Researchers from Rice University’s Brown School of Engineering have shown that 3D printed ceramic structures can be reinforced to be up to 4.5x more shatter-resistant just by coating them with a thin polymer shell.
The structures in question include schwarzites, special lattices that feature ‘negative gaussian curves’ that give them extremely high strength to weight ratios. They’ve been near-impossible to manufacture until now due to their complexity, but with 3D printing now on the cards, the team believes the structures could have extensive applications in everything from buildings and bone implants to load-bearing prosthetics.
Muhammad Rahman, a Materials Scientist at Rice University and co-author of the study, added, “I’m pretty sure that if we can optimize these structures topologically, they also show good promise for use as bioscaffolds.”
Ceramics and the problem of fragility
Ceramic materials are often defined by their heat and chemical resistance, excellent strength and hardness, and low conductivity. They’re also remarkably biocompatible, making them great for biomedical applications such as bone substitutes, dental parts, and even tissue engineering scaffolds. Unfortunately, ceramics also have a tendency to be quite brittle. This means they’re prone to cracking and fracturing when under high compressive loads, which limits their use in heavy-duty structural applications.
In nature, hard ceramic-based structures address the issue of brittleness by infusing soft organic materials into the mix. We see this in mollusk shells, which are composed of fine layered brick-like aragonite platelets (95%) bonded by soft biopolymers (5%). We also see it in the bones of many animals, where hard mineral nanocrystals are arranged alongside collagen fibrils, forming more durable matrices.
Polymer-coated ceramic schwarzites
Drawing inspiration from nature’s tried-and-tested work, the Rice team 3D printed ceramic schwarzites on a Formlabs SLA system and coated them in a thin, flexible epoxy polymer before further curing the parts under UV light.
In the uncoated control group, the structures were proven to be extremely fragile, shattering as expected during drop tests and compressive hydraulic press tests. In the coated samples, all it took was a 100 micron-thick polymer coating to provide the parts with up to 4.5x more resistance to catastrophic fractures. Even when pushed to the point of breakage, the coated structures didn’t completely explode, crumbling and flattening instead.
“We’ve clearly seen that the uncoated structures are very brittle,” said Rahman. “But when we put the coated structures under compression, they will take the load until they completely break. And interestingly, even then they don’t completely break into pieces. They remain enclosed like laminated glass.”
Additionally, when compared to coated solid ceramic materials, the porous 3D printed schwarzite lattices were determined to be inherently tougher. This was attributed to the mechanism by which the polymer coatings infused into the porous structures, ‘filling up’ the pores to improve density and mechanical resistance
“The architecture definitely has a role,” explains Seyed Mohammad Sajadi, lead author of the study. “We saw that if we coat a solid structure, the effect of the polymer was not as effective as with the schwarzite.”
Further details of the study can be found in the paper titled ‘Damage-tolerant 3D-printed ceramics via conformal coating’. It is co-authored by Muhammad Rahman, Seyed Mohammad Sajadi et al.
Ceramic 3D printing has applications in all manner of fields and industries. Earlier this year, researchers from Shenzhen University and the Southwestern Institute of Physics developed a means of additively manufacturing ceramic structures that emit nuclear reactor fuel. Utilizing lithium-loaded ceramics and DLP 3D printing, the team was able to create ‘breeding blankets’ that self-sufficiently generate tritium, a vital element of the nuclear fusion process.
Elsewhere, in the medical field, scientists from the Skolovo Institute of Science and Technology have previously developed a novel method of 3D printing personalized ceramic bone implants. Specifically, the team deployed a simulation-based approach to create flexible, flaw-free 3D models that could be used to print porous implants.
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Featured image shows uncoated and coated ceramic schwarzites under a hydraulic press. Photos via Rice University.