**Preface to "Mechanics of Micro- and Nano-Size Materials and Structures"**

Nanotechnology knowledge is always looking to expand its boundaries to achieve the most significant benefit to human life and meet the growing needs of today. In this case, we can refer to micro- and nanosensors in micro/nano-electromechanical systems (MEMS/NEMS). These electrical devices can detect minimal physical stimuli up to one nanometer in size. Today, micro/nano-sensor devices are widely used in the environment. For example, sensors made of silicon are suspended in the air for hours and can monitor air pollution. In addition to these, micro-nanosize structures can be employed as a reinforcer in advanced composites, advanced concretes, etc. Except for this use, these small size particles can play the role of a filler and make the possibility of cracking for future working of the materials less and less by filling the pores inside the structure.

On the applications of micro/nanosensors in civil engineering, one can state that small-scale sensors and actuators can be developed and used in construction to monitor and/or control the environmental conditions and the materials/structures' performance. As an example, the sensors can be used to monitor concrete corrosion and micro-cracking. The smart sensor can also be employed for structural health monitoring in bridges and other structures. Therefore, the prediction of the mechanical response of such small size particles in different physical and environmental conditions is momentous. To obtain this, micro- and nano-mechanics enable the scientific basis of the structural response of micro/nanostructures based on different situations.

For design and fabrication purposes, these structures can be investigated computationally through several approaches. First, we mention straightforward experiments that need special and highly precise equipment and result in high costs. Second, computer simulation such as molecular dynamics could be used, which requires a lot of computational efforts, in general, and a powerful computer. Finally, the application of continuum models properly modified for modelling materials and structures at small scales is worth mentioning, e.g., multiscale modeling, nonlocal size-dependent models, etc.

For this reprint, we intend to cover theoretical as well as experimental works performed on small scale to predict the material properties and characteristics of any advanced and metamaterials. New studies on mechanics of small-scale structures such as MEMS/NEMS, carbon and non-carbon nanotubes (e.g., CNTs, Carbon nitride, and Boron nitride nanotubes), micro/nano-sensors, nanocomposites, macrocomposites reinforced by micro-/nano-fillers (e.g., graphene platelets), etc., are included in this reprint.

> **Mohammad Malikan and Shahriar Dastjerdi** *Editors*
