The microtubule (MT)-kinesin biomolecular motor system has attracted much attention due to its possible applications in artificial biomachines. Recently an active self-organization (AcSO) method has been established to integrate MT filaments into highly organized assembled structures. The ring-shaped MT assembly, one of the structures derived from the AcSO of MTs, can convert the translational motion of MTs into rotational motion. Due to this attractive feature, the ring-shaped MT assembly appears to be a promising candidate for developing artificial devices and for future nanotechnological applications. In this work, we have investigated the effect of length and rigidity of MT filaments on the size of ring-shaped MT assembly in the AcSO process. We show that the size of ring-shaped MT assembly can be controlled by tuning the length and rigidity of MT filaments employed in the AcSO.Longer and stiffer MT filaments led to larger ring-shaped assemblies through AcSO, while AcSO of shorter and less stiff MT filaments produced smaller ring-shaped assemblies. This work might be important for the development of biomolecular motor based artificial biomachines, especially where size control of ring-shaped MT assembly will play an important role.

Biomolecular motor system microtubule (MT)-kinesin is considered a building block for developing artificial microdevices. Recently, an active self-organization method has been established to integrate MT filaments into ring-shaped assembly that can produce rotational motion both in the clockwise and in the counterclockwise directions. In this work, we have investigated the effect of parameters such as MT and kinesin concentration, length, and rigidity of MT and type of kinesin (structure of tail region) on the preferential rotation of the ring-shaped MT assembly produced in an active self-organization. We elucidated that these factors can significantly affect the bias of rotation of the ring-shaped MT assembly, which seems to be related to the fluctuation of leading tip of moving MT filaments. This new finding might be important for designing handedness regulated artificial biomachine using the ring-shaped MT assembly in future.

Biopolymers such as actin, microtubules and DNA are well known for their fascinating in vivo selforganization phenomena. Considerable efforts have been devoted to mimicking their organization process in vitro that produced ring-shaped or toroid structures in an irreversible manner. However, understanding the factors that lead to formation of such assembled structures deserves more investigation to achieve a unified insight into the assembly process, particularly of the microtubules. Here, we report an active assembly process of microtubules (MTs) at an air-buffer interface that resulted in ring-shaped microtubule structures with a narrow size distribution and a high yield. Using an ''air-buffer interface control system'' combined with the newly developed ''inert chamber system (ICS)'' we have also successfully observed the reversible conformational transition between ring-and linear-shaped microtubules at the air-buffer interface. This is the first ever direct in situ observation of a reversible assembly process of MTs and probably provides us with valuable discernment to understand the in vivo organizational behavior of biopolymers.

Mechanical oscillation is a ubiquitous phenomenon observed in living systems, which emerges from a wide range of well-organized self-assembled structures, and plays important roles in many biological processes. Although considerable efforts have been devoted to demonstrate the mechanical oscillation of organized structures produced through self-assembly in vitro, it has rarely been documented. Here we report the mechanical oscillation of ring-shaped structures, composed of multiple microtubule (MT) filaments, obtained through energy dissipative self-assembly of MT filaments at an air-buffer interface.The MT rings exhibit autonomous oscillation manifested through periodic changes in the size and shape. We propose the oscillation of the MT rings is attributed to a mechanical feedback arising from accumulated stress induced by the driving force of the motor protein system. This work might offer new insights in our current understanding on the mechanical feedback driven oscillation of organized structures and its effect on the dynamic processes in living systems.3