SPECIAL FEATURE: INTRODUCTION Novel materials SPECIAL FEATURE: INTRODUCTION John A. Rogersa,1 and Joseph M. DeSimoneb,1 Materials have central roles in all fields of engineer- The issue begins with three articles on materials for ing; they define, through structures and devices, our classes of biomedical devices that offer capabilities interfaces to the physical and the virtual world. The with direct benefits in human health. The first article, emergence of new materials catalyzes transformative by Ailianou et al. (1), describes fundamental studies of advances in civilizations, to an extent that eras of biodegradable polymers used in advanced vascular human development are often defined by the prevail- scaffolds designed for the treatment of coronary heart ing materials used in engineered systems, from the disease. These devices, known as stents, deploy into Stone, Bronze, and Iron Ages to the present times, blood vessels where they provide structural reinforce- aptly referred to as the Silicon or the Polymer Age. ment following procedures to remove obstructive From an academic standpoint, the fundamental phe- plaques. Traditional metal stents, used on more than nomena that define complex relationships between a half-million patients annually, remain in the body, chemical compositions, structures, and properties in where they present lifelong risks, most significantly advanced materials serve as the basis for some of because of their tendency to nucleate the formation the most intellectually stimulating and dynamic areas of blood clots. Biodegradable polymers provide an of research in the physical sciences. This work has alternative, in the form of stents that dissolve and additional appeal because it is intrinsically interdisci- disappear gradually after their function is no longer plinary and combines essential aspects of traditional needed, thereby eliminating unnecessary device load fields of study in physics, chemistry, and even biology, on the patient. Such types of stents are rapidly replacing to an increasing extent, together with engineering conventional counterparts. The findings reported in processes and control strategies. Progress in materials the Ailianou et al. article provide important insights science and in the engineering application of new into the morphological characteristics of the constitu- materials is essential to the pursuit of solutions to ent polymers that confer the mechanical strength nec- societal grand challenges. Examples span those re- essary for these and related applications. In particular, lated to the development of sustainable sources of the authors discover that deformations caused by de- energy, from high-power magnets for wind turbines to ployment of these stents align the polymer chains in a designer semiconductors for solar cells; to the inven- manner that increases their strength and prevents the tion of technologies that improve human health, from formation of fractures. Such understanding has impor- metal alloys for lightweight prosthetics to polymer tant practical implications for the engineering design matrices for controlled drug release; to progress in of ultrathin, low-profile devices. intra- and interplanetary travel within realms of objec- The second article focuses on materials designed tive and virtual reality alike, from high-efficiency batter- to prevent the formation of clots and biofilms on the ies for emissions-free vehicles, to carbon composites surfaces of stents and other implants. Specifically, for fuel-efficient spacecraft, to atomically thin films for Sunny et al. (2) introduce a composite coating that high-speed integrated circuits. consists of a porous solid matrix filled with a liquid, This Special Feature on Novel Materials presents a to yield a repellent surface that prevents fouling. This collection of perspectives articles, short reviews, and system, as demonstrated in transparent coatings on original research papers designed to capture some of endoscopes through a comprehensive set of animal the breadth and excitement in recent materials research. trials, involves a design inspired by the slippery sur- This representative set of topics intersects critical areas faces of the carnivorous pitcher plant, in which the in electronics, biology, advanced manufacturing, and liquid-infused material spontaneously forms a bio- chemical synthesis, with interdisciplinary foci that com- compatible, lubricating, “nonstick” overlayer. For endo- bine scientific discovery with engineering applications. scopes, the result is significantly enhanced antibacterial aDepartment of Materials Science and Engineering, Northwestern University, Evanston, IL 60208; and bDepartment of Chemistry, University of North Carolina, Chapel Hill, NC 27599 Author contributions: J.A.R. and J.M.D. wrote the paper. Conflict of interest statement: J.M.D. was a co-founder of Bioabsorbable Vascular Solutions, which was acquired by Abbott Vascular and is the subject of the paper by Ailianou et al. J.M.D. is also the co-founder/CEO of Carbon, which is commercializing the 3D printing technology referred to as CLIP. 1To whom correspondence may be addressed. Email: [email protected] or [email protected]. www.pnas.org/cgi/doi/10.1073/pnas.1614927113 PNAS | October 18, 2016 | vol. 113 | no. 42 | 11667–11669 Downloaded by guest on September 24, 2021 and antifouling properties, with an associated reduction in the quality. The resulting high-performance “inks” can be delivered need for time-consuming processes to clean the imaging lenses. by low-cost printing techniques to substrates of interest for the The consequences include decreased time and cost for endo- construction of various types of electronic devices. Demonstra- scopic procedures, with reduced risks to the patient and the tions include field-effect transistors with key properties that ex- ability to visualize previously obscure regions unobstructed and ceed those of devices formed with phosphorene synthesized in uninterrupted. Potential uses extend beyond camera-guided in- other ways. struments, surgical tools, and biomedical implants, to icephobic The second article on electronic materials, by Kim et al. (5), surfaces that can improve the safety of aircraft, clog-resistant oil summarizes recent progress in the development of light-emitting pipelines that can reduce the probability of spills, and marine devices (LEDs) that have the potential to enable displays with antifouling hulls that can increase the fuel efficiency of ships. brighter, more vivid colors and lower materials costs compared The third article in this area, by Fang et al. (3), reports a mate- to those of technologies that currently dominate the consumer rials solution to a long-standing challenge in classes of implant- electronics market. The active materials include both organic able devices that, unlike endoscopes or biodegradable stents, and inorganic constituents, combined in ways that provide great must provide reliable electronic functionality over the lifetime of versatility in their chemical compositions, crystalline structures, and the patient. In established technologies of this type, such as car- associated properties. Although many of these so-called hybrid diac pacemakers and cochlear implants, the electronics reside in materials are historically old, rapid advances over the last three metal or ceramic housings. Interfaces to the body occur through years in methods for chemical modification and physical deposition point contacts established via electrode pads at the terminal ends in forms optimized for operation in LEDs position these technolo- of connecting wires. Recent research establishes materials strate- gies as leading candidates for displays of the future, including gies and device designs for flexible, conformal devices that can those with paper-thin geometries and bendable mechanics. The integrate directly with the curved, moving surfaces of critical in- materials and approaches for flexible and printable electronics em- ternal organs, to provide qualitatively more sophisticated modes bodied in the preceding pair of articles could be relevant in this of operation in which the integrated electronic systems them- context, as backplane driver circuits for these hybrid LEDs. selves, rather than wired electrodes, establish the biotic/abiotic In any complex system, such as a display, materials-processing interface. A key challenge in achieving stable, long-term function strategies and fabrication schemes are critically important. Al- with such systems is in the development of thin, flexible coatings though solution printing approaches such as those used for the as structurally perfect, impermeable barriers to prevent penetra- phosphorene electronic inks in the paper by Kang et al. (4) are tion of surrounding biofluids into the active electronics. Results valuable, they are best suited for forming patterns of thin films in presented by Fang et al. (3) demonstrate that pristine, thin films of largely planar formats. Research over the last decade has estab- silica, thermally grown on the surfaces of device-grade silicon lished a broad range of materials and methods for printing 3D wafers and then physically integrated on top of flexible electronics objects. The article by Janusziewicz et al. (6) reports progress on platforms, can satisfy these demanding requirements, with pro- one of the most powerful and newest of these techniques. Here, jected operational lifetimes of many decades. This advance in specialized photosensitive polymers enable a process