibrils bearing AGEs and this is directly related to their mechanical properties. Collagen fibrils treated with ribose showed increased hydration levels and decreased transverse stiffness compared to controlled samples. Our results show that BLS and AFM yield complementary evidence on the effect of hydration on the nanomechanical properties of collagen fibrils.
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http://dx.doi.org/10.1364/BOE.10.001841DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6484996PMC
April 2019

A Modular Approach to Sensitized Two-Photon Patterning of Photodegradable Hydrogels.

Angew Chem Int Ed Engl 2018 11 18;57(46):15122-15127. Epub 2018 Oct 18.

Institute of Materials Science and Technology, TU Wien, Getreidemarkt 9/308, 1060, Vienna, Austria.

Photodegradable hydrogels have emerged as useful platforms for research on cell function, tissue engineering, and cell delivery as their physical and chemical properties can be dynamically controlled by the use of light. The photo-induced degradation of such hydrogel systems is commonly based on the integration of photolabile o-nitrobenzyl derivatives to the hydrogel backbone, because such linkers can be cleaved by means of one- and two-photon absorption. Herein we describe a cytocompatible click-based hydrogel containing o-nitrobenzyl ester linkages between a hyaluronic acid backbone, which is photodegradable in the presence of cells. It is demonstrated for the first time that by using a cyclic benzylidene ketone-based small molecule as photosensitizer the efficiency of the two-photon degradation process can be improved significantly. Biocompatibility of both the improved two-photon micropatterning process as well as the hydrogel itself is confirmed by cell culture studies.
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http://dx.doi.org/10.1002/anie.201808908DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6391948PMC
November 2018

Dehydration of individual bovine trabeculae causes transition from ductile to quasi-brittle failure mode.

J Mech Behav Biomed Mater 2018 11 1;87:296-305. Epub 2018 Aug 1.

Institute of Lightweight Design and Structural Biomechanics, TU Wien, Getreidemarkt 9, BE02, A-1060 Vienna, Austria. Electronic address:

Trabecular bone is located inside flat bones as well as in the epi- and metaphysis of long bones and plays a key role with respect to load transfer. Disorders, such as osteoporosis, weaken the structural integrity and may also cause changes in the mechanical properties of individual trabeculae, such as Young's modulus. Knowledge of mechanical tissue properties are necessary to assess risk of bone fracture with finite element analysis (FEA). However, such parameters are most often obtained from experiments on air-dried specimens which do not reflect the physiological conditions. In this study, micro-tensile tests of individual bovine trabeculae were performed until fracture to evaluate the influence of hydration state on the elastic and post-yield behavior. Dehydration resulted in significantly (p < 0.001) lower post yield work and ultimate strain, whereas stiffness, yield stress and ultimate stress were significantly (p < 0.001) larger. Further, inelastic strain of dehydrated samples was confined to a small region, whereas it was distributed over a larger area in wet samples. Similarly, microdamage accumulation was confined to a significantly smaller region (p < 0.05) in dry samples, compared to wet ones. Thus, damage localization resulted in a quasi-brittle failure in dry samples. In contrast, hydrated samples showed a much larger area of microdamage accumulation, resulting in a ductile failure. These results emphasize the need to keep bone samples hydrated during mechanical testing. Sequentially, the findings may help to improve clinical applications like FEA-based bone strength predictions.
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http://dx.doi.org/10.1016/j.jmbbm.2018.07.039DOI Listing
November 2018

Evaluation of surface charge shift of collagen fibrils exposed to glutaraldehyde.

Sci Rep 2018 07 4;8(1):10126. Epub 2018 Jul 4.

Automation and Control Institute (ACIN), TU Wien, Gusshausstrasse 27-29, A-1040, Vienna, Austria.

Collagen fibrils are a major component of the extracellular matrix. They form nanometer-scale "cables" acting as a scaffold for cells in animal tissues and are widely used in tissue-engineering. Besides controlling their structure and mechanical properties, it is crucial to have information of their surface charge, as this affects how cells attach to the scaffold. Here, we employed Kelvin-probe Force Microscopy to determine the electrostatic surface potential at the single-fibril level and investigated how glutaraldehyde, a well-established protein cross-linking agent, shifts the surface charge to more negative values without disrupting the fibrils themselves. This shift can be interpreted as the result of the reaction between the carbonyl groups of glutaraldehyde and the amine groups of collagen. It reduces the overall density of positively charged amine groups on the collagen fibril surface and, ultimately, results in the observed negative shift of the surface potential measured. Reactions between carbonyl-containing compounds and proteins are considered the first step in glycation, the non-enzymatic reaction between sugars and proteins. It is conceivable that similar charge shifts happen in vivo caused by sugars, which could have serious implications on age-related diseases such as diabetes and which has been hypothesised for many years.
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http://dx.doi.org/10.1038/s41598-018-28293-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6031691PMC
July 2018

Nanoscale dysregulation of collagen structure-function disrupts mechano-homeostasis and mediates pulmonary fibrosis.

Elife 2018 07 3;7. Epub 2018 Jul 3.

NIHR Southampton Biomedical Research Centre, Clinical and Experimental Sciences, Faculty of Medicine, University of Southampton, Southampton, United Kingdom.

Matrix stiffening with downstream activation of mechanosensitive pathways is strongly implicated in progressive fibrosis; however, pathologic changes in extracellular matrix (ECM) that initiate mechano-homeostasis dysregulation are not defined in human disease. By integrated multiscale biomechanical and biological analyses of idiopathic pulmonary fibrosis lung tissue, we identify that increased tissue stiffness is a function of dysregulated post-translational collagen cross-linking rather than any collagen concentration increase whilst at the nanometre-scale collagen fibrils are structurally and functionally abnormal with increased stiffness, reduced swelling ratio, and reduced diameter. In ex vivo and animal models of lung fibrosis, dual inhibition of lysyl oxidase-like (LOXL) 2 and LOXL3 was sufficient to normalise collagen fibrillogenesis, reduce tissue stiffness, and improve lung function in vivo. Thus, in human fibrosis, altered collagen architecture is a key determinant of abnormal ECM structure-function, and inhibition of pyridinoline cross-linking can maintain mechano-homeostasis to limit the self-sustaining effects of ECM on progressive fibrosis.
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http://dx.doi.org/10.7554/eLife.36354DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6029847PMC
July 2018

Calibration of colloidal probes with atomic force microscopy for micromechanical assessment.

J Mech Behav Biomed Mater 2018 09 17;85:225-236. Epub 2018 May 17.

Institute of Lightweight Design and Structural Biomechanics, TU Wien, 1060 Vienna, Austria; Austrian Cluster for Tissue Regeneration, 1200 Vienna, Austria.

Mechanical assessment of biological materials and tissue-engineered scaffolds is increasingly focusing at lower length scale levels. Amongst other techniques, atomic force microscopy (AFM) has gained popularity as an instrument to interrogate material properties, such as the indentation modulus, at the microscale via cantilever-based indentation tests equipped with colloidal probes. Current analysis approaches of the indentation modulus from such tests require the size and shape of the colloidal probe as well as the spring constant of the cantilever. To make this technique reproducible, there still exist the challenge of proper calibration and validation of such mechanical assessment. Here, we present a method to (a) fabricate and characterize cantilevers with colloidal probes and (b) provide a guide for estimating the spring constant and the sphere diameter that should be used for a given sample to achieve the highest possible measurement sensitivity. We validated our method by testing agarose samples with indentation moduli ranging over three orders of magnitude via AFM and compared these results with bulk compression tests. Our results show that quantitative measurements of indentation modulus is achieved over three orders of magnitude ranging from 1 kPa to 1000 kPa via AFM cantilever-based microindentation experiments. Therefore, our approach could be used for quantitative micromechanical measurements without the need to perform further validation via bulk compression experiments.
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http://dx.doi.org/10.1016/j.jmbbm.2018.05.026DOI Listing
September 2018

Collective Cell Behavior in Mechanosensing of Substrate Thickness.

Biophys J 2018 06;114(11):2743-2755

Centre for Human Development, Stem Cells and Regeneration, Human Development and Health, Institute of Developmental Sciences, University of Southampton, Southampton, United Kingdom; Mechanical Engineering, University of Southampton, Southampton, United Kingdom. Electronic address:

Extracellular matrix stiffness has a profound effect on the behavior of many cell types. Adherent cells apply contractile forces to the material on which they adhere and sense the resistance of the material to deformation-its stiffness. This is dependent on both the elastic modulus and the thickness of the material, with the corollary that single cells are able to sense underlying stiff materials through soft hydrogel materials at low (<10 μm) thicknesses. Here, we hypothesized that cohesive colonies of cells exert more force and create more hydrogel deformation than single cells, therefore enabling them to mechanosense more deeply into underlying materials than single cells. To test this, we modulated the thickness of soft (1 kPa) elastic extracellular-matrix-functionalized polyacrylamide hydrogels adhered to glass substrates and allowed colonies of MG63 cells to form on their surfaces. Cell morphology and deformations of fluorescent fiducial-marker-labeled hydrogels were quantified by time-lapse fluorescence microscopy imaging. Single-cell spreading increased with respect to decreasing hydrogel thickness, with data fitting to an exponential model with half-maximal response at a thickness of 3.2 μm. By quantifying cell area within colonies of defined area, we similarly found that colony-cell spreading increased with decreasing hydrogel thickness but with a greater half-maximal response at 54 μm. Depth-sensing was dependent on Rho-associated protein kinase-mediated cellular contractility. Surface hydrogel deformations were significantly greater on thick hydrogels compared to thin hydrogels. In addition, deformations extended greater distances from the periphery of colonies on thick hydrogels compared to thin hydrogels. Our data suggest that by acting collectively, cells mechanosense rigid materials beneath elastic hydrogels at greater depths than individual cells. This raises the possibility that the collective action of cells in colonies or sheets may allow cells to sense structures of differing material properties at comparatively large distances.
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http://dx.doi.org/10.1016/j.bpj.2018.03.037DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6027966PMC
June 2018

Collagen Fibrils: Nature's Highly Tunable Nonlinear Springs.

ACS Nano 2018 04 21;12(4):3671-3680. Epub 2018 Mar 21.

Institute of Lightweight Design and Structural Biomechanics , Vienna University of Technology , Getreidemarkt 9 , 1060 Vienna , Austria.

Tissue hydration is well known to influence tissue mechanics and can be tuned via osmotic pressure. Collagen fibrils are nature's nanoscale building blocks to achieve biomechanical function in a broad range of biological tissues and across many species. Intrafibrillar covalent cross-links have long been thought to play a pivotal role in collagen fibril elasticity, but predominantly at large, far from physiological, strains. Performing nanotensile experiments of collagen fibrils at varying hydration levels by adjusting osmotic pressure in situ during atomic force microscopy experiments, we show the power the intrafibrillar noncovalent interactions have for defining collagen fibril tensile elasticity at low fibril strains. Nanomechanical tensile tests reveal that osmotic pressure increases collagen fibril stiffness up to 24-fold in transverse (nanoindentation) and up to 6-fold in the longitudinal direction (tension), compared to physiological saline in a reversible fashion. We attribute the stiffening to the density and strength of weak intermolecular forces tuned by hydration and hence collagen packing density. This reversible mechanism may be employed by cells to alter their mechanical microenvironment in a reversible manner. The mechanism could also be translated to tissue engineering approaches for customizing scaffold mechanics in spatially resolved fashion, and it may help explain local mechanical changes during development of diseases and inflammation.
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http://dx.doi.org/10.1021/acsnano.8b00837DOI Listing
April 2018

Structure and collagen crimp patterns of functionally distinct equine tendons, revealed by quantitative polarised light microscopy (qPLM).

Acta Biomater 2018 04 2;70:281-292. Epub 2018 Feb 2.

School of Engineering and Materials Science, Queen Mary University of London, Mile End Rd, London E1 4NS, United Kingdom. Electronic address:

Structure-function relationships in tendons are directly influenced by the arrangement of collagen fibres. However, the details of such arrangements in functionally distinct tendons remain obscure. This study demonstrates the use of quantitative polarised light microscopy (qPLM) to identify structural differences in two major tendon compartments at the mesoscale: fascicles and interfascicular matrix (IFM). It contrasts functionally distinct positional and energy storing tendons, and considers changes with age. Of particular note, the technique facilitates the analysis of crimp parameters, in which cutting direction artefact can be accounted for and eliminated, enabling the first detailed analysis of crimp parameters across functionally distinct tendons. IFM shows lower birefringence (0.0013 ± 0.0001 [-]), as compared to fascicles (0.0044 ± 0.0005 [-]), indicating that the volume fraction of fibres must be substantially lower in the IFM. Interestingly, no evidence of distinct fibre directional dispersions between equine energy storing superficial digital flexor tendons (SDFTs) and positional common digital extensor tendons (CDETs) were noted, suggesting either more subtle structural differences between tendon types or changes focused in the non-collagenous components. By contrast, collagen crimp characteristics are strongly tendon type specific, indicating crimp specialisation is crucial in the respective mechanical function. SDFTs showed much finer crimp (21.1 ± 5.5 µm) than positional CDETs (135.4 ± 20.1 µm). Further, tendon crimp was finer in injured tendon, as compared to its healthy equivalents. Crimp angle differed strongly between tendon types as well, with average of 6.5 ± 1.4° in SDFTs and 13.1 ± 2.0° in CDETs, highlighting a substantially tighter crimp in the SDFT, likely contributing to its effective recoil capacity.

Statement Of Significance: This is the first study to quantify birefringence in fascicles and interfascicular matrix of functionally distinct energy storing and positional tendons. It adopts a novel method - quantitative polarised light microscopy (qPLM) to measure collagen crimp angle, avoiding artefacts related to the direction of histological sectioning, and provides the first direct comparison of crimp characteristics of functionally distinct tendons of various ages. A comparison of matched picrosirius red stained and unstained tendons sections identified non-homogenous staining effects, and leads us to recommend that only unstained sections are analysed in the quantitative manner. qPLM is successfully used to assess birefringence in soft tissue sections, offering a promising tool for investigating the structural arrangements of fibres in (soft) tissues and other composite materials.
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http://dx.doi.org/10.1016/j.actbio.2018.01.034DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5894809PMC
April 2018

Simultaneous visualisation of calcified bone microstructure and intracortical vasculature using synchrotron X-ray phase contrast-enhanced tomography.

Sci Rep 2017 10 16;7(1):13289. Epub 2017 Oct 16.

Biological Sciences, Faculty of Natural and Environmental Sciences, University of Southampton, SO17 1BJ, England, UK.

3D imaging of the bone vasculature is of key importance in the understanding of skeletal disease. As blood vessels in bone are deeply encased in the calcified matrix, imaging techniques that are applicable to soft tissues are generally difficult or impossible to apply to the skeleton. While canals in cortical bone can readily be identified and characterised in X-ray computed tomographic data in 3D, the soft tissue comprising blood vessels that are putatively contained within the canal structures does not provide sufficient image contrast necessary for image segmentation. Here, we report an approach that allows for rapid, simultaneous visualisation of calcified bone tissue and the vasculature within the calcified bone matrix. Using synchrotron X-ray phase contrast-enhanced tomography we show exemplar data with intracortical capillaries uncovered at sub-micrometre level without the need for any staining or contrast agent. Using the tibiofibular junction of 15 week-old C57BL/6 mice post mortem, we show the bone cortical porosity simultaneously along with the soft tissue comprising the vasculature. Validation with histology confirms that we can resolve individual capillaries. This imaging approach could be easily applied to other skeletal sites and transgenic models, and could improve our understanding of the role the vasculature plays in bone disease.
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http://dx.doi.org/10.1038/s41598-017-13632-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5643345PMC
October 2017

Elastic modulus varies along the bovine femur.

J Mech Behav Biomed Mater 2017 07 27;71:279-285. Epub 2017 Mar 27.

Bioengineering Science Research Group, Engineering Sciences, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ, UK; Institute of Lightweight Design and Structural Biomechanics, Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria. Electronic address:

Bone is a heterogeneous material and its mechanical properties vary within the body. Variations in the mechanical response of different bone samples taken from the body cannot be fully explained by only looking at local compositional information at the tissue level. Due to different states of the stress within bones, one might expect that mechanical properties change over the length of a bone; this has not been a matter of systematic research in previous studies. In this study, the distribution of the tissue elastic modulus along the bovine femur is investigated using three-point bending tests. Two bovine femora were split to seven and eight blocks from proximal to distal metaphysis, respectively and twenty beam shaped bone samples were extracted and tested from each block. Based on our findings, the longitudinal elastic modulus follows a gradient pattern along the bovine femur as it increases along the bone from the proximal metaphysis to mid-diaphysis and then decreases toward the distal metaphysis again. Considering long bones to be subjected to bending loads, this mechanism alters the bone structure to support load in the regions where it is needed; similar as outlined by Wolff's law. In another part of this study, microfocus X-ray computed tomography (μCT) was found unable to predict the same trend of changes for the elastic modulus via image-based or density-based elastic moduli calculations. This is insofar important as conventional finite element models of bone are often directly shaped from μCT data. Based on our findings, it seems that current computed tomography based finite element models generated in this manner may not adequately capture the local variation of material behavior of bone tissue, but this may be improved by considering the changes of the elastic modulus along the femur.
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http://dx.doi.org/10.1016/j.jmbbm.2017.03.021DOI Listing
July 2017

Development of X-ray micro-focus computed tomography to image and quantify biofilms in central venous catheter models in vitro.

Microbiology (Reading) 2016 09 6;162(9):1629-1640. Epub 2016 Jul 6.

National Centre for Advanced Tribology at Southampton (nCATS), Faculty of Engineering and the Environment (FEE), University of Southampton, UK.

Bacterial infections of central venous catheters (CVCs) cause much morbidity and mortality, and are usually diagnosed by concordant culture of blood and catheter tip. However, studies suggest that culture often fails to detect biofilm bacteria. This study optimizes X-ray micro-focus computed tomography (X-ray µCT) for the quantification and determination of distribution and heterogeneity of biofilms in in vitro CVC model systems.Bacterial culture and scanning electron microscopy (SEM) were used to detect Staphylococcus epidermidis ATCC 35984 biofilms grown on catheters in vitro in both flow and static biofilm models. Alongside this, X-ray µCT techniques were developed in order to detect biofilms inside CVCs. Various contrast agent stains were evaluated using energy-dispersive X-ray spectroscopy (EDS) to further optimize these methods. Catheter material and biofilm were segmented using a semi-automated matlab script and quantified using the Avizo Fire software package. X-ray µCT was capable of distinguishing between the degree of biofilm formation across different segments of a CVC flow model. EDS screening of single- and dual-compound contrast stains identified 10 nm gold and silver nitrate as the optimum contrast agent for X-ray µCT. This optimized method was then demonstrated to be capable of quantifying biofilms in an in vitro static biofilm formation model, with a strong correlation between biofilm detection via SEM and culture. X-ray µCT has good potential as a direct, non-invasive, non-destructive technology to image biofilms in CVCs, as well as other in vivo medical components in which biofilms accumulate in concealed areas.
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http://dx.doi.org/10.1099/mic.0.000334DOI Listing
September 2016

Commentary on: Mechanical properties of cortical bone and their relationships with age, gender, composition and microindentation properties in the elderly.

Bone 2016 06 16;87:159-60. Epub 2016 Apr 16.

Institute of Lightweight Design and Structural Biomechanics, TU Wien, Vienna, Austria; Bioengineering Science Research Group, Faculty of Engineering and the Environment, University of Southampton, Southampton, UK. Electronic address:

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http://dx.doi.org/10.1016/j.bone.2016.04.009DOI Listing
June 2016

Local Variation in Femoral Neck Cortical Bone: In Vitro Measured Bone Mineral Density, Geometry and Mechanical Properties.

J Clin Densitom 2017 Apr - Jun;20(2):205-215. Epub 2015 Dec 23.

Faculty of Engineering and Environment and Faculty of Medicine, University of Southampton, Southampton, UK; Institute of Lightweight Design and Structural Biomechanics, TU Wien, Vienna, Austria.

Age- and disease (osteoporotic fractured and osteoarthritic tissue)-related changes in the distribution of cortical bone were examined, using a multimodality approach, including measurement of local density, geometry and mechanical properties, where changes in these properties can give rise to instability and increasing probability of fracture. In contrast to the majority of previously reported research, this study also focuses on the characteristic non-circular femoral neck cross-sectional geometry and variation in bone mineral density (BMD) around the femoral neck. Twenty-two osteoarthritic and 7 osteoporotic femoral neck slices, collected from elective and trauma-related arthroplasty, and 16 cadaveric donor tissue controls were tested mechanically using Reference Point Indentation (BioDent™, Active Life Technologies®, Santa Barbara, CA) and then scanned with in vitro-based radiography intended to replicate the dual-energy X-ray absorptiometry technique. All parameters were measured regionally around the circumference of the femoral neck, allowing examination of spatial variability within the cortical bone. Fractured tissue was less resistant to indentation in the thinner superolateral segment compared to other segments and other groups. BMD around the fractured femoral necks appeared more consistent than that of nonfractured tissue, where BMD was reduced in the superolateral segment for the other groups. Cortical bone was thin in the superolateral segment for all groups except for the osteoarthritic group, and was thicker in the inferomedial segment for both osteoarthritic and fractured groups, resulting in the largest variation in buckling ratio (ratio of cortical bone diameter to cortical bone thickness) around the femoral neck for the fractured group. With age, healthy controls appeared to have lower inferomedial cortical thickness, whereas no significant differences in Reference Point Indentation measurements and density were observed. The study has highlighted several (both quality- and quantity-related) parameters that may be used to improve prediction of fracture risk.
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http://dx.doi.org/10.1016/j.jocd.2015.10.003DOI Listing
June 2018

Toughness and damage susceptibility in human cortical bone is proportional to mechanical inhomogeneity at the osteonal-level.

Bone 2015 Jul 9;76:158-68. Epub 2015 Apr 9.

Bioengineering Sciences Research Group, Faculty of Engineering and the Environment, University of Southampton, SO17 1BJ Southampton, UK; Institute for Lightweight Design and Structural Biomechanics, Vienna University of Technology, 1040 Vienna, Austria. Electronic address:

Limitations associated with current clinical fracture risk assessment tools highlight the need for increased understanding of the fracture mechanisms of the bone and, ideally, a means of assessing this in vivo. Being a multi-layered hierarchical structure, the overall properties of the bone are dictated by its structural and compositional properties over multiple length scales. In this study, we investigate the osteonal-, micro- and tissue-level mechanical behaviour of cortical bone tissue samples from young and elderly donors through atomic force microscope (AFM) cantilever-based nanoindentation, reference point microindentation (RPI) and fracture toughness experiments respectively. We demonstrate that bone's fracture toughness and crack growth resistance at the tissue-level are significantly correlated to damage susceptibility at the micro-level, and mechanical inhomogeneity between lamellae and interlamellar areas at the osteonal-level. In more detail, reduced nanoelasticity inhomogeneity of lamellar/interlamellar layers within the osteons correlated to increased indentation depth at the micro-level and an overall reduction in crack-growth toughness and fracture toughness of the tissue. Our data also suggest that deterioration of bone's mechanical properties is expressed concurrently at these three levels, and that mechanical inhomogeneity between the principal structural units of the cortical tissue holds a key role on bone's toughness behaviour. We hypothesise that the reduction in nanoelasticity inhomogeneity is--at least to some extent--responsible for the inability of the microstructure to effectively adapt to the applied load, e.g. by redistributing strains, in a non-catastrophic manner preventing damage formation and propagation. Our hypothesis is further supported by synchrotron radiation micro-computed tomography (SRμCT) data, which show that failure of tougher bone specimens is governed by increased deflection of the crack path and broadly spread damage around the crack-tip. In contrast, shorter and more direct crack paths as well as less-distributed damage were evidenced during failure of the weaker specimens. Overall, this multi-scale study highlights the importance of elasticity inhomogeneity within the osteon to the damage susceptibility and consequently to the fracture resistance of the tissue.
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http://dx.doi.org/10.1016/j.bone.2015.03.020DOI Listing
July 2015

Extracellular DNA impedes the transport of vancomycin in Staphylococcus epidermidis biofilms preexposed to subinhibitory concentrations of vancomycin.

Antimicrob Agents Chemother 2014 Dec 29;58(12):7273-82. Epub 2014 Sep 29.

Faculty of Engineering and the Environment, University of Southampton, Southampton, United Kingdom Centre for Microbial Interface Biology, Departments of Microbial Infection and Immunity and Orthopedics, The Ohio State University, Columbus, Ohio, USA.

Staphylococcus epidermidis biofilm formation is responsible for the persistence of orthopedic implant infections. Previous studies have shown that exposure of S. epidermidis biofilms to sub-MICs of antibiotics induced an increased level of biofilm persistence. BODIPY FL-vancomycin (a fluorescent vancomycin conjugate) and confocal microscopy were used to show that the penetration of vancomycin through sub-MIC-vancomycin-treated S. epidermidis biofilms was impeded compared to that of control, untreated biofilms. Further experiments showed an increase in the extracellular DNA (eDNA) concentration in biofilms preexposed to sub-MIC vancomycin, suggesting a potential role for eDNA in the hindrance of vancomycin activity. Exogenously added, S. epidermidis DNA increased the planktonic vancomycin MIC and protected biofilm cells from lethal vancomycin concentrations. Finally, isothermal titration calorimetry (ITC) revealed that the binding constant of DNA and vancomycin was 100-fold higher than the previously reported binding constant of vancomycin and its intended cellular d-Ala-d-Ala peptide target. This study provides an explanation of the eDNA-based mechanism of antibiotic tolerance in sub-MIC-vancomycin-treated S. epidermidis biofilms, which might be an important factor for the persistence of biofilm infections.
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http://dx.doi.org/10.1128/AAC.03132-14DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4249571PMC
December 2014

Preparation and characterization of bioadhesive microparticles comprised of low degree of quaternization trimethylated chitosan for nasal administration: effect of concentration and molecular weight.

Langmuir 2014 Oct 7;30(41):12337-44. Epub 2014 Oct 7.

Laboratory of Pharmaceutical Technology, Department of Pharmaceutical Sciences, Aristotle University of Thessaloniki , GR-54124 Thessaloniki, Greece.

Toward the development of microparticulate carriers for nasal administration, N-trimethylchitosan chloride (TMC) of low molecular weight (LMW) and high molecular weight (HMW) and low degree of quaternization (16% and 27%, respectively) was co-formulated into microparticles comprising of dipalmatoylphosphatidylcholine (DPPC) and poly(lactic-co-glycolic) acid (PLGA) via the spray-drying technique. The chitosan derivatives were characterized by means of nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and Fourier transfrom infrared (FTIR) spectroscopy. The size and morphology of the produced microparticles were assessed by scanning electron microscopy (SEM), whereas their mucoadhesive properties were investigated by means of atomic force microscopy-force spectroscopy (AFM-FS). The results showed that microparticles exhibit mucoadhesion when TMC is present on their surface above a threshold of TMC (>0.3% w/w).
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http://dx.doi.org/10.1021/la5030636DOI Listing
October 2014

Nanomechanical assessment of human and murine collagen fibrils via atomic force microscopy cantilever-based nanoindentation.

J Mech Behav Biomed Mater 2014 Nov 15;39:9-26. Epub 2014 Jul 15.

Bioengineering Science Research Group, Faculty of Engineering and the Environment, University of Southampton, SO17 1BJ Southampton, UK; Institute for Lightweight Design and Structural Biomechanics, Faculty of Engineering and the Environment, Vienna University of Technology, Gusshausstrasse 27-29, Vienna 1040, Austria. Electronic address:

The nanomechanical assessment of collagen fibrils via atomic force microscopy (AFM) is of increasing interest within the biomedical research community. In contrast to conventional nanoindentation there exists no common standard for conducting experiments and analysis of data. Currently used analysis approaches vary between studies and validation of quantitative results is usually not performed, which makes comparison of data from different studies difficult. Also there are no recommendations with regards to the maximum indentation depth that should not be exceeded to avoid substrate effects. Here we present a methodology and analysis approach for AFM cantilever-based nanoindentation experiments that allows efficient use of captured data and relying on a reference sample for determination of tip shape. Further we show experimental evidence that maximum indentation depth on collagen fibrils should be lower than 10-15% of the height of the fibril to avoid substrate effects and we show comparisons between our and other approaches used in previous works. While our analysis approach yields similar values for indentation modulus compared to the Oliver-Pharr method we found that Hertzian analysis yielded significantly lower values. Applying our approach we successfully and efficiently indented collagen fibrils from human bronchi, which were about 30 nm in size, considerably smaller compared to collagen fibrils obtained from murine tail-tendon. In addition, derived mechanical parameters of collagen fibrils are in agreement with data previously published. To establish a quantitative validation we compared indentation results from conventional and AFM cantilever-based nanoindentation on polymeric samples with known mechanical properties. Importantly we can show that our approach yields similar results when compared to conventional nanoindentation on polymer samples. Introducing an approach that is reliable, efficient and taking into account the AFM tip shape, we anticipate that the present work may act as a guideline for conducting AFM cantilever-based nanoindentation of collagen fibrils. This may aid understanding of collagen-related diseases such as asthma, lung fibrosis or bone disease with potential alterations of collagen fibril mechanics.
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http://dx.doi.org/10.1016/j.jmbbm.2014.06.015DOI Listing
November 2014

The role of nanoscale toughening mechanisms in osteoporosis.

Curr Osteoporos Rep 2014 Sep;12(3):351-6

Institute for Lightweight Design and Structural Biomechanics, Vienna University of Technology, Gusshausstrasse 27-29 A-1040, Vienna, Austria,

Strength is the most widely reported parameter with regards to bone failure. However, bone contains pre-existing damage and stress concentration sites, perhaps making measures of fracture toughness more indicative of the resistance of the tissue to withstand fracture. Several toughening mechanisms have been identified in bone, prominently, at the microscale. More recently, nanoscale toughness mechanisms, such as sacrificial-bonds and hidden-length or dilatational band formation, mediated by noncollagenous proteins, have been reported. Absence of specific noncollagenous proteins results in lowered fracture toughness in animal models. Further, roles of several other, putative influencing, factors such as closely bound water, collagen cross-linking and citrate bonds in bone mineral have also been proposed. Yet, it is still not clear if and which mechanisms are hallmarks of osteoporosis disease and how they influence fracture risk. Further insights on the workings of such influencing factors are of high importance for developing complementary diagnostics and therapeutics strategies.
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http://dx.doi.org/10.1007/s11914-014-0217-0DOI Listing
September 2014

Sox17 is required for normal pulmonary vascular morphogenesis.

Dev Biol 2014 Mar 10;387(1):109-20. Epub 2014 Jan 10.

Perinatal Institute, Division of Pulmonary Biology, Cincinnati Children's Hospital Medical Center, The University of Cincinnati College of Medicine, 3333 Burnet Avenue, Cincinnati, OH 45229-3039, United States. Electronic address:

The SRY-box containing transcription factor Sox17 is required for endoderm formation and vascular morphogenesis during embryonic development. In the lung, Sox17 is expressed in mesenchymal progenitors of the embryonic pulmonary vasculature and is restricted to vascular endothelial cells in the mature lung. Conditional deletion of Sox17 in splanchnic mesenchyme-derivatives using Dermo1-Cre resulted in substantial loss of Sox17 from developing pulmonary vascular endothelial cells and caused pulmonary vascular abnormalities before birth, including pulmonary vein varices, enlarged arteries, and decreased perfusion of the microvasculature. While survival of Dermo1-Cre;Sox17Δ/Δ mice (herein termed Sox17Δ/Δ) was unaffected at E18.5, most Sox17Δ/Δ mice died by 3 weeks of age. After birth, the density of the pulmonary microvasculature was decreased in association with alveolar simplification, biventricular cardiac hypertrophy, and valvular regurgitation. The severity of the postnatal cardiac phenotype was correlated with the severity of pulmonary vasculature abnormalities. Sox17 is required for normal formation of the pulmonary vasculature and postnatal cardiovascular homeostasis.
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http://dx.doi.org/10.1016/j.ydbio.2013.11.018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4422074PMC
March 2014
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