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Princeton Researchers Create Amazing New Substance
Posted by Okachinepa on 01/01/2025 @ 
SynEVOL Source
Stretchable, Flexible, Recyclable 3D Printed Plastic
Courtesy of SynEvol
Credit: Princeton University


Engineers at Princeton have created a scalable 3D printing method that allows them to create soft polymers with tunable stretchiness and flexibility, as well as being economical and recyclable—a combination of properties that are rarely found in materials that are sold commercially.

A team lead by Emily Davidson described how they produced 3D-printed objects with adjustable stiffness using thermoplastic elastomers, a type of commonly accessible polymers, in a research published in Advanced Functional Materials. The developers were able to program the physical characteristics of the plastic by creating the print path for the 3D printer. This allowed the gadgets to flex and stretch in one direction while staying stiff in another.

The potential uses of this approach in areas like soft robotics, medical devices, prostheses, lightweight helmets, and customized high-performance shoe soles were emphasized by Davidson, an assistant professor of chemical and biological engineering.

The smallest level of the material's interior structure is crucial to its performance. The study team employed a block copolymer type that, within a stretchy polymer matrix, generates stiff cylindrical structures that are 5-7 nanometers thick (human hair is roughly 90,000 nanometers thick). These tiny cylinders were oriented by the researchers via 3D printing, resulting in a 3D printed material that is soft and elastic in almost every direction yet hard in one. These cylinders can be oriented in many orientations within a single object by designers, creating soft constructions that show stretchiness and rigidity in different areas.

"We are able to control the nanostructures that the elastomer we are using forms," Davidson stated. This gives designers a lot of influence over the final goods. "We are able to design materials with specific properties in various directions."

Selecting the appropriate polymer was the first stage in creating this procedure. The block copolymer that the researchers selected is a thermoplastic elastomer, which hardens into an elastic substance when cooled but can be heated and treated as a polymer melt. Polymers are extended chains of interconnected molecules at the molecular level. Block copolymers are composed of many homopolymers joined to one another, while traditional homopolymers are lengthy chains of a single repeating monomer. These distinct areas of a block copolymer chain resemble water and oil Rather than combining, they separate. This characteristic was employed by the researchers to create a material with stiff cylinders inside a flexible matrix.

The researchers created a 3D printing method that successfully induces the alignment of these stiff nanostructures by applying their understanding of how these block copolymer nanostructures originate and react to flow. The researchers examined how the physical characteristics of the printed material may be regulated by printing rate and controlled under-extrusion.

The lead author of the paper, Alice Fergerson, a Princeton graduate student, discussed the method and the crucial part thermal annealing—the regulated heating and cooling of a material—plays.

"I think one of the coolest things about this technique is the many functions that thermal annealing performs—it not only significantly enhances the properties after printing, but it also makes the items we print reusable and even capable of self-healing in the event that they break or get damaged."

One of the project's objectives, according to Davidson, was to develop soft materials with regionally adjustable mechanical qualities in a way that is both economical and scalable for industry. Materials like liquid crystal elastomers can be used to produce comparable structures with regionally controlled characteristics. However, according to Davidson, those materials are costly (up to $2.50 per gram) and necessitate a multi-step manufacturing procedure that includes meticulously regulated extrusion and UV light exposure. Davidson's lab uses thermoplastic elastomers that can be manufactured using a commercial 3D printer and cost around one cent per gram.

The researchers have demonstrated that their method can add useful additives to thermoplastic elastomers without compromising material property control. In one instance, they introduced an organic compound created by the group of Professor Lynn Loo that causes the plastic to glow red when exposed to UV radiation. They also showed off the printer's capacity to create intricate, multi-layered structures, such as a little plastic vase and printed lettering that spelled out PRINCETON using sharp turns.

By improving the internal nanostructures' order and perfection, annealing is essential to their process. According to Davidson, annealing also makes the material's self-healing qualities possible. The researchers can anneal a flexible piece of the printed plastic to reattach it after cutting it as part of the projectthe substance. The material that was restored showed the same traits as the original sample. The original and the restored material showed "no significant differences," according to the researchers.

In the future, the study team anticipates investigating novel 3D printable designs that will work with wearable electronics and biomedical devices, among other uses.