4D printed, shape-shifting structures hold significant potential for the future of engineering. Be itself-assembling trusses， 或者medical devices that help inform cell regeneration，该领域在其可能性变得实用之前仍然存在许多挑战。到目前为止，4D打印的最大挑战之一就是能够创建复杂，平滑曲折的形状。很难用单个材料和简单的结构，而需要多材的，异质的设计。
在哈佛大学，来自约翰·鲍尔森工程与应用科学学院（海洋）和WYSS生物学启发工程学院have collaborated to create the challenging 4D printed shapes. Demonstrating the potential of the technology in a paper published in theProceedings of the National Academy of Sciences(PNAS), the methods developed by the team have been used to create a frequency-shifting antenna, and a flat lattice that, when placed in salt water, takes on the shape of a human face.
新的形状变形物质
在为4D打印的文件建模时，设计人员创建了影响其制成材料的转换的功能。通过准确了解材料在刺激时如何扩展或收缩，即通过热或盐水，设计师可以精确地控制2D对象将2D对象转化为可预测的3D形状。
In the recent experiment from SEAS and Wyss, a complex lattice is built-up in several layers using the select, multi-direction repetition of a curved rib. The ribs are deposited in the process using a combination of four different elastomeric inks – each one reacting differently to the proposed stimuli.
为了实现可预测的转换，在设计阶段预定了为创建每个单独的肋骨所选择的确切位置，方向和材料。在一个示例中，对肋骨的转换进行了调整，以创建一个天线，该天线会随着从平坦的移动到圆形的形状而改变谐振频率。在更复杂的示范中，肋骨也被调整为模仿19世纪数学家卡尔·弗里德里希·高斯（Carl Friedrich Gauss）的面貌，后者奠定了差异几何形状的基础。
“使用集成的设计和制造方法，我们可以在这些印刷材料中编码复杂的'指令集'，以驱动其形状变形行为”explainsProfessor Jennifer A. Lewis, leader of the获奖Lewis Lab at Harvard and the Hansjorg Wyss Professor of Biologically Inspired Engineering,
Distilling the importance of such a project, Professor Lewis adds:
“Together, we are creating new classes of shape-shifting matter.”
表格遵循功能
The controlling geometric designs created through this research are ready to be applied to other stimuli-responsive materials, opening up exploration of 4D printed, “scalable, reversible, shape-shifting structures with unprecedented complexity.” Example applications for such a multidisciplinary approach include the soft electronic development, smart fabrics, tissue engineering and robotics, exemplified in some ways by Harvard’s other软机器人技术的发展。
Professor L. Mahadevan, a Harvard professor of physics and organismic and evolutionary biology and co-author on the study, concludes, “Form both enables and constrains function. Using mathematics and computation to design form, and a combination of multiscale geometry and multimaterial printing to realize it, we are now able to build shape-shifting structures with the potential for a range of functions.”
要进一步阅读：“Shape-shifting structured lattices via multimaterial 4D printing” is co-authored by J. William Boley, Wim M. van Rees, Charles Lissandrello, Mark N. Horenstein, Ryan L. Truby, Arda Kotikian, Jennifer A. Lewis, and L. Mahadevan.
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Featured image shows a 4D printed lattice pattern of mathemetician Carl Friedrich Gauss. Photo via Harvard University
