Nucleation is the seminal process in the formation of ordered structures ranging from simple inorganic crystals to macromolecular matrices. Observations over the past 15 years have revealed a rich set of hierarchical nucleation pathways involving higher-order species ranging from multi-ion clusters to dense liquid droplets, as well as transient crystalline or amorphous phases. Despite this complexity, the pathways that lead to nucleation can be described by a holistic framework that is rooted in classical concepts, but which takes into account the coupled effects of perturbations in free-energy landscapes and the impact of dynamical factors. This article describes that framework using a series of in situ transmission electron microscopy and atomic force microscopy studies on inorganic, organic, and macromolecular systems to illustrate the evolution in nucleation processes as these perturbations and dynamical factors come into play. The results provide a common basis for understanding development of order in systems as diverse as simple salt crystals, branched semiconductor nanowires, and microbial membranes.

Carbon nanostructures, especially carbon nanotubes and graphene nanopores, have been suggested for use in a wide range of purification and separation applications, from the desalination of seawater to the separation of liquids and gases. However, achieving the required high degree of selectivity among the molecules passing through the pores while maintaining rapid transport is a difficult challenge. Here, we examine the physical mechanisms by which nanopores distinguish between small ions and reject salts while passing water, as examples of how selectivity and purification can be achieved. The simple principles described can be utilized to design novel nanoporous materials for the separation of a wide range of gases, liquids, and solutes.

A thin-film field-effect transistor (TFT) is a three-terminal device comprising source, drain, and gate electrodes, a dielectric layer, a semiconductor layer, and a substrate. The TFT is a fundamental building component in a variety of electronic devices. Developing an intrinsically stretchable TFT entails availability and usage of a functional material with elastomeric deformability in response to an externally applied stress. This represents a major materials challenge. In this article, we survey strategies to synthesize these elastomeric functional materials, and how these materials are assembled to fabricate intrinsically stretchable TFT devices. Developing solution-based printing technology to assemble intrinsically stretchable TFTs is considered a prospective strategy for wearable electronics for industrial adaptation in the near future.

RNA nanotechnology seeks to exploit the structural and functional properties of the RNA molecule in order to rationally design RNA nanoparticles and devices for applications in biotechnology and medicine, among others. Compared to DNA, RNA can adopt a larger diversity of structural motifs that allows the construction of more complicated nanoparticles that can be self-assembled during synthesis by the RNA polymerase—a process called co-transcriptional folding. RNA nanostructures can be genetically encoded and co-transcriptionally folded in cells, which allows large-scale production of RNA nanoparticles for therapeutic use or the application as scaffolds in cells for manipulating cellular components for use in synthetic biology. In this article, we describe the origins of the RNA nanotechnology research field and how it has been inspired by DNA nanotechnology. Recent developments of co-transcriptionally folded RNA nanostructures and the construction of RNA knots are discussed in relation to design principles and challenges, and speculations about future directions of the field are provided.

Compliant robots, a class of so-called soft robots, made from elastomeric materials, require flexible or stretchable sensors for functional sophistication beyond that of open-loop controls and actuations. These robots have expanded the scope of research in robotics from fast, strong, and precise industrial manufacturing toward new needs of adaptation and safety—the realm of human–robot interactions (HRIs). HRIs include circumstances ranging from existing tasks such as vacuum cleaning to the far-reaching goal of direct contact with the heart for ventricular assist devices, and wearable robots as an intermediate task for force-augmenting exoskeletons. Toward these goals, many efforts are being made to impart sensation for feedback control via flexible or stretchable sensors that can be integrated with the soft bodies of these robots without hindering their motion or reducing their safety. This article briefly reviews the key techniques and tradeoffs for designing and fabricating these sensors. We describe the sensors that our research group uses for fluidically powered soft robots. We conclude with some perspectives about future directions of sensing integration for improved autonomy and interaction with humans in close proximity.

Historical pipe organs offer rich insights into the relationships between materials and music in the past, and they represent a laboratory for contemporary materials science. Recent cross-disciplinary research has explored problems of conservation and corrosion in old organ pipes. The ability of some notable European Baroque organs to produce sound is threatened by atmospheric corrosion of their lead-tin alloy pipes. Organic acids emitted from the wood of organ cases are corrosive agents for lead-rich pipes. Laboratory exposure experiments were used to study the roles of humidity and alloy composition in the susceptibility to organic acid attack. The rates of growth, as well as the compositions and morphologies of the corrosion products were studied using gravimetry, x-ray diffraction, and scanning electron microscopy of surfaces and cross sections. This interdisciplinary project provides one model for the interplay of scientific and humanities research in addressing materials problems in cultural heritage.

In Pixar’s Inside Out, the character Joy proclaims, “Do you ever look at someone and wonder what’s going on inside?” Driven by similar curiosity, the scientific community has developed remarkable in situ characterization tools to visualize the inner workings of complex, dynamic systems, elucidating their functions and enabling next-generation technologies. This article describes our research developing plasmonic techniques to visualize dynamic chemical transformations in situ with nanometer-scale resolution. As a model system, we investigated the hydrogenation and dehydrogenation of palladium nanocrystals. Using environmental electron microscopy and spectroscopy, we monitored this reaction with sub-2-nm spatial resolution and millisecond time resolution. Particles of different sizes, shapes, and crystallinities exhibit distinct thermodynamic and kinetic properties, highlighting several important design principles for next-generation catalysts and energy-storage devices.

Metal additive manufacturing (AM) processes, such as selective laser melting (SLM), enable powdered metals to be formed into arbitrary three-dimensional shapes. For aluminum alloys, which are desirable in many high-value applications for their low density and good mechanical performance, SLM is regarded as challenging due to the difficulties in laser melting aluminum powders. However, a number of recent studies have demonstrated successful aluminum processing, and have gone on to explore its potential for use in advanced AM componentry. In addition to enabling the fabrication of highly complex structures, SLM produces parts with characteristically fine microstructures that yield distinct mechanical properties. Research is rapidly progressing in this field, with promising results opening up a range of possible applications across scientific and industrial sectors. This article reports on recent developments in this area of research and highlights key topics that require further attention.