4D Fabrication of Two-Way Shape Memory Polymeric Composites by Electrospinning and Melt Electrowriting.

ABSTRACT

This work presents a new method for 4D fabrication of two-way shape memory materials that are capable of reversible shapeshifting right after manufacturing, upon application of proper heating and cooling cycles. The innovative solution presented here consists in the combination of highly stretched electrospun shape memory polymer (SMP) nanofibers with a melt electrowritten elastomer. More specifically, the stretched nanofibers are made of a biocompatible thermoplastic polyurethane (TPU) with crystallizable soft segments, undergoing melt-induced contraction and crystallization-induced elongation upon heating and cooling, respectively. Reversible actuation during crystallization becomes possible due to the elastic recovery of the elastomer component, obtained by melt electrowriting of a commercial TPU filament. Thanks to the design freedom offered by additive manufacturing, the elastomer structure also has the role of guiding the shape transformation. Electrospinning and melt electrowriting process parameters are set up so to obtain smart 4D objects capable of two-way shape memory effect (SME), and the possibility of reversible and repeatable actuation is demonstrated. The two components are then combined in different proportions with the aim of tailoring the two-way SME, taking into account the effect of design parameters such as the SMP content, the elastomer pattern, and the composite thickness.