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by Jennifer Maccani, PhD This is part 2 of a 3-part article. This article is part of the "Emerging Biotechnology" series. A network of 3D printers is already beginning to form at Brown. One 3D printer is already in use in the laboratory of Dr. Kenneth Breuer, a fluid mechanist, and Dr. Sharon Swartz, a biologist focused on morphology and functional biology. Cosima Schunk, a graduate student in the lab, is a PhD candidate in the School of Engineering’s Biomedical Engineering Program just entering her fourth year. “My research is inspired by biomimetics, that’s my undergrad degree, and I’m looking at bat flight and possible application towards the development of engineering devices like micro-air vehicles,” Schunk says. One can tell from her undergraduate education at the University of Applied Sciences in Bremen, Germany, that Schunk is serious about the research of biomimetics; as she says, “It was the first school in Germany, actually, where you could directly study biomimetics.” As Schunk describes it, biomimetics is “generally learning from nature and applying biological concepts to engineering.” Although Schunk studies bats, “the idea, generally, is you look at bio-solutions evolved by nature and then you see if you can abstract the concept, and then apply this abstract concept towards an engineering solution.”  A bird emitting brightly colored chain links of goo. Or a model of how a bird's flapping wings create aerodynamic effects. [image via] In a recent publication in the Journal of Bioinspiration and Biomimetics (11), a former graduate student named Joseph Bahlman with whom Cosima Schunk has worked, together with Drs. Breuer and Swartz, characterized the robotic bat wing, or “flapper” as Schunk refers to it, that they designed and 3D-printed to study bat flight. “[Bats] are really agile flyers, very maneuverable, but we don’t know a lot about how they are actually doing it,” Schunk explains. “There’s a lot of engineering work out there looking at aeromechanical, aerodynamical behavior of membranous wings.” But why flapping flight? “Traditional rigid wing airplanes…get problems when they get close to walls or especially when they fly really slowly. [So] you could imagine if you want to be in a building that was destroyed after an earthquake, and you wanted to see if it was worth going in there, saving people, you need something that can hover and be stationary and look around, and traditional aircraft simply cannot do that,” Schunk says. “And that’s when people got the idea that hey, animals can do that.… That’s where this whole interest came back into looking for inspiration in nature.” The lab’s interest in 3D printing began when Dr. Breuer and Dr. Swartz decided to take a closer look at precisely how the lesser dog-faced short-nosed fruit bat (Cynopterus brachyotis) flies, and Bahlman began devising the research that would later comprise his PhD thesis. Schunk tells the story of the project’s inception: “They had the idea that it would be cool to build a robot bat to learn about power consumption in real bats…and then see how the power requirement is changing when you change flapping frequency, amplitude, things like that, which is impossible in a real bat. You can’t tell a bat, hey, just flap with four hertz now because it’s convenient for us.” The method the lab devised was to 3D print the skeleton of a bat wing out of ABS plastic and to attach a compliant membrane to it. As Schunk explains, there are caveats to that method. She says, “The printing process itself [takes] 6 or 7 hours. But the rapid prototype machine we are using here uses a filling material, and then the actual material of which the model is made. And the model has a lot of small holes where screws are supposed to go through or wires are supposed to go through, and they are filled up with this filling material and we have to dissolve that out.” Between the design of the CAD file, the actual printing process, the dissolving of the filler material, and the assembly of the robotic wing and the wires that run to the three motors that move each of its three major joints, Schunk says, the entire process takes three to four days for a complete model. The beauty of using 3D printing, however, is that many of the parts, once printed, can be reused. “That’s what we are working on at the moment…the big pieces that are really time intensive to print, that we don’t have to print them over and over again. First of all, it’s a waste of material and money, but also a waste of time,” Schunk says. Surprisingly, the process is relatively inexpensive once one has a 3D printer—“$200, maybe $250 if you include all the bearings and wires and everything.” Though newer 3D printers can cost as little as $397 for the Buccaneer™ Pirate3D or as much as $2799 for a MakerBot Replicator™ 2X, the actual printing is a fairly cost-effective process, “once you know what you want,” she adds, with a laugh.  Buccaneer: This thing looks like the future. [image via]  A MakerBot printing a chain link at the new Boston store. Each link takes ~13 minutes. [Photo by Matthew Lee] While Schunk was an undergraduate at the University of Applied Sciences in Bremen, Germany, she spent a mandatory semester abroad at Brown in the Breuer and Swartz lab, and decided to return the following summer to help with the investigation. “I came back summer of 2009, I believe, for one semester and took wake measurements with [Bahlman’s] first generation little robot, also already 3D printed. And it had two wings, it was very crude, it only had a shoulder joint, nothing else. But it had a membrane wing and everything, and I did wake measurements with this ‘flapper.’ And that’s also when the idea of coming here for grad school came up.” The current iteration of the robotic bat wing, Schunk says, is “much closer to a real bat in its behavior….Even with this very simple ‘flapper’ we had this really bat-like wake, and we were surprised because it was so cool, so simple.” However, Schunk admits she doesn’t think it’s yet possible for micro-air vehicles, which would be built on these aeromechanical principles, to be entirely 3D printed, partly because of the motors that are required to drive its motion. “I know there’s effort for people to use shape-memory alloys [SMA]”— here she references metals that change shape when voltage is applied to them, and then return to their original shape when the voltage is removed—“but since that’s, to my understanding, metal, you cannot 3D print that. But those shape-memory alloys are attached, then, to the skeleton, and drive the motion.” Interestingly, this is an area already of interest to Tyler Benster. “I’m interested in bringing metal 3D printing more to the mainstream, because I think with plastic you are somewhat restricted with the functional applications,” he says. “There’s this game I like to play where I walk into a room and I look around and I ask myself, what in this room would I rather have 3D printed than however it’s currently made? ... With metal 3D printing, there are some incredibly cool applications…where the 3D-printed version is massively superior to the traditionally manufactured one.” The example Benster cites is one of 3D-printed titanium hip implants, which are already in use and stronger when 3D printed. Perhaps we could one day see 3D-printed micro-air vehicles, or even traditional rigid-wing aircraft, after all. In fact, “The CEO of Airbus says they want to 3D print an airplane by 2050,” Benster smiles (12). And 3D-printed organs? “Those applications are absolutely fascinating,” Benster says—and perhaps not as far away as a 3D-printed plane. “To give you a little timeline of 3D printing in the near and foreseeable future…in ten years we’ll see the first 3D-printed organs.” Benster might be right (13, 14), though the future could be closer than he thinks.
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