One of the beauties of 3D printing pens, like the 3Doodler, is that they further lower the barrier to entry to 3D printing. Many desktop printers are fairly simple to use, but 3D printing pens are 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 Progress of science, 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 the parts of the print that wanted to peel off the substrate in response to water, a process known as surface tension-assisted transformation (STAT). To further control the process, the team developed an ink that could keep the slices anchored when submerged in water. By exchanging the water for a monomer solution including potassium persulfate (KPS), the PVB-coated areas polymerize and lock in place even after removal from solution, known as catalytically initiated radical polymerization in the surface (SCIRP).
“(A) Conceptual illustration of pencil-based 4D printing. Pen-based 4D printing enables simple and intuitive 3D manufacturing through 2D-to-3D transformation of 2D pen drawings. (B) Pencil-based 4D printing process. A ballpoint pen is used to generate a thin hydrophobic 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 form is fixed via SCIRP for 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 dry ink film to strengthen its architecture. (D) Sequential view of the transformation from 2D to 3D depending on the 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.
Together, the team demonstrated a method of being able to control the 3D nature of their drawings by using an ink to anchor, an ink to float, and the KPS solution to harden the material in place. The authors propose that this approach could be scaled up for mass production of 3D parts at speeds faster than traditional 3D printing. Using modified 2D printers, large batches of objects could be produced at once.
“(A) Compositions of floating and anchoring inks. The presence or absence of surfactant determines the buoyant properties of the PVB film. (B) Fracture stress of PVB film depending on the proportions of PVB and plasticizer in the ink (see also Figures 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 compared to 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 show the possibilities, the researchers used a pen plotter, Axidraw, to automatically create 3D objects with high reproducibility and precision. Because drawn objects became 3D in response to environmental variables, the process could be considered a type of 4D printing. The process was applied to a variety of substrates, including glass, plastic, poly(dimethyl siloxane) PDMS, stone, and sheet. This was also extended to a roll-to-roll process, demonstrating the mass production of 3D geometries on a thin, flexible polyvinyl chloride substrate. The researchers believe the technique could overcome some drawbacks 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 enables the fabrication of 3D structures even on curved surfaces. (B) Demonstration of an “impossible bottle” construction. The use of flexible PDMS film enables on-site reconfiguration of a 3D architecture within a narrow space that would be inaccessible to conventional 3D printers. (C) R2R pen-based 4D printing for rapid prototyping and mass production. The quantitative analysis of the products made by R2R manufacturing 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 the possibility of a simple and intuitive method for 3D printing. On the one hand, one could imagine a new range of Crayola products being launched for children to experiment with sculpting. Or we could see researchers rapidly iterating designs using a variety of inks and solutions before sculpting the models in CAD and then fabricating them on a 3D printer for a more refined prototype.
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