Influence of medial collagen organization and axial in situ stretch on XXXX growth.

@entity1 @entity6459 @entity439 @entity438
A model for @entity438 growth, proposed by Kroon and Holzapfel (2007, "A Model for Saccular @entity438 Growth in a @entity1 Middle Cerebral Artery," J. Theor. Biol., 247, pp. 775-787; 2008, "Modeling of @entity439 Growth in a @entity1 Middle Cerebral Artery," ASME J. Biomech. @entity6459 ., 130, p. 051012), is further investigated. A @entity1 middle cerebral artery is modeled as a two-layer cylinder where the layers correspond to the media and the adventitia. The immediate loss of media in the location of the @entity439 is taken to be responsible for the initiation of the @entity439 growth. The @entity439 is regarded as a development of the adventitia, which is composed of several distinct layers of collagen fibers perfectly aligned in specified directions. The collagen fibers are the only load-bearing constituent in the @entity439 wall; their production and degradation depend on the stretch of the wall and are responsible for the @entity439 growth. The anisotropy of the surrounding media was modeled using the strain-energy function proposed by Holzapfel et al. (2000, "A New Constitutive Framework for Arterial Wall Mechanics and a Comparative Study of Material Models," J. Elast., 61, pp. 1-48), which is valid for an elastic material with two families of fibers. It was shown that the inclusion of fibers in the media reduced the maximum principal Cauchy stress and the maximum shear stress in the @entity439 wall. The thickness increase in the @entity439 wall due to material growth was also decreased. Varying the fiber angle in the media from a circumferential direction to a deviation of 10 deg from the circumferential direction did, however, only show a little effect. Altering the axial in situ stretch of the artery had a much larger effect in terms of the steady-state shape of the @entity439 and the resulting stresses in the @entity439 wall. The peak values of the maximum principal stress and the thickness increase both became significantly higher for larger axial stretches.
