New 3D Printing Method to Print Shape-Shifting Objects

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新加坡技术与设计大学（SUTD）的研究人员与佐治亚理工学院合作，最近开发了一种新方法来3D打印形状转换对象。

Martin L. Dunn和Zhen Ding的团队描述了新方法Science Advances作为利用复合聚合物打印3D体系结构的一种，能够在加热后直接转换为新的永久配置¹。

The technology of creating a three-dimensional (3D) object often involves the use of a computer aided design (CAD) or a digital file created by a 3D modelling software or a 3D scanner. Once the design is established, successive two dimensional (2D) slices are laid on top of each other to develop the final 3D object through a process known as additive manufacturing (AM), or more commonly 3D printing²。

3D打印技术的使用使得可以打印由聚合物，陶瓷，金属，3D印刷和纳米复合材料组成的3D结构欧洲杯足球竞彩²。3D printing technology has therefore found a wide variety of applications in areas such as of manufacturing, the automotive industry, robotics, environmental sciences, biology and medicine.

The process of integration of 3D printing and active material technologies in order to create structures that can change conformations/shapes with an environmental stimulus such as heat or moisture is called four-dimensional (4D) printing¹。

活性聚合物，例如水凝胶和形状记忆聚合物（SMP），是4D打印中使用最广泛的活性聚合物。在基于水凝胶的4D印刷品中，非网状聚合物与水凝胶集成¹。当4D打印浸入溶剂中时，水凝胶膨胀，在水凝胶和非固定聚合物之间形成不匹配菌株，从而导致4D结构形状的总体变化¹。

This diffusion-based process is relatively slow, and the actuated final shape is not stable due to the possibility of the hydrogel to lose water with the environmental condition. As a result of the softness of the hydrogels, the 4D prints utilizing hydrogels often lack stiffness, however, this can be avoided by combining the hydrogel with SMPs to create composites¹。

基于SMP的4D打印相对较硬，与水凝胶4D印刷品相比，也具有更高的致动速度¹。但是，使用SMP的4D打印是一个多步骤过程，涉及3D打印，热力学编程的合成和处理，包括加热，机械负载，冷却和负载和部署/驱动，需要良好控制的热环境¹。Therefore, 4D printing with SMPs also requires well-controlled thermal environment, and special jigs and fixtures to apply mechanical loads¹。

To simplify 4D printing with SMPs, Martin L. Dunn and Zhen Ding’s team used a composite consisting of a glassy shape memory polymer and an elastomer, that is programmed with a built-in compressive strain. They then integrated the programming steps into the 3D printing process by controlling the photopolymerization step during printing^1,3。

所得的4D结构在高空间分辨率下具有复杂的几何形式，同时还表现出具有控制内置菌株的高保真功能。涉及简单加热的部署步骤会导致玻璃记忆聚合物变软，从而使弹性体释放其压力，从而导致形状永久性急剧变化³。

This new permanent shape can also be reprogrammed into multiple subsequent shapes. To demonstrate their new process, the team created several models, including a flower that opens its petals upon heating and a lattice model that can expand up to eight times the original size after heating³。

研究人员认为，他们生产基于SMP的4D结构的新方法可以改善印刷时间和最高90％的材料节省，同时还可以从设计和制造工作流中消除机械编程的麻烦³。

这种创建4D结构的简单方法在医疗技术领域以及航空航天和消费品（例如包装材料）中具有有希望的应用欧洲杯足球竞彩¹。

References:

1. "New 3-D Printing Method Creates Shape-shifting Objects."欧洲杯线上买球Sciencedaily。欧洲杯线上买球Sciencedaily, 12 Apr. 2017. Web.https://www.欧洲杯线上买球sciencedaily.com/releases/2017/04/170412155112.htm。
2. Strikwerda, Pieter, and Robert Dehue. "What Is 3D Printing? How Does 3D Printing Work? Learn How to 3D Print."3D打印。网络。https://3dprinting.com/what-is-3d-printing。。
3. Ding, Zhen, Chao Yuan, Xirui Peng, Tiejun Wang, H. Jerry Qi, and Martin L. Dunn. "Direct 4D Printing via Active Composite Materials."Science Advances。American Association for the Advancement of Science, 01 Apr. 2017. Web.http://advances.sciencemag.org/content/3/4/e1602890/tab-pdf。