Inside the Laboratory for Advanced Materials and Bioinspiration at McGill University in Montreal, Canada, a desktop 3D printer from EnvisionTEC is enabling researchers to develop and test all kinds of bioinspired materials—from scale-inspired protective materials to strong and impact resistant sutured materials. The advanced materials being developed in the lab could be used to produce more effective personal protective gear and more.
In recent years, researchers have increasingly been turning to nature for inspiration in the design and development of new materials and mechanical structures. In the case of protective gear, people have been particularly interested in learning more about animal scales, shells and carapaces, which all serve protective functions.
One of the projects being undertaken by the McGill researchers has involved studying the natural armours of fish, alligators and armadillos to gain insight into how they are structured and how hardness, flexibility and lightweight properties are combined in them. One of the practical aspects of the research has consisted of 3D printing various sizes and shapes of scales to test and optimize puncture resistance and flexibility.
By creating physical models using its in-house EnvisionTEC Micro Plus Hi-Res 3D printer, the researchers say they can more easily determine mechanical properties than by virtually testing and analyzing computer models.
“Computer models quickly become complex and have a hard time trying to capture the physics of what’s going on in cases like this,” said Francois Barthelat, lab leader and associate professor of McGill’s Department of Mechanical Engineering. “It’s very straightforward to compute the stresses and deformation of a single component under a specified load. But if you have two components in contact, you need to manage what’s happening in the contact, and this …creates numerical problems and becomes very expensive to model, even for only one contact pair.”
“If you try to capture what’s happening with things like fish scales, where you may have 10, 20, or 30 contact pairs to handle, it becomes a nightmare. It’s just not practical to analyze numerically with a computer,” he continued. “Interestingly for these cases it’s much faster, easier, more reliable and accurate to 3D print the scales, up to 10 or 20 objects that will interact, and do mechanical tests directly.”
In the research, Barthelat and his students 3D printed scale-like pieces using ABS and arranged them into 5 x 5 arrays which were glued to a soft, flexible substrate (a polyurethane material). The team then conducted a series of puncture tests on the surface using a 3D printed needle (also made from ABS).
The researchers tested various different geometries of the 3D printed scales, beginning with a single rectangular scale and working up to different types of interlocking or overlapping arrays. Many of the arrays were inspired by scale compositions found in nature. In the end, they found that the 3D printed scales that closely mimicked the ganoid scales (from the primitive polypterus senegalus fish) and teleost scales were the most effective.
As a study published last year in Acta Biomaterialia stated: “The interactions between the scales can significantly increase the resistance to puncture, and these interactions can be maximized by tuning the geometry and arrangement of the scales.”
Notably, the McGill researchers emphasize that the use of EnvisionTEC’s DLP 3D printer and its Perfactory ABS-like material offered a number of properties that were beneficial for their research. For example, they were able to manufacture fully isotropic and dimensionally accurate parts which, compared to FDM printed parts, offered good strength for mechanical testing purposes.
“What we really like about the EnvisionTEC printer is that its DLP technology exposes the polymer through a membrane to build a part that is dense, without any pores, and fully isotropic,” Barthelat elaborated. “This means that the stiffness and the strength are the same in all directions, which greatly facilitates the testing and analysis of the 3D printed parts.”
“In other technologies we looked at, like fused deposition and other more common technologies building layer by layer, you’re left with cleavage planes, which you see with mechanical testing. In general, if you build your parts along the Z axis, when you try to break the component there will be a cleavage plane across that axis. That’s very bad news, because it makes it extremely difficult to compare your mechanical tests with the model. When things are not isotropic, it complicates the whole story. The EnvisionTEC produces material that is really isotropic, so that we could get very good agreements between modeling and experimental data.”
Another research avenue that the lab is pursuing is the developing of sutured materials, or materials that fit together like puzzle pieces and which display superior strength and impact resistance than single-piece parts of the same material. For these tests (and others), the EnvisionTEC printer’s high resolution was crucially important. Working with resolutions of +/- four microns, Barthelat and his team were able to 3D print shapes that could fit together perfectly with virtually no gaps.
“We programmed an eight micron gap, which for mechanical testing purposes is essentially in contact, and our parts fit together without any undo force,” he said. “The polymer shrinks a bit when it cures, so there is a bit of trial and error to determine how best to program the gap at the beginning. But it’s a repeatable process, so you can rely on the same gap between components in all the structures you make.”
The surface finish of the DLP printed parts is also important, as many of the sutured shapes that the lab is creating are designed to slide into place or slide on each other. Unlike FDM prints which require post-processing to achieve a uniformly smooth surface, the DLP prints are smooth from the beginning and showcase uniform friction for the advanced materials tests.
The research team has primarily been working with EnvisionTEC’s Perfactory materials, though it says it is also working with other photopolymers offered by the company. Eventually, McGill could even make its own DLP materials with specialized reinforcing properties. Overall, the Advanced Materials and Bioinspiration lab has been making good headway in its efforts to develop more advanced and specialized materials for protective gear applications, and 3D printing has proved a valuable tool in testing different geometries to determine the most optimal arrangements.
“With 3D printing we can explore many more geometries,” added Barthelat. “And once we have the right geometry we can put resources and time into applying these geometries to materials like ceramics.”