Nanofibrous ε-polycaprolactone scaffolds containing Ag-doped magnetite nanoparticles: Physicochemical characterization and biological testing for wound dressing applications in vitro and in vivo

Abstract

Skin wounds can lead to numerous complications with dangerous health consequences. In this work, magnetite nanoparticles were doped with different concentrations of antimicrobial silver (Ag) ions and incorporated into the electrospun nanofibrous ε-polycaprolactone (PCL) scaffolds. Nanoparticles and scaffolds with various Ag contents were characterized using a range of physicochemical techniques. Ag entered magnetite as cations and preferentially positioned at tetrahedral sites, introducing lattice distortions and topographic irregularities. Amorphization of the structure due to accommodation of Ag expanded the lattice in the bulk and contracted it on the surface, where broadened distribution of Fe-O coordinations was detected. Promoting spin canting and diminishing the double exchange interaction through altered distribution of ferric and ferrous ions, Ag softened the magnetism of magnetite. By making the nanoparticle structure more defective, Ag modified the interface with the polymer and promoted the protrusion of the nanoparticles from the surface of the polymeric nanofibers, thus increasing their roughness and hydrophilicity, with positive repercussions on cell adhesion and growth. Both the viability of human melanocytes and the antibacterial activity against E. coli and S. aureus increased with the concentration of Ag in the magnetite phase of the scaffolds. Skin wound healing rate in rats also increased in direct proportion with the concentration of Ag in the magnetite phase, and no abnormalities in the dermal and epidermal tissues were visible on day 10 in the treatment group. These results imply an excellent potential of these composite nanofibrous scaffolds for use as wound dressings and in other reconstructive skin therapies.

Keywords: Magnetic nanoparticles; Nanofiber; Skin; Tissue engineering; Wound healing.

Graphical abstract

Fig. 1

Flow chart for the synthesis of MNPs doped with different concentrations of Ag ions, and their incorporation inside nanofibrous PCL scaffolds.

Fig. 2(a, b)

XRD patterns for Ag-MNPs powders (a) and Ag-MNPs@PCL nanofibers (b) with different concentrations of Ag in the MN phase, along with the linear dependence of the average crystallite size of xAg-MNP on the stoichiometric parameter x.

Fig. 3

FTIR spectra of Ag-MNPs powders (a) and Ag-MNPs@PCL nanofibers (b) with different concentrations of Ag in the MN phase.

Fig. 4

Comparative XPS spectra of MNPs (0.0Ag-MNPs) and MNPs doped with the highest concentration of the Ag ions (0.2Ag-MNPs): (a) survey scan, (b) Fe 2p region, (c) O 1s region, and (d) Ag 3d region.

Fig. 5

Hysteresis loops (H–M) for MNPs doped with different concentrations of Ag ions.

Fig. 6(a–f)

FESEM micrographs showing the morphology and surface roughness profiles for Ag-MNPs with different concentrations of Ag ions: (a, b) 0.0Ag-MNPs, (c, d) 0.1Ag-MNPs and (e, f) 0.2Ag-MNPs.

Fig. 7(a–f)

FESEM micrographs of nanofibrous Ag-MNPs@PCL scaffolds with different concentrations of Ag ions: (a, b) 0.0Ag-MNPs@PCL, (c, d) 0.1Ag-MNPs@PCL, and (e, f) 0.2Ag-MNPs@PCL.

Fig. 8(a–c)

Dependency of the surface roughness of Ag-MNPs@PCL scaffolds on the concentration of Ag ions: (a) 0.0Ag-MNPs@PCL, (b) 0.1Ag-MNPs@PCL and (c) 0.2Ag-MNPs@PCL.

Fig. 9

Tensile stress-strain curve for nanofibrous Ag-MNPs@PCL scaffolds with different concentrations of Ag ions.

Fig. 10

Variation of the contact angle as a function of the concentration of Ag in the MNP phase of nanofibrous MNPs@PCL scaffolds.

Fig. 11

Cell viability after the cultivation of the HFB4 cell line in vitro on nanofibrous Ag-MNPs@PCL with different concentrations of Ag ions for 3 days.

Fig. 12(a–f

FESEM micrographs showing the HBF4 cell attachment on nanofibrous Ag-MNPs@PCL scaffolds after in vitro cultivation for 3 days: (a, b) 0.0Ag-MNPs@PCL, (c, d) 0.1Ag-MNPs@PCL and (e, f) 0.2Ag-MNPs@PCL.

Fig. 13

Antibacterial behavior of nanofibrous Ag-MNPs@PCL scaffolds with different concentrations of the Ag ion against E. coli and S. aureus after 3 days of exposure, including the representative agar plates for (b) S. aureus and (c) E. coli.

Fig. 14

Representative optical images of rat skin wound healing for Ag-MNPs@PCL nanofibrous scaffolds with different concentrations of the Ag ion after 0, 3, 7 and 10 days of treatment.

Fig. 15

Photomicrographs at 60× (a) and 40× (b–d) magnification of untreated rat skin showing the atrophy of sebaceous glands (a) as well as the necrosis of hair follicles (b). Photomicrographs of treated rat skin with 0.0Ag-MNPs@PCL (c) and 0.2Ag-MNPs@PCL (d), showing normal histological structure of the epidermis and the underlying dermal layer with the sebaceous glands and hair follicles.