Mechanical characterization of nanofibrous small-diameter vascular grafts

F. MONTINI BALLARIN; D. SUAREZ BAGNASCO; L. CYMBERKNOP; P.C. CARACCIOLO; G. BALAY; C.A. NEGREIRA; R.L. ARMENTANO; G.A. ABRAHAM

Rosario

Congreso; 8vo Congreso Latinoamericano de Organos Artificiales, Biomateriales e Ingeniería de Tejidos, COLAOB; 2014

Sociedad Latinoamericana de Biomateriales, Organos Artificiales e Ingenieria de Tejidos (SLABO)

Small-diameter vascular grafts still represent an enormous challenge in the blood vessel replacement field. Most of the existing solutions fail in vivo mainly due to mechanical mismatch. Arterial conduits present a complex layer structure constituted by collagen and elastin fibers, including smooth muscle cells. The behavior can be well characterized by the assessment of mechanical response to a pulsatile stimulus. Therefore, the success of a vascular graft lies in structures that mimic adequately the pressure-diameter relationship observed in the vascular wall. Poly(L-lactic acid) (PLLA) is a FDA-approved biodegradable polyester commonly used in biomedical applications, such as drug delivery systems, tissue engineering and biomedical devices. It exhibits semicrystalline structure and good electro-spinnability. PLLA presents a relatively high elastic modulus, with the capability to withstand high pressure and flow conditions without suffering collapses or degradation. Additionally, segmented polyurethane (SPU) elastomers, consisting of alternating soft and hard segments, are generally thermoplastic and exhibit excellent properties, such as tensile strength, variable compliance and biocompatibility. SPU have been used in cardiovascular devices for almost 50 years and are essentially characterized by a viscoelastic nature. Electrospinning constitutes a versatile technique which allows the production of small-diameter nanofibrous vascular grafts with a biomimetic extra cellular matrix like structure. The present work is focused on the development of PLLA and SPU electrospun vascular grafts in order to obtain an elastic modulus behavior which could be compared to collagen and elastin values. Mechanical characterization of PLLA and SPU grafts was performed in vitro by means of a circulating loop. 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. Measurement of pressure and diameter allowed the estimation of dynamical compliance (C%, 10-2 mmHg) and the pressure-strain elastic modulus (EPε, 106 dyn cm-2). 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 110 to 150 mmHg, respectively. Under similar conditions, SPU vascular grafts showed a decrease in %C (4.56 ± 0.24, 3.35 ± 0.18 and 2.38 ± 0.17) concomitant to an increase in EPε (3.49 ± 0.42, 4.69 ± 0.41 and 6.09 ± 0.55) corresponding to the same PLLA pressure ranges, respectively. As a result, a higher elastic modulus was observed in PLLA grafts compared to SPU elastic response. Accordingly, pressure-strain modulus quantified in PLLA and SPU vascular grafts might be related to collagen and elastin elastic ranges, respectively. For this reason, PLLA and SPU could be considered as interesting candidates for the production of bi-layered vascular grafts with PLLA/SPU blended.