High-resolution x-ray morphological investigation of Nylon 6,6 electrospun assemblies reproducing the hierarchical structure and mechanical performances of tendons and ligaments

The surgery of tendons and ligaments ruptures, especially in old patients, requires permanent prosthetic devices with a biomimetic hierarchical structure and mechanical properties [1]. The electrospinning technique has demonstrated to produce complex hierarchical structures mimicking the morphology and properties of tendons and ligaments [2, 3]. The aims of the present study were: (i) to develop innovative hierarchically arranged electrospun structures made of inert Nylon 6,6 for tendon and ligament replacement; (ii) to investigate their structure with high-resolution x-ray computed tomography (XCT); (iii) to characterize their mechanical properties. In order to mimic the arrangement of tendons and ligaments fibrils [4], mats of aligned Nylon 6,6 nanofibers were electrospun on a rotating drum collector [5]. To reproduce the tendons and ligaments fascicles morphology [4], mats were cut in stripes and wrapped up on the drum, producing ring-shaped bundles of axially aligned nanofibers [2]. In order to mimic a whole tendon or ligament with their epitenon-epiligament membranes [4], 2-level hierarchical structures were developed. Several bundles were aligned and packed together using a nanofibrous sheath produced through an innovative electrospinning setup [2]. Finally, to mimic also the endotenon-endoligament membranes [4], a 3-level hierarchical structure was obtained by grouping together three 2-level hierarchical structures, produced as previously described, with an additional electrospun sheath. A morphological investigation of the different electrospun structures was carried out with scanning electron microscopy (SEM) and XCT with different voxel sizes (0.4 up to 5 m). The alignment of the nanofibers of the electrospun sheaths and of the internal bundles was quantified with a previously validated methodology [6]. The ring-shaped bundles and the 2-level hierarchical structures were also mechanically characterized with a monotonic tensile test with physiological strain rates (70%/sec.). The high-resolution imaging confirmed that the morphology of the different hierarchical structures was comparable to the corresponding structures of biological tendons and ligaments [4]. The mechanical test on the structures showed a biofidelic biomimicking of the mechanical performances of the corresponding tendons and ligaments structures. In conclusion, this innovative electrospinning approach to produce hierarchically-arranged structures will be suitable to develop tendons and ligaments prosthetic devices.