Cell surface properties are crucial to the mechanisms by which groups of cells organize themselves during embryogenesis, cancer metastases and tissue engineering. Measured surface tension values provide a quantitative basis for predicting a range of cell behaviors including sorting of embryonic cells, self-organization of pancreatic islet cells and invasive potential of tumor cells. Tissue surface tensions are a measurement of the tension that acts along the interface between a cell aggregate and its surrounding media and it is typically measured by compressing an aggregate of cells. In this study a novel apparatus is used to measure the surface tensions of aggregated embryonic chick cells from heart, liver, neural retina and mesencephalon tissues. These surface tension values are consistent with the known engulfment behavior of the cells involved and are in close agreement with measurements made previously by other means. It has been suggested that surface tensions and cell rearrangement patterns are a direct result of adhesion forces between cells arising from cadherins. However, cadherin binding alone is insufficient to account for observed engulfment phenomena and recent experimental evidence suggests that actin dynamics are involved. A cell surface property referred to as interfacial tension or cortical tension takes into account both adhesion forces and forces derived from actin microfilaments and could shed new light on the mechanisms involved in cell interactions. Computer simulations indicate that the interfacial tension between cells can be measured through a modified compression test experiment. In this cell aggregate compression study, cell shapes as well as the aggregate profile are measured in addition to the compression force in attempts to measure cell interfacial tensions.

Cell surface properties are crucial to the mechanisms by which groups of cells organize themselves during embryogenesis, cancer metastases and tissue engineering. Measured surface tension values provide a quantitative basis for predicting a range of cell behaviors including sorting of embryonic cells, self-organization of pancreatic islet cells and invasive potential of tumor cells. Tissue surface tensions are a measurement of the tension that acts along the interface between a cell aggregate and its surrounding media and it is typically measured by compressing an aggregate of cells. In this study a novel apparatus is used to measure the surface tensions of aggregated embryonic chick cells from heart, liver, neural retina and mesencephalon tissues. These surface tension values are consistent with the known engulfment behavior of the cells involved and are in close agreement with measurements made previously by other means. It has been suggested that surface tensions and cell rearrangement patterns are a direct result of adhesion forces between cells arising from cadherins. However, cadherin binding alone is insufficient to account for observed engulfment phenomena and recent experimental evidence suggests that actin dynamics are involved. A cell surface property referred to as interfacial tension or cortical tension takes into account both adhesion forces and forces derived from actin microfilaments and could shed new light on the mechanisms involved in cell interactions. Computer simulations indicate that the interfacial tension between cells can be measured through a modified compression test experiment. In this cell aggregate compression study, cell shapes as well as the aggregate profile are measured in addition to the compression force in attempts to measure cell interfacial tensions.

Reproduction de : Thèse de doctorat : Génie électrique : Toulouse, INPT : 2005. / Titre provenant de l'écran-titre. Bibliogr. 105 réf.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

A seven segment model of the right leg and foot was developed with segments: thigh, lower leg, talus, hindfoot, midfoot and lateral and medial forefoot. Three-dimensional mapping of internal structures was made from CT scans and anatomical photographs (Visible Human Project). Twelve healthy subjects performed level walking and medial walking turns at slow, preferred and fast speed. Equilibrium about the two joints of the ankle complex (ankle and subtalar), was solved using Muscle Model Assisted Optimisation (MMAO). A three component, Hill-type muscle model determined tensions in eight muscles of the lower leg using EMG. Linear optimisation then corrected muscle tensions and solved for ligament tensions and articular surface compression. MMAO was successful in modeling ankle complex equilibrium during walking and walking turn. External forces acting on the right foot were similar for all subjects. Despite similar external loading, subjects employed different muscle tension strategies to produce equilibrium about the ankle and subtalar joints. For all subjects, triceps surae muscle tensions were largest. Peak tension in achilles tendon was 7.9xBW during walking and 8.0xBW during walking turn. The two heads of gastrocnernius behaved as distinct muscles performing different roles during stance. Peroneus brevis produced movement about the subtalar joint while peroneus longus had a stabilising role. The dorsi-flexors were significantly active during stance phase, antagonistic to triceps surae muscle group. This antagonism has not been predicted by previous models. Ligaments acted in an all-or-nothing manner when constraining the ankle complex. Ligaments were either slack or tensed at constant tension. Maximum ligament tension was 1.75xBW in the lateral ligaments of the ankle joint during walking turn. No difference between the walking and walking turn was seen in compressive loading of articular surfaces. Maximum compression of ankle joint was 10.0xBW and of subtalar joint was 8.0xBW.