Mécanique des milieux fibreux auto-enchevêtrés : application à un alliage à mémoire de forme de type Nickel-Titane

The aim of this work is to process and characterize for biomedical applications,self-entangled structures made of a single NiTi shape memory fiber. We have optimizeda processing route consisting in entangling and shape-setting a spring bythermomechanical treatments. The samples were characterized in compression andtension, using optical and x-ray tomographic observations. The structures thus obtainedare homogeneous, isotropic, superelastic at room temperature up to strains ofat least 30%, and can become ferroelastic with a shape memory effect up to at least16% strain by an additional heat treatment. The mechanical behavior in compressionis first consolidating and then dilating, while in tension, the samples are slightlyauxetic. A comparison with similar media made of ductile and viscoelastic fibers,as well as with discrete element simulations on friction-free elastic fibers, show thatthe mechanical properties of these self-entangled structures are controlled by theirunique architecture, in-between continuous and discrete media.L’objectif de ce travail est d’élaborer et de caractériser pour des applications biomédicalesun matériau auto-enchevêtré à base d’une seule fibre d’alliage à mémoire deforme de type Nickel-Titane. Nous avons optimisé un procédé de fabrication consistantà enchevêtrer et figer un ressort par des traitements thermiques. Les échantillonsont été caractérisés en compression et traction, avec suivi par caméra optique ettomographie in-situ. Les structures obtenues sont homogènes, isotropes, superélastiquesà température ambiante jusqu’à des déformations d’au moins 30%, et peuventdevenir ferroélastiques avec un effet mémoire d’au moins 16% par un traitement thermiqueadditionnel. Leur comportement en compression est consolidant puis dilatantet en traction, légèrement auxétique. Une comparaison avec des milieux similairesconstitués de fils ductiles et viscoélastiques, ainsi qu’avec des simulations par élémentsdiscrets sur des milieux élastiques sans frottement, montre que les propriétésmécaniques des structures auto-enchevêtrées sont contrôlées par leur architecturesingulière, à mi-chemin entre milieux continus et discrets

A new shape memory porous material made up of a single entangled NiTi wire

Avec leur architecture légère et leurs propriétés mécaniques potentiellement exceptionnelles, les matériaux poreux en alliages à mémoire de forme NiTi se positionnent comme des solutions intéressantes pour un large spectre d'applications, e.g. prothèses biomédicales, systèmes absorbeurs de chocs... Aujourd'hui, la plupart de ces matériaux sont produits par frittage de poudres (naturel ou SPS). Cependant, leurs propriétés mécaniques sont bien loin d’être aussi bonnes qu'attendues (peu ou pas de superélasticité ou d’effet mémoire) : ceci est en grande partie dû aux grandes difficultés pour induire des microstructures appropriées lors du frittage. Pour contourner ces problèmes, nous proposons un procédé de fabrication alternatif et original, basé sur l'auto-enchevêtrement d'un fil de NiTi, sans frittage. D’une part, les mésostructures des pelotes ainsi produites, caractérisées par microtomographie RX, sont relativement homogènes ; elles peuvent être architecturées à façon en adaptant les conditions de mise en forme. D’autre part, les propriétés thermomécaniques des pelotes peuvent être pilotées simplement par des traitements thermiques. Ces deux atouts procurent à ces matériaux de grandes possibilités. Par exemples, le comportement superélastique des pelotes en compression simple est excellent et étonnant : il combine (i) très grandes déformations recouvrables en décharge (30 à 40%), (ii) niveaux de contraintes raisonnables (5 à 10 MPa), peu dépendants de la température (0.05MPa/K) et (iii) variations de volume importantes avec des séquences complexes de consolidation et de dilatance. Le comportement ferroélastique est quant à lui très proche de celui des milieux fibreux élastoplastiques, avec un écrouissage notable en charge et une forte déformation rémanente en décharge (de l’ordre de 20%). Enfin, un simple chauffage à charge nulle permet de recouvrir totalement cette déformation par effet mémoire de forme

Poisson's function of single-wire entangled materials : below 0 in traction and above ½ in compression

The mechanics of fibrous materials is both complex and intriguing. Here, we explore one class of such materials, made of the disordered entanglement of a single long fiber. This architected material is of both fundamental and technological interests. From a theoretical point of view, this system can be seen as a disordered material, akin to glasses, but with very long (possibly infinite) ranged correlations transmitted along the single fiber. From an applied point of view, this material is a potential replacement for sintered materials, because with comparable porosities, entangled structures are highly ductile while sintered powders are often intrinsically brittle. We study the mechanics of single-wire materials using a combination of experiments and simulations. Experimentally, we produce cylindrical samples by entangling a single fiber made either of NiTi, polyamide or copper. Spatial homogeneity and stress relaxation are achieved by series of thermomechanical treatments that allow to first transform the wire into a coil and then entangle the coil. The samples are subjected to cycles of compressions followed by unloading, tracking the local deformations in the samples with optical cameras and x-ray microtomography. Numerically, we employed Kirchhoff's elastic rod theory to simulate the same mechanical cycles on both numerical substitutes of the experimental samples (i.e. cylindrical samples of geometry and density comparable to the experiments) and idealized samples with a cubic and periodic geometry. We will discuss our main observations on the mechanical properties of the single-wire systems. First, stress-strain curves show a prolonged regime of non-linear elasticity and a marked hysteresis between compression loading and unloading. Also, by tracking the sample shape variations, we observe surprising non-monotonous variations of the sample volume, both in the experiments and in the simulations. At the local level, we use image analysis to follow the evolution of the local orientation of the fiber and of the number and orientation of the contacts, the latter two quantities also showing non-monotonous behaviors.  In particular, we show that this material exhibits at finite strains an unexpected variation of its Poisson's function, beyond the usual bounds: Poisson's function is above ½ in compression and below zero in tension. This material is thus reversibly compress dilatant in compression and auxetic in tension. This means that the structure expands laterally in both traction and compression and so rapidly in compression that its volume increases. This unusual variation of Poisson's function arises from the interplay between the elongation of the coiled segments that constitute the entanglement and fiber rearrangements due to steric effects.  This work illustrates that a property (Poisson's function not limited to 0 or ½), rare in bulk materials, can be readily obtained in "simple" architected materials and opens the way to developing architectures with very large, negative but also positive, Poisson's functions

Inhibition of DNA methylation promotes breast tumor sensitivity to netrin-1 interference

In a number of human cancers, NTN1 upregulation inhibits apoptosis induced by its so-called dependence receptors DCC and UNC5H, thus promoting tumor progression. In other cancers however, the selective inhibition of this dependence receptor death pathway relies on the silencing of pro-apoptotic effector proteins. We show here that a substantial fraction of human breast tumors exhibits simultaneous DNA methylation-dependent loss of expression of NTN1 and of DAPK1, a serine threonine kinase known to transduce the netrin-1 dependence receptor pro-apoptotic pathway. The inhibition of DNA methylation by drugs such as decitabine restores the expression of both NTN1 and DAPK1 in netrin-1-low cancer cells. Furthermore, a combination of decitabine with NTN1 silencing strategies or with an anti-netrin-1 neutralizing antibody potentiates tumor cell death and efficiently blocks tumor growth in different animal models. Thus, combining DNA methylation inhibitors with netrin-1 neutralizing agents may be a valuable strategy for combating cancer

Auto-entangled fibrous materials mechanics : application to a shape memory alloy NiTi

L’objectif de ce travail est d’élaborer et de caractériser pour des applications biomédicalesun matériau auto-enchevêtré à base d’une seule fibre d’alliage à mémoire deforme de type Nickel-Titane. Nous avons optimisé un procédé de fabrication consistantà enchevêtrer et figer un ressort par des traitements thermiques. Les échantillonsont été caractérisés en compression et traction, avec suivi par caméra optique ettomographie in-situ. Les structures obtenues sont homogènes, isotropes, superélastiquesà température ambiante jusqu’à des déformations d’au moins 30%, et peuventdevenir ferroélastiques avec un effet mémoire d’au moins 16% par un traitement thermiqueadditionnel. Leur comportement en compression est consolidant puis dilatantet en traction, légèrement auxétique. Une comparaison avec des milieux similairesconstitués de fils ductiles et viscoélastiques, ainsi qu’avec des simulations par élémentsdiscrets sur des milieux élastiques sans frottement, montre que les propriétésmécaniques des structures auto-enchevêtrées sont contrôlées par leur architecturesingulière, à mi-chemin entre milieux continus et discrets.The aim of this work is to process and characterize for biomedical applications,self-entangled structures made of a single NiTi shape memory fiber. We have optimizeda processing route consisting in entangling and shape-setting a spring bythermomechanical treatments. The samples were characterized in compression andtension, using optical and x-ray tomographic observations. The structures thus obtainedare homogeneous, isotropic, superelastic at room temperature up to strains ofat least 30%, and can become ferroelastic with a shape memory effect up to at least16% strain by an additional heat treatment. The mechanical behavior in compressionis first consolidating and then dilating, while in tension, the samples are slightlyauxetic. A comparison with similar media made of ductile and viscoelastic fibers,as well as with discrete element simulations on friction-free elastic fibers, show thatthe mechanical properties of these self-entangled structures are controlled by theirunique architecture, in-between continuous and discrete media

Non-canonical NOTCH3 signalling limits tumour angiogenesis.

Notch signalling is a causal determinant of cancer and efforts have been made to develop targeted therapies to inhibit the so-called canonical pathway. Here we describe an unexpected pro-apoptotic role of Notch3 in regulating tumour angiogenesis independently of the Notch canonical pathway. The Notch3 ligand Jagged-1 is upregulated in a fraction of human cancer and our data support the view that Jagged-1, produced by cancer cells, is inhibiting the apoptosis induced by the aberrant Notch3 expression in tumour vasculature. We thus present Notch3 as a dependence receptor inducing endothelial cell death while this pro-apoptotic activity is blocked by Jagged-1. Along this line, using Notch3 mutant mice, we demonstrate that tumour growth and angiogenesis are increased when Notch3 is silenced in the stroma. Consequently, we show that the well-documented anti-tumour effect mediated by γ-secretase inhibition is at least in part dependent on the apoptosis triggered by Notch3 in endothelial cells.info:eu-repo/semantics/publishe

Sonic Hedgehog Promotes Tumor Cell Survival by Inhibiting CDON Pro-Apoptotic Activity

International audienceThe Hedgehog signaling is a determinant pathway for tumor progression. However, while inhibition of the Hedgehog canonical pathway-Patched-Smoothened-Gli-has proved efficient in human tumors with activating mutations in this pathway, recent clinical data have failed to show any benefit in other cancers, even though Sonic Hedgehog (SHH) expression is detected in these cancers. Cell-adhesion molecule-related/down-regulated by Oncogenes (CDON), a positive regulator of skeletal muscle development, was recently identified as a receptor for SHH. We show here that CDON behaves as a SHH dependence receptor: it actively triggers apoptosis in the absence of SHH. The pro-apoptotic activity of unbound CDON requires a proteolytic cleavage in its intracellular domain, allowing the recruitment and activation of caspase-9. We show that by inducing apoptosis in settings of SHH limitation, CDON expression constrains tumor progression, and as such, decreased CDON expression observed in a large fraction of human colorectal cancer is associated in mice with intestinal tumor progression. Reciprocally, we propose that the SHH expression, detected in human cancers and previously considered as a mechanism for activation of the canonical pathway in an autocrine or paracrine manner, actually provides a selective tumor growth advantage by blocking CDON-induced apoptosis. In support of this notion, we present the preclinical demonstration that interference with the SHH-CDON interaction triggers a CDON-dependent apoptosis in vitro and tumor growth inhibition in vivo. The latter observation qualifies CDON as a relevant alternative target for anticancer therapy in SHH-expressing tumors

CDON induces apoptosis in the absence of SHH.

<p>(A) Schematic representation of CDON protein structural domains. (B) CDON immunofluorescence staining of HEK293T transfected with a full-length mouse CDON expression plasmid. CDON (green) and nuclei (Hoechst in blue) staining are shown. (C–E) Cell death induction in HEK293T cells was quantified by trypan blue exclusion assay (C), caspase-3 activity assay (D), or TUNEL staining (E) after transfection with mock, CDON, or Ptc expression vectors. Increasing amounts of recombinant SHH added in the culture medium are indicated. Recombinant netrin–1 (NTN1) was added in the culture medium as a negative control. The general caspase inhibitor z-VAD-fmk was used to block caspase-dependent cell death. In (D), lower panel shows detection of CDON, Ptc, and β-actin proteins by Western Blot. In (E), TUNEL-stained cells (orange) and nuclei (Hoechst staining in blue) are shown. (F) Apoptotic cell death induction as measured by caspase-3 activity was quantified in HEK293T cells transfected either with full-length rat CDON or with rat CDON deleted from its SHH-binding site (CDONΔFbn3) alone or with recombinant SHH (rSHH) added in excess in the culture medium. Lower panel shows PCR products obtained after amplification with rat CDON and human HPRT-specific primers. For (B–D), F error bars indicate s.d. Statistical treatment of the data was performed using a two-sided Mann–Whitney test compared to mock-transfected condition (*<i>p</i><0.05; **<i>p</i><0.01).</p

CDON is a <i>bona fide</i> tumor suppressor.

<p>(A) Cohorts of CDON^−/− APC^+/1638N mice were generated to analyze the effect of <i>CDON</i> genetic invalidation on intestinal tumorigenesis compared to CDON^+/+ APC^+/1638N. (B–E) Representative images of Haematoxylin–Eosin–Saffron (HES) staining of normal intestinal epithelium (B) compared to adenocarcinomas with mucosa (C) muscularis (D) or serosa (E) local invasion observed in CDON^−/− APC^+/1638N mice. m, mucosa; M, muscularis; S, serosa; scale bar, 200 µm. (F) Frequency and incidence of adenocarcinomas (ADK) in CDON^+/+ APC^+/1638N mice (<i>n</i> = 28) compared to CDON^−/− APC^1638N mice (<i>n</i> = 18). Tumour classification was performed according to international recommendations (χ² test; *<i>p</i><0.05 and Student <i>t</i> test; **<i>p</i><0.01). (G) Cell death was quantified in high grade adenomas from three mice of each genotype. Representative images of pyknotic cells from HES CDON^+/+ APC^+/1638N mice compared to CDON^−/− APC^+/1638N mice are shown in right panels. Scale bar, 10 µm. Error bars indicate s.e.m. Statistical treatment of the data was performed using a two-sided Mann–Whitney test (**<i>p</i><0.01).</p

Interference with SHH/CDON interaction as a promising therapeutic strategy.

<p>(A) Quantification of CDON mRNA was performed after treatment of A549 cells either with 1 µM or 5 µM cyclopamine (cyclo.) or with 50 nM or 200 nM Smoothened Agonist (SAG). (B) Apoptotic cell death induction as measured by caspase-3 activity was quantified in A549 cells treated with cyclopamine (cyc.) and transfected either with scramble (siScr.) or with CDON siRNA. A549 cells were also treated with SAG and transfected either with siScr or with SHH siRNA. For (A) and (B), data are means of a minimum of three independent assays. Error bars indicate s.d. Statistical treatment of the data was performed using a two-sided Mann–Whitney test compared to scramble siRNA-transfected condition (*<i>p</i><0.05). (C) <i>Nude</i> mice were engrafted with A549 cells by subcutaneous injection of 10 million cells. When the mean tumor volume reached approximately 40 mm³, animals were treated daily by intra-tumoral injection of cyclopamine and either scramble or CDON siRNA alone during 13 d. Mean tumor volume and number of animals for each group are indicated (*<i>p</i><0.05). (D) Schematic representation of the Fc-CDO_3FbnIII recombinant protein including the CDON juxtamembrane fibronectin domain associated with a human IgG1 Fc fragment. (E) Apoptotic cell death induction as measured by caspase-3 activity was quantified in A549 cells treated with 2 µg/mL Fc-CDO_3FbnIII alone or together with an excess recombinant SHH added in the culture medium. Data are means of a minimum of three independent assays. Error bars indicate s.d. Statistical treatment of the data was performed using a two-sided Mann–Whitney test compared to control condition (*<i>p</i><0.05). (F) <i>Nude</i> mice were engrafted with A549 cells by subcutaneous injection of 10 million cells. When the mean tumor volume reached approximately 100 mm³, animals were treated twice a week by i.p. injection of 10 mg/kg Fc-CDO_3FbnIII during 3 wk. Mean tumor volume and number of animals for each group are indicated. Error bars indicate s.e.m. Statistical treatment of the data was performed using a two-sided Mann–Whitney test compared to PBS-treated condition (***<i>p</i><0.001). (G) <i>Nude</i> mice were engrafted with A549 cells by subcutaneous injection of 10 million cells. When the mean tumor volume reached approximately 100 mm³, animals were treated twice a week by i.p. injection of 20 mg/kg Fc-CDON_3FbnIII together with 3 µg siRNA (scramble or CDON siRNA) during 3 wk. Mean tumor volume and number of animals for each group are indicated. Error bars indicate s.e.m. Statistical treatment of the data was performed using a two-sided Mann–Whitney test compared to PBS-treated condition (***<i>p</i><0.001).</p