Nanoarchitectonics of molecular machines, biomolecular machines, and microrobots in their collective behaviour

Nanoarchitectonics of small-scale molecular units into functional materials is a key strategy in materials science. The central challenge lies in assembling, integrating, and nanoarchitecting fundamental functional units, such as molecular machines and microrobots, to innovate materials. This review examines collective behaviours typical in molecular and biomolecular machines and microrobots. We categorize collective behaviours into six types: (i) small-scale units operating cooperatively or collaboratively (often seen in macroscopic objects such as crystals); (ii) free-moving units in the bulk material; (iii) mechanical coupling between units resulting in chain interactions (not unlike gears); (iv) assembly of units to generate macroscopic output functions; (v) macroscopic stimuli controlling individual units; and (vi) cooperation between different molecular species to generate functional flows within a single system. After categorizing collective behaviours in molecular machines, we consider examples of material systems exhibiting this behaviour, such as MOFs, COFs and crystals. Furthermore, we examine the collective behaviours of molecular machines at solid surfaces and liquid interfaces. Additionally, we highlight the behaviour of biomolecular machines and microrobots in separate sections. Each section identifies and discusses trends in the relevant examples. This approach to utilizing molecular machines is anticipated to create highly functional systems, realizing the ultimate goal of functional materials chemistry.