When I interviewed Voxel8 CEO Jennifer Lewis last year, she told me that she didn’t want me to conflate her research with her commercial work, namely the multi-material, electronics 3D printer she developed at Voxel8. This meant that my questions regarding 4D printing and bioprinting would have to be reserved for a separate interview. While the exact date for that interview is yet to be determined, her team at Harvard’s Wyss Institute for Biologically Inspired Engineering and the Harvard John A. Paulson School of Engineering and Applied Sciences has continued to make progress, publishing a paper in Nature Materials outlining an experiment in “Biomimetic 4D printing”.
Inspired by plant life, Lewis’s team sought to 4D print objects that would change with its environment in pre-programmed ways. To do so, they 4D printed objects using a hydrogel made up of aligned cellulose fibres from wood pulp, meant to constrain the material’s motion, and acrylamide hydrogel, which expands when put in water. When printed and submerged, the fibers force the object to swell lengthwise, but not laterally. With a mathematical model, the team was able to predict this behavior and print objects with predetermined behaviors. Prof. Lewis tells New Scientist, “Depending on how we actually print the material, we can encode bending, twisting and ruffling.”
A press release for the paper describes this process in this way, “Like wood, which can be split more easily along the grain than across it, the hydrogel-cellulose fibril ink undergoes differential swelling behavior along and orthogonal to the printing path when immersed in water. Combined with a proprietary mathematical model developed by the team that predicts how a 4D object must be printed to achieve prescribed transformable shapes, the method opens up potential applications for 4D printing including smart textiles, soft electronics, biomedical devices, and tissue engineering.”
The study sees the team print two flower shapes with similar shapes, but with different pre-programmed responses when exposed to water, as well as an orchid shape that actually moves like an orchid when submerged. The glowing seen throughout the study are the result of fluorescent dye added to the gel for observation purposes. As beautiful as the result is, the printed flowers demonstrate that the team is able to program the toolpath for their printer to produce objects with predictable, desired behavior. Dr. Elisabetta Matsumoto, a post-doctoral fellow on the team, elaborates, “Our mathematical model prescribes the printing pathways required to achieve the desired shape-transforming response. We can control the curvature both discretely and continuously using our entirely tunable and programmable method.”
To expand the research further, the team envisions replacing the cellulose fibrils, possibly with a conductive material, and the environment of the prints to trigger other behavior. The applications of the technology include 3D printing biological tissue, possibly for creating organs by printing a flat sheet that might fold into the proper shape. Lewis tells New Scientist, “Right now most tissue culture is done in two dimensions, but most applications of these cells are in 3D.”
Though I’m not supposed to conflate this sort of work with what Prof. Lewis is exploring at Voxel8, she did tell me that an important component to Voxel8’s technology is the pneumatic dispensing system that acts as the printhead. The only hint she gave about what the next generation of their multi-material machine would be capable of was that it might be able to print elastomers. If this 4D printing research relied on the same pneumatic printhead, it’s not difficult to imagine that the Voxel8 platform could be capable of 4D printing one day, as well. There might even be a Voxel8 4D modeling software to go with it.