Creating molecular microrobots that mimic the abilities of living organisms has a number of challenges. One of the most significant of these is the creation of directed self-propulsion in water. There are two major challenges to achieving this: the first is to make a molecular robot that can reciprocally deform and the second is converting this deformation into propulsion of the molecular robot.
A team of scientists has created a microcrystal that utilizes self-continuous reciprocating motion for propulsion. The team built on their previous research that had solved the challenge of creating molecular robots that can reciprocally deform. However, tiny objects cannot convert their reciprocal motion into progressive motion, in general. In the current study, the scientists succeeded in realizing self-propulsion of the molecular robot in an experimental system where motion was confined to two dimensions — in this system, viscous resistance acts anisotropically, making it negligibly weak.
The microrobot was powered by blue light, which drove a series of reactions leading to the fin flipping and the propulsion. Due to the nature of the reactions, the motion was not continuous but occurred intermittently. In addition, the molecular robots exhibited one of three different styles of propulsion: a “stroke” style, with the fin in front; a “kick” style, with the fin behind; or a “side-stroke” style, with the fin to one side. The nature of mobility was affected by the area of the fin and its angle of elevation; individual crystals propelled themselves in different directions and styles.
The scientists then created a computational minimum model to understand the variables that affected the propulsion in a two-dimensional tank. They were able to determine that fin length, fin ratio, and elevation angle were the key variables affecting the direction and the pace of propulsions.