QNAS
QNAS
QnAs with John Rogers Farooq Ahmed, Science Writer
From soft, stretchable biosensors that move naturally with the human body, to transient, biocompatible electronics that dissolve after use, John Rogers’ inventions seem to have sprung out of science fiction. He has received both a MacArthur Genius Grant and the Lemelson–Massachusetts Institute of Technology Prize for inventors and holds more than 100 patents, the vast majority of which have been licensed, including many by companies that he founded. As a materials scientist, Rogers is interested in novel function, but with a practical bent. As an example, instead of exploring exotic, so-called “wonder” materials, such as carbon nanotubes or graphene for his transient and stretchable electronic systems, he focused on new ways to use wellestablished materials, such as silicon, to leverage capabilities from the semiconductor industry. This fall, Rogers will become the Louis Simpson and Kimberly Querrey Professor and the director of the newly endowed Center for Bio-Integrated Electronics at Northwestern University, in Chicago. In keeping with his varied interests, Rogers will hold appointments in the Medical School, the School of Engineering and Applied Science, as well as the College of Arts and Sciences. PNAS recently spoke to Rogers, who was elected to the National Academy of Sciences in May 2015, about his current work. PNAS: You have developed a number of skin-like biosensor devices with healthcare applications. However, your Inaugural Article (1) describes methods for creating 3D micro- and nanoscale structures. What are the differences between what you can achieve with 2D vs. 3D materials? Rogers: This expanded emphasis on 3D systems was prompted by the structure of biology itself. Soft, 2D devices are great if you’re interested in technologies that can laminate onto the epidermis or wrap around organs, like the heart or brain. With this type of surface integration, you can record clinical quality physiological data in a continuous fashion, you can sense and stimulate cardiac function, and you can study certain aspects of the way that the brain processes information. But biology is inherently 3D. If you want to interface directly into the 3D neural networks that support the brain’s essential functions, for example, you need to think beyond traditional 2D architectures. You need
3D, open network constructs, capable of interacting with biology throughout volumes, not just across surfaces. PNAS: You use a method akin to origami, the Japanese art of paper-folding, called kirigami, to create these 3D structures. What was the inspiration for this approach? Rogers: Our techniques have some similarities to these art forms, especially in terms of creating complex, 3D geometries from 2D precursors. Manual folding methods, however, work fine for paper art, but they can’t be applied to the range of dimensions or the classes of materials that we have in mind for 3D, bio-integrated John Rogers. Image courtesy of the University of Illinois. electronics. Rather, with our theoretical collaborators, we’ve come up with techniques that rely on the physics of controlled buckling, related to the schemes that we originally developed to create stretchable forms of silicon. For example, if you take an ultrathin ribbon of silicon and bond it to a stretched rubbery support, then the silicon will spontaneously adopt a “wavy” geometry when the stretch is relaxed. This type of buckling creates a system that is much like a microscale version of an accordion bellows. As you stretch or compress the structure, the geometry changes in a way that avoids fracture in the silicon; you effectively get the mechanical properties of the rubber with the electronic properties of the silicon. What we’re doing now is different, but it starts with this core idea. We use much larger levels of stretch, and we exploit patterned surface chemistry to bond a 2D precursor of a hard material, such as silicon or any collection of inorganic materials, devices, or systems, to the support only at specific strategic locations. When the stretch is released, the nonbonded regions spontaneously delaminate and move upward, out of
This is a QnAs with a recently elected member of the National Academy of Sciences to accompany the member’s Inaugural Article on p. 11757 in issue 38 of volume 112.
www.pnas.org/cgi/doi/10.1073/pnas.1610865113
PNAS | August 9, 2016 | vol. 113 | no. 32 | 8881–8882
Kirigami in silicon microstructures (colorized scanning electron micrographs). Image courtesy of the University of Illinois and Northwestern University.
the plane, in a combination of coupled translational and rotational motions, thereby “grow” into a targeted 3D layout. PNAS: What are the benefits of using this technique, compared with other methods of creating 3D structures of minute sizes? Rogers: [Three-dimensional] printing is a hot topic these days, and the tools and techniques are impressive. High-performance semiconductors cannot be used, however, and the feature sizes that can be achieved are thousands of times larger than those found in commodity-integrated circuits. The length scalability of our
3D assembly process, from centimeters to nanometers, its high speed, parallel operation, and its compatibility with existing 2D electronic and optoelectronic materials and systems, make it very attractive for our broader goals. Although we chose a range of specific structures, including cube-, pyramid-, and jellyfish-like shapes, to highlight in the Inaugural Article (1), we are not focused on any particular geometry. Instead, we are establishing a set of capabilities, and a basic understanding of the mathematics that defines the accessible space of 3D geometries. It’s almost certainly the case that we won’t be able to build absolutely anything, but we’ve shown that we can access a very wide range. Another interesting feature is that this process is nearly agnostic to material type. Once you understand the fracture thresholds and the intrinsic mechanical stiffnesses, you can design the 2D precursor geometries and bonding sites to realize a targeted 3D shape. We’ve created demonstration structures in materials ranging from silicon, which is very brittle, to malleable metals, polymers, and plastics, and even fully formed semiconductor devices. We can mix and match them in a single plane or bond them so that they all move and transform into a 3D geometry as one unit. PNAS: How do you envision integrating these structures into next-generation devices? Rogers: Because our main interest is at the biotic/ abiotic interface, the short-term answer is to grow living tissues around our 3D constructs. We can seed cells so that they naturally proliferate, spread, and differentiate across these “active” scaffolds in a way that allows us to sense, stimulate, and interact with them as they grow. From optogenetics to biochemical sensors to neural circuitry, there are many exciting opportunities, and we feel like we’re still in a discovery mode, just beginning to scratch the surface of what will be possible.
1 Zhang Y, et al. (2015) A mechanically driven form of Kirigami as a route to 3D mesostructures in micro/nanomembranes. Proc Natl Acad Sci USA 112(38):11757–11764.
8882 | www.pnas.org/cgi/doi/10.1073/pnas.1610865113
Ahmed
QNAS
QnAs with John Rogers Farooq Ahmed, Science Writer
From soft, stretchable biosensors that move naturally with the human body, to transient, biocompatible electronics that dissolve after use, John Rogers’ inventions seem to have sprung out of science fiction. He has received both a MacArthur Genius Grant and the Lemelson–Massachusetts Institute of Technology Prize for inventors and holds more than 100 patents, the vast majority of which have been licensed, including many by companies that he founded. As a materials scientist, Rogers is interested in novel function, but with a practical bent. As an example, instead of exploring exotic, so-called “wonder” materials, such as carbon nanotubes or graphene for his transient and stretchable electronic systems, he focused on new ways to use wellestablished materials, such as silicon, to leverage capabilities from the semiconductor industry. This fall, Rogers will become the Louis Simpson and Kimberly Querrey Professor and the director of the newly endowed Center for Bio-Integrated Electronics at Northwestern University, in Chicago. In keeping with his varied interests, Rogers will hold appointments in the Medical School, the School of Engineering and Applied Science, as well as the College of Arts and Sciences. PNAS recently spoke to Rogers, who was elected to the National Academy of Sciences in May 2015, about his current work. PNAS: You have developed a number of skin-like biosensor devices with healthcare applications. However, your Inaugural Article (1) describes methods for creating 3D micro- and nanoscale structures. What are the differences between what you can achieve with 2D vs. 3D materials? Rogers: This expanded emphasis on 3D systems was prompted by the structure of biology itself. Soft, 2D devices are great if you’re interested in technologies that can laminate onto the epidermis or wrap around organs, like the heart or brain. With this type of surface integration, you can record clinical quality physiological data in a continuous fashion, you can sense and stimulate cardiac function, and you can study certain aspects of the way that the brain processes information. But biology is inherently 3D. If you want to interface directly into the 3D neural networks that support the brain’s essential functions, for example, you need to think beyond traditional 2D architectures. You need
3D, open network constructs, capable of interacting with biology throughout volumes, not just across surfaces. PNAS: You use a method akin to origami, the Japanese art of paper-folding, called kirigami, to create these 3D structures. What was the inspiration for this approach? Rogers: Our techniques have some similarities to these art forms, especially in terms of creating complex, 3D geometries from 2D precursors. Manual folding methods, however, work fine for paper art, but they can’t be applied to the range of dimensions or the classes of materials that we have in mind for 3D, bio-integrated John Rogers. Image courtesy of the University of Illinois. electronics. Rather, with our theoretical collaborators, we’ve come up with techniques that rely on the physics of controlled buckling, related to the schemes that we originally developed to create stretchable forms of silicon. For example, if you take an ultrathin ribbon of silicon and bond it to a stretched rubbery support, then the silicon will spontaneously adopt a “wavy” geometry when the stretch is relaxed. This type of buckling creates a system that is much like a microscale version of an accordion bellows. As you stretch or compress the structure, the geometry changes in a way that avoids fracture in the silicon; you effectively get the mechanical properties of the rubber with the electronic properties of the silicon. What we’re doing now is different, but it starts with this core idea. We use much larger levels of stretch, and we exploit patterned surface chemistry to bond a 2D precursor of a hard material, such as silicon or any collection of inorganic materials, devices, or systems, to the support only at specific strategic locations. When the stretch is released, the nonbonded regions spontaneously delaminate and move upward, out of
This is a QnAs with a recently elected member of the National Academy of Sciences to accompany the member’s Inaugural Article on p. 11757 in issue 38 of volume 112.
www.pnas.org/cgi/doi/10.1073/pnas.1610865113
PNAS | August 9, 2016 | vol. 113 | no. 32 | 8881–8882
Kirigami in silicon microstructures (colorized scanning electron micrographs). Image courtesy of the University of Illinois and Northwestern University.
the plane, in a combination of coupled translational and rotational motions, thereby “grow” into a targeted 3D layout. PNAS: What are the benefits of using this technique, compared with other methods of creating 3D structures of minute sizes? Rogers: [Three-dimensional] printing is a hot topic these days, and the tools and techniques are impressive. High-performance semiconductors cannot be used, however, and the feature sizes that can be achieved are thousands of times larger than those found in commodity-integrated circuits. The length scalability of our
3D assembly process, from centimeters to nanometers, its high speed, parallel operation, and its compatibility with existing 2D electronic and optoelectronic materials and systems, make it very attractive for our broader goals. Although we chose a range of specific structures, including cube-, pyramid-, and jellyfish-like shapes, to highlight in the Inaugural Article (1), we are not focused on any particular geometry. Instead, we are establishing a set of capabilities, and a basic understanding of the mathematics that defines the accessible space of 3D geometries. It’s almost certainly the case that we won’t be able to build absolutely anything, but we’ve shown that we can access a very wide range. Another interesting feature is that this process is nearly agnostic to material type. Once you understand the fracture thresholds and the intrinsic mechanical stiffnesses, you can design the 2D precursor geometries and bonding sites to realize a targeted 3D shape. We’ve created demonstration structures in materials ranging from silicon, which is very brittle, to malleable metals, polymers, and plastics, and even fully formed semiconductor devices. We can mix and match them in a single plane or bond them so that they all move and transform into a 3D geometry as one unit. PNAS: How do you envision integrating these structures into next-generation devices? Rogers: Because our main interest is at the biotic/ abiotic interface, the short-term answer is to grow living tissues around our 3D constructs. We can seed cells so that they naturally proliferate, spread, and differentiate across these “active” scaffolds in a way that allows us to sense, stimulate, and interact with them as they grow. From optogenetics to biochemical sensors to neural circuitry, there are many exciting opportunities, and we feel like we’re still in a discovery mode, just beginning to scratch the surface of what will be possible.
1 Zhang Y, et al. (2015) A mechanically driven form of Kirigami as a route to 3D mesostructures in micro/nanomembranes. Proc Natl Acad Sci USA 112(38):11757–11764.
8882 | www.pnas.org/cgi/doi/10.1073/pnas.1610865113
Ahmed
