Hierarchical design draws inspiration from analysis of biological materials and has opened new possibilities for enhancing performance and enabling new functionalities and extraordinary properties. With the development of nanotechnology, the necessary technological requirements for the manufacturing of hierarchical materials are advancing at a fast pace, opening new challenges and opportunities. This article presents an overview of possible applications of and perspectives on hierarchical materials.

Hierarchical structure is a hallmark of many biological materials that naturally originate from their growth process, which starts with the biosynthesis of molecular building blocks that self-assemble into larger units. Compartmentalization is used to locally control the synthesis and self-assembly and, thus bridge multiple length scales between the atomistic and macroscopic worlds. Multiscalar structures have the advantage that different physical properties may be adjusted at various structural levels. In particular, when these properties are conflicting, the result can lead to exceptional multifunctional materials. The fiber is a ubiquitous structural motif of biological materials, although its biochemical basis can be diverse. While fibers perform well under tension, they do not under compression. Biological materials are also adaptive and possess self-repair capabilities—properties that require the transport of matter and information. This requires networks of transport and communication that are also hierarchically organized to conciliate the conflicting goals of maximum accessibility and minimal perforation of the material volume. Several examples are discussed in this article.

Hierarchical design down to the nanoscale has become possible in structural composite materials with the discovery of carbon nanomaterials such as carbon nanotubes (CNTs) and graphene. Composites that simultaneously combine microscopic continuous fibers and nanoscale reinforcements are known in the field as hierarchical or nanoengineered composites. The additional reinforcement at the nanoscale promises high-performance composites with unique combinations of mechanical properties and new functionalities. Here, we review advances in fiber-reinforced polymers modified with CNTs. Three routes for integration of CNTs in composites are discussed: deposition on fibers/plies, dispersion in the matrix, and assembly into fibers. We highlight opportunities and challenges focusing on mechanical performance and processing.

Machining is an important technological process in many areas of industry. The efficiency of machining determines the quality of many industrial products. Machining efficiency and cost depend on the properties, strength, and microstructure of the machining materials. One of the promising ways to increase the reliability and wear resistance of machining tools is the development and use of hierarchical machining materials. In the area of machining materials, designed typically as binder/reinforcement composites, hierarchical structures are realized as lower-scale secondary reinforcements (such as nanoparticles in the binder, or polycrystalline, aggregate-like reinforcements, also at several scale levels). Such materials can ensure better productivity, efficiency, and lower costs of drilling, cutting, grinding, and other technological processes. This article reviews the main groups of hierarchical machining materials and their performance.

Establishing strategies for high-resolution micrometer to subnanometer structural control is an essential feature of any versatile materials design paradigm. Colloidal crystal (CC) templating not only establishes tunable replica pore topologies, but interfacial- and confinement-mediated phenomena extend its impact for tailoring properties such as pore hierarchy, topological diversity, and macroscopic morphology, as well as nucleation, growth, and crystallinity. Coupled with emerging strategies for “single-pot” template-replica co-assembly and efforts to expand the accessible materials palette, CC-templating offers promise for application-driven, rational materials design.

Zeolite molecular sieves are indispensable materials for acid-based catalysis and separation processes. This article overviews zeolite-type microporous materials containing a secondary system of larger (meso-/macro-) pores. These materials, often referred to as hierarchical zeolites, show better performance in reactions where slow mass transport impedes the reaction rate. A critical analysis of different synthetic strategies for preparation of hierarchical zeolites is presented. The industrial prospects of these materials are also discussed.

Structural hierarchy coupled with material heterogeneity is often identified in natural materials, from the nano- to the macroscale. It combines disparate mechanical properties, such as strength and toughness, and multifunctionality, such as smart adhesion, water repellence, self-cleaning, and self-healing. Hierarchical architectures can be employed in synthetic bioinspired structured materials, also adopting constituents with superior mechanical properties, such as carbon nanotubes or graphene. Advanced computational modeling is essential to understand the complex mechanisms that couple material, structural, and topological hierarchy, merging phenomena of different nature, size, and time scales. Numerical modeling also allows extensive parametric studies for the optimization of material properties and arrangement, avoiding time-consuming and complex experimental trials, and providing guidance in the fabrication of novel advanced materials. Here, we review some of the most promising approaches, with a focus on the methods developed by our group.

Timber, steel, and concrete form the triumvirate of structural materials used in construction. Each material possesses particular attributes, with cost and ease of use often providing the determining factor in selection when structural requirements are equal. This article aims to provide insight into the unique capabilities that steel can offer in construction. Beginning with the advent of the Industrial Revolution, developments in alloy chemistry, impurity control, and thermomechanical processing to produce different geometries have continued to make steel an attractive choice in residential and commercial construction. Changing demographics and the needs of future cities are discussed in terms of steel construction members, construction strategies, and functional coatings.