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.
Background China is one of the world’s fastest-aging countries. Population aging and social-economic development show close relations. This study aims to illustrate the spatial-temporal distribution and movement of gravity centers of population aging and social-economic factors and thier spatial interaction across the provinces in China. Methods Factors of elderly population rate (EPR), elderly dependency ratio (EDR), per capita gross regional product (GRPpc), and urban population rate (UPR) were collected. Distribution patterns were detected by using global spatial autocorrelation, Kernel density estimation, and coefficient of variation. Further, Arc GIS software was used to find the gravity centers and their movement trends yearly from 2002 to 2018. The spatial interaction between the variables was investigated based on bivariate spatial autocorrelation analysis. Results The results showed a larger variety of global spatial autocorrelation indexed by Moran’s I and stable trends of dispersion degree without obvious convergence in EPR and EDR. Furthermore, the gravity centers of the proportion of EPR and EDR moved northeastward. In contrast, the economic and urbanization factors showed a southwestward movement, which exhibited an reverse trend compared to population aging indicators. Moreover, the movement rates of EPR and EDR (15.12 and 18.75 km/year, respectively) were higher than that of GRPpc (13.79 km/year) and UPR (6.89 km/year) annually during the study period. Further, the bivariate spatial autocorrelation variation is in line with the movement trends of gravity centers which showed a polarization trend of population aging and social-economic factors that the difference between southwest and northeast directions and exhibited a tendency to expand in China. Conclusions In sum, our findings revealed the difference in spatio-temporal distribution and variation between population aging and social-economic factors in China. It further indicates that the opposite movements of gravity centers and the change of the BiLISA in space which may result in the increase of the economic burden of the elderly care in northern China. Hence, future development policy should focus on the social-economic growth and distribution of old-aged supporting resources, especially in northern China.
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