Modulus In Circumferential Direction Research Articles

An investigation on the correlation between the mechanical property change and the alterations in composition and microstructure of a porcine vascular tissue underwent trypsin-based decellularization treatment.

The nonlinear pseudoelastic behavior of a native/decellularized vascular tissue is closely related to the detailed composition and microstructure of the extracellular matrix and is important in maintaining the patency of a small-caliber vascular graft. A commonly used enzyme-detergent based decellularization protocol is effective in cell component removal but it also changes the microstructure and composition of the decellularized tissues. Previous studies provide limited information to correlate the mechanical property change with the alterations in composition and microstructure in a decellularization process. In this study, the correlations were studied by implementing a previously established fiber-progressive-engagement model to describe the nonlinear pseudoelastic behavior of a vascular tissue and to evaluate the effects of trypsin concentration and exposure duration on porcine coronary artery decellularization RESULTS: Results showed that tissue length and width increased and thickness and wet weight decreased with the exposure of trypsin. The effects of trypsin exposure times on the four mechanical parameters, i.e. initial strain, turning strain, initial modulus and stiffness modulus, in the longitudinal and circumferential directions were similar, but stronger in the circumferential direction. Major components of the extracellular matrix were vulnerable to the trypsin-based decellularization process. The decreases in initial and turning strain and the increase in initial modulus in circumferential direction were correlated with the significant decrease of collagen and glycosaminoglycans in the media layer. Although trypsin-based decellularization achieved cell component removal and preservation of ultimate tensile stress, the microstructure and composition changed with alterations in the pseudoelastic behavior of the porcine coronary artery. Taken together, the current observations suggested less waviness, early engagement, or re-alignment of insoluble collagen fibers in the media layer, which resulted in turning from anisotropic into isotropic uniaxial mechanical property of porcine vascular tissue. Selecting the proper trypsin concentration (< 0.03-0.5%) and duration (< 12 h) of trypsin exposure in combination with other methods will achieve optimal porcine coronary artery decellularization.

Biomechanical Remodeling of the Chronically Obstructed Guinea Pig Small Intestine

Small intestinal obstruction is a frequently encountered clinical problem. To understand the mechanisms behind obstruction and the clinical consequences, data are needed on the relation between the morphologic and biomechanical remodeling that takes place in the intestinal wall during chronic obstruction. We sought to determine the effect of partial obstruction on mechanical and morphologic properties of the guinea pig small intestine. Partial obstruction was created surgically in 2 groups of animals living for 2 and 4 weeks. Controls were sham operated and lived for 4 weeks. A combined impedance planimetry-high-frequency ultrasound system was designed to measure the luminal cross-sectional area and wall thickness. These measures were used to compute the circumferential stress and strain of the excised intestinal segments. The incremental elastic modulus was obtained by using nonlinear fitting of the stress-strain curve. Histologic analysis and the measurements of total wall collagen were also performed. The luminal cross-sectional area, wall thickness, and elastic modulus in circumferential direction increased in a time-dependent manner proximal to the obstruction site (P < 0.01), whereas no differences in these parameters were found distal to the obstruction site (P > 0.25). The circumferential stress-strain curves of the proximal segments in 2- and 4-week groups shifted to the left, indicating the intestinal wall became stiffer. Histologic examination revealed a massive increase in the thickness of the muscle layer especially the circular smooth muscle layer (P < 0.05). The collagen content proximal to the obstruction site was significantly larger in the partially obstructed animals compared to controls (P < 0.05). No difference was found distal to the obstruction site. Strong correlation was found between the collagen content and the elastic modulus at stress levels of 70 kPa stress (P < 0.01) and 10 kPa (P < 0.05) proximal to the obstruction site suggesting that the alteration of collagen has great impact on the mechanical remodeling. The morphologic and biomechanical remodeling likely influence the function of the intestine affected by partial obstructed intestine.

Changes in the mechanical properties, biochemical contents and wall structure of the human coronary arteries with age and sex

An experimental study of the mechanical properties, biochemical composition and structure was carried out on the proximal and distal parts of the right and the anterior descending branch of left human coronary arteries. The vessels were removed during an autopsy of 121 males and 84 females being 1 day to 80 years old. The material was divided into six age groups. Branchless segments of vessels 15–20 mm long were cut from proximal and distal parts. The mechanical properties of the coronary arteries were determined by passing fluid at pressures ranging from 0 to 240 mmHg. It was found that the part of the wall of the coronary artery adjacent to the myocardium is thicker in all cases than the other part of the arterial wall. With increasing age the mean thickness of the wall of both coronary arteries increases but the wall-thickening process is non-uniform in nature in both the proximal and distal parts and in the individual layers. The changes in the stretch ratio and tangential modulus in circumferential direction with age and sex were investigated. The greatest changes in the wall thickness and in the mechanical parameters were found for the left coronary artery wall in men over 40 years of age and for the right coronary artery wall in women over 50 years of age. The results of biochemical and densitometrical investigations were compared.