Force Scaling in Active Swarm of Microtubules via Magnetic Manipulation
Scalability refers to the ability of a system to enhance performance with increasing size. This ability is a defining feature of natural swarms such as ant and bee colonies. Extending this principle to artificial active matter has motivated the creation of molecular swarms composed of myosin-driven actin filaments and kinesin-driven microtubules (MTs). While these swarms exhibit cooperative transport behaviors that surpass the abilities of individual filaments, their collective force generation has remained unquantified. Here, we introduce a straightforward electromagnetic tweezer approach to directly measure the forces generated by MT swarms propelled by surface-bound kinesin motors. We find that force output changes with swarm size, demonstrating quantitative scalability and linking collective organization to mechanical performance. These results establish MT swarms as a model system for scalable, force-producing active matter and provide a foundation for designing biomolecular devices that exploit collective dynamics for microscale actuation and transport. Significance StatementThe cooperative activity of multiple motile agents is observed in nature, known as swarming. In artificial systems, swarming has been demonstrated using active agents like kinesin and MTs, successfully enabling efficient cargo transportation. However, the force generated by the swarm remains unexplored, which is one of the keys to understanding the principles underlying swarm systems. This study introduces a simple method employing electromagnetic tweezers and magnetic beads to measure the force of the MT swarm accurately. The measured forces within the microtubule swarms of different sizes unveil the scaling effect, the additive nature of force generation as the kinesin unit increases. The force study sheds light on the fundamental properties, work performance, efficiency, and execution of the MT swarm.