Princeton engineers have developed an easily scalable 3D printing technique to manufacture soft plastics with programmed stretchiness and flexibility that are also recyclable and inexpensive—qualities not typically combined in commercially manufactured materials.
In an article in the journal Advanced Functional Materials, a team led by Emily Davidson reported that they used a class of widely available polymers called thermoplastic elastomers to create soft 3D printed structures with tunable stiffness. Engineers can design the print path used by the 3D printer to program the plastic’s physical properties so that a device can stretch and flex repeatedly in one direction while remaining rigid in another. Davidson, an assistant professor of chemical and biological engineering, said this approach to engineering soft architected materials could have many uses, such as soft robots, medical devices and prosthetics, strong lightweight helmets, and custom high-performance shoe soles.
The key to the material’s plastic performance is its internal structure at the tiniest level. The research team used a type of block copolymer which forms stiff cylindrical structures that are 5-7 nanometers thick (for comparison, human hair measures about 90,000 nanometers) inside a stretchy polymer matrix. The researchers used 3D printing to orient these nanoscale cylinders, which leads to a 3D printed material that is hard in one direction but soft and stretchy in nearly all others. Designers can orient these cylinders in different directions throughout a single object, leading to soft architectures which exhibit stiffness and stretchiness in different regions of an object.
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