Effects of elastase and collagenase on the nonlinearity and anisotropy of porcine aorta

Abstract

We use enzymatic manipulation methods to investigate the individual and combined roles of elastin and collagen on arterial mechanics. Porcine aortic tissues were treated for differing amounts of time using enzymes elastase and collagenase to cause degradation in substrate proteins elastin and collagen and obtain variable tissue architecture. We use equibiaxial mechanical tests to quantify the material properties of control and enzyme treated tissues and histological methods to visualize the underlying tissue microstructure in arterial tissues. Our results show that collagenase treated tissues were more compliant in the longitudinal direction as compared to control tissues. Collagenase treatment also caused a decrease in the tissue nonlinearity as compared to the control samples in the study. A one hour collagenase treatment was sufficient to cause fragmentation and degradation of the adventitial collagen. In contrast, elastase treatment leads to significantly stiffer tissue response associated with fragmented and incomplete elastin networks in the tissue. Thus, elastin in arterial walls distributes tensile stresses whereas collagen serves to reinforce the vessel wall in the circumferential direction and also contributes to tissue anisotropy. A microstructurally motivated strain energy function based on circumferentially oriented medial fibers and helically oriented collagen fibers in the adventitia is useful in describing these experimental results.

Creating a model of diseased artery damage and failure from healthy porcine aorta

“…Dobrin and coworkers found that there was no change in axial compliance with collagenase treatment, contradicting the results of this study [49,50]. However Gundiah et al found collagenase treatment affected wall compliance in both directions, which supports the findings here [18]. The differences in behaviour in this study are most pronounced in the axial direction, with both the fracture stress and stretch being significantly different, whilst only the stretch is significantly different in the circumferential direction.…”

“…Their tensile test data, correspondingly, showed increased stiffness in diseased tissue and curves shifted towards lower strains. This behaviour coincides with results reported in Gundiah et al when elastin was artificially degraded [18]. However, it was not reflected in our results, wherein curves for elastase treated samples showed a shift towards higher strains.…”

“…Control samples produced similar k 1 values to those reported by Weisbecker, et al, but lower k 2 values [33]. Gundiah, et al reported decreases in k 2 in collagenase samples compared with controls, as here, but with an accompanying increase in k 1 , the latter not seen here [18]. Zeinali-Davarani, et al performed gradual elastase digestion of porcine aorta [19].…”

“…Fibre angle for collagenase samples can be compared to the findings in Gundiah et al: for controls and collagenase treated samples, θ was greater than found here, however the difference between the control and collagenase samples was similarly small: < 4 o [18]. Zeinali-Davarani et al reported an increase in θ compared to control samples for partial digestion, whereas a decrease is reported here [19].…”

“…Both uniaxial and biaxial testing have been performed on tissue treated with collagenase and elastase to understand the alteration in material behaviour [18,19,20]. In addition, inflation tests have been performed to enhance physiological relevance [21,22,23,24].…”