Liquid Crystal Elastomer Metamaterials with Giant Biaxial Thermal Shrinkage for Enhancing Skin Regeneration

Abstract

excellent actuation performances (e.g., large reversible strain and fast response), LCEs have been widely exploited for applications in artificial muscles, [8,9] soft actuators, [10][11][12] and flexible robots. [13][14][15][16] Owing to the liquid crystalline anisotropy, [17][18][19] the solid LCE films only offer excellent uniaxial actuation performances (i.e., along the direction of the liquid crystalline alignment), which has been utilized to enable complex modes (e.g., bending, [20,21] rolling, [22] and twisting [23] ) of actuation. Compelling application opportunities (e.g., tissue regeneration, viscera repair, and artificial organs) would be opened up, if LCEs are equipped with comparable biaxial actuation capabilities (e.g., actuation strain > 40%). However, in conventional fabrication techniques, the alignment of solid LCE films is primarily achieved by molecular interactions with command surface, [24,25] external mechanical stretching, [14] or magnetic fields, [9,26] which could not be used to fabricate LCE films with high biaxial actuation strains (e.g., >10%). While the recently developed 3D printing technique [27][28][29] enables fabrication of LCE structures with predesigned alignments, the reported biaxial actuation strain (≈20%) is not high, due to limited mechanical performances (e.g., stretchability and strength) of 3D-printed LCE structures. So far, the development of LCE materials capable of offering excellent biaxial actuation Liquid crystal elastomers (LCEs) are a class of soft active materials of increasing interest, because of their excellent actuation and optical performances. While LCEs show biomimetic mechanical properties (e.g., elastic modulus and strength) that can be matched with those of soft biological tissues, their biointegrated applications have been rarely explored, in part, due to their high actuation temperatures (typically above 60 °C) and low biaxial actuation performances (e.g., actuation strain typically below 10%). Here, unique mechanics-guided designs and fabrication schemes of LCE metamaterials are developed that allow access to unprecedented biaxial actuation strain (−53%) and biaxial coefficient of thermal expansion (−33 125 ppm K −1 ), significantly surpassing those (e.g., −20% and −5950 ppm K −1 ) reported previously. A low-temperature synthesis method with use of optimized composition ratios enables LCE metamaterials to offer reasonably high actuation stresses/strains at a substantially reduced actuation temperature (46 °C). Such biocompatible LCE metamaterials are integrated with medical dressing to develop a breathable, shrinkable, hemostatic patch as a means of noninvasive treatment. In vivo animal experiments of skin repair with both round and cross-shaped wounds demonstrate advantages of the hemostatic patch over conventional strategies (e.g., medical dressing and suturing) in accelerating skin regeneration, while avoiding scar and keloid generation.

Metamaterials and Metasurfaces: A Review from the Perspectives of Materials, Mechanisms and Advanced Metadevices

“…Kowerdziej et al [ 231 ] reported on the shortening of switching times of various soft-matter-based tunable metamaterials to improve the functionality of modern active devices. As a matter of fact, the frequency-convertible dielectric anisotropy of the dual-frequency mixture has shown to provide the opportunity to create a fast-response in-plane switching metasurface at the nanoscale, which could be tuned by an electrical signal with different frequencies [ 232 , 233 , 234 ].…”

Self-Sustained Collective Motion of Two Joint Liquid Crystal Elastomer Spring Oscillator Powered by Steady Illumination

“…Due to the unique advantages of self-excited oscillation systems, they have broad application prospects in the fields of energy acquisition, sensing with electronic skins [10], soft robotics [11][12][13], medical instruments [14][15][16][17], and motors [18]. The self-excited oscillations are generally based on responsive materials, including liquid crystal elastomers (LCEs) [19,20], dielectric elastomers [21], hydrogels [22][23][24], and ion gels [25,26]. Based on different stimuli-responsive materials and structures, different feedback mechanisms are proposed to realize energy compensation, such as the coupling of chemical reactions and large deformation [25,26], the self-shadowing effect [14,27], the coupling of liquid volatilization, and membrane deformation [28].…”

Thermally Driven Self-Rotation of a Hollow Torus Motor

“…In recent years, based on various stimuli-responsive materials including thermally responsive polymer materials [ 26 , 27 ], liquid crystal elastomers (LCEs) [ 28 , 29 , 30 , 31 ], dielectric elastomer [ 32 , 33 , 34 , 35 ], hydrogels [ 36 , 37 ], and ion gels [ 38 , 39 ], a wealth of self-excited motion modes have been proposed, such as rolling [ 40 , 41 ], vibration [ 24 , 31 , 40 , 41 ], torsion [ 41 , 42 ], stretching and shrinking [ 10 , 40 , 43 ], swinging [ 44 ], buckling [ 45 , 46 ], jumping [ 47 , 48 , 49 ], rotation [ 25 , 28 ], eversion or inversion [ 27 , 50 ], expansion and contraction [ 51 , 52 ], swimming [ 53 ] and even group behavior of several coupled self-excited oscillators [ 54 ]. The self-oscillating system is usually accompanied with damping dissipation, and its motion is a non-equilibrium dissipation process.…”