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The Mechanical Engineering Future Is Caught Up in a 3D-Printed Spider Web

MIT researchers explore the poorly-understood structures of spider webs thanks to new computational methods.

Famously, spider silk is tougher than both steel and kevlar. That is, out of the three materials, it can absorb the most energy before breaking—a strand of silk may be able to stretch to up to five times the length of its relaxed state before giving way. With a material that's both as light as a parachute and strong as a bullet-proof vest, nature really figured something out with its arachnids. And, gradually, human scientists are figuring it out too.

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Mechanical engineering researchers at MIT have devised a new method of studying the still somewhat mysterious properties of spider silk via computational modeling and mechanical analysis, with the result being a technique for 3D printing the material—weaving synthetic spider webs, in other words. Their work is described in a paper published Friday in Nature Communications.

Spider silk isn't just durable, it's awesomely multi-purpose. The stuff is useful for tasks including but not limited to catching prey, sensing vibration, protecting offspring, route-finding, and even flying (a talent known as "ballooning". This range comes courtesy of not just the particular properties of individual silk strands, but of how they're put together into webs. Unfortunately, collecting natural web samples suitable for experimental testing is all but impossible, according to the MIT engineers.

Enter 3D printing. Thanks to computer-guided micro-scale fabrication technology, researchers can create and test whatever sort of web they desire. "3D printing offers unique advantages over traditional fabrication routes (for example, casting or weaving) in that the geometry can be easily altered without requiring fabrication of new moulds," the MIT group, led by materials scientist Markus Buehler, writes. "For example, reactive, resin-based materials can be patterned into complex web structures that would be cumbersome, if not impossible, with existing textile methods."

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"Ultimately we merged the physical with the computational in our experiments," Buehler says.

The computational nature of web-weaving has to do with a central optimization problem involving relationships between three competing web features: spider web structure, loading points, and failure mechanisms. By adjusting the distribution of materials around the web, a spider can optimize for a specific sort of prey. This was mirrored in the 3D-printed webs by varying the diameters of individual silk strands across different portions of the web architecture.

"For the case of localized loading, more uniform thread diameters (and hence equivalent failure loads) are required for optimized strength," Buehler and co. write. "By contrast, distributed loads require thicker radial threads (hence higher failure loads) relative to the spiral threads. Our observations reveal that the web strength depends on the material distribution, offering insight into the observations of the thickness ratio within natural spider webs."

It's not terribly difficult to see how the spider web optimization problem extends into the realm of human engineering. For one thing, we don't have anything in our materials arsenal quite like spider silk. We know what it's made of, of course, and can recreate the stuff—as the MIT group did here—but that can only count for so much when you're not using it in the same ways as spiders themselves. The researchers' next tasks involve testing their 3D-printed webs in controlled impact and vibration experiments, allowing them to observe their changing properties in real-time.

Via MIT, Marc Meyers, a professor of mechanical and aerospace engineering at the University of California at San Diego (that's unaffiliated with the current work), offers: "Biological materials and structures are the new frontier of engineering. This most recent significant contribution by Markus Buehler and colleagues goes beyond the first stage, which is to understand nature, and make significant inroads into creating a bioinspired structure."