[نتائج البحث]Developing self-driving objects that open new paths through interactions between molecules – Expectations of the development of microscopic robots programmed with molecules that do not need electronic circuits – | Hiroshima University

• Benzoic acid(benzoic acid)He discovers that crystals can slide spontaneously on the surface of water
• Building a system creates its own path of movement
• Amplification of interactions between molecules (micro) and their reversal in motion control (macro)

The research results of a research group composed of Risa Fujita (our graduate student), Assistant Professor Muneyuki Matsuo, and Professor Satoshi Nakata from the Laboratory of Self-Organization Chemistry, Mathematical and Life Sciences Program, Graduate School of Integrated Life Sciences, Hiroshima University, will be published in February 2024. It was published in the academic journal “Journal of Colloid and Interface Science” on the 24th.
Our research group has developed small robots (hereinafter referred to as self-propelled robots) that can glide autonomously on the water surface. Until now, the speed and direction of autonomous objects have been determined by the size and shape of the propelling object, or controlled by external forces such as magnets. There are also small robots equipped with software and electronic circuits to control their movements. However, these animals were not able to adapt to changing environments and independently choose the method of movement. On the other hand, in contrast to circuit synthesis as described above, we have developed a method that uses molecules by coupling the millimeter-sized “kinetic aspect of an autonomous body” with nanometer-sized “molecular level agents.” I took on the challenge of programming how to exercise independently.
In this study, we found that benzoic acid crystals, which are used as food preservatives, are largely self-active. They then synthesized a new motion control molecule that interacts with benzoic acid molecules and succeeded in automatically controlling the direction of motion.

Paper title: A self-propelled object creates a boundary with amphiphiles at an air/water interface
Published journal: Journal of Colloidal and Interface Sciences
Author: Risa Fujita, Munyuki Matsuo, Satoshi Nakata*
Affiliation: Graduate School of Integrated Life Sciences, Hiroshima University (*: corresponding author)
doi: https://doi.org/10.1016/j.jcis.2024.02.156

A variety of small robots are being developed domestically and internationally for the purpose of moving materials in microscopic spaces. Most of the “robots” we usually imagine have electronic circuits and can be programmed to move according to instructions. We thought that by implementing a self-driving body that moved in the direction of high surface tension like a small robot, we could develop a robot that had no electronic circuits and looked like a living being. Our robot is easy to build, converts chemical energy directly into kinetic energy, and maintains motion for long periods of time.

In this study, benzoic acid (BA) was added to the end of the molecule.^※14-Stearoyl intermediate benzoic acid (SABA), which has a similar structure and is amphiphilic (compatible with both oil and water)^※2It is synthesized as a movement control molecule. Because they have similar structures, BA molecules easily interact with SABA molecules. Therefore, as shown in Figure 1, the BA disk^※3The released BA molecules enter the SABA membrane and form a mixed BA-SABA membrane. Furthermore, the BA-SABA mixed film is compressed by the movement of the BA disc, forming a cohesive film. This cohesive film played the role of a “path-guiding wall,” and the BA disk, which normally moves freely on the water surface, moves only within the wall that is built on part of the water surface.

Figure 2 is a graph of the relationship between pressure and film density for a SABA monolayer. The higher the density of SABA, the greater the membrane pressure. Here the ease of movement of the BA disk changes due to the pressure generated by the membrane. In other words, high membrane pressure makes it difficult to move, and conversely, low pressure makes it easy to move. BA discs can move freely on the surface of the water in “unrestricted motion,” “restricted motion” in which the area of ​​movement is limited, “reciprocating motion” in which they move back and forth in the same space, and “stop” at each intensity Four exercise modes are chosen automatically. In this way, by changing the density of the membrane, we can control where and how quickly it moves. In addition, motions such as reciprocating motion (right side of Figure 2) and bound motion are produced by the formation of a solid aggregate film made of BA and SABA molecules. The locally assembled film plays the role of the “water canal wall.” The main point of this research is that the pushing body automatically creates a “molecular wall” that is the origin of the movement path. For example, this is like an animal that digs a hole in the ground and lives in it. We succeeded in expressing the movement trajectory using the movement control molecule (SABA) and the driving molecule (BA), i.e. automatically selecting the movement pattern compatible with the environment.

※1: Benzoic acid (BA)
…BA molecules, BA molecules are several nanometers long, and BA molecules are released on the surface of the water, not into the water.

※2:4-Stearoyl stobenzoic acid (SABA)
…SABA molecules SABA molecules are several nanometers in size, and SABA molecules do not dissolve in water and are distributed on the surface of the water.

*3: BA disc
…The self-driving object in this paper, the BA disk, is several millimeters long and typically moves freely on the water surface.

In this research, we succeeded in controlling the direction of movement through intermolecular interactions between movement control molecules and driving molecules. In the future, we will build a self-driving body that “controls the direction and speed of the self-driving body’s movement” and aims to “develop microscopic robots programmed with molecular information.”
In the future, we believe it will be possible to move materials into microscopic spaces in response to the environment, such as bacteria.