A facile approach towards fabrication of multi-walled nanotubes embedded polyurethane high performance nanocomposite with efficient shape recovery

Shape-memory responses compared between random and aligned electrospun fibrous mats

Significant progress has been made in the design of smart fibers toward achieving improved efficacy in tissue regeneration. While electrospun fibers can be engineered with shape memory capability, both the fiber structure and applied shape-programming parameters are the determinants of final performance in applications. Herein, we report a comparison study on the shape memory responses compared between electrospun random and aligned fibers by varying the programming temperature T _prog and the deforming strain ε _deform . A PLLA-PHBV (6:4 mass ratio) polymer blend was first electrospun into random and aligned fibrous mat forms; thereafter, the effects of applying specific T _prog (37°C and 46°C) and ε _deform (30%, 50%, and 100%) on the morphological change, shape recovery efficiency, and switching temperature T _sw of the two types of fibrous structures were examined under stress-free condition, while the maximum recovery stress σ _max was determined under constrained recovery condition. It was identified that the applied T _prog had less impact on fiber morphology, but increasing ε _deform gave rise to attenuation in fiber diameters and bettering in fiber orientation, especially for random fibers. The efficiency of shape recovery was found to correlate with both the applied T _prog and ε _deform , with the aligned fibers exhibiting relatively higher recovery ability than the random counterpart. Moreover, T _sw was found to be close to T _prog , thereby revealing a temperature memory effect in the PLLA-PHBV fibers, with the aligned fibers showing more proximity, while the σ _max generated was ε _deform -dependent and 2.1-3.4 folds stronger for the aligned one in comparison with the random counterpart. Overall, the aligned fibers generally demonstrated better shape memory properties, which can be attributed to the macroscopic structural orderliness and increased molecular orientation and crystallinity imparted during the shape-programming process. Finally, the feasibility of using the shape memory effect to enable a mechanoactive fibrous substrate for regulating osteogenic differentiation of stem cells was demonstrated with the use of aligned fibers.

Enhanced Shape Memory Metal-Coordinated Poly(aryl ether ketone)s with Tunable Gradient-Deformation Behaviors as well as Self-Healing and Reprocessing Abilities

Reversible dynamic bonds are able to crack and recombine upon external stimuli, which endow polymers with exceptional self-healing, reprocessing, and reversible deformation ability. In this paper, we integrated the metal coordination bonds into shape memory poly(aryl ether ketone) (PAEK) to fabricate smart materials with multifunctionalities. Through tuning the metal ion content and species, the enhancement of shape memory behaviors was achieved, including the high recovery ratio (over 98%) and fixity ratio (over 98%), which was closely related to the synergic effect of the intrinsic motion ability of PAEK matrix and the cracking-recombination of coordination bonds. Besides, through the combination of the components with different Cu²⁺ contents, in addition to the components with Fe²⁺ coordination bonds, we fabricated the gradient shape memory structures with controllable shape memory and recovery behaviors. The manipulation of gradient coordination bonds resulted in different shape recovery speeds and directions. Furthermore, due to the dynamic cracking-recombination of coordination bonds, the metal-coordinated PAEK material exhibited the great self-healing and reprocessing performances, which were significant for largely extending its application range.