Biomimetic microstructural reorganization during suture retention strength evaluation of electrospun vascular scaffolds

Abstract

Suture retention strength (SRS) is commonly used as a measure the ability of sutures to adhere implants to surrounding tissue. While SRS is widely employed, surprisingly its effects on graft microstructure have not been characterized. This is particularly germane to the broad utilization of electrospun implants in tissue engineering. These implants need to retain their initial nanoscale topography while simultaneously preserving clinically critical mechanical properties. We examined the suture-driven microstructural deformation of polycaprolactone electrospun to form both square and tubular SRS samples. The impact of fiber orientation (generally parallel or random orientation, orthogonally aligned) on the SRS of these vascular tissue equivalents was analyzed and compared to native and decellularized porcine vasculature. The initial state of the fiber clearly dictates the overall efficiency of scaffold utilization. SRS values for as-spun fibers at a thickness of 300 μm were found to be in the range of 1.59-4.78 N for the three orientations. Unexpectedly, random fibers provided the optimal SRS values based on both resistance to suture motion and the percentage of scaffold involvement. A "V-shaped" failure morphology is observed for both electrospun scaffolds and native tissue during SRS testing. Post-test fiber alignment in the tensile direction was visible in all initial fiber orientations similar to that of native tissue. These findings are significant as they allow us to employ new, counterintuitive biomimetic design criteria for nanofiber-based scaffolds in which reliable mechanical integration with the surrounding tissues via suture-based methods is important. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1525-1534, 2016.

Design parameters for electrospun biodegradable vascular grafts

“…Above 300 m/min, mechanical deformation was observed on the fibers because of the high mechanical stress and affected the fiber orientation in a negative way [45]. In a study by Chaparro et al [46], randomly distributed PCL fibers were spun onto a 53 mm diameter steel rod rotated at 9000 r/min (net peripheral speed of 84.6 m/min), while aligned PCL fibers were spun onto a rotating Yalcin Enis and Gok Sadikoglu mandrel having a 2.01 m circumference (diameter: 640 mm), rotated at 500 r/min (providing a peripheral speed of 2000 m/min) [46].…”

“…Therefore, most of the studies use large diameter collectors (630 mm [42], 102 mm [44], 32 mm [45], and 640 mm [46]) for accessible rotational speeds. Matsuda et al [43] reported that they achieved partial fiber orientation at 32.02 m/min for a 3 mm rotating mandrel diameter [43] which had been explained by Edwards et al as having an insufficient peripheral velocity [45].…”

The Self-Assembling Process and Applications in Tissue Engineering

“…Often referred to as the tissue-engineering “triad,” this foundational concept of cells, scaffolds, and signals has informed strategies for numerous outcomes, such as bone regeneration following complex fractures or the development of vasculature in vitro to replace diseased vessels (3, 4). Significant advances in the field have resulted from this paradigm.…”

Fabrication and characterization of air-impedance electrospun polydioxanone templates

“…Suture retention (SR) testing (n = 10) was performed using the same TestResources TM frame with 0.75 cm × 4 cm rectangular strips cut from the electrospun templates (along the same direction and orientation as the dogbone punches), following the "straight-across" method with a "v-shape" failure mode, consistent with SR testing methods outlined in the American National Standard ANSI/AAMI VP20:1994 entitled "Cardiovascular Implants -Vascular Graft Prostheses" [16]. Briefly, the SD templates fabricated from all three deposition plates were tested using an Ethicon 6-0 (0.7 metric) PDS II (polydioxanone) suture fed through one end of the rectangular strip (3 mm from the center of the edge).…”

“…The "V" shaped failure mode indicates a successful failure during SR testing [16]. LD templates, however, were in fact too strong for the Ethicon sutures.…”