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UBC Theses and Dissertations

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UBC Theses and Dissertations

Elastin as a kinetic elastomer : an analysis of its conformational, mechanical, and photoelastic properties Aaron, Ben-Meyer Benson

Abstract

The elastic tissue composite is made up of a number of materials that are characterized by different chemical and mechanical properties. The protein elastomer elastin makes up almost 80% of bovine ligamentum nuchae with collagen and the matrix substances making up the other 20%. The analysis of the mechanical properties of the unpurified and purified tissue indicates that elastin is the dominant mechanical component at low strains with collagen contributing significantly at the higher extensions. The physical properties of single, 5 to 8um diameter, water-swollen elastin fibres were investigated on a micro-test apparatus attached to a polarizing microscope, and the results were analyzed by using the kinetic theory relationships. The analysis of the mechanical properties at extensions below 100% indicate that elastic modulus, G = 4.1 x 10⁵Nm⁻², the average molecular weight of the chains between cross-links is in the range of 6000 to 7 100g/mol, and the stress-optical coeffecient, C' = 1 x 10⁻⁹m²N⁻¹ at 24°C. Analysis of the temperature dependence of the stress-optical coeffecient indicated that the polarizability of the random link decreases with increasing temperature. The apparent activation energy for this process is in the order of 1.6 kcal/mole. Analysis of the non-Gaussian mechanical and optical properties at extensions above 100% suggest that the chain between cross-links contains approximately 10 'effective' random links, with each link consisting of 7 to 8 amino acid residues. The explicit assumption of a random network that is made by the kinetic theory was tested by a number of techniques. 400 MHz pmr spectra of the soluble alpha-elastin closely resembled the spectra that were predicted for the random-coil conformation, and the spectra obtained for it's amino acid hydrolysate. Polarized microscopy studies showed intact elastin fibres to be devoid of any crystalline structures. Finally, the parameters for the random chains in the elastin network were used to predict the dimensions of other random proteins. The close correlation of these predictions with published values for a series of proteins in solution in 6M GuHCl provided an independent test of the random conformation, validating the use of the kinetic theory relationships to analyze the macroscopic properties of elastin.

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