Four-dimensional (4D) printing relies on multimaterial printing, reinforcement patterns, or micro/nanofibrous additives as programmable tools to achieve desired shape reconfigurations. However, existing programming approaches still follow the so-called origami design principle to generate reconfigurable structures by self-folding stacked 2D materials, particularly at small scales. Here, we propose a programmable modular design that directly constructs 3D reconfigurable microstructures capable of sophisticated 3D-to-3D shape transformations by assembling 4D micro-building blocks. 4D direct laser writing is used to print two-photon polymerizable, stimuli-responsive hydrogels to construct building blocks at micrometer scales. Denavit-Hartenberg (DH) parameters, used to define robotic arm kinematics, are introduced as guidelines for how to assemble the micro-building blocks and plan the 3D motion of assembled chain blocks. Last, a 3D-printed microscaled transformer capable of changing its shape from a race car to a humanoid robot is devised and fabricated using the DH parameters to guide the motion of various assembled compartments.

中文翻译：

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四维微构建基块。

四维（4D）打印依靠多材料打印，增强图案或微/纳米纤维添加剂作为可编程工具来实现所需的形状重新配置。然而，现有的编程方法仍然遵循所谓的折纸设计原理，以通过自折叠堆叠的2D材料来生成可重新配置的结构，特别是在小规模的情况下。在这里，我们提出了一种可编程的模块化设计，该设计可以通过组装4D微型积木来直接构建能够进行复杂的3D到3D形状转换的3D可重构微结构。4D直接激光写法用于打印两光子可聚合的，对刺激有反应的水凝胶，以微米级构建积木。Denavit-Hartenberg（DH）参数，用于定义机械臂运动学，介绍了有关如何组装微型构建块和计划组装的链块的3D运动的准则。最后，使用DH参数设计和制造了3D打印的微型变压器，该变压器能够将其形状从赛车变为类人机器人，以指导各种组装隔间的运动。