A New Method for 3D Printing Optics with Flexible Thermoplastic Polymer

December 2, 2019 by Vanesa Listek 3D Printers 3D Printing 3D Printing Materials

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Despite the high demand, most optical materials are difficult to fabricate into desired shapes using state-of-the-art manufacturing technologies, but researchers at the University of Arkansas (UARK) have now developed a new method of microextrusion-based 3D printing that can be used with a soft and stretchable thermoplastic polymer, commercially known as Clear Ballistic gel. This new technological invention provides an inexpensive way to enable a regular fused deposition modeling (FDM) printer to print with ballistics gel, a new type of material that will enable many applications in defense, medical and optical industries.

“3D printing of optics has great potential in enabling the fabrication of complex optical devices for a wide range of applications. However, it has proven to be challenging and costly to print with conventional optical materials, such as glass. At the University of Arkansas, we developed a new low-cost method for 3D printing of optical devices with a soft and stretchable optical material, which opens a new door for this specific field,” Edidiong Nseowo Udofia, co-creator of the method and recent Mechanical Engineering doctoral graduate from UARK, explained to 3DPrint.com.

According to a paper published by Udofia and Whechao Zhou, Assistant Professor in the Department of Mechanical Engineering at UARK, although there are many commercial FDM printers for 3D printing of thermoplastic polymers, no existing printers are compatible with printing the ballistic gel due to its flexibility. To overcome this issue, they developed a low-cost syringe-based printhead for continuous melt and extrusion of the ballistic gel, which starts to melt at around 70 °C. The custom-designed printhead consists of a 30 ml glass syringe which functions as the ink reservoir, and a deposition nozzle, both housed within a heated aluminum chamber to facilitate gel heating and extrusion. They then mounted the printhead onto their own custom 3D printer. The gel is first melted and then pushed out of the nozzle by controlling the deposition pressure with a digital valve, which is connected to a pressure source.

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The researchers claim that the printhead was specifically designed to avoid clogging. It is also capable of maintaining a constant temperature between 70 and 130 °C with minimal variation and can print with a needle size smaller than 100 micrometers (μm).

“Clear Ballistics gel is a commercially available soft gelatine material, with ballistic testing as its primary market. The idea of creating a printing system for the gel was birthed due to the demand in the medical market for making anatomical phantoms for pre-surgical planning, medical research, education, and training; and was initiated by my advisor, Wenchao Zhou. In the course of our research, however, it became clear that the optical clarity of the gel could make it an appealing material for making soft and stretchable optics, which is an entirely new direction in the field of optics,” went on Udofia.

Custom-designed printhead and deposition nozzle housed within a heated aluminum chamber to facilitate gel heating and extrusion

Udofia explained that “in addition to printing Clear Ballistics gelatin, the printing system developed by our group can theoretically enable the printing of any material that can be melted into a liquid form at a relatively low temperature.”

The research was done at the Advanced Manufacturing AM³ Lab, nestled in the Department of Mechanical Engineering at the University of Arkansas, a place Udofia has been working at since 2015 as a Ph.D. student, and which is equipped with Stereolithography and FDM 3D printers, CNC mill, multi-material 3D printers, 3D scanners, high-magnification microscopes and much more. The researcher also mentioned that a patent has already been filed on this technology by AMBOTS, a startup company spun off from the AM³ Lab last year.

Their microextrusion-based 3D printer technology can print the gel in the open air without the need for a support bath or supporting materials. According to Udofia, existing methods of printing optics require either carefully-designed support materials during the printing process or extreme post-processing conditions, which makes this approach very appealing for a wide variety of applications.

They demonstrated how it works with a series of optical developments, including unique artistic illumination, lightwave splitters and combiner circuits on planar and 3D conformal surfaces, as well as an optical encoder. They also printed waveguides (devices for transporting electromagnetic energy) and noticed that they exhibit outstanding optical transparency of more than 98%.

Compared to the molding of gel, gel printing has several advantages, mainly, complex models can be made at low cost, with fast turnaround time and ease of use.

Some target applications include selling the printhead to customers who own an FDM printer or FDM printer suppliers, such as Ultimaker or Makerbot, or even providing a whole FDM printer packaged with both thermoplastic and gel printing capabilities.

The simplicity of the fabrication process, low-cost, excellent optical properties, and flexibility provide an attractive pathway for fabricating integrated optical devices and new opportunities for controlling light. Companies around the world are searching for low-cost methods for creating complex optical structures with materials possessing the required properties and compatibility to use with optics.