Will 3D printing fulfill the predictions of those who say it will have a “transformative” effect on manufacturing? The development of custom designs for additive manufacturing, and the emergence of faster, more versatile and accurate 3D printers, are raising the expectations of those who believe it will.
Engineers at MIT, for instance, have developed techniques to tailor the flexibility and stiffness of 3D-printed mesh materials for use in ankle and knee braces. The stretchy materials, capable of supporting the soft tissues of the human body, also hold promise for use in implantable devices.
A startup out of MIT is also making headlines for its development of a multi-material inkjet 3D printer with machine-vision and machine-learning capabilities. The 3D printer can print parts with integrated electronic components and is reported to be the first 3D printer to learn the properties of a material and predict its behavior.
Following are reports by MIT News writers Jennifer Chu and Zach Winn, who detail the work behind these developments.
Engineers 3D Print Flexible Mesh for Ankle and Knee Braces
Techniques could lead to personalized wearable and implantable devices.
Jennifer Chu | MIT News
Hearing aids, dental crowns, and limb prosthetics are some of the medical devices that can now be digitally designed and customized for individual patients, thanks to 3D printing. However, these devices are typically designed to replace or support bones and other rigid parts of the body, and are often printed from solid, relatively inflexible material.
Now MIT engineers have designed pliable, 3D-printed mesh materials whose flexibility and toughness they can tune to emulate and support softer tissues, such as muscles and tendons. They can tailor the intricate structures in each mesh, and they envision the tough yet stretchy fabric-like material being used as personalized, wearable supports, including ankle or knee braces, and even implantable devices, such as hernia meshes, that better match to a person’s body.
As a demonstration, the team printed a flexible mesh for use in an ankle brace. They tailored the mesh’s structure to prevent the ankle from turning inward — a common cause of injury — while allowing the joint to move freely in other directions. The researchers also fabricated a knee brace design that could conform to the knee even as it bends. And, they produced a glove with a 3D-printed mesh sewn into its top surface, which conforms to a wearer’s knuckles, providing resistance against involuntary clenching that can occur following a stroke.
“This work is new in that it focuses on the mechanical properties and geometries required to support soft tissues,” said Sebastian Pattinson, who conducted the research as a postdoc at MIT.
Pattinson, now on the faculty at Cambridge University, is the lead author of a study published [June 19] in the journal Advanced Functional Materials. His MIT co-authors include Meghan Huber, Sanha Kim, Jongwoo Lee, Sarah Grunsfeld, Ricardo Roberts, Gregory Dreifus, Christoph Meier, and Lei Liu, as well as Sun Jae Professor in Mechanical Engineering Neville Hogan and associate professor of mechanical engineering A. John Hart.
Riding Collagen’s Wave
The team’s flexible meshes were inspired by the pliable, conformable nature of fabrics.
“3D-printed clothing and devices tend to be very bulky,” Pattinson said. “We were trying to think of how we can make 3D-printed constructs more flexible and comfortable, like textiles and fabrics.”
Pattinson found further inspiration in collagen, the structural protein that makes up much of the body’s soft tissues and is found in ligaments, tendons, and muscles. Under a microscope, collagen can resemble curvy, intertwined strands, similar to loosely braided elastic ribbons. When stretched, this collagen initially does so easily, as the kinks in its structure straighten out. But once taut, the strands are harder to extend.
Inspired by collagen’s molecular structure, Pattinson designed wavy patterns, which he 3D-printed using thermoplastic polyurethane as the printing material. He then fabricated a mesh configuration to resemble stretchy yet tough, pliable fabric. The taller he designed the waves, the more the mesh could be stretched at low strain before becoming stiffer — a design principle that can help to tailor a mesh’s degree of flexibility and helped it to mimic soft tissue.
The researchers printed a long strip of the mesh and tested its support on the ankles of several healthy volunteers. For each volunteer, the team adhered a strip along the length of the outside of the ankle, in an orientation that they predicted would support the ankle if it turned inward.
They then put each volunteer’s ankle into an ankle stiffness measurement robot — named, logically, Anklebot — that was developed in Hogan’s lab. The Anklebot moved their ankles in 12 different directions, and then measured the force the ankle exerted with each movement, with the mesh and without it, to understand how the mesh affected the ankle’s stiffness in different directions.
In general, they found the mesh increased the ankle’s stiffness during inversion, while leaving it relatively unaffected as it moved in other directions.
“The beauty of this technique lies in its simplicity and versatility. Mesh can be made on a basic desktop 3D printer, and the mechanics can be tailored to precisely match those of soft tissue,” Hart said.
Stiffer, Cooler Drapes
The team’s ankle brace was made using relatively stretchy material. But for other applications, such as implantable hernia meshes, it might be useful to include a stiffer material that is, at the same time, just as conformable. To this end, the team developed a way to incorporate stronger and stiffer fibers and threads into a pliable mesh, by printing stainless steel fibers over regions of an elastic mesh where stiffer properties would be needed, and then printing a third elastic layer over the steel to sandwich the stiffer thread into the mesh.
The combination of stiff and elastic materials can give a mesh the ability to stretch easily up to a point, after which it starts to stiffen, providing stronger support to prevent, for instance, a muscle from overstraining.
The team also developed two other techniques to give the printed mesh an almost fabric-like quality, enabling it to conform easily to the body, even while in motion.
“One of the reasons textiles are so flexible is that the fibers are able to move relative to each other easily,” Pattinson said. “We also wanted to mimic that capability in the 3D-printed parts.”
In traditional 3D printing, a material is printed through a heated nozzle, layer by layer. When heated polymer is extruded, it bonds with the layer underneath it. Pattinson found that, once he printed a first layer, if he raised the print nozzle slightly, the material coming out of the nozzle would take a bit longer to land on the layer below, giving the material time to cool. As a result, it would be less sticky. By printing a mesh pattern in this way, Pattinson was able to create layers that, rather than being fully bonded, were free to move relative to each other, and he demonstrated this in a multi-layer mesh that draped over and conformed to the shape of a golf ball.
Finally, the team designed meshes that incorporated auxetic structures — patterns that become wider when you pull on them. For instance, they were able to print meshes, the middle of which consisted of structures that, when stretched, became wider rather than contracting as a normal mesh would. This property is useful for supporting highly curved surfaces of the body. To that end, the researchers fashioned an auxetic mesh into a potential knee brace design and found that it conformed to the joint.
“There’s potential to make all sorts of devices that interface with the human body,” Pattinson said. Surgical meshes, orthoses, even cardiovascular devices like stents — you can imagine all potentially benefiting from the kinds of structures we show.”
This research was supported in part by the National Science Foundation, the MIT-Skoltech Next Generation Program, and the Eric P. and Evelyn E. Newman Fund at MIT.
Reprinted with permission of MIT News (http://news.mit.edu/).
A 3D Printer Powered by Machine Vision and Artificial Intelligence
MIT startup Inkbit is overcoming traditional constraints to 3D printing by giving its machines “eyes and brains.”
Zach Winn | MIT News
Objects made with 3D printing can be lighter, stronger, and more complex than those produced through traditional manufacturing methods. But several technical challenges must be overcome before 3D printing transforms the production of most devices.
Commercially available printers generally offer only high speed, high precision, or high-quality materials. Rarely do they offer all three, limiting their usefulness as a manufacturing tool. Today, 3D printing is used mainly for prototyping and low-volume production of specialized parts.
Now Inkbit, a startup out of MIT, is working to bring all of the benefits of 3D printing to a slew of products that have never been printed before — and it’s aiming to do so at volumes that would radically disrupt production processes in a variety of industries.
The company is accomplishing this by pairing its multi-material inkjet 3D printer with machine-vision and machine-learning systems. The vision system comprehensively scans each layer of the object as it’s being printed to correct errors in real-time, while the machine-learning system uses that information to predict the warping behavior of materials and make more accurate final products.
“The company was born out of the idea of endowing a 3D printer with eyes and brains,” said Inkbit co-founder and CEO Davide Marini, Ph.D., ’03.
That idea unlocks a range of applications for Inkbit’s machine. The company said it can print more flexible materials much more accurately than other printers. If an object, including a computer chip or other electronic component, is placed on the print area, the machine can precisely print materials around it. And when an object is complete, the machine keeps a digital replica that can be used for quality assurance.
Inkbit is still an early-stage company. It currently has one operational production-grade printer. But it will begin selling printed products later this year, starting with a pilot with Johnson and Johnson, before selling its printers next year. If Inkbit can leverage current interest from companies that sell medical devices, consumer products, and automotive components, its machines will be playing a leading production role in a host of multi-billion-dollar markets in the next few years, from dental aligners to industrial tooling and sleep apnea masks.
“Everyone knows the advantages of 3D printing are enormous,” Marini said. “But most people are experiencing problems adopting it. The technology just isn’t there yet. Our machine is the first one that can learn the properties of a material and predict its behavior. I believe it will be transformative, because it will enable anyone to go from an idea to a usable product extremely quickly. It opens up business opportunities for everyone.”
A Printer with Potential
Some of the hardest materials to print today are also the most commonly used in current manufacturing processes. That includes rubber-like materials, such as silicone, and high-temperature materials, such as epoxy, which are often used for insulating electronics and in a variety of consumer, health, and industrial products.
These materials are usually difficult to print, leading to uneven distribution and print process failures, like clogging. They also tend to shrink or round at the edges over time. Inkbit co-founders Wojciech Matusik (an associate professor of electrical engineering and computer science), Javier Ramos (BS ’12, SM ’14), Wenshou Wang, and Kiril Vidimce (SM ’14) have been working on these problems for years in Matusik’s Computational Fabrications Group within the Computer Science and Artificial Intelligence Laboratory (CSAIL).
In 2015, the co-founders were among a group of researchers that created a relatively low-cost, precise 3D printer that could print a record 10 materials at once by leveraging machine vision. The feat got the attention of many large companies interested in transitioning production to 3D printing, and the following year, the four engineers received support from the Deshpande Center to commercialize their idea of joining machine vision with 3D printing.
At MIT, Matusik’s research group used a simple 3D scanner to track its machine’s progress. For Inkbit’s first printer, the founders wanted to dramatically improve “the eyes” of their machine. They decided to use an optical coherence tomography (OCT) scanner, which uses long wavelengths of light to see through the surface of materials and scan layers of material at a resolution the fraction of the width of a human hair.
Because OCT scanners are traditionally only used by ophthalmologists to examine below the surface of patients’ eyes, the only ones available were far too slow to scan each layer of a 3D printed part — so Inkbit’s team “bit the bullet,” as Marini described it, and built a custom OCT scanner that he said is 100 times faster than anything else on the market today.
When a layer is printed and scanned, the company’s proprietary machine-vision and machine-learning systems automatically correct any errors in real-time and proactively compensate for the warping and shrinkage behavior of a fickle material. Those processes further expand the range of materials the company is able to print with by removing the rollers and scrapers used by some other printers to ensure precision, which tend to jam when used with difficult-to-print materials.
The system is designed to allow users to prototype and manufacture new objects on the same machine. Inkbit’s current industrial printer has 16 print heads to create multi-material parts, and a print block big enough to produce hundreds of thousands of fist-sized products each year (or smaller numbers of larger products). The machine’s contactless inkjet design means increasing the size of later iterations will be as simple as expanding the print block.
“Before, people could make prototypes with multi-material printers, but they couldn’t really manufacture final parts,” Matusik said, noting that the post-processing of Inkbit’s parts can be fully automated. “This is something that’s not possible using any other manufacturing methods.”
The novel capabilities of Inkbit’s machine mean that some of the materials the founders want to print with are not available, so the company has created some of its own chemistries to push the performance of their products to the limit. A proprietary system for mixing two materials just before printing will be available on the printers Inkbit ships next year. The two-part chemistry mixing system will allow the company to print a broader range of engineering-grade materials.
Johnson and Johnson, a strategic partner of Inkbit, is in the process of acquiring one of the first printers. The MIT Startup Exchange Accelerator (STEX25) has also been instrumental in exposing Inkbit to leading corporations, such as Amgen, Asics, BAE Systems, Bosch, Chanel, Lockheed Martin, Medtronic, Novartis, and others.
Today, the founders spend a lot of their time educating product design teams that have never been able to 3D print their products before — let alone incorporate electronic components into 3D-printed parts.
It may be a while before designers and inventors take full advantage of the possibilities unlocked by integrated, multi-material 3D printing. But for now, Inkbit is working to ensure that, when that future comes, the most imaginative people will have a machine to work with.
“Some of this is so far ahead of its time,” Matusik said. “I think it will be really fascinating to see how people are going to use it for final products.”
Reprinted with permission of MIT News (http://news.mit.edu/).