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Shape-Shifting Liquid Crystals Created from 3D Printing

Researchers from the Department of Mechanical and Aerospace Engineering at the UC San Diego Jacobs School of Engineering present a proof-of-concept for 3D printed liquid crystals by controlling the printing temperature.

3D printing has a wide range of applications across many fields, methods for 3D printing makes use of different types of materials for constructing the printed product. A new method of 3D printing demonstrated by researchers from UC San Diego shows how tuning the printing temperature could make the manufacturing process easier to control. Flexibility in the material is important in controlling the printing of soft robots, artificial muscles, and wearable devices.

The team of researchers was led by Professor Cai Shengqiang, and showed that they were able to control the printing temperature of liquid crystal elastomer (LCE) to determine the material’s malleability, and ability to contract. Exposure to heat at specific areas could also change the degree stiffness.

In this proof-of-concept, which was published in Science Advances showed that with a single ink, the stiffness of the resulting structure was different throughout. This concept was inspired by examples in biology and nature. For example, the resulting LCE structure is able to be flexible at some parts and contract at others, much like a combination of muscle and tendon. The researchers took cues from the beak of the squid, which is extremely stiff at the tip but much softer and malleable where it is connected to the mouth of the squid.

“3D-printing is a great tool to make so many different things–and it’s even better now that we can print structures that can contract and stiffen as desired under certain stimuli, in this case, heat,” said Wang Zijun, the paper’s first author and a Ph.D. student in Professor Cai’s research group.

Properties of the LCE was analysed to understand how it could be manipulated. They found that LCE filament is made of a shell and a core. While the shell cools off quickly after printing, becoming stiffer, the core cools more slowly, remaining more malleable.

As a result, researchers were able to determine how to control several parameters in the printing process, especially temperature, to tune the mechanical properties of LCE. They found that the higher the printing temperature, the more flexible and malleable the material. While the preparation of the LCE ink takes a few days, the actual 3D print can be done in just one to two hours, depending on the geometry of the structure being printed.

“Based on the relationship between the properties of LCE filament and printing parameters, it’s easy to construct structures with graded material properties,” said Professor Cai.

The team also printed structures made up of two layers of LCE with different properties to demonstrate that the material had degrees of freedom to contract. Lattice structures were also printed that the researchers suggest could be applied in the medical field.

A tube made of LCE was also printed that showed that at high temperatures it could stick to a rigid glass plate for a much long period. This property could be useful in development of robotic feet and grippers. Contraction of LCE could be triggered by hot water, heat-sensitive particles or particles that absorb light and convert it to heat – including black ink powder or graphene.

The research team is now looking to modify the LCE ink for the 3D printed structures to be self-repairable, reprogrammable, and recyclable. [APBN]