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).
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.
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.
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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