The long-term success of an orthopedic implant largely depends on the extent of its osseointegration in the surrounding bone. During recent decades, there have been several attempts to develop porous structures and coatings in order to maximize the bone ingrowth on prosthesis surfaces. Innovative additive manufacturing technologies, such as electron beam melting (EBM), which are based upon building components by adding layers of material rather than by removing material from a raw shape, can provide a breakthrough solution, both to overcome the major limitations of the actual technologies and to significantly enhance the performance of porous scaffolds. This article reviews the latest developments in EBM technology applied to the preparation of highly biocompatible porous materials such as Trabecular Titanium and the production of orthopedic prostheses with enhanced characteristics.
This article addresses recent advances in the application of microscopy techniques to characterize crystallization processes as they relate to biomineralization and bioinspired materials synthesis. In particular, we focus on studies aimed at revealing the role organic macromolecules and functionalized surfaces play in modulating the mechanisms of nucleation and growth. In nucleation studies, we explore the use of methods such as in situ transmission electron microscopy, atomic force microscopy, and cryogenic electron microscopy to delineate formation pathways, phase stabilization, and the competing effects of free energy and kinetic barriers. In growth studies, we emphasize understanding the interactions of macromolecular constituents with growing crystals and characterization of the internal structures of the resulting composite crystals using techniques such as electron tomography, atom probe tomography, and vibrational spectromicroscopy. Examples are drawn from both biological and bioinspired synthetic systems.
The materials characterization universe is as large and multifaceted as the materials and engineering fields combined. Many methods have evolved over decades, or even centuries, from quite rudimentary tools to extremely sophisticated instruments. Measurement and testing of materials span properties from mechanical, to electrical, to thermal; materials classes from metals, to semiconductors, to insulators, with ceramics, polymers, and composites somewhere in between; scales from atomic through nano-, micro-, meso-, and macroscopic; and times spanning picoseconds to years in practice, to eons in simulation. The technical context of a materials measurement ranges from fundamental science, often with no immediately transparent connection, to future engineering applications, to quite practical real-world field tests that can predict performance andone hopesprevent component failure. Materials measurement methods have grown out of distinct disciplinary homes: physics, chemistry, metallurgy, and, more recently, biology and environmental science. Drawing from the broad expanse of materials characterization techniques, we offer a perspective on that breadth and cite examples that are illustrative of the crucial role such techniques have played and are playing in the technologies of today.
To meet the challenge of precise nanoscale arrangement of emitter and plasmonic nanoantenna, synthesis and assembly methods continue to evolve in accuracy and reproducibility. This article reviews some of the many strategies being developed for "soft" chemical approaches to precision integration and assembly. We also discuss investigations of the Purcell effect, emission directionality control, and near-unity collection efficiency of photons, emitter emitter coupling, and higher-order emission processes that have been most deeply explored using individual-emitter- (or several-emitter-) nanoantenna pairs fabricated using traditional lithographic methods or dynamically and controllably manipulated using scanning probe methods. Importantly, these results along with theoretical analyses inspire and motivate continued advancements in large-scale synthesis and assembly. We emphasize assembly approaches that have been used to create nanosemiconductor-nanometal hybrids and, in particular, those that have afforded specific plasmonic effects on excitonic properties. We also review direct-synthesis and chemical-linker strategies to creating discrete, though less spatially extended, semiconductor-metal interactions.
Learning from nature and starting from the lotus leaf, we have used a four-step strategy to develop a superwetting system ranging from two-dimensional interfaces to nanochannels and fibers. First, we explored unique superwetting properties in nature from lotus leaves, mosquito eyes, strider legs, rose petals, rice leaves, and butterfly wings, to fish scales, spider silks, and cacti. Second, we investigated the correlation between the multiscale structures and superwettability. Third, we designed target molecules to prepare bioinspired functional materials with promising applications, such as self-cleaning coatings, water/oil separation, water collection, and energy conversion. Finally, by combining two complementary properties and achieving reversible switching between them, we were able to develop bioinspired smart interfacial materials with superwettability.
Certain biocomposites exploit the combination of soft and hard elements to achieve high strength and toughness. In nacre, found inside certain seashells or on the surface of pearls, hard layers of micron-scale thickness are glued together by thin layers of soft proteins to realize remarkable strength and toughness. In spider webs, stiffer radial threads are connected by softer spiral threads to produce a light and resistant structure. In the exoskeleton of lobsters, organic fibers form a chiral structure in an inorganic matrix. This article reviews progress in the understanding of the mechanical superiority of such soft-hard biocomposites. In particular, simple physical views are presented that allow an intuitive understanding of how their remarkable structures contribute to enhancing their fracture resistance in the presence of cracks, and how such structures are physically optimized in terms of mechanical properties. Such fundamental insights could be useful as guiding principles for developing artificial, reinforced materials.
Several organisms possess a genetic program enabling them to form a mineral, a process termed biomineralization. The structure and composition of biominerals equip the biomineralizing organisms with functionalities that abiotic materials made of the same mineral do not necessarily possess. Even primary organisms such as bacteria are able to produce materials with properties superior to those of human-made equivalents. Magnetotactic bacteria represent a paradigm of such microorganisms. These organisms synthesize a hierarchical one-dimensional magnetic nanostructure based on the alignment of magnetosomes-organelles embedded in a vesicle dedicated to biomineralization and made of magnetic nanoparticles (magnetite (Fe3O4) or greigite (Fe3S4)). This article focuses on factors that play a role in the organization of these magnetosomes. The chains, which are based on aligned particles that have biologically controlled ultrastructure, size, morphology, organization, and orientation, serve as actuators and area means to align the bacteria with the Earth's magnetic field lines when they swim in search of particular habitats in the aqueous environments they live in.
The physics underlying operation of cold (room-temperature) ionic-liquid emitter sources for use in propulsion shows that such thrusters are advantaged relative to all other rockets because of the direct scaling of power with emitter array density. Nanomaterials and their integration through nano- and microfabrication can propel these charged-particle sources to the forefront and open up new applications including mass-efficient in-orbit satellite propulsion and high-thrust-density deep-space exploration. Analyses of electrostatic, fluid-dynamic, and electrochemical limits all suggest that arrays of such ionic-liquid thrusters can reach thrust densities beyond most in-space propulsion concepts, with a limit on nanoporous thruster packing density of approximate to 1 m due to ionic-liquid viscous flow and electrochemistry. Nanoengineered materials and manufacturing schemes are suggested for the implementation of microfabricated and nanostructured thruster arrays.
The evolution of materials; their synthesis, shaping, and performance; and the engineering of artifacts and systems to meet societal demands are inextricably interwoven. In this article, we describe an evolving scenario of the relationship between materials and engineering that provides a framework for the articles that explore various facets of this theme in this special issue of MRS Bulletin.
I look 50 years into the future of materials science to assess possible technological advances and their impacts on engineering, society, and culture. Themes such as cities, energy, food and drink, and healthcare are explored in terms of their materials requirements and our likelihood of fulfilling them. Possible directions for materials science and engineering are explored, such as metamaterials and technical textiles, along with their potential impacts on human expression in design, fashion, and architecture. As the number of available materials increases, I assess the likelihood that the methodology of materials development itself might evolve. Will experiments continue to dominate, or will approaches that combine big data and theory become more important forms of materials discovery? Or, more controversially, will our 10,000-year-old track record of materials innovation come to an end, as we run out of new materials to invent?
The mobile revolution has enabled broad applications with a faster response, small form factors, and more data bandwidth, sensing, and processing power. The industry is pursuing three-dimensional (3D) stacked integrated circuits (ICs) in order to provide higher density interconnects between chips and/or functional blocks, which translates to enhanced system performance. These value propositions are attractive, especially for wireless applications, and will likely lead to further growth of this sector. Recent progress has been reported for development of IC stacking technologies, specifically for wireless applications. However, for full high volume deployment of 3D stacked ICs, a number of technical challenges remain, including many opportunities to be addressed by material enhancements. This article reviews the state-of-the-art technology solutions used for 3D IC stacking and highlights the material properties and remaining technology challenges required to meet the demanding specifi cations for high volume manufacturing of consumer devices. In particular, it focuses on the electrical (dielectrics and metallic) properties of the interconnects, the thermal and mechanical properties of the integrated components, and the ultimate component level/board level reliability characteristics.
Heterogeneous gas-solid catalyst reactions occur at the atomic level, and understanding and controlling complex catalytic reactions at this level is crucial for the development of improved processes and materials. There are postulations that single atoms and very small clusters can act as primary active sites in chemical reactions. Early applications of our novel aberration-corrected (AC) environmental (scanning) transmission electron microscope (E(S) TEM) with single-atom resolution are described. This instrument combines, for the first time, controlled operating temperatures and a continuous gas environment around the sample with full AC STEM capabilities for real-time in situ analysis and visualization of single atoms and clusters in nanoparticle catalysis. ESTEM imaging and analysis in controlled gas and temperature environments can provide unique insights into catalytic reaction pathways that may involve metastable intermediate states. Benefits include new knowledge and more environmentally friendly technological processes for health care and renewable energy as well as improved or replacement mainstream technologies in the chemical and energy industries.
Biomineralization is the process by which living organisms orchestrate the synthesis and organization of minerals (biominerals), and it may be viewed as an ancient process for accumulation of metal ions in living systems. The structure and properties of biominerals have yet to be rivaled by any synthetic effort by scientists to date. Therefore, deciphering the assembly algorithms and the components that initiate and promote hierarchical deposition of cations has significant implications for the development of nanocomposites and nanotechnology as a whole. This issue of MRS Bulletin highlights some of the challenges in characterizing and replicating the biomineralization processes, and the role of non-collagenous proteins in the biomineralization process.
Modern materials design is largely based on composite structures aimed at a synergistic integration of multiple components with a diverse range of properties. Biologically grown minerals provide an intriguing example of sophisticated organic-inorganic nanocomposite structures resulting in excellent mechanical characteristics. Among the mineral phases utilized by living organisms to generate hard tissues, calcium carbonate-especially the calcite polymorph-is ubiquitous and has been studied intensively. Biogenic calcite crystals often show hierarchical organization spanning multiple length scales, and the occluded organic phases are now known to be intimately associated with the mineral host. Here, we discuss the internal micro- and nanostructure of two selected types of calcite biominerals-the sea urchin spine and prismatic single crystals extracted from mollusk shells. This article highlights recent advances in translating the key principles of biological mineralization into design strategies for synthetic materials and presents analogies between biogenic and synthetic calcite single crystals.
During the past two decades, numerous biomaterials and soft materials, including ceramics, polymers, and their composites, have been fabricated for various biomedical devices and applications in tissue engineering using three-dimensional (3D) printing. This article offers a brief overview of some of the biomaterials and soft materials fabricated using some notable 3D printing techniques and related applications. A brief perspective regarding future directions of this field is also provided.
Biomineralization is the matrix-directed calcification of tissue in living organisms. The deposition of different polymorphs of calcium phosphate or calcium carbonate is a highly regulated process. It may involve cell-controlled mechanisms with vesicular delivery of inorganic material to the extracellular matrix and cell-independent processes mediated by dedicated matrix proteins. These proteins promote the formation of microscopic crystals of defined size and shape, which combine to form bio-inorganic materials with unique properties. Successful biomineralization is correlated with structural elements, such as matrix proteins involved in the nucleation process. Circular dichroism (CD) is a spectroscopic technique for the determination of a secondary structure of proteins and has therefore been applied for studying numerous biomineralization promoter proteins. This article reviews and compares CD data on matrix proteins from different contexts, such as eggs, seashells, and teeth. It highlights the potential of CD for secondary structure determination and quantification and points out pitfalls that may lead to misinterpretation of CD spectra. The data suggest that most biomineralization promoter proteins contain domains of different secondary structure with predominantly unordered conformation. However, they may acquire a higher degree of order initiated by environmental factors such as pH, presence of cations, or charged surfaces.
Space missions have unique requirements for payloads of electronics, sensors, instruments, and other components in terms of mass, footprint, power consumption, and resistance to various types of radiation. Nanomaterials offer the potential for future radiation-hardened or radiation-immune electronics. Gas-sensing needs in planetary exploration and crew-cabin air-quality monitoring are currently being met by bulky instruments. Routine health checkups of astronauts and testing of water in space habitats are being done on a delayed basis by bringing samples back to Earth. Instead, nanomaterials can be used to construct ultrasmall, postage-stamp-sized gas/vapor sensors with selective discrimination and also lab-on-a-chip biosensors for water-quality monitoring and crew health monitoring.
The domain of mesoscale science, where the discrete granularity of atoms and quantization of energy give way to apparently continuous and infi nitely divisible matter and energy, presents a new frontier of scientifi c opportunity and yields new complex architectures, phenomena, and functionalities. In this article, we describe some hallmarks of mesoscale science and highlight research directions that are described in greater detail in subsequent articles in this issue of MRS Bulletin. The exciting progress of the past several years and the rich unexplored opportunities at the mesoscale offer extraordinary prospects for future advances.