Development of a growing rat model for broad in vivo assessment of bioengineered aortic conduits

Objectives: Alternative heart valve prostheses are warranted to overcome numerous limitations of implants currently used in pediatric patients. In order to determine the fate of decellularized aortic conduit transplants beyond histological measures, including detailed functional evaluation, we created a growing rodent model as described below.

Methods: Young Wistar rats (70–80g) were anesthetized and underwent median laparotomy for exposition of the abdominal aorta. After administration of heparin and aortic clamping, a U-shaped aortic conduit was sutured to the infrarenal aorta in an end-to-side manner. Intermittent reperfusion was used to keep limb ischemia times below 30 minutes. Following release of blood flow via the conduit, the native aorta between the two anastomoses was ligated to improve perfusion of the graft. According to the small size of the animals, functional assessment could be performed not only by doppler sonography after explantation, but also via high resolution rodent MRI. Histology, immunohistochemistry and graft plastination followed after 8 weeks.

Results: Eighty percent of the operated rats (n=10) recovered without adverse effects. Conforming with clinical observations, postoperative MRI on day 5 and doppler sonography after 8 weeks revealed unimpaired perfusion of both, the conduit and the distal aorta. Explanted prostheses were luminally completely covered by neoendothelium, whereat local hyperplasia of α-smooth muscle actin (+) cells occurred. Moreover, a mild microcalcification of the tunica media of the decellularized scaffolds was shown. Staining against inflammatory cell markers (CD3 & CD68) was negative at 8 weeks.

Conclusions: Our downsized variant of aortic conduit transplantation enables an overall characterization with detailed analysis of graft maturation along with an evaluation of growth potential of tissue engineered and native grafts in a growing organism. Furthermore, with the advent of novel contrast agents specific for inflammatory cells (such as emulsified perfluorocarbons), MRI measurements may elucidate early immune response against the implants.