Additive manufacturing technology is a promising venture wherein there have been noted time savings for production, cost savings on materials and time as well as the capability of fabricating parts that have complex architectures not easily achievable by conventional methods. Silicone, already used in numerous products, with its exceptional thermal stability, water & chemical resistance, mechanical flexibility, dielectric properties, and biocompatibility characteristics would be an excellent material for use in additive manufacturing. Using the direct ink write (DIW) process, 3D printing with silicone inks would be ideal for many applications, including advanced material such as soft robotics, biomedical devices, and metamaterials.
However, silicone, an inherently flowable liquid, does require modifications to its physical properties in order for it to be a suitable 3D printing feedstock material. 3D printing silicone ink must exhibit shear-thinning behavior and a transition from a gel to a liquid at high shear rates. In addition, the gelled state must be able to retain its shape well enough support its own weight during printing. The interplay between ink development, post-processing, material properties, and performance is a difficult challenge to overcome.
LLNL researchers, through careful control over the chemistry, network formation, and crosslink density of the ink formulations as well as introduction of selected additives, have been successful in preparing 3D printable silicone inks with tunable material properties. For DIW (direct in writing) applications, LLNL has a growing IP portfolio around 3D printable silicone feedstocks for diverse applications. They include:
- Custom 3D printable silicone with tunable stiffness with the use of rheological modifying agents. Intricate structures can be produced by the rendering of a nanoscale network between reinforcement filler and rheological additive, thus allowing shape retention of the printed structure
- 3D printed transparent siloxanes, in which refractive indices of the siloxane to match the reinforced filler
- 3D printed porous siloxanes using leachable spherical urea or leachable PVP/glycerol matrix additives that provides tunable porosity and characteristic pore size
- 3D printed polysiloxane foams with closed-cell pores using hydrogen-blowing agents
- 3D printed structural siloxanes with controlled release properties by incorporating core-shell microspheres with encapsulated liquid phase
Durban, M. M., Lenhardt, J. M., Wu, A. S., Small IV, W., Bryson, T. M., Perez-Perez, L., Nguyen, D. T., Gammon, S., Smay, J. E., Duoss, E. B., Lewicki, J. P., Wilson, T. S., Custom 3D Printable Silicones with Tunable Stiffness Macromol. Rapid Commun. 2018, 39. (https://doi.org/10.1002/marc.201700563)
Rodriguez, N.; Ruelas, S.; Forien, J.-B.; Dudukovic, N.; DeOtte, J.; Rodriguez, J.; Moran, B.; Lewicki, J.P.; Duoss, E.B.; Oakdale, J.S. 3D Printing of High Viscosity Reinforced Silicone Elastomers. Polymers 2021, 13, 2239. (https://doi.org/10.3390/polym13142239)
Colin K. Loeb, Du T. Nguyen, Taylor M. Bryson, Eric B. Duoss, Thomas S. Wilson, Jeremy M. Lenhardt, Hierarchical 3D Printed Porous Silicones with Porosity Derived from Printed Architecture and Silicone-Shell Microballoons, Additive Manufacturing, 55, 2022. (https://doi.org/10.1016/j.addma.2022.102837)
Ford, M. J., Loeb, C. K., Pérez, L. X. P., Gammon, S., Guzorek, S., Gemeda, H. B., Golobic, A. M., Honnell, A., Erspamer, J., Duoss, E. B., Wilson, T. S., Lenhardt, J. M., 3D Printing of Transparent Silicone Elastomers. Adv. Mater. Technol. 2022, 7. (https://doi.org/10.1002/admt.202100974)
DIW with silicone inks combines the main advantages of the 3D printing technique and the intrinsic properties of the material. It allows for the production of 3D printed parts that have complex geometries and intricate structures while also possessing the characteristics of silicone, e.g. excellent thermal stability, resistance to chemical attack and biocompatibility.
LLNL researchers have developed various formulations and methods for 3D printable thixotropic silicone inks that can be modified in various ways depending on the application and/or desired material properties:
- Formulations of DIW silicone inks can be modified for wide-range of hardness and stiffness.
- The resin system can be custom-formulated to produce clear 3D printed silicone parts.
- The siloxane formulation can be modified to accept leachable porogens such as spherical urea particles or PVP/glycerol matrix additive. which would allow for controlled intrastrand porosity.
- Formulation of 3D printable siloxane resin could be tuned to accept blowing agents to produce a closed-cell pore structure. When combined with the void spaces created by the 3D printing process, materials with dynamic, controllable stress responses and lower average densities (compared to conventionally produced hydrogen-blown silicone foam) could be produced.
- If controlling intra-filament micro-structure is required, microstructure particles could be incorporated into the DIW silicone inks to introduce functionality and specialized properties to the structure that previously were unattainable (e.g. ink loaded with liquid-filled microspheres containing active pharmaceutical ingredients for controlled release drug delivery).
Electronics, 3D print engineered cellular solids, biomedical devices, prosthetics, metamaterials, space applications, Controlled Release Drug Delivery System (CRDDS), engineered foam structures, shock-absorbing cushions, soft robotics, optics system transparent parts, elastomeric lenses.
Current stage of technology development: TRL 3
US Patent No.10,689,491 Silicone formulations for 3D printing issued 06/23/2020 (https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/10689491)
US Patent No. 11,180,670 Three-dimensional porous siloxanes using leachable porogen particles issued 11/23/2021 (https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/11180670)
US Patent Application Publication No. 2022/0064463 Three-dimensional porous siloxanes using leachable porogen particles published 3/3/2022 (https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/20220064463)
US Patent Application Publication No. 2021/0269659 Three-dimensional printed porous silicone matrix using leachable porogen published 9/2/2021 (https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/20210269659)
US Patent Application Publication No. 2020/0190345 Three-dimensional printed gas blown polysiloxane foams published 6/18/2020 (https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/20200190345)
US Patent Application Publication No. 2020/0315975 Three-dimensional printed structural siloxanes having controlled drug release published 10/8/2020 (https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/20200315975)
US Patent Application Publication No. 2022/0119657 Transparent 3D printed siloxane elastomers published 4/21/2022 (https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/20220119657)