A proof of concept to define the parameters affecting poly-L-lactide-co-poly-ε-caprolactone shape memory electrospun nanofibers for biomedical applications

Abstract

This study is a proof of concept performed to evaluate process parameters affecting shape memory effect of copolymer poly-L-lactide-co-poly-ε-caprolactone (PLA:PCL) 70:30 ratio based nanofibrous scaffolds. A design of experiment (DOE) statistical approach was used to define the interaction between independent material and process variables related to electrospun scaffold manufacturing, such as polymer solution concentration (w/v%), spinning time (min), and needle size (Gauge), and their influence on Rf% (ability of the scaffold to maintain the induced temporary shape) and Rr% (ability of the scaffold to recover its original shape) outputs. A mathematical model was obtained from DOE useful to predict scaffold Rf% and Rr% values. PLA-PCL 15% w/v, 22G needle, and 20-min spinning time were selected to confirm the data obtained from theoretical model. Subsequent morphological (SEM), chemical-physical (GPC and DSC), mechanical (uniaxial tensile tests), and biological (cell viability and adhesion) characterizations were performed.

Keywords: Design of experiment; Electrospinning; Nanofibers; Poly-L-lactide-co-poly-ε-caprolactone; Shape memory polymer.

Fig. 1

a DOE (CCD 2³ + 3) set up and minimum (− 1), maximum (+ 1) and intermediate (0) values of independent variables (x) concentration (x₁), needle size (x₂), and spinning time (x₃). b Experimental design and results obtained for dependent variables y₁ (Rf%) and y₂ (Rr%)

Fig. 2

a Pareto diagram for Rf% (y₁) dependent variable (p value < 0.0001). b Deviation plot for Rf% (y₁) dependent variable (R²: 87.58%). c Pareto diagram for Rr% (y₂) dependent variable (p value < 0.0001). d Deviation plot for Rr% (y₂) dependent variable (R²: 89.89%)

Fig. 3

Contour plot concentration vs needle at three different times for dependent variable y₁ Rf% and y₂ Rr%

Fig. 4

Shape memory treatment (SMT). a Scaffold configuration before treatment, C1. b After first heating treatment (T₁ > Tg°) and cooling bath (T₂ < Tg°), scaffolds maintained rolled shape (configuration C2) and c after temperature treatment close to Tg° (37° C), scaffolds recovered original shape (configuration C1r). Morphological characterization of 15% PLA-PCL electrospun nanofibers obtained using 22 G needle for 20 min spinning time before SMT. d SEM image. e Fiber porosity analysis. f Fiber orientation analysis. Morphological characterization after SMT. g SEM image. h Fiber porosity analysis. i Fiber orientation analysis

Fig. 5

a Results of GPC analyses reporting Mw, Mn, and PI of PLA-PCL powder and non-irradiated and gamma-irradiated PLA-PCL electrospun scaffolds. b–d Results of DSC analysis performed on b PLA-PCL powder; c non-irradiated PLA-PCL electrospun nanofibers; and d gamma-irradiated PLA-PCL electrospun nanofibers

Fig. 6

a Results of cell viability % determined by MTT assay on NHDF, incubated with non-irradiated and gamma-irradiated PLA-PCL electrospun scaffold after 7 days of incubation and 6 h after SMT. b–g Merge of LIVE (green)/DEAD (red) staining of Human Dermal Fibroblast after 7 days of incubation: b control; c non-gamma-irradiated shape memory electrospun scaffold; d gamma-irradiated shape memory electrospun scaffold. DAPI staining of NHDF after 7 days of incubation: e control; f non-gamma-irradiated shape memory electrospun scaffold; g gamma-irradiated shape memory electrospun scaffold. SEM images of Human Dermal Fibroblast after 7 days of incubation on h non-gamma-irradiated shape memory electrospun scaffold and i gamma-irradiated shape memory electrospun scaffold