Additive Manufacturing Strategies

Researchers Draw 4D Objects with Pens

ST Medical Devices

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One of the beauties of 3D printing pens, like the 3Doodler, is that they lower the barrier to entry of 3D printing even further. Many desktop printers are pretty simple to use, but 3D printing pens are just about as easy as drawing with a standard utensil. Scientists at Seoul National University have taken this advantage a step further by demonstrating the use of traditional pens to create 4D printed objects.

As described in an article for Science Advances, researchers See Woo Song et al. use a method to transform 2D drawings made with an ink pen into 3D geometries. Once a figure was drawn, an ink made from polyvinyl butyral (PVB) could be applied to parts of the print they wanted to lift off of the substrate in response to water, a process referred to as surface tension–assisted transformation (STAT). To further control the process, the team developed an ink that could keep portions anchored when submerged in water. By swapping water for a monomer solution including potassium persulfate (KPS), the areas coated with PVB polymerize and are fixed in place even after removed from the solution, referred to as surface catalytically initiated radical polymerization (SCIRP).

“(A) Conceptual illustration of pen-based 4D printing. Pen-based 4D printing enables simple and intuitive 3D fabrication via 2D-to-3D transformation of 2D pen drawings. (B) Pen-based 4D printing process. A pen is used to generate a hydrophobic thin film after the ink dries. This 2D pen drawing transforms into a 3D structure via STAT when immersed in a monomer solution. The transformed 3D shape is fixed via SCIRP during a 3-min incubation period in the monomer solution. (C) STAT and SCIRP mechanisms. The type of ink applied determines whether a specific part of the structure floats or is anchored. A polymer coating layer is generated around the 3D structure of the dried ink film to strengthen its architecture. (D) Sequential view of the 2D-to-3D transformation depending on water level. The 3D structure can be further fixed by SCIRP using a monomer solution including KPS ions (right). Scale bars: 5 mm.” Photo credit: Seo Woo Song, Sumin Lee, and Junwon Kang; Seoul National University.

Altogether, the team demonstrated a method for being able to control the 3D nature of their drawings through the use of an ink for anchoring, an ink for floating, and the KPS solution for hardening the material into place. The authors propose that this approach could be scaled for mass production of 3D parts at faster speeds than traditional 3D printing. Using modified 2D printers, large batches of objects could be produced at once.

“(A) Compositions of the floating and anchoring inks. The presence or absence of surfactant determines the floating properties of the PVB film. (B) Fracture strain of the PVB film depending on the proportions of PVB and plasticizer in the ink (see also figs. S4 and S5). Error bars represent SD. (C) Pen drawing combined with an automatic printing system for precise drawing and mass production. (D) Sequential transformations at different water level heights as compared with simulated transformation results. (E and F) Scalability of pen-based 4D printing. (E) Millimeter scale (see also fig. S13). (F) Meter scale (see also fig. S14). Scale bars: 5 cm (C) and 2 cm (D).” Photo credit: Seo Woo Song and Sumin Lee, Seoul National University; Jun Kyu Choe, Ulsan National Institute of Science and Technology.

To showcase the possibilities, the researchers used a pen plotter, Axidraw, to automatically create 3D objects with high reproducibility and accuracy. Because the drawn objects became 3D in response to environmental variables, the process could be considered a type of 4D printing. The process applied to a variety of substrates, including glass, plastic, poly (dimethyl siloxane) PDMS, stone and leaf. This was also expanded to a roll-to-roll process, demonstrating mass production of 3D geometries on a thin, flexible polyvinyl chloride substrate. The researchers believe that the technique could overcome some disadvantages of 3D printing, producing on-site in difficult locations and modifying printed objects on the fly. Using magnetic materials, they were also able to test a magnetically actuated soft robotics design.

“(A) Pen-based 4D printing on various substrates. A pen-based approach allows the fabrication of 3D structures even on curved surfaces. (B) Demonstration of an “impossible bottle” construction. Drawing on the flexible PDMS film enables on-site reconfiguration of a 3D architecture inside a narrow space that would be inaccessible to conventional 3D printers. (C) R2R pen-based 4D printing for rapid prototyping and mass production. Quantitative analysis of the products made by R2R fabrication is presented in fig. S24. Scale bars: 2 cm.” Photo credit: Seo Woo Song and Sumin Lee, Seoul National University.

At the same time, the team also demonstrated a possibility for a very intuitive, simple method for 3D printing. On the one hand, one could imagine a new range of Crayola products released on the market for kids to experiment with sculpting. Or we could see researchers quickly iterating designs using a variety of inks and solutions before sculpting the models in CAD and then fabricating them with a 3D printer for a more refined prototype.

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