Special issue: bioinspired architectural and architected materials

Many natural materials have a hierarchical structure whereby building blocks are assembled into larger units in several successive steps, from molecules to fiber, layers and larger units [6]. Structural motifs can be related to mechanical performance in a wide range of natural protein materials, for example in [7]. Besides wood, bamboo is a traditional building material with exceptional mechanical properties. In addition to high tensile strength, this allows for extraordinary large deflection due to its hierarchically structured materiality. The contribution to this collection by Chen et al [8] quantifies these properties and relates them to the inner architecture of the bamboo culm. Bone is another example of a natural material that is structured over multiple length scales. The contribution by Tertuliano et al [9] analyses the role of different structural levels, such as layers and fibers, in the fracture resistance of this material.

Prospective scarcity of resources demands novel sustainable material concepts in architecture. Granular materials are random loose assemblies of particles, such as sand piles for example. If the particles have non-convex shapes they will entangle and reach topological interlocking. The contribution by Dierichs and Menges [10] shows how the assembly of particles can actually be used to design reconfigurable granular building elements at an architectural scale. Further, Thomsen and Tamke [11] report on bio-design as a material practice that challenges the paradigm of stability and predictability in architecture by exploring the heterogeneity of designed, harvested and living materials as a positive attribution for properties and performance.

Heat exchange is an important property of skin-like boundaries at all dimensions, such as for wearable devices or for building skins. The contribution by Grinham et al [12] shows that an optimized design of the channel architecture within a flexible and transparent heat exchanger can significantly improve its functional properties. Another approach to heat management is evaporative cooling. In their contribution, Rupp and Gruber [13] show that optimizing the design of surface structures inspired by the geometries of plant leaves may improve mass transfer, especially considering aerodynamic effects related to air movements. The proof of concept includes ceramic tiles for architectural application. Porous silica ceramic materials with a lamellar structure and high anisotropy, fabricated by a freezing method, are shown in the contribution by Zhao et al [14] to provide both thermal insulation (across the layers) and high strength (along the layers) with application potential for building insulation.

Textile technology is a traditional approach to additive manufacturing where new properties emerge through a combination of fiber entangling (or interlocking according to the scheme of figure 2) and weaves that may be considered mechanical metamaterials (figure 2). The paper by Guiducci et al [15], investigates the shape-generating effect of internal stresses generated by printing rigid rod-like structures onto a pre-stretched textile, which generates an architected material with potential applications in architecture. Another contribution by Shafiei et al [16] shows that, with an appropriate design, scaled skins serving as flexible armors for example, acquire increased flexibility in compression by allowing the formation of wrinkles and folds. The paper provides insights into how wrinkles can form reliably based on stable buckling of the scaled skin. Water absorption by cellulosic materials such as wood confers shape-change properties to seed dispersal systems, for example. The contribution by Tahouni et al [17] shows how additive manufacturing can be used to generate architected materials that show sequential motion steps based on different levels of responsiveness to humidity.

The contribution by Zhilayev et al [18] investigates how artificial wings for flying robotic devices can be designed based on periodic honeycomb patterns. The authors start from the designs observed in insect wings and then use multi-parameter optimization to improve the flapping flight dynamics and the sound of a robotic drone.

Architected materials use patterns instead of chemical composition to modify the physical properties of materials. The contribution by Milazzo et al [19] shows how the patterns of musical composition translate into a three-dimensionally folded protein structure and this structure back into music.

This collection of a dozen papers shows the enormous potential of structure at multiple scales to reveal properties and functions that are not inherent to homogeneous materials. The role models for this type of approach are natural materials that nearly always have a multiscale structure where building blocks are assembled into respectively larger units over several length scales. Architectural design typically addresses a size range similar or beyond humans, while materials science makes use of smaller dimensions. Recent efforts explore the inner structure of architectural materials as a means of interacting with their environments at building dimensions. This collection gives an overview over the whole scale from nanometers to meters covering disciplinary approaches that are still not likely to interact but may clearly profit from each other. The analysis of nature leads to design principles, but also the analysis of a design principle like a musical composition can lead to a new scientific viewpoint [19]. The scope of approaches identifies a wide range of possible applications in the field of façade, construction, clothing or products with architected properties and performance. The multidisciplinary contributions open up resilient and sustainable perspectives for shaping our future environment.

No new data were created or analysed in this study.