Engineering tendon and ligament tissues from biocompatible materials presents chemical, biological, and mechanical challenges. Serious injuries requiring tendon and ligament repairs are quite common. Effective restoration materials are necessary to reestablish functionality after a repair. Nikos Karathanasopoulos and Oraib Al-Ketan at New York University in the Abu Dhabi campus worked to find tissue and ligament restoration metamaterials that can inherently mimic native tissue mechanics. To do this, they needed to identify metamaterial architectures that are strong upon normal loading, soft in shear loading and contract much more than common engineering materials.
Additive Manufacturing and Testing for Different Metamaterial Architectures
Karathanasopoulos and Al-Ketan were looking for additive manufacturing solutions to test six different unit-cell metamaterial architectures. The mechanical properties of the architectures were tested using both shear and uniaxial compression tests.
Using Boston Micro Fabrication’s microArch S240, they were able to fabricate metamaterial architectures at scales requiring features sized in the order of tenths of µm and overall specimen lengths in the order of mm. After trying multiple printers, they found that the S240 was the 3D printer that could fabricate the specimens with the highest accuracy possible at the required scales. The printed parts included diagonal strut elements with diameters in the order of 50µm.
Experimental Performance
The 3D printed samples demonstrated very good reproducibility as of the robustness of the system for the investigated metamaterial architectures at the specified scales. The dimensions of the printed samples were within the range of the dimensions observed in native tissues.
Metamaterial designs that allow for substantial normal stiffness along the primal tissue loading direction, upon a low shear resistance and Poisson’s ratio values well above unity have been identified for moderate relative density values, a combination of material attributes that is highly desirable in restoration praxis. Advanced architected materials that are up to 18 times stiffer when normally loaded rather than sheared have been identified, well-beyond the limits of isotropic, common engineering materials that cannot exceed normal to shear loading ratios of 3.
To learn more, read the full research paper here.
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