Researchers Use 3D Printing Technology To Develop Magical New Materials

Engineers at Princeton University have developed a scalable 3D printing technology, which is used to produce flexible plastics with customizable extensibility and flexibility, but also has recyclability and cost-effectiveness – these characteristics are rarely found in commercial materials at the same time.

Unlike similar materials that require complex processing, this plastic can be made with a 3D printer.

In a study published in Advanced Functional Materials, Emily Davidson Davidson) introduced in detail how they used thermoplastic elastomer, a widely used polymer, to produce 3D printing structures with adjustable stiffness. By designing the printing path of the 3D printer, engineers can program the physical properties of the plastic, so that the device can stretch and bend in one direction and remain rigid in the other.

Davidson, assistant professor of chemical and biological engineering, emphasized the potential applications of this technology in soft robots, medical equipment, artificial limbs, lightweight helmets and customized high-performance soles.

The key to material performance lies in its smallest internal structure. The research team used a block copolymer, which can form a hard cylindrical structure with a thickness of 5-7 nm (in contrast, the thickness of human hair is about 90000 nm) in an elastic polymer matrix. The researchers used 3D printing technology to orient these nanoscale cylinders, thus obtaining a 3D printing material that is hard in one direction but soft and elastic in almost all other directions. Designers can orient these cylinders to different directions of a single object, thus designing soft structures that exhibit hardness and extensibility in different areas of the object.

"The elastomers we use can form nanostructures that we can control," Davidson said. This allows the designer to control the finished product to a large extent. We can create materials with customized characteristics in different directions ".

The first step in developing this process is to select suitable polymers. The researchers chose a thermoplastic elastomer, which is a block copolymer that can be heated and processed as a polymer melt, but will solidify into an elastic material after cooling. At the molecular level, polymers are long chains of interconnected molecules. The traditional homopolymer is a long chain composed of a repeating molecule, while the block copolymer is composed of different homopolymers connected with each other. These different regions on the block copolymer chain are like oil and water, they separate from each other rather than mix. The researchers used this property to produce a material containing hard cylinders in a flexible matrix.

Using their understanding of how these block copolymer nanostructures form and their reaction to flow, researchers have developed a three-dimensional printing technology that can effectively facilitate the alignment of these hard nanostructures. The researchers analyzed how to use printing speed and controlled under extrusion to control the physical properties of printing materials.

The first author of the article, Alice Ferguson, a graduate student of Princeton University Ferguson) introduced this technology and the key role played by thermal annealing – controlled heating and cooling of materials.

By controlling the internal structure of materials, engineers can create objects with various characteristics. Image source: Sameer A. Khan/Fotobuddy

"I think one of the coolest parts of this technology is the multiple roles played by thermal annealing - it can not only greatly improve the performance after printing, but also enable us to reuse the printed items for many times, and even self repair when the items are damaged or damaged."

Davidson said that one of the goals of the project is to create soft materials with locally adjustable mechanical properties, so that the industry can not only afford it, but also expand its scale. Similar structures with local controllable characteristics can be fabricated by using liquid crystal elastomer and other materials. But Davidson said that these materials are both expensive (up to 2.50 per gram USD and above), and needs to go through multiple processes, including carefully controlling extrusion, and then exposed to ultraviolet light. The cost of thermoplastic elastomer used by Davidson Laboratory is about 1 cent per gram, which can be used in commercial 3D Printer printing.

The researchers demonstrated the ability of their technology to add functional additives to thermoplastic elastomers without reducing the ability to control material properties. In one example, they added a The organic molecules developed by the professor's research team can make plastics emit red light under ultraviolet radiation. They also demonstrated the printer's ability to produce complex multi-layer structures, including a small plastic vase and sharp turns PRINCETON printed text.

Annealing plays a key role in their process, improving the perfection of the internal nanostructure order. Davidson said that annealing can also achieve self-healing properties of materials. As part of this work, researchers can cut and print flexible samples of plastic and reconnect the materials through annealing. The repaired material shows the same properties as the original sample. The researchers said that they observed "no significant difference" between the original material and the repair material.

Next, the research team will begin to explore new 3D printable architectures, which will be compatible with applications such as wearable electronic devices and biomedical devices.