University researchers develop new 4D printing method for creation of shape changing objects

Image 1: The collapsed lattice structure being immersed in hot water

A research team comprising members of the Georgia Institute of Technology, USA, Singapore University of Technology and Design (SUTD), Singapore, and Xi’an Jiatong University, China, has developed a new 4D printing method for the creation of objects that permanently change shape in response to heat.

The method involves printing shape-memory polymers (SMPs) in layers that have each been designed to react differently upon exposure to heat. It is claimed to significantly simplify and increase the potential of 4D printing by incorporating the post-processing step of mechanical programing directly into the 3D printing process. High-resolution 4D objects are therefore said to be achievable in three steps, namely design by computer simulation, 3D printing and application of heat.

It has been suggested that the method is a game-changer as it allows for the rapid transformation of the 3D printed object into a not only different but also permanent configuration. Other 4D printing efforts by researchers at, for example, Harvard University and the Massachusetts Institute of Technology (MIT), have relied upon hydrogels to execute the transformation process but it has proved slow to take effect and quick to reverse.

To demonstrate their 4D printing method’s capabilities, the research team has produced several objects that expand or bend on being subjected to heat in the form of hot water or air. These include:

  • a collapsed lattice structure that expands almost eight times into an open configuration (see images 1 and 2);
  • a flat star-shaped structure that bends and raises up to stand on each of its points in a dome configuration (see images 3 and 4); and  
  • a flat flower comprising several layers of petals that bend, or rather curl, upwards to varying degrees as well as in sequence—from the center/top petals to the bottom/outer petals—resulting in a so-called ‘blooming’ configuration (see images 5 and 6).

It takes around five seconds for the transformations to complete and the objects to reach their intended configurations.

Zhen Ding, a postdoctorate researcher at the SUTD, explained: ‘Our composite materials at room temperature have one material that is soft but can be programmed to contain internal stress, while the other material is stiff. We use computational simulations to design composite components where the stiff material has a shape and size that prevents the release of the programmed internal stress from the soft material after 3D printing. Upon heating, the stiff material softens and allows the soft material to release its stress and this results in a change, often dramatic, in the product shape.’

The method could pave the way for components that respond in a precisely-timed way to temperature, moisture and light, and could be used in a number of applications including space structures, medical devices and robots.

The research was funded by the US Air Force Office of Scientific Research (AFOSR), the US National Science Foundation (NSF) and the Singapore National Research Foundation (NRF) through the SUTD Digital Manufacturing and Design (DManD) Centre. It was published as a research article titled Direct 4D printing via active composite components in Science Advances—a journal of the American Association for the Advancement of Science (AAAS)—on April 12, 2017.

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