MECHANICAL ROLE OF ELASTIN-ASSOCIATED MICROFIBRILS IN PIG AORTIC ELASTIC TISSUE

The contribution of microfibrils to the mechanical performance of the meshwork of elastic tissue in mature pig aorta was investigated by com paring the properties of autoclaved tissue containing elastin and micr ofibrils with autoclaved tissue that had been treated with dithiothrei tol (DTT) or hot alkali to remove the microfibrils from the elastin, T he uniaxial tensile stress-strain curve of the autoclaved tissue was l inear to a. strain of 0.6 or 0.7 and increased nonlinearly up to the b reaking strain. The nonlinearity at high strains could not be accounte d for by nonGaussian behavior and was attributed to the progressive al ignment of the elastic fibers with strain. Removal of the microfibrils with DTT or treatment with calcium reduced the modulus at low strains by 12% and 4% respectively and increased the modulus at high strains, suggesting that the microfibrils have the capacity to change the orie ntation of the elastin fibers, possibly transmitting some of the load from one elastin fiber to another. Our findings suggest two possible r oles for the microfibrils in vivo: distributing the load throughout th e elastic fibers of the arterial wall and direct load bearing. The mod ulus and the breaking stress of the rings decreased linearly with the duration of alkali treatment starting immediately, By 45 min the modul us had dropped by 30% and the breaking stress by 50%, even though the amino acid content of the extract gave little evidence of elastin hydr olysis. Alkali treatment should not be used on autoclaved pig aortic t issue to be used for mechanical testing.