Nacre-Inspired Polymeric Materials with Body Heat-Responsive Shape-Memory Effect, High Optical Transparence, and Balanced Mechanical Properties

Abstract

In this work, inspired by the hierarchical architecture of nacre, we have fabricated poly­(propylene carbonate) (PPC)/thermoplastic polyurethane (TPU) alternating multilayer films via layer-multiplying coextrusion. Based on the glass transition at around 37 °C of PPC, the multilayer films exhibited an outstanding body heat-responsive shape-memory effect (SME) with high shape fixation and recovery ratios (96.1 and 93.6%), much better than the conventional cocontinuous blend with the same compositions. It was revealed that the high phase continuity and abundantly two-dimensional interfaces both capable of promoting stress transferring and load distribution maximally contributed to the SME. Furthermore, the multilayer films showed a superior recovery stress storage capacity and the force generated by shape recovery allowed automatic expansion of the spiral in 37 °C water and efficient lifting of a load 880 times its weight. Different from the opacity of the blend, a high optical transparence was observed in the multilayers because of the parallel assembly of transparent PPC and TPU enabling light to directly pass through the films. Besides, the nacre-like films had layer debonding and layer stepwise breaking during stretching, resulting in a 90% increase in tensile strength, a 70% increase in elongation at break, and onefold improvement in yield stress, compared with those of the blend. Our approach paves a new way for developing bioinspired structural materials with excellent optical, mechanical, and shape-memory properties, which can be extended to different amorphous polymers and elastomers. Also, the materials presented herein have great potential in applications of biomedical devices and soft robotics.

In Situ Constructed Nanocrystal Structure and Its Contribution in Shape Memory Performance of Pure Polylactide

“…However, the NCs are fully compatible with aPLA molecular chains and sufficient NCs form a stress-conducting network with aPLA, with a significant enhancement effect, as shown in Figures A and A. As shown in Figure C, after taking the same tensile process at 80 °C as in Figure A, the sample was not cooled down and fixed, but the strain and temperature were both maintained to detect the relaxation of the stress . It can be seen that the strain starts to be constant around 250 s. In the following time of more than 30 min, the stress of the material is maintained at 4–5 MPa, which can represent the initial stress in the process of shape recovery of the material to some extent.…”

“…As shown in Figure 8C, after taking the same tensile process at 80 °C as in Figure 8A, the sample was not cooled down and fixed, but the strain and temperature were both maintained to detect the relaxation of the stress. 57 It can be seen that the strain starts to be constant around 250 s. In the following time of more than 30 min, the stress of the material is maintained at 4−5 MPa, which can represent the initial stress in the process of shape recovery of the material to some extent. Second, in terms of material purity, the method eliminates the adverse effects of adding other polymers, nanofillers, chemical modifications, solvents, etc., which may affect the green properties of PLA materials such as biocompatibility, biodegradability, and renewability.…”

Adaptive IR- and Water-Gating Textiles Based on Shape Memory Fibers

“…SMPs change the elastic modulus according to the stimulus; thus, they can memorize a permanent shape while maintaining a temporary shape. , SMPs have the advantages of facile shaping, high shape stability, low cost, lightweight, and biocompatibility; therefore, they have many potential applications in sensors, , actuators, and medical devices . However, SMPs have rarely been used in the field of wearable textiles because of their relatively weak mechanical properties , and extreme fabrication conditions such as hot extrusion or melt molding. , In addition, SMPs are intrinsically hydrophobic or hydrophilic and do not present both characteristics at the same time; therefore, it is difficult to obtain directional water transportation from the hydrophobic to hydrophilic side using the SMPs on their own . Porous SMP fibers can be fabricated by a nonsolvent-induced phase separation, which was suggested to prepare porous SMP films with excellent thermal insulation performance, but the practical application of a porous hairy structure of SMP films is limited due to their relatively thick structures including long SMP hairs .…”

Photo‐Programmed Deformations in Rigid Liquid Crystalline Polymers Triggered by Body Temperature

“…In this context, the moduli of body temperature-responsive hydrogels have been found to range from 10 kPa to no more than 10 MPa, [19][20][21] while the moduli of SMPs and LCEs are generally higher than those of hydrogels because they exploit phase transitions. For example, some polyurethane SMPs with T g values close to body temperature retain a modulus of ≈15-300 MPa, [4,[22][23][24][25] while those of LCEs are ≈10-200 MPa. [18,26,27] The soft nature of body temperatureresponsive polymers raises issues when considering their integration with microelectronics since the deposited conducting layers break down under large strains (i.e., during response or programming).…”