Morphologically bioinspired hierarchical nylon 6,6 electrospun assembly recreating the structure and performance of tendons and ligaments

Abstract

Reconstructions of ruptured tendons and ligaments currently have dissatisfactory failure rate. Failures are mainly due to the mechanical mismatch of commercial implants with respect to the host tissue. In fact, it is crucial to replicate the morphology (hierarchical in nature) and mechanical response (highly-nonlinear) of natural tendons and ligaments.The aim of this study was to develop morphologically bioinspired hierarchical Nylon 6,6 electrospun assemblies recreating the structure and performance of tendons and ligaments. First, we built different electrospun bundles to find the optimal orientation of the nanofibers. A 2nd-level hierarchical assembly was fabricated with a dedicated process that allowed tightly joining the bundles one next to the other with an electrospun sheath, so as to improve the mechanical performance. Finally, a further hierarchical 3rdlevel assembly was constructed by grouping several 2nd-level assemblies. The morphology of the different structures was assessed with scanning electron microscopy and high-resolution X-ray tomography, which allowed measuring the directionality of the nanofibers in the bundles and in the sheaths. The mechanical properties of the single bundles and of the 2nd-level assemblies were measured with tensile tests. The single bundles and the hierarchical assemblies showed morphology and directionality of the nanofibers similar to the tendons and ligaments. The strength and stiffness were comparable to that of tendons and ligaments. In conclusion, this work showed an innovative electrospinning production process to build nanofibrous Nylon 6,6 hierarchical assemblies which are suitable as future implantable devices and able to mimic the multiscale morphology and the biomechanical properties of tendons and ligaments.

Biomimetic Hierarchically Arranged Nanofibrous Structures Resembling the Architecture and the Passive Mechanical Properties of Skeletal Muscles: A Step Forward Toward Artificial Muscle

“…When random fibers were used, the mechanical properties of mats and bundles had a similar stressstrain pattern (Figure 7A). After a first overlapping linear region, the bundles showed a lower asymptotic stiffness compared to the mats, as previously observed (Pauly et al, 2016;Sensini et al, 2019a). The obtained curves are similar to those commonly reported in the literature for random electrospun structures (Ridruejo et al, 2011;Molnar et al, 2012;Sinha-Ray et al, 2014).…”

“…To reproduce a muscle fiber, bundles of nanofibers were prepared by following a previously reported procedure (Sensini et al, 2019a). Briefly, once obtained the random and aligned flat mats as described above, several stripes of the electrospun membranes were cut circumferentially directly on the drum collector.…”

Hierarchical electrospun tendon‐ligament bioinspired scaffolds induce changes in fibroblasts morphology under static and dynamic conditions

“…This behaviour can be probably ascribed to the combination of three factors: the electrospinning production process of the sheath, the hydration and mechanical component, and the crosslinking of the nanofibres. First, the mechanism to produce the sheath was proved to tune the level of compacting of the internal bundles of the hierarchical scaffolds (Sensini et al ., ; Sensini et al ., ,b). This effect causes a pretensioning of the sheath nanofibres and of the internal bundles.…”

“…To reproduce the structure of a whole tendon or ligament (Kastelic et al ., ; Murphy et al ., ), each bundle was pulled out from the drum, obtaining a ring‐shaped structure that was twisted in the middle and bent over itself. Then, each assembly was covered with an electrospun epitenon/epiligament‐like sheath, as previously described (Sensini et al ., ; Sensini et al ., ,b). The scaffolds were finally crosslinked with a mixture of N ‐(3‐dimethylaminopropyl)‐ N′‐ ethylcarbodiimide hydrochloride (EDC) and N ‐hydroxysuccinimide (NHS) (Sigma‐Aldrich, Saint Louis, USA) as previously described (Alberto Sensini et al ., ) (cross‐sectional diameter = 1.46 ± 0.08 mm; length of the scaffolds = 89.4 ± 2.1 mm).…”

Investigation of the Mechanical and Dynamic-Mechanical Properties of Electrospun Polyvinylpyrrolidone Membranes: A Design of Experiment Approach

“…Due to the great versatility and the high production rate compared to other fibre-forming technique [5], electrospinning has gained increasing interest from both the academic and industrial points of view, with a great range of possible applications and, indeed, several patents have been already registered [6][7][8]. For example, several electrospun membranes based on both synthetic and natural polymers were prepared for biomedical [9][10][11][12][13][14][15], environmental [16][17][18], air filtration [19][20][21], energy storage [22,23], sensing [24,25], and textile purposes [26,27], thus showing the huge future potentialities of this technique. The typical electrospinning set-up leads to randomly oriented nano-or microfibers exhibiting isotropic mechanical properties which usually show a lesser performance compared to other types of polymeric products (e.g., films, hydrogels, etc.)…”