The buildings that populate our cities as well as the homes that populate our suburbs all have something in common with the bones that support our bodies: they are made up of columns and beams. In our homes and building, the columns are the studs inside of the walls, and the beams are the plates and rafters that connect them together. As it turns out, our bones are constructed in a similar fashion with columns supporting the vertical load and beams spreading that load out across multiple columns. Now a team of researchers thinks these column and beam structures found in our bones might be key to stronger 3D printed structures out in the physical world.
Comprised of researchers from Cornell University, Purdue University, and Case Western Reserve University, the team has discovered that by modifying this beam and column structure so that its beams were 30% thicker, they could achieve a durability increase of about 100-fold. “Bone is a building. It has these columns that carry most of the load and beams connecting the columns. We can learn from these materials to create more robust 3D-printed materials for buildings and other structures,” said Pablo Zavattieri, a professor in Purdue’s Lyles School of Civil Engineering.
Researchers 3D-printed polymer models of trabecula in human bone and applied loads to them, investigating if certain structures play more significant roles in bone durability than previously thought. Credit: Purdue University / Pablo Zavattieri
For years biologist have thought that the majority of a bone’s strength came from the vertical structures in the spongy part of the bone known as the trabecula. The trabecula are comprised of an interconnected series of vertical and horizontal struts, the columns and beams if you will, and that the denser the vertical struts were, the stronger the bone was. It was thought that the horizontal struts were insignificant in bone strength. This was widely believed to be true because as a person aged, the less dense the trabecula became, thus weakening the bone and making it less resilient to wear and tear from everyday activities.
The researchers from Cornell had a suspicion that the horizontal struts (the beams) played a more significant role in bone strength and durability than what was widely accepted. They were right! The researchers found that while the vertical struts played a role in bone stiffness and strength, it was, in fact, the horizontal struts that significantly increase bone strength. “When people age, they lose these horizontal struts first, increasing the likelihood that the bone will break from multiple cyclic loads,” said Christopher Hernandez, a professor of mechanical, aerospace and biomedical engineering at Cornell.
Zavattieri’s lab at Perdue has been working on developing designed materials that are inspired by nature that are stronger and more resilient and contributed to the project by designing and running mechanical analysis simulations to test how thickening the horizontal struts in the trabecula affects bone strength, and they then applied their results to models that could be 3D Printed. They found that by thickening the horizontal struts by just 30%, significant structural integrity gains were made. This meant that structures could be designed significantly stronger using this method while keeping the overall mass of the structure low.
“When we ran simulations of the bone micro-structure under cyclic loading, we were able to see that the strains would get concentrated in these horizontal struts, and by increasing the thickness of these horizontal struts, we were able to mitigate some of the observed strains,” said Adwait Trikanad, a co-author on this work and civil engineering Ph.D. student at Purdue.
Engineers designed a material with the same amount of rod- and plate-like structures as human trabecula and arranged them in a periodic pattern, presenting a new way to strengthen lightweight 3D-printed structures. Credit: Purdue University / Pablo Zavattieri
This means that the same methodology could be used to design stronger 3D printed buildings and homes that are capable of withstanding natural disaster level fatigue events while reducing the amount of material needed to build the structure. Furthermore, this technology could be used to create other wear-resistant structures such as dams, toxic waste storage facilities, and possibly even lightweight habitats that allow us to survive in harsh environments such as on the planet Mars. It’s also not a hard stretch to see this discovery affecting the way rocket engine nozzles and biomedical devices are 3D printed.
“When something is lightweight, we can use less of it,” Zavattieri said. “To create a stronger material without making it heavier would mean 3D-printed structures could be built in place and then transported. These insights on human bone could be an enabler for bringing more designed materials into the construction industry.”