Elastic mismatch between ePTFE and PLLA vascular grafts in relation to femoral and carotid arteries in humans: in vivo, in vitro and in silico assessment
2019/11/27 21:41:30
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Many factors have been held responsible for the elevated failure rates of vascular substitutes. Several studies have shown that the lower the mismatches regarding mechanical or functional properties between the native vessel and its vascular substitute, the lower the hemodynamic alterations. From a theoretical point of view, the best substitutes have similar characteristics to the tissue or organ to be replaced. In the present work, samples of electrospun nanofibrous Poly(L-lactic acid) (PLLA) and expanded polytetrafluoroethylene (ePTFE) vascular grafts were subjected to pulsated pressure conditions using an experimental setup. Graft dynamic response was obtained from experimental measurements applying an ultrasonic gold standard method (to measure graft diameter) and a high frequency response pressure transducer (to obtain intraluminal pressure). Similarly, femoral and carotid arteries of normotensive male control subjects and ambulatory male patients with mild to moderate hypertension were explored in vivo in order to relate their mechanical performance to that observed in the synthetic grafts. The obtained results verified the existence of important biomechanical differences between vascular grafts and human arteries. Under normal physiological conditions, the pressure-strain modulus (10(6)dyn/cm(2)) of ePTFE and PLLA (1095 +/- 21.5 and 12.4 +/- 1.47, respectively) resulted significantly higher (p < 0.05) than the carotid and femoral modulus values (4.47 +/- 1.36 and 5.9 +/- 1.42, respectively). During the hypertensive condition (higher pressure levels) ePTFE and PLLA increased their elasticity values to 1136 +/- 21.6 and 15.97 +/- 2.6, respectively, with respect to an increase of 9.27 +/- 3.59 and 15.70 +/- 5.96 of carotid and femoral arteries. Additionally, the elastic mismatch generated by the interposition of both grafts between native arteries (carotid or femoral) was quantified by means of computational simulations. PLLA tubular structures manifested a mechanical behavior that mimics the response to pulsatile hypertensive pressure regimes (the lowest reflection coefficient was observed) which constitutes a highly desired property for vascular tissue-engineered scaffold production.

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