RESUMO
Development of successful small-diameter vascular grafts constitutes a real challenge to biomaterial engineering. In most cases these grafts fail in-vivo due to the presence of a mechanical mismatch between the native vessel and the vascular graft. Biomechanical characterization of real native vessels provides significant information for synthetic graft development. Electrospun nanofibrous vascular grafts emerge as a potential tailor made solution to this problem. PLLA-electrospun nanofibrous tubular structures were prepared and selected as model bioresorbable grafts. An experimental setup, using gold standard and high resolution ultrasound techniques, was adapted to characterize in vitro the poly(L-lactic acid) (PLLA) electrospun structures. The grafts were subjected to near physiologic pulsated pressure conditions, following the pressure-diameter loop approach and the criteria stated in the international standard for cardiovascular implants-tubular vascular prostheses. Additionally, ovine femoral arteries were subjected to a similar evaluation. Measurements of pressure and diameter variations allowed the estimation of dynamical compliance (%C, 10(-2) mmHg) and the pressure-strain elastic modulus (E(Pε), 10(6) dyn cm(-2)) of the abovementioned vessels (grafts and arteries). Nanofibrous PLLA showed a decrease in %C (1.38±0.21, 0.93±0.13 and 0.76±0.15) concomitant to an increase in EPε (10.57±0.97, 14.31±1.47 and 17.63±2.61) corresponding to pressure ranges of 50 to 90 mmHg, 80 to 120 mmHg and 100 to 150 mmHg, respectively. Furthermore, femoral arteries exhibited a decrease in %C (8.52±1.15 and 0.79±0.20) and an increase in E(Pε) (1.66±0.30 and 15.76±4.78) corresponding to pressure ranges of 50-90 mmHg (elastin zone) and 100-130 mmHg (collagen zone). Arterial mechanics framework, extensively applied in our previous works, was successfully used to characterize PLLA vascular grafts in vitro, although its application can be directly extended to in vivo experiences, in conscious and chronically instrumented animals. The specific design and construction of the electrospun nanofibrous PLLA vascular grafts assessed in this work, showed similar mechanical properties as the ones observed in femoral arteries, at the collagen pressure range.
