UF researchers develop VIPS-3DP vapor-induced 3D printing method

The engineers at the University of Florida have developed a method called Vapor-Induced Phase-Separation 3D Printing, or VIPS-3DP, that enables the creation of single-material and multi-material objects. Yong Huang, Ph.D., a professor in UF’s Department of Mechanical and Aerospace Engineering, explained that this novel approach is both cost-effective and sustainable. The process details were published in the journal Nature Communications.

To better understand the process, imagine using environmentally friendly liquids as “ink” for a 3D printer. These liquids are polymer-based and may contain metal or ceramic particles. When printing with this ink, a non-solvent vapor is released into the printing area, causing the liquid component of the ink to solidify. This results in the vapor-induced phase-separation process, leaving behind the solid material.

The VIPS-3DP technique for 3D-printing polymers, metals, and composites offers a simple and economical solution. During the VIPS-3D printing process, a dissolved polymer-based ink is deposited in the presence of a nebulized non-solvent. This causes the low-volatility solvent to be extracted from the filament in a controlled manner due to its stronger chemical affinity with the non-solvent.

As a result, the polymeric phase hardens in situ due to the induced phase separation process. The low volatility of the solvent permits its reclamation after printing, minimizing its environmental impact. Initially, the researchers demonstrated the use of VIPS-3DP for polymer printing, highlighting its ability to create intricate structures. They then expanded on this by using VIPS-3DP to deposit polymer-based metallic inks and composite powder-laden polymeric inks, which can transform into metallic parts or composites after a thermal cycle is applied. Furthermore, the VIPS-3D printing method facilitates the production of porous structures and functionally graded parts by controlling the printing path and employing an inorganic space-holder as an intra-filament porogen.

Yong Huang, Ph.D., explained that the VIPS-3DP process allows manufacturers to 3D print multi-material parts with varying levels of porosity. This means fabricating structures with different substances and different levels of small holes or gaps. The porosity of the object is regulated by adjusting printing conditions and the amount of sacrificial material used during the process. This can be advantageous for manufacturing porous medical implants or lightweight aerospace products.

Marc Sole-Gras, Ph.D., the first author of the paper and a former graduate student in Huang’s lab, adds that this method shows particular promise for creating metallic products with varying levels of porosity. For instance, it can be used in bone tissue engineering to print an implant that integrates well with human cells.

The VIPS-3DP process offers both manufacturing advantages and sustainability benefits compared to traditional printing methods. It utilizes sustainable materials and consumes less energy.

To summarize, the research demonstrates the effectiveness of the VIPS-3DP process in printing polymer-based parts by utilizing a nebulized non-solvent to enable solidification. The solvent used can be reused, making the process efficient. This solidification mechanism can also be applied to printing composite parts using polymer-based colloidal inks, allowing for the fabrication of polymer-metal and polymer-ceramic parts. However, the VIPS concept is required for the solidification and binding of ceramic and metallic particle-based suspensions. By introducing a thermal cycle to remove the polymer and induce solid-state sintering, pure metallic, ceramic, and composite parts can be created. Additionally, the VIPS-3DP process allows for the creation of parts with varying levels of porousness by combining inter-filament and intra-filament porosities using a mixer. Such parts might find applications in areas like multi-scale porosity bone implants.

VIPS-3DP provides an alternative approach to printing engineering polymers without the need for heating or tailoring them for specific solidification mechanisms. It also enables the creation of heterogeneous composite structures using polymer as a binder material. However, it is important to note that the resulting microstructure will be porous due to the phase-separation process. While this porosity can be advantageous for certain applications, load-bearing purposes are not intended.

For applications that require load-bearing properties, further investigation is needed to understand how the printing process with sacrificial template additives affects or controls pore size. It is worth mentioning that the VIPS-3D process can be economically implemented by creating a nebulized environment, whereas typical DIW processes require the ink to solidify in place to maintain the printed form.

The printing speed in VIPS-3DP is determined by the solidification rate of the ink, which is influenced by factors such as the diffusion speed of non-solvent vapor, polymer demixing rate during phase separation, non-solvent concentration (in this case, relative humidity), and polymer concentration. Similarly, the printing resolution is limited by the size of the smallest usable nozzle for a given polymeric ink.

It is important to consider post-printing variations in polymer parts created using the VIPS-3DP process during the design phase. These variations occur as a result of the phase-separation mechanism for solidification.

The development of this UF-licensed technology has received two patents and has been supported by funding from federal agencies, including the National Science Foundation and the Department of Energy.