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The Study Of Mechanical Behavior Of Soft Tissues Biology Essay

Fung proposed a strain energy function to describe the elasticity property of soft biological tissues in simple elongation. The strain energy function was based on the fact that in simple elongation, the tensile stress is nearly an exponential function of the strain in the lower strain range. This model consists of only first strain invariant which is responsible for capturing the stiffening at lower strain.

Since, when a load is applied to the tissues of apple or potato, tissues are not deform in one direction. Furthermore, it is possible that on potato tissues a large strain, up to 50 %, can be imposed [Gates et al. (1986)] during loading. Consequently this model (Eq. 20) cannot characterize the mechanical behavior of apple and potato tissues. Therefore, we have proposed a generalized form of this strain energy function by adding a term of second strain invariant. The basic idea of adding this term in the expression of W is that, this term provides a better sensitivity to the rapid stiffening characteristic at large stretches of the tissues. Another reason of adding this term in existing model is that the new model shows the better fit with tension-stretch data for apple and potato in comparison to the previously established model.

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We also keep in the mind that proposed strain energy function satisfies necessary properties [Darijani and Naghdabadi (2010)], which are as follows:

1. The strain energy function must be non-negative for all deformations.

2. The strain energy function must be invariant under coordinate transformations.

3. The strain energy must be a function of either the stretch or strain invariants. Also because of isotropy, the strain energy function is symmetrical with respect to the principal stretches.

4. The strain energy function must have a zero value at the undeformed state.

A strain energy function (W), which satisfies all above properties is given by Eq. (21). This strain energy function represents the strain energy stored in the tissues during deformation.

The mechanical properties of tissue depend on turgor and temperature. Tissue cracking during mechanical test can be analysed using contact acoustic emission (AE). The goal of the research is analysis of changes in fracture properties of potato tuber tissue in a function of turgor and temperature. The experiment shows that fracture properties significantly change with turgor. Turgor is a tension of cell walls caused by intracellular pressure. It decreases during storage. Turgor can change as a result of osmotic process as well (Lin and Pitt, 1986). High turgor changes the strength of cell-cell adhesion, because intracellular pressures of neighbouring cells act in opposite directions. It decreases the failure susceptibility in the middle lamellas (Niklas, 1982). The turgor changes are noticeable as changes in samples firmness. Samples treated in low mannitol concentration show low osmolality and are more firm. The experiment shows that the mechanical and fracture properties of potato tissue are affected by turgor. Turgor and temperature have a significant effect on the fracture properties of potato tuber tissue. These two parameters can change the failure mode of the tissue between cell wall rupturing and cell-cell debonding

A. Zdunek, M. Gancarz, J. Cybulska, Z. Ranachowski, and K. Zg&oacute;rska. Turgor and temperature effect on fracture properties of potato tuber (Solanum tuberosumcv. Irga). Int. Agrophysics, 2008, 22, 89-97.

((Niklas K.J., 1982. Plant Biomechanics, an Engineering Approach to Plant form and Function. Chicago Univ. Press, Chicago, IL, USA.)).

Turgor pressure is much harder to evaluate, predict, and control than temperature, but in crops such as potatoes, management may be accomplished through careful irrigation scheduling and control of the storage environment. The easiest way to change tissue turgor pressure experimentally is by dehydration (Bajema et al., 1998c). To reduce this possible experimental error, Lin and Pitt (1986) used mannitol (C6H14O6) to adjust turgor in potatoes and apples, and reported that the failure stress and strain under axial compression can be reduced by increasing turgor. Results of this work confirm that mannitol solutions alter both turgor and the potato tuber tissue failure properties under dynamic loading and therefore should not be used to adjust turgor pressure in experiments investigating failure properties.

R.W. Bajema, G.M. Hyde , A.L. Baritelle. Effects of mannitol on turgor and on failure stress and strain in potato tuber tissue. Postharvest Biology and Technology 14 (1998) 199 - 205

((Bajema, R.W., Hyde, G.M., Baritelle, A.L., 1998c. Turgor and temperature effects on dynamic failure properties of potato tuber tissue. Trans. ASAE 41, 741 - 746.))

The effect of turgor on the micromechanical properties of apples (Malus domesticaBorkh. cv Jonagored) and its relation to structural parameters of the cells was investigated.

Texture is one of the primary quality attributes of fruit and vegetables. It is determined by the mechanical properties of the tissue, which are affected by factors such as ripening stage and water status. These properties also determine the susceptibility to mechanical damage that can occur during harvest, transport and storage, and that eventually leads to a loss of commercial value.

Texture of fruit is commonly evaluated based on the macroscopic mechanical properties of the whole fruit. However, fruit are not a homogenous material, but consist of a complex conglomerate of cells. The macroscopic mechanical properties of the tissue are thus determined by various microscopic cellular and histological features, such as cell size, amount of intercellular space, mechanical properties of the cell wall and middle lamella, and turgor pressure. Texture of fruit is commonly evaluated based on the macro-scopic mechanical properties of the whole fruit.

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The objective of the present work is therefore two-fold: first, to describe in detail the influence of turgor on the micromechanical proper-ties of apple parenchyma, and second, to quantify for the first time the influence of tu rgor on the cellular deformations and to relate them to the mechanical tests.

M.L. Oey, E. Vanstreels, J. De Baerdemaeker, E. Tijskens, H. Ramon, M.L.A.T.M. Hertog, B. Nicola¨i. Effect of turgor on micromechanical and structural properties of apple tissue: A quantitative analysis. Postharvest Biology and Technology 44 (2007) 240-247.

Mechanical properties of plant tissue are determined by their intracellular pressure and cellular structure. The aim of the presented paper is to study influence of turgor and cell size on the process of potato tissue cracking. The method of acoustic emission has been used to determine failure conditions as the critical strain and the critical stress for potato tuber tissue with different turgor and cell size distribution. Increase in turgor causes decrease in the compressive strength, critical strain and stress. The aim of the presented paper is to study influence of turgor and cell size on the process of potato tissue cracking.

K. Konstankiewicz* and A. Zdunek. Influence of turgor and cell size on the cracking of potato tissue. Int. Agrophysics, 2001, 15, 27-30.

Potato tissue samples with varying cell turgor pressures were prepared by soaking them in mannitol solutions (0 M to 0.9 M). Increased concentration of mannitol in the soaking solutions decreased the cell turgor pressure in potato tissues, providing samples with varying degrees of turgidity or plasmolysis.

Mar&iacute;a Dolores 7 David Edward John Saunders Julian Francis Vincent Vincent. Effect of turgor pressure on the cutting energy of stored potato tissue. Eur Food Res Technol (2000) 210 : 331-339.

To determine turgor pressure of melon and kiwifruit edible parts (Cucumis melo, L. and Actinidia deliciosa, A. Chev., respectively), we measured volume change of tissue cylinders immersed in diÂ€erent mannitol or polyethylene glycol 400 (PEG) solutions up to equilibrium, and sought the osmotic potential that led to incipient plasmolysis.

C. Sajnin1, L.N. Gerschenson, A.M. Rojas. Turgor pressure in vegetable tissues: comparison of the performance of incipient plasmolysis technique using mannitol and polyethylenglycol. Food Research International 32 (1999) 531±537.

Karl J. Oparka and Kathryn M. Wright. Influence of cell turgor on sucrose partitioning in potato tuber storage tissues. Planta (1988)175:520-526.

Experiments were performed on two varieties of apple tissue and one variety of potato tissue, in which cell turgor pressure was varied and the concomitant mechanical properties of the tissue were tested. Turgor pressure was controlled by immersion in solutions of various mannitol concentrations, and the degree of swelling or contraction of the tissue samples was measured. Pitt and Chen (1983) observed that higher turgor pressures decreased the failure strain of apple tissue, but failure stress was unaffected. The objective of this study was to quantify the effect of turgor pressure and strain rate on the mode of failure, tissue stiffness, failure stress, and failure strain of apple and potato tissue. Potato parenchyma exhibited a drop in cell-wall stiffness at large stretch ratios,

TA-TE LIN and R. E. PITT. RHEOLOGY OF APPLE AND POTATO TISSUE AS AFFECTED BY CELL TURGOR PRESSURE. Journal of Texture Studies 17 (1986) 291.313.

((PITT, R. E. and CHEN, H. L. 1983. Time-dependent aspects of the strength and rheology of vegetative tissue. Trans. Am. SOC. Agr. Eng. 26, 1275-1280.))

ERNST STEUDLE AND ULRICH ZIMMERMAN ULRICH LUTTGE. Effect of Turgor Pressure and Cell Size on the Wall Elasticity of Plant Cells. Plant Physiol. (1977) 59, 285-289.

E. E. FINNEY, JR. AND H. FINDLEN, INFLUENCE OF PREHARVEST TREATMENTS UPON TURGOR OF KATAHDIN POTATOES. AMERICAN POTATO JOURNAL, 44, 383-386.

The effect of turgor on the micromechanical properties of apples (Malus domesticacv 'Jonagored') and its relation to structural parameters of the cells was investigated. Texture is one of the primary quality attributes of fruits and vegetables and is determined by the mechanical properties of the tissue which are affected by factors as ripening stage and water status. The macroscopic mechanical properties of the tissue are thus determined by various microscopic cellular and histological features, such as cell size, amount of intercellular space, mechanical properties of the cell wall and middle lamella, and turgor pressure. Besides cell wall structure, turgor pressure is thought to have major influence on tissue strength and macroscopic fruit firmness. It is exerted by intracellular liquids on the cellular membrane and cell wall and imparts turgidity, rigidity, crispness and a fresh appearance to the plant tissue. Turgor is lost when fruits or vegetables are deprived of water, through transpiration, or when they cease to respire. In this work the effect of turgor on micromechanical properties of fresh and soft apples was studied. We showed that cell structural parameters were homogenous throughout the used apples and not influenced by manipulation of turgor. In both tests, manipulation of turgor had aprofound influence on strain at failure and stiffness at different strains.

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Oey, M.L., Vanstreels, E., De Baerdemaeker, J., Tijskens, E., Ramon, H., Nicolaï, B. Influence of Turgor on Micromechanical and Structural Properties of Apple Tissue. IUFoST 2006 DOI: 10.1051/IUFoST:20060855

Alamar Since macroscopic mechanical behaviour of fruits depends on several microscopic properties (cell size, internal turgor pressure, cell wall mechanical properties and thickness, etc), a micromechanical approach is useful to understand the relative importance of these cellular and histological attributes on the overall mechanical behaviour of fruits and vegetables.

M.C. Alamar, M.Zarzo, R.Suay and E. Molt&Ucirc; Micromechanical Behaviour of Apple Tissue in Tensile and Compression Tests. Information and Technology for Sustainable Fruit and Vegetable Production FRUTIC 05, 12 &ntilde; 16

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