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Multi-functional microbots are here. So is a 3D printing technique that creates 'piece of mind.'
A hybrid approach to fabricating soft materials at the millimeter scale could pave the way for a new generation of flexible micro-robots for medical and environmental tasks. Also new is a 3D printing technique that enables faster and better physical models of patient-specific medical data.
Soft Multi-functional Robots Get Really Small
By Benjamin Boettner
CAMBRIDGE, Mass. – Roboticists are envisioning a future in which soft, animal-inspired robots can be safely deployed in difficult-to-access environments, such as inside the human body or in spaces that are too dangerous for humans to work, in which rigid robots cannot currently be used. Centimeter-sized soft robots have been created, but thus far, it has not been possible to fabricate multifunctional flexible robots that can move and operate at smaller size scales.
A team of researchers at Harvard's Wyss Institute for Biologically Inspired Engineering, Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), and Boston University now has overcome this challenge by developing an integrated fabrication process that enables the design of soft robots on the millimeter scale with micrometer-scale features. To demonstrate the capabilities of their new technology, the team created a robotic soft spider–inspired by the millimeter-sized colorful Australian peacock spider–from a single elastic material with body-shaping, motion, and color features. The study is published in Advanced Materials.
"The smallest soft robotic systems still tend to be very simple, with usually only one degree of freedom, which means that they can only actuate one particular change in shape or type of movement," said Sheila Russo, Ph.D., co-author of the study. Russo helped initiate the project as a postdoctoral fellow in Robert Wood's group at the Wyss Institute and SEAS and now is assistant professor at Boston University. "By developing a new hybrid technology that merges three different fabrication techniques, we created a soft robotic spider made only of silicone rubber with 18 degrees of freedom, encompassing changes in structure, motion, and color, and with tiny features in the micrometer range."
Wood, Ph.D., is a core faculty member and co-leader of the Bioinspired Soft Robotics platform at the Wyss Institute and the Charles River Professor of Engineering and Applied Sciences at SEAS. "In the realm of soft robotic devices, this new fabrication approach can pave the way towards achieving similar levels of complexity and functionality on this small scale as those exhibited by their rigid counterparts. In the future, it can also help us emulate and understand structure-function relationships in small animals much better than rigid robots can," he said.
In their Microfluidic Origami for Reconfigurable Pneumatic/Hydraulic (MORPH) devices, the team first used a soft lithography technique to generate 12 layers of an elastic silicone that together constitute the soft spider's material basis. Each layer is precisely cut out of a mold with a laser-micromachining technique, and then bonded to the one below to create the rough 3D structure of the soft spider.
Key to transforming this intermediate structure into the final design is a pre-conceived network of hollow microfluidic channels that is integrated into individual layers. A third technique, known as injection induced self-folding, pressurized one set of these integrated microfluidic channels with a curable resin from the outside. This induces individual layers and, with them, also their neighboring layers, to locally bend into their final configuration, which is fixed in space when the resin hardens. This way, for example, the soft spider's swollen abdomen and downward-curved legs become permanent features.
"We can precisely control this origami-like folding process by varying the thickness and relative consistency of the silicone material adjacent to the channels across different layers or by laser-cutting at different distances from the channels. During pressurization, the channels then function as actuators that induce a permanent structural change," said first and corresponding author Tommaso Ranzani, Ph.D., who started the study as a postdoctoral fellow in Wood's group and now also is assistant professor at Boston University.
The remaining set of integrated microfluidic channels were used as additional actuators to colorize the eyes and simulate the abdominal color patterns of the peacock spider species by flowing colored fluids; and to induce walking-like movements in the leg structures. "This first MORPH system was fabricated in a single, monolithic process that can be performed in a few days and easily iterated in design optimization efforts," said Ranzani.
"The MORPH approach could open up the field of soft robotics to researchers who are more focused on medical applications where the smaller sizes and flexibility of these robots could enable an entirely new approach to endoscopy and microsurgery," said Wyss Institute Founding Director Donald Ingber, M.D., Ph.D., who is also the Judah Folkman Professor of Vascular Biology at HMS and the Vascular Biology Program at Boston Children's Hospital, as well as professor of bioengineering at SEAS.
Additional authors on the study are Nicholas Bartlett, a graduate student on Wood's team, and Michael Wehner, Ph.D., a former postdoctoral fellow with Wood, who now is assistant professor at University of California Santa Cruz. The study was funded by Harvard's Wyss Institute, the Defense Advanced Research Project Agency (DARPA), and a National Defense Science and Engineering Graduate Fellowship.
The Wyss Institute for Biologically Inspired Engineering at Harvard University (http://wyss.harvard.edu) uses nature's design principles to develop bioinspired materials and devices that will transform medicine and create a more sustainable world. Wyss researchers are developing innovative new engineering solutions for healthcare, energy, architecture, robotics, and manufacturing that are translated into commercial products and therapies through collaborations with clinical investigators, corporate alliances, and formation of new startups.
The Harvard John A. Paulson School of Engineering and Applied Sciences (http://seas.harvard.edu) serves as the connector and integrator of Harvard's teaching and research efforts in engineering, applied sciences, and technology.
Benjamin Boettner is a science writer for the Wyss Institute for Biologically Inspired Engineering at Harvard University.
Creating Piece of Mind
By Lindsay Brownell
Three of the co-authors of the paper, left to right: Ahmed Hosny holding models of Steven Keating's tumor, Steven Keating holding a model of his own skull, and James Weaver holding models of Keating's MRI scan. Credit: Wyss Institute at Harvard University
BOSTON – What if you could hold a physical model of your own brain in your hands, accurate down to its every unique fold? That's just a normal part of life for Steven Keating, Ph.D., who had a baseball-sized tumor removed from his brain at age 26 while he was a graduate student in the MIT Media Lab's Mediated Matter group.
Curious to see what his brain actually looked like before the tumor was removed, and with the goal of better understanding his diagnosis and treatment options, Keating collected his medical data and began 3D printing his MRI and CT scans, but was frustrated that existing methods were prohibitively time-intensive, cumbersome, and failed to accurately reveal important features of interest. Keating reached out to some of his group's collaborators, including members of the Wyss Institute at Harvard University, who were exploring a new method for 3D printing biological samples.
"It never occurred to us to use this approach for human anatomy until Steve came to us and said, 'Guys, here's my data, what can we do?" said Ahmed Hosny, who was a research fellow with at the Wyss Institute at the time and is now a machine learning engineer at the Dana-Farber Cancer Institute.
The result of that impromptu collaboration–which grew to involve James Weaver, Ph.D., senior research scientist at the Wyss Institute; Neri Oxman, Ph.D., director of the MIT Media Lab's Mediated Matter group and associate professor of Media Arts and Sciences; and a team of researchers and physicians at several other academic and medical centers in the U.S. and Germany–is a new technique that allows images from MRI, CT, and other medical scans to be easily and quickly converted into physical models with unprecedented detail. The research is reported in 3D Printing and Additive Manufacturing.
"I nearly jumped out of my chair when I saw what this technology is able to do," said Beth Ripley, M.D., Ph.D., an assistant professor of radiology at the University of Washington and clinical radiologist at the Seattle VA, and co-author of the paper. "It creates exquisitely detailed 3D-printed medical models with a fraction of the manual labor currently required, making 3D printing more accessible to the medical field as a tool for research and diagnosis."
Imaging technologies like MRI and CT scans produce high-resolution images as a series of "slices" that reveal the details of structures inside the human body, making them an invaluable resource for evaluating and diagnosing medical conditions. Most 3D printers build physical models in a layer-by-layer process, so feeding them layers of medical images to create a solid structure is an obvious synergy between the two technologies.
High-throughput tissue filtering, a major feature of the approach developed by the authors of the study, can help quickly remove extraneous tissues to reveal the desired underlying structures (right) without sacrificing the resolution or intensity gradients present in the native imaging data (left and center). Credit: James Weaver and Steven Keating/Wyss Institute at Harvard University
However, there is a problem: MRI and CT scans produce images with so much detail that the objects of interest need to be isolated from surrounding tissue and converted into surface meshes in order to be printed. This is achieved via either a very time-intensive process called "segmentation," where a radiologist manually traces the desired object on every single image slice (sometimes hundreds of images for a single sample), or an automatic "thresholding" process, in which a computer program quickly converts areas that contain grayscale pixels into either solid black or solid white pixels, based on a shade of gray that is chosen to be the threshold between black and white. However, medical imaging data sets often contain objects that are irregularly shaped and lack clear, well-defined borders. As a result, auto-thresholding (or even manual segmentation) often over- or under-exaggerates the size of a feature of interest and washes out critical detail.
The new method described by the paper's authors gives medical professionals the best of both worlds, offering a fast and highly accurate method for converting complex images into a format that can be easily 3D printed. The key lies in printing with dithered bitmaps, a digital file format in which each pixel of a grayscale image is converted into a series of black and white pixels, and the density of the black pixels is what defines the different shades of gray rather than the pixels themselves varying in color.
Similar to the way images in black-and-white newsprint use varying sizes of black ink dots to convey shading, the more black pixels that are present in a given area, the darker it appears. By simplifying all pixels from various shades of gray into a mixture of black or white pixels, dithered bitmaps allow a 3D printer to print complex medical images using two different materials that preserve all the subtle variations of the original data with much greater accuracy and speed.
The team of researchers used bitmap-based 3D printing to create models of Keating's brain and tumor that faithfully preserved all of the gradations of detail present in the raw MRI data down to a resolution that is on par with what the human eye can distinguish from about 9-10 inches away.
Using this same approach, they were also able to print a variable stiffness model of a human heart valve using different materials for the valve tissue versus the mineral plaques that had formed within the valve, resulting in a model that exhibited mechanical property gradients and provided new insights into the actual effects of the plaques on valve function.
"Our approach not only allows for high levels of detail to be preserved and printed into medical models, but it also saves a tremendous amount of time and money," said Weaver, who is the corresponding author of the paper. "Manually segmenting a CT scan of a healthy human foot, with all its internal bone structure, bone marrow, tendons, muscles, soft tissue, and skin, for example, can take more than 30 hours, even by a trained professional. We were able to do it in less than an hour."
The researchers hope that their method will help make 3D printing a more viable tool for routine exams and diagnoses, patient education, and understanding the human body.
Unlike grayscale photographs, which require several shades of gray to convey gradients (left), halftones (common in newsprint images) can preserve grayscale intensity gradients using only a single color of ink (right). A similar approach was used for processing the image stacks for the 3D printed models described in the paper. Credit: James Weaver/Wyss Institute at Harvard University
"Right now, it's just too expensive for hospitals to employ a team of specialists to go in and hand-segment image data sets for 3D printing, except in extremely high-risk or high-profile cases. We're hoping to change that," said Hosny.
For that to happen, some entrenched elements of the medical field need to change as well. Most patients' data are compressed to save space on hospital servers, so it's often difficult to get the raw MRI or CT scan files needed for high-resolution 3D printing. Additionally, the team's research was facilitated through a collaboration with leading 3D printer manufacturer Stratasys, which allowed access to their 3D printer's intrinsic bitmap printing capabilities. New software packages also still need to be developed to better leverage these capabilities and make them more accessible to medical professionals.
Despite these hurdles, the researchers are confident that their achievements present a significant value to the medical community.
"I imagine that sometime within the next five years, the day could come when any patient that goes into a doctor's office for a routine or non-routine CT or MRI scan will be able to get a 3D-printed model of their patient-specific data within a few days," said Weaver.
Keating, who has become a passionate advocate of efforts to enable patients to access their own medical data, still 3D prints his MRI scans to see how his skull is healing post-surgery and check on his brain to make sure his tumor isn't coming back. "The ability to understand what's happening inside of you, to actually hold it in your hands and see the effects of treatment, is incredibly empowering," he said.
"Curiosity is one of the biggest drivers of innovation and change for the greater good, especially when it involves exploring questions across disciplines and institutions. The Wyss Institute is proud to be a space where this kind of cross-field innovation can flourish," said Wyss Institute Founding Director Donald Ingber, M.D., Ph.D., who is also the Judah Folkman Professor of Vascular Biology at Harvard Medical School (HMS) and the Vascular Biology Program at Boston Children's Hospital, as well as professor of bioengineering at Harvard's John A. Paulson School of Engineering and Applied Sciences (SEAS).
A 3D-printed multi-material model of a calcified heart valve shows hard calcium plaque deposits (white) with fine-scale gradients in mineral density that are impossible to fully capture using conventional biomedical 3D printing approaches. Credit: James Weaver and Ahmed Hosny/Wyss Institute at Harvard University
This work was supported by a grant from the Human Frontier Science Program, the National Heart, Lung, and Blood Institute, the National Institute of Biomedical Imaging and Bioengineering, and a Gottfried Wilhelm Leibniz-Preis 2010.
About the Wyss Institute for Biologically Inspired Engineering
The Wyss Institute creates transformative technological breakthroughs by engaging in high risk research, and crosses disciplinary and institutional barriers, working as an alliance that includes Harvard's Schools of Medicine, Engineering, Arts & Sciences and Design, and in partnership with Beth Israel Deaconess Medical Center, Brigham and Women's Hospital, Boston Children's Hospital, Dana–Farber Cancer Institute, Massachusetts General Hospital, the University of Massachusetts Medical School, Spaulding Rehabilitation Hospital, Boston University, Tufts University, Charité – Universitätsmedizin Berlin, University of Zurich and Massachusetts Institute of Technology.
About the MIT Media Lab
The MIT Media Lab (http://media.mit.edu) came into being in 1980 through the efforts of Professor Nicholas Negroponte and former MIT President and Science Advisor to President John F. Kennedy, Jerome Wiesner. The Lab grew out of the work of MIT's Architecture Machine Group and remains within MIT's School of Architecture + Planning. The Media Lab opened the doors to its I.M. Pei-designed Wiesner Building in 1985, and in its first decade was at the vanguard of the technology that enabled the digital revolution and enhanced human expression: innovative research ranging from cognition and learning, to electronic music, to holography.
In its second decade, the Lab literally took computing out of the box, embedding the bits of the digital realm with the atoms of our physical world. This led to expanded research in wearable computing, wireless "viral" communications, machines with common sense, new forms of artistic expression, and innovative approaches to how children learn.
Now, in its fourth decade, the Media Lab continues to check traditional disciplines at the door. Product designers, nanotechnologists, data-visualization experts, industry researchers, and pioneers of computer interfaces work side by side to invent–and reinvent–how humans experience, and can be aided by, technology.
Lindsay Brownell is a science writer for the Wyss Institute for Biologically Inspired Engineering at Harvard University.
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