2023 MRS Communications Lecture

Blair Brettmann, Georgia Institute of Technology

Rheology and Formulation in Material Extrusion Additive Manufacturing of Dense Pastes

Written by Cullen Walsh

When developing products, we can now easily customize and alter their shape using 3D printing. However, we still have a limited ability to customize the materials that make up 3D-printed products. To address this limitation, Professor Blair Brettmann at the Georgia Institute of Technology researches the benefits and limitations of an emerging technique known as direct-ink-writing (DIW). This is a form of additive manufacturing in which a filament of paste is extruded by a nozzle, layer-by-layer, to form a 3D-printed structure.

As part of her MRS Communications lecture, Brettmann discussed her group’s research into the extrusion of dense pastes in which particle loading exceeds 50 percent. These dense formulations are desirable in many applications in which the particle, and not the binder, provides functionality, such as in pharmaceutical pills. The problem is, these mixtures are viscous and often inhomogeneous, making them difficult to process. To better optimize this technique, Brettmann’s group has implemented a quality-by-design framework in which the quality of a product is optimized by systematically analyzing both the design and performance of the final product along with the processes that go into making that product. Using this approach, the researchers are creating printed products made from dense pastes that are of high quality, which they define as having good shape fidelity, solidity, and homogeneity of voids and particle dispersion.

The researchers split their research across four different areas of the DIW process—particle characteristics, suspension stability, mixing procedure, and printing via direct-ink-writing. Brettmann first discussed how the particle characteristics affect the printing process by comparing spherical glass beads to simulated lunar soil, as this aligns with their goal of extending the use of direct-ink-writing to lunar and Martian soils for 3D printing on the lunar surface. What they found was that the maximum number of particles that can be added to the suspension, while still achieving flowability, decreased drastically going from glass beads to simulated lunar regolith due to an increase in particle roughness. The research team also looked at the curing process and found that the simulated lunar soil had a lower cure depth and degree of curability in comparison to the glass bead suspension. Beyond particle characteristics, Brettmann discussed the suspension stability of their formulations via their shear stability, settling, and aging. For instance, the research team found that in the aging process there were differences in the particle-to-binder ratio at the start versus the end of the print due to stresses during the printing process.

Overall, Prof. Brettmann’s work demonstrates how numerous steps in the design and implementation of DIW can be optimized to achieve high-quality printed products with high shape fidelity, solidity, and homogeneity. Additionally, by using a quality-by-design framework to understand how materials affect the 3D printing process, the research team increased the likelihood of a product being production-ready when implemented at scale. This could result in the 3D printing of suspensions, especially those with a high active particle loading, becoming a more versatile platform that could revolutionize the production of products from energetic materials to in-space waste products and pharmaceuticals.

The 2023 MRS Communications Lecture recognizes excellence in the field of materials research through work published in MRS Communications.  It is intended to honor the authors of an outstanding paper published in the journal during the preceding year.