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Pressurized solids are ubiquitous in nature. Mechanical properties of biological tissues arise from cell turgor pressure and membrane elasticity. Flat contact between cells generate nonlinear forces. In this work, cells are idealized as pressurized elastic membranes in frictionless contact with one another. Contact forces are experimentally measured on rubber-like membranes and computed using finite element analysis (FEA). FEA matches experimental force-indentation relationships from small to large indentations. With the chosen dimensionless numbers, data gather on a master curve. The isobaric force exhibits a 4/3 power law over 1.5 decades of indentation. Forces for other thermodynamic processes (adiabatic, isothermal/osmotic and isochoric) are interpolated from isobaric data. Regarding stiffness, the isochoric process is superlinear contrary to the sublinear isobaric stiffness. Simple force-indentation relationships are given for each process. [Display omitted] [ABSTRACT FROM AUTHOR]

Keywords: Grand Rapids; State:Michigan; United States; North and Central America; Wound Management and Prevention; Health and Medicine EN Grand Rapids State:Michigan United States North and Central America Wound Management and Prevention Health and Medicine 4008 4008 1 05/29/23 20230602 NES 230602 2023 JUN 2 (NewsRx) -- By a News Reporter-Staff News Editor at Health & Medicine Week -- A new study on Health and Medicine - Wound Management and Prevention is now available. Grand Rapids, State:Michigan, United States, North and Central America, Wound Management and Prevention, Health and Medicine. [Extracted from the article]

Rain cracking of sweet cherry (Primus avium L.) fruit is commonly thought to result from excessive net water uptake. This excess increases flesh turgor, which then strains and eventually ruptures the skin at the weakest point. This idea--the critical turgor hypothesis--assumes the fruit comprises a semifluid flesh, held under pressure by a taut skin. The objectives of this study were to test the validity of this popular hypothesis. We investigated the effects of 1) the different pathways of water uptake and 2) the fruit's water balance on cracking. Incubating fruit of 19 cultivars in water resulted in rapid fruit cracking. The time to 50% cracking (T50) averaged 7.5 ± 1.3 hours with considerable variability between cultivars (T50 range from 1.5 to 18.6 hours). The amount of water taken up at 50% cracking (WU50) averaged 96.5 ± 17.6 mg (WU50 range from 17.7 to 331.5 mg). There was no correlation between either the Tso or the WUS0, and the rate of water uptake. Also, there was no correlation between the values of Tso (r = 0.58) and only a weak correlation between the values of WU50 (r = 0.80*) determined in different years. Comparing the value of WU50 under incubation vs. under perfusion revealed a 3.9- to 38-fold higher WU50 under perfusion (397.6 to 1840 mg) than under incubation (48.8 to 102.6 mg). This marked dissimilarity remained, regardless of pretreatments with isotonic polyethylene glycol (PEG) 6000 to induce microcracking or by manipulation of skin wetness during perfusion. Sealing the pedicel/fruit junction markedly decreased the rate of water uptake under incubation. It had no effect on the Tso, and it markedly decreased the WU50. Similarly, manually induced skin defects greatly increased the rate of water uptake but, with few exceptions, had no effect on the T50i whereas, the WU50 had increased. The location on the fruit surface of the resulting cracks was not related to the region of the skin in which the manual defect was induced. Allow ing the fruit to transpire increased both, the T50 and the WU50. Interestingly, the amount of water lost by transpiration exceeded the amount that was subsequently required to cause cracking up to 5-fold. Incubating fruit with their stylar ends immersed in water, whereas their remaining surfaces were in air of 0%, 28%, 75%, or 100% relative humidity (RH) resulted in net losses of water of up to 5.9 ± 0.7 mg h-1, nevertheless their stylar ends still cracked. All our results indicate rain cracking in sweet cherries is a localized phenomenon that is not related to the net fruit water balance (the critical turgor hypothesis) but is the result of more local exposure of the fruit skin to liquid-phase water (the zipper hypothesis). [ABSTRACT FROM AUTHOR]

The skins of all fruit types are subject to sustained biaxial strain during the entire period of their growth. In sweet cherry (Prunus avium L.), failure of the skin greatly affects fruit quality. Mechanical properties were determined using a biaxial bulging test. The factors considered were the following: ripening, fruit water relations (including turgor, transpiration, and water uptake), and temperature. Excised discs of fruit skin were mounted in a custom elastometer and pressurized from their anatomically inner surfaces. This caused the skin disc to bulge outwards, stretching it biaxially, and increasing its surface area. Pressure (p) and biaxial strain (ε) due to bulging were quantified and the modulus of elasticity [E (synonyms elastic modulus, Young's modulus)] was calculated. In a typical test, ε increased linearly with p until the skin fractured at pfracture and εfracture. Stiffness of the skin decreased in ripening late stage III fruit as indicated by a decrease in E. The value of pfracture also decreased, whereas that of εfracture remained about constant. Destroying cell turgor decreased E and pfracture relative to the turgescent control. The E value also decreased with increasing transpiration, while pfracture and (especially) εfracture increased. Water uptake had little effect on E, whereas εfracture and pfracture decreased slightly. Increasing temperature decreased E and pfracture, but had no effect on εfracture. Only the instantaneous elastic strain and the creep strain increased significantly at the highest temperatures. A decrease in E indicates decreasing skin stiffness that is probably the result of enzymatic softening of the cell walls of the skin in the ripening fruit, of relaxation of the cell walls on eliminating or decreasing turgor by transpiration and, possibly, of a decreasing viscosity of the pectin middle lamellae at higher temperatures. The effects are consistent with the conclusion that the epidermal and hypodermal cell layers represent the structural "backbone" of the sweet cherry fruit skin. [ABSTRACT FROM AUTHOR]

Plants move, and not only under the action of the wind or during growth. Although they lack muscle, some have developed mechanisms to generate surprisingly fast movements, with speeds (about 10 m/s) and accelerations (thousands of g) that compete and even surpass those encountered in the animal kingdom. [ABSTRACT FROM AUTHOR]

The skin is the primary load-bearing structure in a sweet cherry fruit (Prunus avium L.). Failure of the skin in rain cracking is considered to be related to water uptake. Little is known of the skin's water potential, its osmotic potential (ΨπS), and turgor. The objective here was to quantify ΨπF relative to the osmotic potential of the flesh (ΨπF). Spatial resolution was achieved by monitoring plasmolysis in epidermal cells in tissue sections, incubated in selected osmotica using a light microscope method. Decreasing the osmotic potential [Ψπ (more negative)] of the incubation medium increased the proportion (percent) of plasmolyzed epidermal cells. The pattern of increasing plasmolysis was sigmoidal with increasing osmolyte concentration. The value of Ψπ for 50% of cells plasmolyzed, depended to some extent on the osmolyte used. The value of Ψπ became slightly less negative for the osmolytes tested in the order: 1) mannitol, 2) sucrose, and 3) artificial cherry juice (a solution comprising the five major osmolytes of sweet cherry juice in the appropriate proportions and concentrations). There was little difference in the value of Ψπ at 50% plasmolysis between the cultivars Hedelfinger, Sam, and Sweetheart. In all three cultivars, the value of ΨπF (measured for expressed juice using an osmometer) was markedly more negative than that of ΨπS(measured for 50% plasmolysis). Incubating skin segments in juice from the same fruit resulted in the plasmolysis of most (85.7% to 96.4%) of the epidermal cells. As fruit development progressed from stage II [27 day after full bloom (DAFB)] to the fully mature stage III (97 DAFB), plasmolysis occurred for increasingly more negative values of Ψπ. Moreover, the difference between the osmotic potential values recorded for the flesh ΨπF and for the skin ΨπS increased. Plasmolysis of epidermal cells was accompanied by a marked swelling of their walls. The results indicate a marked difference in the osmotic potential of flesh (ΨπF trended more negative) and skin cells (ΨπS trended less negative). [ABSTRACT FROM AUTHOR]

Abstract: Plant based dried food products are popular commodities in global market where much research is focused to improve the products and processing techniques. In this regard, numerical modeling is highly applicable and in this work, a coupled meshfree particle-based two-dimensional (2-D) model was developed to simulate microscale deformations of plant cells during drying. Smoothed Particle Hydrodynamics (SPH) was used to model the viscous cell protoplasm (cell fluid) by approximating it to an incompressible Newtonian fluid. The visco-elastic characteristic of the cell wall was approximated to a Neo-Hookean solid material augmented with a viscous term and modeled with a Discrete Element Method (DEM). Compared to a previous work [44], this study proposes three model improvements: linearly decreasing positive cell turgor pressure during drying, cell wall contraction forces and cell wall drying. The improvements made the model more comparable with experimental findings on dried cell morphology and geometric properties such as cell area, diameter, perimeter, roundness, elongation and compactness. This single cell model could be used as a building block for advanced tissue models which are highly applicable for product and process optimizations in Food Engineering. [Copyright &y& Elsevier]

Susceptibility of sweet cherry (Prunus avium L.) fruit to rain cracking increases toward maturity and is thought to be related to increases in both tissue pressure ψpfruit) and cell pressure ψpcell). Furthermore, at a given water potential (ψfruit), one might expect the increase in ψpfruit and the ψpcell to balance the decrease in osmotic potential (ψpgr;fruit). The objectives of our study were to quantify ψpfruit and ψpcell in developing sweet cherry using vapor pressure osmometry (VPO), compression plate (CP), and the cell pressure probe (CPP). In addition, the tissue water potential ψtissue was determined by quantifying the bending of strips of fruit skin and the change in projected area of discs excised from the flesh when incubated in a range of sucrose solutions of varying osmotic potentials (ψpgr;solution). Fruit growth followed a sigmoid pattern with time with the Stage II/Stage III transition occurring at ≈55 days after full bloom (DAFB). The ψtissue and the ψpgr;fruit were constant up to ≈55 DAFB but decreased to -2.8 MPa at maturity. The ψpcell calculated by subtracting the ψpgr;fruit from ψtissue averaged ≈350 kPa up to 48 DAFB and then decreased at a decreasing rate to ≈21 kPa toward maturity. The ψtissue determined from bending assays using excised skin strips or from water uptake of excised flesh discs was essentially constant up to ≈48 DAFB, then decreased until ≈75 DAFB and remained constant thereafter. These ψtissue values were in good agreement with those determined by VPO. The ψpfruit as determined by CP passed through a transient peak at ≈41 DAFB, then decreased until ≈63 DAFB and remained constant and low until maturity. Similarly, ψpcell by CPP increased from 27 to 48 DAFB, remained constant until ≈55 DAFB, and then decreased until maturity. Our data demonstrate a consistent decrease in ψpfruit and ψpcell that coincides with a decrease in ψpgr;fruit of sweet cherry during Stage III. Because ψpfruit and ψpcell are low relative to ψpgr;fruit, the change in ψfruit parallels that in ψpgr;fruit. The reason for the low turgor most likely lies in the accumulation of apoplastic solutes. These prevent a catastrophic increase in pressure that would otherwise lead to the bursting of individual cells and the cracking of entire fruit. [ABSTRACT FROM AUTHOR]

The pressure inside a mature sweet cherry (Prunus avium L.) fruit is thought to be an important factor in rain cracking. However, to our knowledge, this pressure has never been quantified directly. The objectives of this study are to quantify: 1) the cell turgor (ΨPcell) in fruit using a cell pressure probe (CPP) and a vapor pressure osmometer (VPO); and 2) the tissue pressure in a fruit (ΨPfruit) using both a fruit pressure probe (FPP) and a compression-plate technique (CP). The value of ΨPcell in mesocarp cells of mature sweet cherry fruit averaged 28.1 kPa in 'Samba' and 17.5 kPa in 'Sam' at depths below the fruit surface between 200 and 400 μm. A ΨPcell (range 38 to 64 kPa for different cultivars) calculated from the tissue water potential (Ψtissue = -2968 to -4035 kPa) and the osmotic potential (ΨΠfruit) (ΨΠfruit = -3020 to -4116 kPa) of excised mesocarp discs as determined by VPO was of the same order of magnitude as that by CPP. Similar low ΨPfruit values were obtained by FPP (range 8.0 to 11.8 kPa across cultivars). The ΨPfruit were consistently lower than the ΨPcell values measured by CPP or by VPO. The ΨPfruit value in the mesocarp increased slightly with increasing depth below the surface. However, ΨPfruit was always negligible (e.g., 'Samba' ΨPfruit = 10 kPa) compared with either ΨΠfruit ('Samba' ΨΠfruit = -2395 kPa) or calculated water potential (Ψfruit) ('Samba' Ψfruit = -2385 kPa). When subjecting intact fruit to CP, linear relationships were obtained between the forces applied and the resulting aplanation areas. The ΨPfruit values obtained by CP (range in sweet cherry 18.4 to 36.1 kPa) were somewhat larger than the ΨPfruit values obtained by FPP (range in sweet cherry 8.0 to 11.8 kPa). Incubating fruit for up to 7.5 h in deionized water or for up to 96 h in air enclosed above dry silica gel had no measurable effects on ΨPfruit. The low ΨPcell and the low ΨPfruit values are not unique to sweet cherry. Values of the same order of magnitude were obtained also in mature sour cherry (Prunus cerasus L.), european plum (Prunus domestica L.), grape (Vitis vinifera L.), gooseberry (Ribes uva-crispa L.), red currant (Ribes rubrum L.), black currant (Ribes nigrum L.), blueberry (Vaccinium corymbosum L.), and tomato (Solanum lycopersicum L.). Possible explanations for the very low values of ΨPcell and ΨPfruit are discussed. [ABSTRACT FROM AUTHOR]

The article presents information on a study which analyzed the diversity of plant movements and finds certain guiding principles to the sorts of movements that can be accommodated and at what speeds. Many of these movements depend on alterations in turgor pressure, and the analysis lends insights into the design of mechanical systems that are driven by hydraulic forces.