Cyanine-Doped Nanofiber Mats for Laser Tissue Bonding

Abstract

In spite of an extensive body of academic initiatives and innovative products, the toolkit of wound dressing has always revolved around a few common concepts such as adhesive patches and stitches and their variants. Our work aims at an alternative solution for an immediate restitutio ad integrum of the mechanical functionality in cutaneous repairs. We describe the fabrication and the application of electrospun mats of bioactive nanofibers all made of biocompatible components such as a natural polysaccharide and a cyanine dye for use as laser-activatable plasters, resembling the ultrastructure of human dermis. In particular, we investigate their morphological features and mechanical moduli under conditions of physiological relevance, and we test their use to bind a frequent benchmark of connective tissue as rabbit tendon and a significant case of clinical relevance as human dermis. Altogether, our results point to the feasibility of a new material for wound dressing combining translational potential, strength close to human dermis, extensibility exceeding 15% and state-of-art adhesive properties.

Keywords: chitosan; dermis; electrospun nanofibers; indocyanine green; wound dressing.

Figure 1

Visual appearance and ultrastructure of the films: Photographs of specimens of the films of a size around 1 cm${}^2$ (a) before (left) and after (right) hydration in a physiological buffer and (b) upon hydration before (left) and after (right) cross-linking. The green spots in the dry sample are usual defects originating from occasional instabilities and dripping in the process of electrospinning. Note that the sample before cross-linking undergoes partial dissolution upon soaking in physiological buffer for 30 min, and so it is only partially recovered after hydration. (c) Spectrum of optical extinction of a cross-linked sample after a slight hydration taken with a V-770 device from Jasco (Tokyo, Japan). The pink line represents the optical emission of the diode laser used for welding. (d) Representative SEM micrograph of a sample before hydration. The scale bar corresponds to 5 $\mathsf{\mu }$m.

Figure 2

Tensile testing of the films and its microscopic interpretation: (a) representative stress–strain curves for the samples before (blue) and after (green) hydration in physiological buffer both before (dotted) and after (continuous) cross-linking. All curves were drawn from the nominal thickness of the films in air, i.e., 11 $\mathsf{\mu }$m. The 10 $\mathsf{\mu }$m × 6 $\mathsf{\mu }$m SEM micrographs of cross-linked (b,c) and as-spun (d,e) samples both before (b,d) and after (c,e) hydration. (f) Relevant distributions of fiber diameters computed both before (blue) and after (green) hydration, and before (light) and after (dark) cross-linking. Note that it was impossible to assess the fiber diameters in the case of the as-spun samples after hydration due to their largely compromised morphology.

Figure 3

Laser bonding to biological tissue and its mechanical strength: Photographs of films welded to a segment of rabbit tendon (a) and a simulated wound in human skin (b). The irradiated spots look clearer than their neighborhood probably due to the photobleaching of ICG and an ultrastructural modification of the mats. (c) Snapshots taken during a measuring run in the case of shear testing of the adhesion between a sample and a piece of rabbit tendon. (d) Relevant stress–strain curve calculated by normalizing by the total nominal surface area of the 20 spots. The arrows roughly correspond to the snapshots reported in panel (c) and illustrate that the breakdown of the seam occurs by the progressive failure of individual spots one by one or in small subgroups.