Elastin stress/strain

Our last example of the mechanical properties of a protein is that of keratin found in the top layer of skin. The stratum corneum in skin is almost exclusively made up of different keratins that have an a-helical structure. The helices do not run continuously along the molecule so the structure is not ideal. However, the stress-strain characteristics are shown in Figure 6.4 and demonstrate that at low moisture content the stress-strain curve for keratins in skin is approximately linear with a UTS of about 1.8 GPa and a modulus of about 120 MPa. These values are between the values reported for elastin and silk, which is consistent with the axial rise per amino acid being 0.15 nm for the a helix. Thus the a helix with an intermediate value of the axial rise per amino acid residue has an intermediate value of the... 

Uny et also reported the chemical synthesis of protein polymers based on the (Val-Pro- Ala-Val-Gly) repeat sequence in which glycine is replaced by the D-alanine residue. The hetero-chiral Pro- Ala diad would be erqrected on the basis of stereochemical considerations to adopt a type-II p-tum conformation. Stmctural analyses of small-molecule "Pro- Ala turn models support the formation of the type-II p-mm conformation in solution and the solid state. Polymers based on the (Val-Pro- Ala-Val-Gly) repeat sequence display a thermo-reversible phase transition similar to the corresponding polypeptides derived from the parent (Val-Pro-Gly-Val-Gly) sequence, albeit with a shift of the Tt to approximately 5-10 ° G below the latter due to a slight inaease in hydrophobic character due to the presence of the alanine residue. NMR spectroscopic analyses of the (Val-Pro- Ala-Val-Gly) polymer suggest that the repeat unit retains the p-tum stmcture on the basis of comparison to the corresponding behavior of the (Val-Pro-Gly-Val-Gly) polymer. Stress-strain measurements on cross-linked matrices of the (Val-Pro- Ala-Val-Gly) polymer indicate an elastomeric mechanical response in which the elastic modulus does value in comparison to the (Val-Pro-Gly-Val-Gly) polymer. These smdies of glycine suhstitution support the hypothesis that type-II p-tum formation can he associated with the development of elastomeric behavior with native elastins and elastin-derived polypeptide sequences. Several investigators have proposed that the (Val-Pro-Gly-Val-Gly) pentapeptide represents the minimal viscoelastic unit... 

Blood and lymphatic vessels are soft tissues with densities which exhibit nonlinear stress-strain relationships [1]. The walls of blood and lymphatic vessels show not only elastic [2, 3] or pseudoelastic [4] behavior, but also possess distinctive inelastic character [5, 6] as well, including viscosity, creep, stress relaxation and pressure-diameter hysteresis. The mechanical properties of these vessels depend largely on the constituents of their walls, especially the collagen, elastin, and vascular smooth muscle content. In general, the walls of blood and lymphatic vessels are anisotropic. Moreover, their properties are affected by age and disease state. This section presents the data concerning the characteristic dimensions of arterial tree and venous system the constituents and mechanical properties of the vessel walls. Water permeability or hydraulic conductivity of blood vessel walls have been also included, because this transport property of blood vessel wall is believed to be important both in nourishing the vessel walls and in affecting development of atherosclerosis [7-9]. 

Stress-strain isotherms have also been calculated with this approach. Examples are unimodal networks of polyethylene and POMS, " polymeric sulfur and seleniirm, short n-alkane chains, natural rubber, several polyoxides, and elastin, and bimodal networks of PDMS. It is possible to include excluded volume effects, in such simulations. In the case of the partially helical polymer polyoxymethylene, the simulations were used to resolve the overall distributions into contributions from imbroken rods, once-broken rods, twice-broken rods, and so on. It was also shown how applying stresses to the ends of chains of this typ>e can be used to bias the distributions in the direction of increased helical content and increased average end-to-end distances. In this sense, imposition of a stress has the same effect on the helix-coil equilibriirm as a decrease in temperature. ... 

Figure 7.3 Stress-strain curves from tensile testing experiments performed on electrospun nanofiber scaffolds made by blends of collagen/elastin and various synthetic polymers. Reproduced with permission from Ref. 80, J. Biomed. Mater. Res. A, 2007, 83, 999-1008. Doi 10.1002/jbm.a.31287. Copyright 2007, Wiley Periodicals, Inc.

The reaction of the arteriolar wall to changes in the blood pressure is considered to consist of a passive, elastic component in parallel with an active, muscular response. The elastic component is determined by the properties of the connective tissue, which consists mostly of collagen and elastin. The relation between strain e and elastic stress ae for homogeneous soft tissue may be described as [18] ... 

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