Assembly of Materials Building Blocks into Integrated Complex Functional Systems

Abstract

It is hard to overstate the importance of developing novel functional materials and surfaces, which are often essential for meeting challenges in diagnostics, biotechnology, tissue engineering, optics, microfluidics, and many other fields. A central question is how to generate novel complex functionality or properties that would go beyond those of existing materials and surfaces. This question is being approached from numerous angles, among them inspiration from biological systems (biomimetics), combinatorial synthesis and high-throughput screening of novel materials, synergistic combination of different components or processes, as well as the assembly of microscopic building blocks into macroscopic materials. In this Special Issue of Advanced Functional Materials, “Assembly of Materials Building Blocks into Integrated Complex Functional Systems” we received 22 excellent papers presenting original research as well as reviews on this topic. These articles demonstrate the growing diversity of strategies for fabricating novel classes of materials in which complex functionalities emerge from the assembly of materials building blocks or the synergistic combination of components and processes. This editorial highlights a subset of representative examples to give a flavor of published research articles and the future potential of this scientific field. One example where large complex 3D functional materials are created through the assembly of small materials building blocks (voxels) is discussed in an article by Wegener et al. (article number 1907795), in which the authors review 3D additive manufacturing approaches in terms of maximum voxel printing rate and minimum voxel size. The authors also present a new multi-focus two-photon 3D printing technology that approaches total printing speeds of ten million voxels per second at sub-µm voxel sizes, which significantly surpasses previous top printing speeds. Fabrication of functional responsive 3D materials is reviewed by Blasco et al. (article number 1907615). The article discusses 3D printing of adaptive and dynamic structures (4D printing), where the additional dimension refers to the ability of the structures to change their shape in response to a stimulus. One example of such dynamic properties is based on the formation of hetero-microstructures combining materials with different swellability or different response characteristics. Assembling such microscopic “hetero” building blocks into a macroscopic structure can lead to interesting dynamic macroscopic properties. In nature, tissues are built through the hierarchical organization of microscopic “building blocks” into progressively larger and more complex structures. Bioinspired tissue engineering often relies on the assembly of microscopic artificial soft building blocks into macroscopic functional tissue-like structures. Stevens et al. (article number 1909009) give an overview of the recent progress and trends in the fabrication and assembly of living building blocks, with a key highlight on emerging bioprinting technologies that can be used for modular assembly and complexity in tissue engineering. Such living building blocks include single cells, cell fibers, cell sheets, cell spheroids and cell organoids, which can be assembled into various complex functional living structures (tissue engineering). Development of methods to create functional soft materials is essential due to the complexity of living tissues and organs that have to be mimicked to meet need in areas such as regenerative medicine and novel functional implants. Thus, cell-instructive multiphasic gel-in-gel materials based on combination of different types of hydrogel building blocks are reviewed by Werner et al. (article number 1908857). The final functionality and properties of such materials depend, to a great extent, on the architecture of such heterogeneous and multiphasic materials, for example, layered, embedded or bundled organization. Design of adhesives