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  • Khalifat, Nada; Beaune, Gregory; Nagarajan, Usharani; Winnik, Francoise M.; Brochard-Wyart, Francoise (2016)
    Tissues belong to the broad field of active matter, a novel class of non-equilibrium materials composed of many interacting units that individually consume energy and collectively generate motion or mechanical stresses. Active systems span an enormous range of length scales, from individual living cells, to tissues and organisms, to animal groups. We introduce the concept of biological tissues as examples of entangled active matter, where the units (cell) are bound by transient links. We focus here on the mechanical properties (surface tension, elasticity, and viscosity) of cells and tissues derived from measurements performed by the pipette aspiration technique. This approach has been very fruitful in unveiling striking analogies between the physics of inert soft matter (polymer, viscous pastes, and Silly Putty (R)) and the behavior of biological tissues. The results obtained from such analogies suggest important implications in the fields of tissue engineering and development. (C) 2016 The Japan Society of Applied Physics
  • Wang, Yaqin; Tacer Caba, Zeynep; Immonen, Mikko; Kemell, Marianna; Varis, Jutta Johanna; Jian, Ching; Maina, Ndegwa (2022)
    Rheological tests performed under conditions relevant to those experienced during proof and oven rise are necessary for understanding the mechanisms of dextran addition on wheat dough baking performance. This study evaluated the effect of a high molecular weight (Mw) dextran, produced in situ by Weissella confusa A16 or externally added, on wheat dough rheological properties including, (i) proofing behavior using a maturograph; (ii) bi-axial extensional profile using a dough inflation system; and (iii) viscoelastic characters (proof) and thermo-mechanical properties (simulated baking) by dynamic mechanical thermal analysis (DMA). The externally-added dextran increased dough elasticity, tenacity, and viscoelastic characters, but reduced dough extensibility at bubble rupture. DMA tests of doughs under dynamic heating conditions showed a sharp increase of elastic and loss moduli until maximum between 75 and 95 degrees C, accompanied by a drastic decrease of Tan delta (dough stiffening). Dextran addition exhibited a weakening effect on the dough thermal properties i.e., decreased peak moduli during heating. On the other hand, the mild acidic conditions during sourdough fermentation favored the activity of in situ produced dextran, conferring significantly improved thermal-mechanical properties and dough extensibility. This may explain the superior ability of in situ produced dextran to improve bread volume and crumb softness compared to the external-added dextran. By analyzing rheological parameters, we showed that the maximum proofing moduli in DMA, fermentation stability, dough level, and elasticity in maturogram were predictors of good baking quality. Overall, our study provides the mechanistic underpinning and optimum of dextran as a natural improver of bread quality.