Publications

Bicuspid aortic valve (BAV) is the most common congenital heart malformation occurring in 1–2% of the population with a high rate of morbidity [1]. There is a significantly higher rate of dilation of the aortic root in adults with a BAV when compared to the normal population and this condition is often associated with ascending thoracic aortic aneurysm (ATAA). ATAA is characterized as an enlargement of the aorta to twice its normal diameter. If left untreated, ATAA can lead to aortic dissection or rupture. Therefore, ATAA is recommended for prophylactic surgery when its diameter reaches about 5.5 cm. However, in certain high-risk cases, such as patients with BAV, ATAA may rupture when its diameter is less than 5.5 cm. Since ATAA dissection and rupture are biomechanical phenomena, better mechanical models are needed to more accurately predict these events over the predictive capability of diameter alone.

For the sizes, strain, and strain rates tested, our results suggest that ovine PAC mechanical behavior is isotropic, and that the Mooney-Rivlin model is an appropriate curve-fitting constitutive equation for obtaining material parameters of PAC tissues.

We have observed distinct differences in functional and mechanical properties of the SD and Lewis urethra and have shown that the Lewis rat may not be suitable as a chronic model of SUI via nerve transection.

Abstract: A recent study investigated the association of gender with the growth rate of AAAs and found a significant increase in the growth rate of AAAs in women than in men. On the basis of these observations, we hypothesize that there are gender‐associated differences in AAA wall integrity and mechanical strength. The purpose of this study was to explore this hypothesis by comparing the tensile strength of freshly resected AAA tissue specimens between women and men. Seventy‐six rectangular specimens (20 mm long × 5 mm wide) from 34 patients (24 male, 10 female) were excised from the anterior wall of patients undergoing open repair of their abdominal aortic aneurysm and tested in a uniaxial tensile tester. Ultimate tensile strength (UTS) was taken as the peak stress obtained before specimen failure. While there were no statistical differences in strength between specimens taken from male and female patients, there was a trend toward a decrease in strength in females as compared to males (87.6 ± 6.7 N/cm 2 vs. 67.6 ± 8.1 N/cm 2 , p = 0.09). To the authors knowledge this work represents the first report of differences in biomechanical properties as a function of gender. The nearly significant decrease in UTS in women versus men reported here may be important in assessing the risk of rupture in AAA. Further testing is warranted to confirm the current trends.

Accurate estimation of the wall stress distribution in an abdominal aortic aneurysm (AAA) may prove clinically useful by predicting when a particular aneurysm will rupture. Appropriate constitutive models for both the wall and the intraluminal thrombus (ILT) found in most AAA are necessary for this task. The purpose of this work was to determine the mechanical properties of ILT within AAA and to derive a more suitable constitutive model for this material. Uniaxial tensile testing was carried out on 50 specimens, including 14 longitudinally oriented and 14 circumferentially oriented specimens from the luminal region of the ILT, and 11 longitudinally oriented and 11 circumferentially oriented specimens from the medial region. A two-parameter, large-strain, hyperelastic constitutive model was developed and used to fit the uniaxial tensile testing data for determination of the material parameters. Maximum stiffness and strength were also determined from the data for each specimen. Scanning electron microscopy (SEM) was conducted to study the regional microstructural difference. Our results indicate that the microstructure of ILT differs between the luminal, medial, and abluminal regions, with the luminal region stronger and stiffer than the medial region. In all cases, the constitutive model fit the experimental data very well (R2>0.98). No significant difference was found for either of the two material parameters between longitudinal and circumferential directions, but a significant difference in material parameters, stiffness, and strength between the laminal and medial regions was determined (p<0.01). Therefore, our results suggest that ILT is an inhomogeneous and possibly isotropic material. The two-parameter, hyperelastic, isotropic, incompressible material model derived here for ILT can be easily incorporated into finite element models for simulation of wall stress distribution in AAA.

This paper aims to identify the rupture locations of abdominal aortic aneurysms. Dow Corning Sylgard 184 was mechanically characterised. Five idealised models were then manufactured using this silicone rubber which were subsequently inflated to rupture with the images recorded using a high speed camera. Four of the five models tested ruptured at inflection points in the proximal and distal regions of the aneurysm sac, and not at regions of maximum diameter.

Sneeze induced stress urinary incontinence in a rat model of birth trauma was caused by decreased active closure mechanisms at the mid urethra without affecting the passive transmission of abdominal pressure in the proximal urethra.

Ascending thoracic aortic aneurysm (ATAA) is among the most devastating forms of cardiovascular disease, causing a significant mortality despite current medical and surgical treatments [1]. Moreover these therapies themselves are associated with great risk of mortality or morbidity, complicated by the advanced age of the typical patient, and high surgical costs. The mechanics of spontaneous aortic dissection is not fully understood. It is generally believed that aortic dissection initiates as an intimal tear in which a separation of wall layers produces the formation of a ‘false’ lumen. The dissection may propagate axially and/or circumferentially due to blood flow and pressure. Dissection may lead to several possible complications. For example, the septum between the false lumen and true lumen may fracture, resulting in embolism and ischemic damage. Another possibility is that the thinned and weakened residual outer aortic wall may fail, resulting in rapid blood loss and tamponade.