<p>Tendon healing is a slow process and the tendon may not regain its initial mechanical properties after rupture. Mechanical stimuli have shown to have positive effect on tendon healing. This study is the first to investigate the effect of vibration stimuli on healing tendons. Vibration was also compared to treadmill running, which has previously been used for mechanical stimuli.63 female Sprauge-Dawley rats were used. A 3 mm segment was removed from the Achilles tendon and the tendon was left to heal. The animals were subjected to 15 min of daily exercise, vibration or treadmill running or acted as controls without exercise. The study was divided into three experiments. Experiment 1; the animals had full time cage activity and was randomized into running, vibration and control group. Experiment 2; the animals were unloaded and randomized into vibration, running and control group. There was also a control group with full time cage activity in experiment 2. Experiment 3; the animals were unloaded and randomized into vibration and placebo group. 14 days after surgery the animals were killed and mechanical testing of the Achilles tendons was performed. The results showed no significant difference between the groups in experiment 1. Experiment 2 showed that controls with full time cage activity had higher peak load, stiffness and cross sectional area than unloaded running, vibration and control groups. In experiment 3, there was no significant difference between vibration and placebo group. In conclusion, this study shows that vibration, as applied here, does not affect tendon healing.</p>

Tendon healing is a slow process and the tendon may not regain its initial mechanical properties after rupture. Mechanical stimuli have shown to have positive effect on tendon healing. This study is the first to investigate the effect of vibration stimuli on healing tendons. Vibration was also compared to treadmill running, which has previously been used for mechanical stimuli.63 female Sprauge-Dawley rats were used. A 3 mm segment was removed from the Achilles tendon and the tendon was left to heal. The animals were subjected to 15 min of daily exercise, vibration or treadmill running or acted as controls without exercise. The study was divided into three experiments. Experiment 1; the animals had full time cage activity and was randomized into running, vibration and control group. Experiment 2; the animals were unloaded and randomized into vibration, running and control group. There was also a control group with full time cage activity in experiment 2. Experiment 3; the animals were unloaded and randomized into vibration and placebo group. 14 days after surgery the animals were killed and mechanical testing of the Achilles tendons was performed. The results showed no significant difference between the groups in experiment 1. Experiment 2 showed that controls with full time cage activity had higher peak load, stiffness and cross sectional area than unloaded running, vibration and control groups. In experiment 3, there was no significant difference between vibration and placebo group. In conclusion, this study shows that vibration, as applied here, does not affect tendon healing.

Bone growth and remodeling are complex phenomena that are influenced by a variety of factors including mechanical stimuli. However, it is still unclear how to identify and quantitatively characterize the mechanical stimuli responsible for bone cell growth. The objective of this study is to design and simulate an experimental apparatus to cyclically apply pressure and shear stresses to bone cells and observe their growth (or lack thereof) as a function of the applied loads.

<p>To elucidate the mechanisms of cellular mechanotransduction, it is necessary to employ biomaterials that effectively merge biofunctionality with appropriate mechanical characteristics. Agarose is a standard biopolymer used in cartilage mechanobiology but lacks necessary adhesion motifs for cell-matrix interactions to complete mechanostransduction studies. Collagen type I is a natural biomaterial used in cartilage mechanotransduction studies but creates an environment much softer than native cartilage tissue.  In these studies, agarose was blended at two final concentrations (2% w/v and 4% w/v) with collagen type I (2 mg/mL). The overarching goal was to determine whether a composite hydrogel of agarose and collagen can create a mechanically and biologically suitable matrix for chondrocyte studies. First, hydrogels were characterized by rheologic and compressive properties, contraction, and structural homogeneity. Following baseline characterization, primary murine chondrocytes were embedded (1 × 106 cells/mL) within the hydrogels to assess the longer-term <em>in vitro</em> impact on matrix mechanics, cell proliferation, sulfated glycosaminoglycan (sGAG) content, and cellular morphology. To begin probing questions about physiologic loading conditions that chondrocytes experience <em>in</em> <em>vivo</em>, a custom compression loading system was validated using cell-laden hydrogels. Briefly, the 4% agarose – 2 mg/mL collagen I hydrogel composites were able to retain chondrocyte morphology over 21 days in culture, resulted in continual sGAG production, and had bulk mechanics similar to that of the stiffest hydrogel material tested, indicating this hydrogel class may be promising towards developing an effective hydrogel for chondrocyte mechanotransduction and mechanobiology studies, a critical step towards a fuller understanding of cell-matrix interactions. </p>

Les arbres ont la capacité de percevoir des sollicitations mécaniques quotidiennes dues au vent et d’acclimater leur croissance et leur développement en conséquence. Ce stress mécanique se traduit essentiellement par des flexions des organes, en particulier des branches et de la tige. Des études antérieures ont montré que la croissance en diamètre du peuplier était stimulée en réponse aux flexions mimant l’effet du vent. Cette augmentation de la croissance s’accompagne d’une modification de la nature du bois mis en place, qui a pu être observé chez quelques conifères et angiospermes, et nommé « bois de flexion ». Mais la caractérisation anatomique de ce bois a été peu approfondie, et les acteurs moléculaires de sa formation n’ont jamais été recherchés. De plus, dans la plupart de ces études les sollicitations mécaniques appliquées à la tige sont des flexions multidirectionnelles et d’intensité non contrôlée. Or, la déformation étant la variable physique perçue par la plante, il est nécessaire de contrôler l’amplitude de la flexion appliquée à la tige. Grâce à un dispositif expérimental original, nous avons appliqué des flexions unidirectionnelles sur de jeunes tiges de peupliers tout en contrôlant l’intensité des déformations appliquées. Cette étude a montré que la perception des déformations s’effectuait à une échelle locale, conduisant à une ovalisation de la tige. Nous avons pu également différencier le bois formé sous des déformations en tension, que nous avons nommé Tensile Flexure Wood, du bois formé sous des déformations en compression, que nous avons nommé Compressive Flexure Wood. Les analyses anatomiques et moléculaires montrent que l’intensité des déformations en valeur absolue ne suffit pas à expliquer toutes les réponses et que le signe (tension ou compression) de ces déformations joue également un rôle. Chez des arbres stimulés par des flexions unidirectionnelles plus fréquentes, la croissance et la différenciation cellulaire sont modulés encore différemment, notamment dans la zone en compression, apportant à la tige un bénéfice adaptatif face aux sollicitations suivantes. Le gène CLE12.2 appartenant à la famille des gènes CLAVATA, gènes impliqués dans les régulations méristématiques, a été montré mécanosensible. Une approche de génomique fonctionnelle du gène CLE12.2 par l’utilisation de plants transgéniques présentant une sous- ou une surexpression du gène nous a permis d’émettre l’hypothèse d’une implication du peptide CLE12.2 dans la régulation des voies de biosynthèse de la paroi cellulaire. Cette étude a permis de mettre en avant la complexité des mécanismes moléculaires impliqués dans la formation du bois et apporte de nouvelles connaissances pour la poursuite des études sur l’acclimatation des arbres au vent. / Trees have the ability to perceive daily mechanical stresses related to wind and to acclimate their growth and development accordingly. Wind essentially results in organs bending, in particular in branches and stem. Previous studies have shown that growth diameter of poplar stem increased in response to bending; mimicking wind mechanical effect. This growth increment goes along with a change in the structure of the wood formed under bending stimulation. This type of reaction wood has been described for some conifers and angiosperms species, and was called "flexure wood". Until now, its anatomical characteristics have been poorly described, and the molecular actors of its formation have never been investigated. In addition, in most of these previous studies the mechanical stresses applied to the stem were bidirectional bendings with an uncontrolled intensity. Because mechanical strains constitute the physical variable perceived by the plant, it appeared necessary to carefully control the bending amplitude applied to the stem. Thanks to an original experimental setup, we applied unidirectional bendings on young poplar stems, while controlling its intensity. This study showed that the strains are perceived at a local scale and that the secondary growth response was also local, leading to stem ovalization. We also distinguished the wood formed under tension we named “Tensile Flexure Wood” from the wood formed under compression we named “Compressive Flexure Wood”. The anatomical and molecular analyzes show that the strain intensity in absolute value is not enough to explain all the answers and that the sign (tension or compression) of these strains also plays a role. In trees stimulated by more frequent unidirectional bendings, growth and cell differentiation are modulated even differently, especially in the area under compression, bringing to the stem an adaptive benefit to the following solicitations. The CLE12.2 gene, which belongs to the CLAVATA gene family involved in meristematic regulation, has been shown to be mechanosensitive. Functional analysis of the CLE12.2 gene in transgenic plants with under- or overexpression of the gene allowed us to hypothesize that the CLE12.2 peptide is involved in the regulation of the cell-wall biosynthesis pathways. This work highlighted the complexity of the molecular mechanisms involved in wood formation and brings new knowledge for further studies on trees acclimation to wind.

Les changements de forme des cellules épithéliales sont cruciaux pour la morphogenèse embryonnaire. Chez les embryons de C. elegans, l'activité musculaire sous les cellules épidermiques est l'une des deux forces mécaniques qui dirigent ce processus. Cependant, les mécanismes moléculaires détaillés à travers lesquels l'activité musculaire favorise l'allongement polarisé le long de l'axe antérieur / postérieur (A / P) restent à être totalement compris. Ici, en utilisant l'imagerie rapide-3D, on découvre que les embryons tournent après l'activation musculaire et on décrit le schéma local et global de la rotation de l'embryon induite par activité musculaire. En outre, on a observé que les muscles des côtés opposés de l'embryon se contractent alternativement, expliquant les rotations de l'embryon. Par conséquent, les jonctions adhérentes sont étirées le long de la direction A / P pendant les rotations de l'embryon et sont donc sous une tension plus élevée. Nos résultats préliminaires d'imagerie en molécule unique ont montré que plus de E-cadhérine, matériau de jonction, fusionne avec des jonctions orientées A / P quand il y a une tension élevée sur ces jonctions. / Epithelial cell shape changes is essential for embryonic morphogenesis. In C. elegans embryos, muscle activity from underneath epidermal cells is one of the two mechanical force inputs driving this process. However, the detailed molecular mechanisms through which muscle activity promotes the polarized elongation along the anterior/posterior (A/P) axis remains to be fully understood. Here, using fast-3D imaging, we discover that embryos rotate after muscle activation and we describe the local and global pattern of embryo rotation induced by muscle activity. Furthermore, we observed that muscles located on opposite sides of the embryo mostly contract alternatively, accounting for embryo rotations. As a consequence, adherens junctions get stretched along the A/P direction during embryo rotations and therefore are under higher tension. Our preliminary results from single molecule imaging showed that more junction material E-cadherin fuses with A/P oriented junctions when there is high tension on these junctions.