However, some degree of off-axis alignment or crimping of these fibers explains the non-linearity seen in the early portions of their stress-strain curves.
(2003) found the modulus of both the toe-region and linear region to be two orders of magnitude greater in the fiber-aligned direction and the Poisson’s ratio to be six times greater for loading in the direction of the fibers than transversely. This alignment explains the highly anisotropic properties of tendon tissues. The mechanical behavior of intact and injured T/L tissue is related to deformation on these various scales, but the exact mechanisms are still not completely clear.Ĭollagen fibers are the main providers of structural stiffness and strength in tendons and are predominately, but not perfectly, aligned in the axial, load-bearing direction of the tissue. Scaling up the T/L structure, bunches of collagen fibrils group together aligning their axis in the direction of the whole tissue longitudinal axis, producing the typical T/L fascicles (diameter range from few tens up to hundreds of micrometers) ( Kastelic et al., 1978 Kannus, 2000 Murphy et al., 2016). In particular, the nanometric collagen type I fibrils (diameter 50–250 nm) are the building blocks of this hierarchical arrangement ( Kannus, 2000). Tendons and ligaments (T/L) have a complex and multiscale fibrous structure ( Kastelic et al., 1978 Kannus, 2000 Goh et al., 2014). The results of this study will be of extreme interest for the material scientists working in the field, to model and improve the design of their electrospun structures and scaffolds and enable building a new generation of artificial tendons and ligaments. Moreover, for each sample category the transition and the inflection points were defined to study how these points can shift with the nanofiber arrangement and to compare their values with those of tendons. A tensile mechanical characterization was carried out showing an elastic-brittle biomimetic behavior for the higher speed bundles with a progressively more ductile behavior at slower speeds. The scanning electron microcopy revealed a fibril-inspired structure of the nanofibers with an orientation at the higher speed similar to those in tendons and ligaments (T/L). To fill this gap, in this work fascicle-inspired electrospun nylon 6,6 bundles were produced with different collector peripheral speeds (i.e., 19.7 m s –1 13.7 m s –1 7.9 m s –1), obtaining different patterns of nanofibers alignment. Comparing their behavior with that of the natural counterpart is important to adequately replicate their behavior at physiological strain levels. Despite the fact that several groups have developed electrospun tendon-inspired structures, an investigation of the inflection and transition point mechanics is missing. These nanofibrous mats can be easily assembled in higher hierarchical levels to reproduce the whole tissue structure.
With the aim to simulate and replace tendons, electrospinning has been demonstrated to be a suitable technology to produce nanofibers similar to the collagen fibrils in a mat form. This phenomenon often results in a progressive macroscopic failure of these tissues.
It is well established however, that the inflection and transition points in tendon stress-strain curves represent thresholds that may signal the onset of irreversible fibrillar sliding. Tendon and ligament injuries are triggered by mechanical loading, but the specific mechanisms are not yet clearly identified.
0 kommentar(er)
