Emerging 4D printing techniques have enabled the realization of smart materials whose shape or properties can change with time. Two important phenomena play important roles in the 4D printing of shape memory polymeric materials. First, the anisotropic deformation of the printed filaments due to residual stresses can be harnessed to create out-of-plane shape transformations. Second, the unavoidable formation of micro-defects during the printing processes often affects the programmability of the printed object. Here, we propose a design approach that harnesses these two effects occurring during fused deposition modeling to create tailor-made curved geometries from initially 2D flat disks. We first determined the size and distribution of the imperfections formed within printed structures by varying two printing parameters namely the printing speed and the number of printed materials. Spatially varying the printing speed and combining polylactic acid filaments with a softer material without shape memory properties allowed us to cover a variety of shapes from negative to positive values of the mean and Gaussian curvature. We propose an analytical model to calculate the magnitude of the maximum out-of-plane deformation from the anisotropic expansion factor of the constituting microstructures. Furthermore, we develop computational models to predict the complex shape-changing of thermally actuated 4D printed structures given the distribution of rationally introduced imperfections and we demonstrate the potential applications of such defect-based metamaterials in drug delivery systems.

新兴的 4D 打印技术使得形状或属性可随时间变化的智能材料成为可能。有两个重要现象在形状记忆聚合物材料的 4D 打印中发挥着重要作用。首先，可以利用残余应力引起的打印细丝的各向异性变形来产生面外形状转变。其次，在打印过程中不可避免地形成微缺陷，通常会影响打印对象的可编程性。在这里，我们提出了一种设计方法，利用熔融沉积建模过程中发生的这两种效应，从最初的二维平面磁盘创建定制的弯曲几何形状。我们首先通过改变两个打印参数（即打印速度和打印材料的数量）来确定打印结构内形成的缺陷的尺寸和分布。在空间上改变打印速度并将聚乳酸长丝与不具有形状记忆特性的较软材料相结合，使我们能够覆盖从平均曲率和高斯曲率的负值到正值的各种形状。我们提出了一种分析模型，用于根据构成微结构的各向异性膨胀系数计算最大面外变形的大小。此外，考虑到合理引入的缺陷的分布，我们开发了计算模型来预测热驱动 4D 打印结构的复杂形状变化，并展示了这种基于缺陷的超材料在药物输送系统中的潜在应用。