In a project funded by the U.S. Army, researchers at MIT have 3D printed a new material that they say is fracture-resistant and resembles human bone. The goal, one might think, would be to develop ideal replacements for transplant, the perfect hip bone or something along those lines. That may be one application of the research, but, in actuality, one of the major goals of the study was to develop a meta-material that could be used for engineering purposes.
Assistant Professor Markus Buehler, of the Department of Civil and Environmental Engineering at MIT, sought to develop a composite that mimics the structure of human bone because bone is both lightweight and durable. Bones are made up of two different biological components, stretchy and soft collagen protein and stiff and brittle hydroxyapatite mineral, locked in a hierarchical pattern. The hydroxyapatite provides the bone’s structure, while the collagen helps redistribute energy along the bone. Combined in the hierarchical pattern, the result is perfect to support a fast moving and tough human body.
The composition of human bones has been understood and diagrammed for quite awhile. What’s been missing is the ability to physically reproduce this composition. Using a dual material Stratasys 3D printer, Buehler, along with his graduate students, Leon Dimas and Graham Bratzel, and Stratasys’s own Ido Eylon have been able to translate 3D models of this hierarchical combination of hard and soft materials into a physical sample. They printed three different patterns to determine which would be the most fracture-resistant using a hard and a soft polymer. First, a simulation of bone and the material lining the inner shells of mollusks (known as nacre), which looks something like a wall of hard polymer bricks fused together with soft polymer. Second, a pattern that resembles the structure of calcite, soft polymer bricks connected by hard polymer. Finally, a metamaterial with a snakeskin pattern, to see if they could improve on the structure of bone.
Dimas explained the outcomes of the experiment, saying: “the experiments confirmed the computational prediction of the bonelike specimen exhibiting the largest fracture resistance. And we managed to manufacture a composite with a fracture resistance more than 20 times larger than its strongest constituent.”
This bonelike material could be used for a variety of purposes, such as to create replacement bones in medical procedures, but it could serve more creative purposes, as well. Buehler believes, according to the results of the study published at Advanced Functional Materials, that this could pave the way for the large-scale manufacturing of meta-materials for use in the aerospace, automobile and even architectural industries so that we may, one day, find ourselves in buildings constructed from multiple materials printed simultaneously into the most sound and efficient geometries possible.
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