Nanocomposite electrospun fibers of poly(ε-caprolactone)/bioactive glass with shape memory properties

Abstract

Electrospun fibers of shape memory triethoxysilane-terminated poly(epsilon-caprolactone) (PCL-TES) loaded with bioactive glasses (BG) are here presented. Unloaded PCL-TES, as well as PCL/BG nanocomposite fibers, are also considered for comparison. It is proposed that hydrolysis and condensation reactions take place between triethoxysilane groups of the polymer and the silanol groups at the BG particle surface, thus generating additional crosslinking points with respect to those present in the PCL-TES system. The as-spun PCL-TES/BG fibers display excellent shape memory properties, in terms of shape fixity and shape recovery ratios, without the need of a thermal crosslinking treatment. BG particles confer in vitro bioactivity to PCL-based nanocomposite fibers and favor the precipitation of hydroxycarbonate apatite on the fiber surface. Preliminary cytocompatibility tests demonstrate that the addition of BG particles to PCL-based polymer does not inhibit ST-2 cell viability. This novel approach of using bioactive glasses not only for their biological properties, but also for the enhancement of shape memory properties of PCL-based polymers, widens the versatility and suitability of the obtained composite fibers for a huge portfolio of biomedical applications.

Keywords: Benign solvents; Bioactive glasses; Bioactivity; Electrospinning; PCL-TES; Shape memory polymers.

Graphical abstract

Fig. 1

SEM micrographs of the electrospun meshes obtained from glacial acetic acid solutions of (A) PCL, (B) PCL/BG, (C) PCL-TES, (D) PCL-TES/BG. Scale bars = 2 μm. TEM images of (E) PCL/BG as spun fibers, (F) PCL-TES/BG as spun fibers. Scale bars = 500 nm.

Fig. 2

Scheme of the proposed mechanism of polymer/BG binding in the PCL-TES/BG system with the formation of additional crosslinking points derived from the hydrolysis and condensation reactions of PCL-TES chain ends with BG particle surface.

Fig. 3

A) TGA curves of PCL (black), PCL/BG (blue), PCL-TES (red), PCL-TES/BG (green) and BG particles (pink); B) DSC heating scan after cooling of PCL (black), PCL/BG (blue), PCL-TES (red) and PCL-TES/BG (green). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 4

A) Thermo-mechanical cycle for evaluating shape memory properties: a) sample is kept at 80 °C (above polymer T_m) at a ε₀ = 0%; a-b deformation stage load control (loading rate: 0.04 N min⁻¹) up to ε_applied; b-c cooling under fixed strain; c-d unloading (sample deformation in d is ε_unload) and d-e heating and recovery up to ε_rec. B) Normalized shape recovery evolution over temperature for the different samples: PCL-TES post-crosslinked (blue), PCL-TES/BG as spun (red) and PCL-TES/BG post-crosslinked (black). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 5

SEM images of electrospun meshes after 7 days of incubation in simulated body fluid. (A) PCL, (B) PCL/BG, (C) PCL-TES, (D) PCL-TES/BG. Scale bar = 1 μm.

Fig. 6

SEM/EDX analysis on PCL/BG and PCL-TES/BG samples before (d0) and after 7 days (d7) of immersion in SBF. Scale bar = 10 μm.

Fig. 7

FTIR analysis of PCL, PCL-TES, PCL/BG and PCL-TES/BG fibers as-spun (A) and after 7 days of immersion in SBF (B). Main peaks indicated on the spectra are discussed in the text.

Fig. 8

(A) WST-8 assay results: OD at 450 nm after 1 and 7 days from cell seeding; (B,C) cell nuclei (blue, DAPI) and cytoskeleton (red, rhodamine phalloidin) of ST-2 cells on PCL-TES (B) and PCL-TES/BG (C) 7 days after seeding. Scale bar = 50 μm. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)