Experimental characterization of the distribution of collagen fiber recruitment

Abstract

The passive biomechanical behavior of blood vessels is generally modeled by a parallel arrangement of elastin and collagen, with collagen recruitment depending on vessel strain. We experimentally determined the collagen recruitment distribution using confocal microscopy. Digital images from sections of rabbit carotid artery under increasing circumferential stretch ratio were acquired. The straightness of the fibers was measured to compute the fraction of recruited fibers for each stretch ratio. The experimental distribution obtained was then used in the model proposed by Zulliger et al. This model is based on a strain energy function (SEF), which provides a constituentbased description of the wall mechanics. Using this model, a fit of the pressure-radius curve was then performed by using the experimental collagen recruitment distribution with the collagen elastic constant as a free fit parameter. The fit was good, but the value of the collagen elastic constant obtained was below values reported in the literature. A second fit of the pressure-radius curve was also performed, whereby the collagen distribution was left free to adapt while the collagen elastic constant was set to a physiological value. The differences between the experimental collagen engagement distribution and the distribution obtained when the collagen elastic constant was fixed were analyzed. Good qualitative agreement was found between the experimental distribution of collagen recruitment and the model. Some experimental limitations and modeling approximations remain. Nevertheless, experimental proof of progressive collagen recruitment was established, which validates the basic hypothesis of the model.

Kinematics of collagen fibers in carotid arteries under tension-inflation loading

“…The aforementioned experimental findings enhanced the first generation of structural models based on the definition of a strain energy function, which considered the arterial wall as a soft matrix material reinforced by variously distributed fibers families [24,58,25,19], with the addition of a fiber activation stretch or of a probability distribution function, accounting for gradual recruitment at finite strain [42,23]. All these models assume an affine deformation of the collagen network, as experimentally evidenced by several contributions [43,52], i.e.…”

“…3 (a1) and (a2)), revealing optimal in-plan morphology. In fact, previous studies have investigated the transmural angle (radial direction) of the fibers and showed that it is negligible in comparison to the in-plane angle [42,41,44]. As a result, although the negligible transmurality information is lost, the fibers are represented with maximal effective length, strongly improving the interpretation of their in-plane orientation.…”

Structure-based constitutive model can accurately predict planar biaxial properties of aortic wall tissue

“…In addition, the undulation parameters of medial collagen were set to k M min ¼ 1:0 and k M max ¼ 1:1 according to Ref. [40] for rabbit aortas. The relatively low medial collagen undulation has also been observed in humans [56].…”

Biomechanics of Blood Vessels: Structure, Mechanics, and Adaptation

“…4.6) and align obliquely to the circumferential direction [9], while elastic fibers are straight, and thus, the incremental elastic modulus is low (Table 4.1). In high-pressure region, stiff collagen fibers become straight and begin to be stretched [10], resulting in the strain hardening of the blood vessel wall. Since collagen fibers are not stretched in low-pressure region, breaking strain of the aorta (~100 %) is in Mean ± SEM, n = 16…”