Flexible Packaging for High Pressure Treatments: Delamination Onset and Design Criteria of Multilayer Structures

Multi-layer flexible polymeric films employed for high pressure treatments of food packaging for pasteurization and sterilization frequently display delamination phenomena. This problem limits packaging reliability used for this treatment technology. This contribution is aimed at understanding the delamination phenomena of packaging structures under high pressures. Development of interlaminar stress fields, which promote localized delamination events, is here addressed by considering the case of mechanical failure of bi-layer structures. Analytical models and Finite Element based numerical simulations are exploited to this purpose. The theoretical and numerical results, that highlight the crucial role played by the mismatch of Young moduli and Poisson ratios of the laminated film sheets, are in full agreement with experimental findings on high pressure-treated food multilayer packages realized coupling different polymeric materials (i.e. polypropylene-polyethyleneterephthalate, polypropylene-cast polyamide and polypropylene-bioriented polyamide)

Stability Analysis of Circular Beams with Mixed-Mode Imperfections under Uniform Lateral Pressure

The elastic-plastic collapse of circular beams under uniform lateral pressure with an initial imperfection represented by a combination of different modes and amplitudes and with varying material properties is analysed from a computational viewpoint. The work is stimulated by a number of accurate experimental tests recently performed and it is found that both the initial imperfection and the material inhomogeneity along the beam axis can affect the collapse and produce a sensible variation in the carrying capacity of the structure on account of the changes between the underlying buckling modes. This can give reason for some apparently anomalous observed experimental results

An Analytical Approach to the Analysis of Inhomogeneous Pipes under External Pressure

Pipes for deep-water applications possess a diameter-to-thickness ratio in a region where failure is dominated by both instability and plastic collapse. This implies that prior to failure the compressive yield strength of the material must be exceeded, followed by ovalisation and further local yielding. This paper presents an investigation into the mechanics of this specific problem and develops an analytical approach that accounts for the effects of geometrical and material data on the collapse pressure of inhomogeneous rings under external hydrostatic pressure. The analytical expressions have been correlated to numerical and experimental test data, proving their accuracy

An Analytical Approach to the Analysis of Inhomogeneous Pipes under External Pressure

Pipes for deep-water applications possess a diameter-to-thickness ratio in a region where failure is dominated by both instability and plastic collapse. This implies that prior to failure the compressive yield strength of the material must be exceeded, followed by ovalisation and further local yielding. This paper presents an investigation into the mechanics of this specific problem and develops an analytical approach that accounts for the effects of geometrical and material data on the collapse pressure of inhomogeneous rings under external hydrostatic pressure. The analytical expressions have been correlated to numerical and experimental test data, proving their accuracy

Wrinkling prediction, formation and evolution in thin films adhering on polymeric substrata

Wrinkling has recently attracted an increasing interest by suggesting a number of unforeseeable applications in many emerging material science and engineering fields. If guided and somehow designed, wrinkles could be in fact used as an alternative printing way for realizing complex surface geometries and thus employed as an innovative bottom-up process in the fabrication of nano- and micro-devices. For these reasons, the prediction of wrinkles of films adhering on flat as well as on structured substrata is a challenging task, genesis and development of the phenomenon being not yet completely understood both when thin membranes are coupled with soft supports and in cases where the geometry of the surfaces are characterized by complex three-dimensional profiles. Here we investigate the experimental formation of new intriguing and somehow unforeseeable wrinkled patterns achieved on periodic structures, by showing prediction through a new hybrid analytical-numerical strategy capable to overcome some common obstacles encountered in modeling film wrinkling on flat and 3D-shaped substrata. The proposed approach, which drastically reduces the computational effort, furnishes a helpful way for predicting both qualitative and quantitative results in terms of wrinkling patterns, magnitude and wavelength, by also allowing to follow the onset of film instabilities and the progressive evolution of the phenomenon until its final stage. Keywords: Thin film, Wrinkling, PDMS substrates, Lithium niobate crystals, FEM simulation

TENSILE INTEGRITY ACROSS THE SCALES OF THE LIVING MATTER: A STRUCTURAL PICTURE OF THE HUMAN CELL

Tensile integrity principle governs the existence of stable constructs in which sets of pre-tensed cables and pre-compressed struts mutually interconnect according to specific topological rules and exchange forces in a way to guarantee the structure’s overall self-equilibrium. Starting from the simplest form of 2-element bow-like system, several structural components can be arranged together to assemble increasingly intricate tensegrity architectures where bars levitate sustained by a precise interplay with tensed cables, whose peculiar organization balances the vector field of axial forces. Modulation of the internal pre-stress tunes tensegrity systems towards disparate forms with different rigidities and stored elastic energies, while the floating arrangement of the compressed elements and the possible chirality confer to the whole structure pronounced deployability. This makes tensile integrity a persuasive structural paradigm for explaining and reproducing some underlying mechanisms at the basis of several dynamics experimentally observed in single cells as well as at different scales of biological architectures. In particular, by deeply exploring the intra-cellular environment, one discovers that the cytoskeleton mechanically sustains the cell’s membrane, structurally integrates cellular sub-constituents and steers migration, adhesion and division activities by behaving as a dynamic tensegrity lattice, hierarchically assembled by protein filaments, in turn made of continuously reacting polymeric tensegrity-chains at the lower nano-scale

Best to clarify to avoid misunderstandings in the biomechanics of Ross Operation: parentheses matter

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Growth and remodeling in highly stressed solid tumors

Growing biological media develop residual stresses to make compatible elastic and inelastic growth-induced deformations, which in turn remodel the tissue properties modifying the actual elastic moduli and transforming an initially isotropic and homogeneous material into a spatially inhomogeneous and anisotropic one. This process is crucial in solid tumor growth mechanobiology, the residual stresses directly influencing tumor aggressiveness, nutrients walkway, necrosis and angiogenesis. With this in mind, we here analyze the problem of a hyperelastic sphere undergoing finite heterogeneous growth, in cases of different boundary conditions and spherical symmetry. By following an analytical approach, we obtain the explicit expression of the tangent elasticity tensor at any point of the material body as a function of the prescribed growth, by involving a small-on-large procedure and exploiting exact solutions for layered media. The results allowed to gain several new insights into how growth-guided mechanical stresses and remodeling processes can influence the solid tumor development. In particular, we highlight that— under hypotheses consistent with mechanical and physiological conditions—auxetic (negative Poisson ratio) transformations of the elastic response of selected growing mass districts could occur and contribute to explain some not yet completely understood phenomena associated to solid tumors. The general approach proposed in the present work could be also helpfully employed to conceive composite materials where ad hoc pre-stress distributions can be designed to obtain auxetic or other selected mechanical properties

Multistep, sequential control of the trafficking and function of the multiple sulfatase deficiency gene product, SUMF1 by PDI, ERGIC-53 and ERp44.

Sulfatase modifying factor 1 (SUMF1) encodes for the formylglicine generating enzyme, which activates sulfatases by modifying a key cysteine residue within their catalytic domains. SUMF1 is mutated in patients affected by multiple sulfatase deficiency, a rare recessive disorder in which all sulfatase activities are impaired. Despite the absence of canonical retention/retrieval signals, SUMF1 is largely retained in the endoplasmic reticulum (ER), where it exerts its enzymatic activity on nascent sulfatases. Part of SUMF1 is secreted and paracrinally taken up by distant cells. Here we show that SUMF1 interacts with protein disulfide isomerase (PDI) and ERp44, two thioredoxin family members residing in the early secretory pathway, and with ERGIC-53, a lectin that shuttles between the ER and the Golgi. Functional assays reveal that these interactions are crucial for controlling SUMF1 traffic and function. PDI couples SUMF1 retention and activation in the ER. ERGIC-53 and ERp44 act downstream, favoring SUMF1 export from and retrieval to the ER, respectively. Silencing ERGIC-53 causes proteasomal degradation of SUMF1, while down-regulating ERp44 promotes its secretion. When over-expressed, each of three interactors favors intracellular accumulation. Our results reveal a multistep control of SUMF1 trafficking, with sequential interactions dynamically determining ER localization, activity and secretion