Shape-memory properties of degradable electrospun scaffolds based on hollow microfibers


Multifunctional thermo-responsive and degradable porous materials exhibiting a shape-memory effect are explored in biomedicine as actively moving scaffolds or switchable substrates. One example are electrospun shape-memory polymer-based scaffolds comprising solid microfibers or nanofibers. In this work, we explored whether fibrous scaffolds composed of hollow microfibers can be prepared from a degradable shape-memory copolyetheresterurethane named PDC, which is composed of crystallizable oligo(p-dioxanone) (OPDO) hard and oligo(ε-caprolactone) (OCL) switching segments. Scaffolds based on PDC microfibers with identical outer diameter around 1.4 ± 0.3 µm and different hollowness of 0%, 13%, and 33% related to the outer diameter (determined by scanning electron microscopy) were prepared by coaxial electrospinning using poly(ethylene glycol) (PEG) as sacrificial core. Thermal characterization of the scaffolds by differential scanning calorimetry (DSC) and thermogravimetric analysis confirmed a successful removal of PEG. DSC results revealed that the degree of crystallinity increased with increasing microfiber hollowness. The Young's modulus and the failure stress of the prepared scaffolds determined by tensile tests at ambient temperature and 50 °C were found to increase with rising hollowness, while the elongation at break decreased. Cyclic, thermomechanical uniaxial tensile tests showed a pronounced dual-shape effect for all tested materials. Scaffolds comprising microfibers with a hollowness of 33% exhibited the highest shape recovery ratio. Here, we could demonstrate that the degree of hollowness of microfibers, which alters the degree of macromolecular chain orientation, is a suitable design parameter to tailor the mechanical properties as well as the shape-memory performance of electrospun shape-memory polymer fibrous scaffolds.
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