Mechanical stretch

Mechanical stretch tests were made with the speed of (0,3-3,0) 10" m/s and with the simultaneous registration of the AE signals. Number of the AE impulses (Nl ) and AE amplitude (A) were selected as the measurable parameters of the AE. 

The physical characteristics of current commercial mbber and spandex fibers are summarized ia Table 1. Typical stress—straia curves for elastomeric fibers, hard fibers, and hard fibers with mechanical stretch properties ate compared ia Eigute 1. 

Fig. 1. Stress—strain curves A, hard fiber, eg, nylon B, biconstituent nylon—spandex fiber C, mechanical stretch nylon D, spandex fiber E, extruded latex...

Natriuretic Peptide Diuretics. Atrial natriuretic peptide (ANP), an endogenous diuretic, natriuretic, and vasodilator, is a peptide hormone primarily synthesized and stored by atrial cardiocytes, and secreted by the atria in response to mechanical stretch of the atria. It was discovered in the cmde extracts of atria in 1981 (51). ANP is also known as anaritide [95896-08-5] atrial natriuretic factor [104595-79-1] (ANF) auriculin ... 

We studied the effect of the mechanical stretching field on the conformations of the macromolecules in the melt. It is known that for a freely jointed chain the Maxwell distribution of end-to-end distances holds50). 

Recently, Genzer and coworkers [85] presented an interesting new approach for the preparation of stable silane-based SAM systems. As a substrate, cross-linked polydimethylsiloxane (PDMS) was oxidized by UV/ozone treatment to yield a thin sihcon dioxide surface. The surface was then treated with fluorinated alkyltrichlo-rosilanes from the gas phase while being mechanically stretched by a certain length Ax. After modification, the elastomer was allowed to relax resulting in a mecdianically assembled monolayer (MAM) at the surface (Fig. 9.8). 

Fig. 9.8 Schematic illustration of the preparation of mechanically assembled monolayers (MAMs). (A) A cross-linked PDMS film is (B) mechanically stretched by Ax (C), oxidized by UV/ozone treatment to yield a thin Si02 sur-...

Earlier attempts to use the AFM for mechanically stretching chromatin fibers have run into a rather unexpected artifact. Long native chromatin fibers isolated from chicken erythrocytes, or fibers assembled in vitro from purified histones and relatively short, tandemly repeated DNA sequences were deposited on mica or glass surfaces and pulled with the AFM tip [69,70]. In such stretching experiments the scanning of the sample in the x- and y-direction used for imaging was disabled, and the cantilever-mounted tip was allowed to move only in the z-direction, i.e., upwards and downwards, away and towards the surface. When the AFM tip is pushed into the sample, it may attach to the sample by non-specific adsorption upon retraction it stretches the sample and force-extension curves are recorded (see Fig. lb for an explanation of a typical force curve). 

The experimental approach used to mechanically stretch a chromatin fiber with the AFM is depicted schematically in Fig. 8a, and some example curves obtained with native chicken erythrocyte chromatin fibers are presented in Fig. 8b. These curves exhibited a saw-tooth pattern, similar to the patterns obtained upon stretching of multi-domain proteins like titin [71] or tenascin [72] (Fig. 8c). Each of... 

Polymers with rigid, cyclic structures in the polymer chain, as in cellulose and poly(ethy-leneterephthalate), are difficult to crystallize. Moderate crystallization does occur in these cases, as a result of the polar polymer chains. Additional crystallization can be induced by mechanical stretching. Cellulose is interesting in that native cellulose in the form of cotton is much more crystalline than cellulose that is obtained by precipitation of cellulose from... 

A number of other characteristics are required in order to ensure a viable polymeric conductor. Chain orientation is needed to enhance the conducting properties of a polymeric material, especially the intermolecular conduction (i.e., conduction of current from one polymer molecule to another). This is a problem with many of the polymers that are amorphous and show poor orientation. For moderately crystalline or oriented polymers, there is the possibility of achieving the required orientation by mechanical stretching. Liquid crystal polymers would be especially advantageous for electrical conduction because of the high degree of chain orientation that can be achieved. A problem encountered with some doped polymers is a lack of stability. These materials are either oxidants or reductants relative to other compounds, especially water and oxygen. 

Muller (1959) and co-workers have made many interesting and important studies of heat effects during the mechanical stretching and relaxing of polymeric fibers. However, Dole (1959) in reviewing calculations of the enthalpy differences between drawn and undrawn fibers and annealed samples as computed from specific heat-temperature data could find no differences that could not be explained on the basis of the extent of crystallinity of the samples. 

When describing liquid surfaces, the surface tension was of fundamental importance. If we try to extend the definition of surface tension to solids, a major problem arises [324], If the surface of a liquid increases, then the number of surface atoms increases in proportion. For a solid surface this plastic increase of the surface area is not the only possible process. Usually more important is an elastic increase of the surface area. If the solid surface is increased by mechanically stretching, the distance between neighboring surface atoms changes, while the number of surface atoms remains constant. The change in surface area is commonly described in terms of the surface strain. The total surface strain etot is given by the change in surface area divided by the whole surface area detot = dA/A. The surface strain may be divided into a plastic strain dep and an elastic strain dse so that dstot = dep + dee. 

MacKenna DA, Dolfi F, Vuori K, Ruoslahti E. 1998. Extracellular signal-regulated kinase and c-Jun NH2-terminal kinase activation by mechanical stretch is integrin-dependent and matrix-specific in rat cardiac fibroblasts. J Clin Invest 101 301-10. 

Knoll, R., Hoshijima, M., and Hoffman, H. M. (2002). The cardiac mechanical stretch sensor machinery involves a Z disc complex that is defective in a subset of human dilated cardiomyopathy. Cell 111, 943-955. 

Another possible application using the hierarchical nature of the wrinkles has been discussed by Efimenko and coworkers [46], They treated a mechanically stretched PDMS sheet with UV-ozone in order to create a stiff surface layer. A detailed analysis with AFM and profilometry of the wrinkles after releasing the strain showed that the wrinkling patterns are hierarchical themselves. They observed up to five generations of different wavelengths with different periodicities. These features made so structured surfaces valuable candidates for separate colloidal particles of different sizes by acting as a micro fluidic sieve. A suspension... 

Lin PC, Yang S (2007) Spontaneous formation of one-dimensional ripples in transit to highly ordered two-dimensional herringbone structures through sequential and unequal biaxial mechanical stretching. Appl Phys Lett 90 241903... 

---