Abstract
Shrinkage is observed in many electrospun membranes. The stretched conformation of the macromolecular chains has been proposed as the possible cause. However, so far, our understanding of the fundamentals is still qualitative and cannot provide much help in the shrinkage control. In this paper, based on the crimped fibers after stimulus-induced shrinkage, a clear evidence of buckling, the gradient pre-strain field in the cross-section of the electrospun fibers, which is the result of a gradient solidification field and a tensile force in the fibers during electrospinning, is identified as the underlying mechanism for the stimulus-induced shrinkage. Subsequently, two buckling conditions are derived. Subsequently, a series of experiments are carried out to reveal the influence of four typical processing parameters (namely, the applied voltage, solution concentration, distance between electrodes, and rotation speed of collector), which are highly relevant to the formation of the gradient pre-strain field. It is concluded that there are some different ways to achieve the required shrinkage ratios in two in-plane directions (i.e., the rotational and transverse directions of the roller collector). Some of the combinations of these parameters are more effective at achieving high uniformity than others. Hence, it is possible to optimize the processing parameters to produce high-quality membranes with well-controlled shrinkage in both in-plane directions.
Highlights
Electrospinning is a commonly used technology for producing fiber/nanofiber membranes and has been widely used in tissue engineering, filtration systems, flexible electronics, etc. [1,2,3,4,5,6]
The scanning electron microscope (SEM) images of the as-fabricated membrane samples and the distribution of the fiber alignment in three samples fabricated at different rotation speeds are presented in Figures S4 and S5 in the Supplementary Materials
About 4% shrinkage in both directions as we observed during taking the membranes out of the roller does not induce any apparent crimping in the fibers
Summary
Electrospinning is a commonly used technology for producing fiber/nanofiber membranes and has been widely used in tissue engineering, filtration systems, flexible electronics, etc. [1,2,3,4,5,6]. Many electrospinning fiber membranes (e.g., polyvinyl alcohol (PVA), poly (lactic acid) (PLA), poly(lactide-co-glycolide) (PLGA), polysulfone (PSF), polyvinylpyrrolidone (PVP), poly-ε-caprolactone (PCL)) shrink under certain conditions, e.g., upon heating and/or immersing in a right solvent [4,5,7,8,9,10,11,12] Such a kind of shrinkage may cause some serious problems (such as scaffold deformation, collapse, etc.) in tissue engineering applications, but they can be utilized, e.g., to prepare crimped fibers and self-folding electrospun scaffolds [4,5,9,13]. It leads to a steady high molecular orientation and is frozen due to the rapid evaporation of the solvent
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