Significant differences in the material properties between aged human and porcine aortic tissues

Objective: Currently, percutaneous aortic valve (PAV) replacement devices are being investigated to treat aortic stenosis in patients deemed to be of too high a risk for conventional open-chest surgery. Successful PAV deployment and function are heavily reliant on the tissue–stent interaction. Many PAV feasibility trials have been conducted with porcine models under the assumption that these tissues are similar to human; however, this assumption may not be valid. The goal of this study was to characterize and compare the biomechanical properties of aged human and porcine aortic tissues. Methods: The biaxial mechanical properties of the left coronary sinus, right coronary sinus, non-coronary sinus, and ascending aorta of eight aged human (90.1±6.8 years) and 10 porcine (6–9 months) hearts were quantified. Tissue structure was analyzed via histological techniques. Results: Aged human aortic tissues were significantly stiffer than the corresponding porcine tissues in both the circumferential and longitudinal directions (p<0.001). In addition, the nearly linear stress–strain behavior of the porcine tissues, compared with the highly nonlinear response of the human tissues at a low strain range, suggested structural differences between the aortic tissues from these two species. Histological analysis revealed that porcine samples were composed of more elastin and less collagen fibers than the respective human samples. Conclusions: Significant material and structural differences were observed between the human and porcine tissues, which raise questions on the validity of using porcine models to investigate the biomechanics involved in PAV intervention.