As one of the most promising intelligent materials, polymeric hydrogel actuators could produce reversible shape change upon external stimuli. Although complex shape deformation from 2D to 3D have been achieved, the realization of actuating behavior from 3D to 3D is still a significant challenge. Herein, an effective strategy to develop a novel bilayer hollow spherical hydrogel actuator is proposed. Through immersing a Ca2+ incorporated gelatin core into alginate solution, an ionic-strength-responsive alginate layer will be formed along the gelatin core via alginate-Ca2+ crosslinks, and then another thermo-responsive alginate-poly(2-(dimethylamino)ethyl methacrylate)(Alg-PDMAEMA) layer is introduced to achieve a bilayer hydrogel with ionic strength and temperature dual responsiveness. A hollow hydrogel capsule could be obtained if a spherical gelatin core is applied, and it could produce complex shape deformations from 3D to 3D upon the trigger of ionic strength and temperatures changes. The present work may offer new inspirations for the development of novel intelligent polymeric hydrogel actuators.

中文翻译：

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离子强度和热双响应双层空心球形水凝胶致动器。

作为最有前途的智能材料之一，聚合物水凝胶致动器可以在外部刺激下产生可逆的形状变化。尽管已经实现了从2D到3D的复杂形状变形，但是实现从3D到3D的驱动行为仍然是一个重大挑战。本文提出了一种开发新型双层空心球形水凝胶致动器的有效策略。通过将掺入Ca2 +的明胶核浸入藻酸盐溶液中，将通过藻酸盐-Ca2 +交联沿明胶核形成离子强度响应性藻酸盐层，然后再形成另一个热响应性藻酸盐-聚甲基丙烯酸2-（二甲氨基）乙酯引入（Alg-PDMAEMA）层可实现具有离子强度和温度双重响应性的双层水凝胶。如果使用球形明胶芯，则可以获得空心水凝胶胶囊，并且在触发离子强度和温度变化时，它可能会产生从3D到3D的复杂形状变形。本工作可能会为新型智能聚合物水凝胶致动器的开发提供新的启示。