Printing artificial bone

Researchers at MIT have developed a method to design synthetic bone-like materials and quickly turn the design into reality using computer optimisation and 3D printing.

The research, detailed in Advanced Functional Materials, uses computer-optimised designs of soft and stiff polymers placed in geometric patterns that replicate structures seen in nature. A 3D printer then prints two polymers at once to produce samples of synthetic materials that have fracture behaviour similar to bone.

“The geometric patterns we use in the synthetic materials are based on those seen in natural materials like bone or nacre, but also include new designs that do not exist in nature,” said Professor Markus Buehler of the Department of Civil and Environmental Engineering. “As engineers, we are no longer limited to the natural patterns. We can design our own, which may perform even better than the ones that already exist.”

The researchers created three synthetic composite materials, each of which is one-eighth inch thick and about 5-by-7 inches in size.

The first material stimulates the mechanical properties of bone and nacre (mother of pearl), possessing a microscopic pattern that looks like a staggered brick-and-mortar wall: a soft black polymer acts as the mortar with a stiff blue polymer forming the bricks.

Another composite is similar to the mineral calcite, which has an inverted brick-and-mortar pattern featuring soft bricks enclosed in stiff polymer cells.

The third composite was tailored specifically to improve upon one aspect of bone’s ability to shift and spread damage and has a diamond pattern resembling snakeskin.

To confirm the accuracy of their method, the researchers put their samples through a series of tests to determine whether the new composites fracture in the same way as their computer-simulated counterparts.

The scientists found the composites passed the tests which enabled them to validate the process and prove the efficacy and accuracy of the computer-optimised design.

“Most importantly, the experiments confirmed the computation prediction of the bone-like specimen exhibiting the largest fracture resistance,” said first author of the paper Leon Dimas. “We managed to manufacture a composite with a fracture resistance more than 20 times larger than its strongest constituent.”

The researchers hope the process could be scaled up to provide a cost-effective means of making materials that have more than two constituents, arranged in patterns of any variation and tailored for specific functions in different parts of structure, perhaps one day providing the structure for entire buildings.

“The possibilities seem endless, as we are just beginning to push the limits of the kind of geometric features and material combinations we can print,” added Buehler.

Reference: Molecular mechanics of mineralized collagen fibrils in bone