Gender differences in biomechanical properties, thrombus age, mass fraction and clinical factors of abdominal aortic aneurysms.

The main purpose of the present study is the investigation of gender differences in the biomechanical properties, thrombus age, mass fraction and key clinical factors of abdominal aortic aneurysms (AAAs). A total of 90 AAA samples (78 males and 12 females) were harvested from open surgical aneurysm repairs. Biaxial extension and peeling tests were performed to characterise the biaxial mechanical responses and to determine dissection properties of both the intraluminal thrombi (ILTs) and the thrombus-covered walls. Relative thrombus age was determined by characterising the ILT histological microstructure. Mass fraction analyses quantified dry weight percentages of elastin and collagen within the AAA walls. Moreover, we statistically compared clinical factors between male and female. The luminal layers of the female thrombi and the female AAA walls showed a significantly lower tissue stiffness (modulus) in the longitudinal direction when compared to males. Gender differences were also shown in the dissection properties of the intima-media composite within the AAA walls, in which a statistically significantly lower energy to propagate a dissection was quantified for females than for males. Moreover, 82% of female thrombi were relatively older (ILT age phases III and IV), twice that of male thrombi (43%). A pronounced lower elastin content was identified for the intima-media composites of male AAA walls, whereas female AAA walls had significantly lower dry weight percentages of collagen. Regarding clinical factors, nicotine pack years, serum creatinine and AAA expansion rate were found to be much higher for male patients. These findings may help to explain higher risks for AAA growth in males and the ruptures of smaller-sized AAAs in females.