Abstract
Porous electrospun poly(ε-caprolactone) (PCL) fibres were produced through a non-solvent induced phase separation mechanism, using binary solvent systems with different properties. The effect of the solvent properties on the size and surface morphology of electrospun PCL fibres was investigated. Chloroform (CF), dichloromethane (DCM), tetrahydrofuran (THF) and formic acid (FA) were used as good solvents in mixtures with a poor solvent, dimethyl sulfoxide (DMSO), in order to generate pores on the fibre surface. The production of porous, bead free fibres with an average diameter ranging from 1470 to 2270nm was achieved using 12.5% w/v PCL in CF/DMSO solution with good/poor solvent ratios varying from 75% to 90% v/v at the applied voltage of 15kV, a spinning distance of 20cm, and the feed flow rate of 1ml/h. DCM and THF were proven to be less suitable good solvents for the process due to the formation of a solid skin on the jet surface, caused by the limited diffusivity of the polymer molecules from the jet surface to the liquid core and its subsequent collapse. FA was found to be unsuitable due to its similar evaporation rate to DMSO. The pore formation was favoured at high good/poor solvent ratios, whereas, the production of fibres with ribbon cross sections or fibres with beads was more pronounced at low good/poor solvent ratios. Data fitting was used for the development of a second order polynomial equation, correlating the produced fibre average diameter to the solution parameters (conductivity, surface tension, and viscosity), for the given polymer and solvent systems, under the specific experimental conditions used in this study. The ternary mixture compositions that lead to the formation of porous fibres were mapped on a ternary graph.
Highlights
Electrospinning is a straightforward method that uses an external electric field to produce polymer fibres with diameters down to nanometre scale [8]
The role of the scaffolds is to mimic the behaviour of the extracellular matrix (ECM) and provide the appropriate environment for the cellular growth, a porous fibrous structure is required in order to improve the cell attachment on the scaffold [23,26]
Four different good solvents were used in this study, in order to investigate their effect on the morphology and size of the obtained fibres
Summary
Electrospinning is a straightforward method that uses an external electric field to produce polymer fibres with diameters down to nanometre scale [8]. Megelski et al [22] investigated the phase separation mechanism during electrospinning of PS in a THF solution They identified two different phase separation mechanisms responsible for the pore formation: Thermal Induced Phase Separation (TIPS), caused by lowering the temperature on the fibres due to solvent evaporation and Vapour Induced Phase Separation (VIPS), induced by absorption of water vapour from the atmosphere. A different approach involves the addition of non-solvent with higher boiling point than that of the good solvent, in the polymer solution prior to electrospinning (non-solvent induced phase separation, NIPS) [27,19,31,9].
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