Molecular Robotics

Molecular Robotics: A New Paradigm for Artifacts 

Satoshi MURATA, Akihiko KONAGAYA, Satoshi KOBAYASHI, Hirohide SAITO, Masami HAGIYA
New Generation Computing, 31(2013)27-45 Ohmsha, Ltd. and Springer.

Received 19 July 2012
(c) The Author(s) 2013. This article is published with open access at Springerlink.com
https://doi.org/10.1007/s00354-012-0121-z

0th Generation Molecular Spider

DNA molecular robots consist of a supra-molecular assembly of DNA fragments and other bio-molecules. Typical examples are the DNA molecular

spiders constructed by DNA nanotechnologies. Some DNA molecular robots can move, recognize and carry other molecules. However, their movement is

based on a random walk, and their functionalities are limited by the ability of molecular recognition.

1st Generation: Amoeba Robots

The first generation molecular robots, called amoeba robots, introduce a compartment and an actuator to overcome the limitation of 0th generation. A compartment can be made from a lipid bilayer, such as liposome or vesicle, or capsules made of DNA nanostructure. A compartment allows to encapsulate various functional and computational molecular devices to realize higher func-tions by means of molecular-device-circuitry like metabolic pathways and signal transduction pathways in organisms. An actuator controls the movement of an amoeba robot. The goal of the first generation molecular robots is to mimic the behavior of an amoeba. Amoeba robots, however, have a scale limit which prevents their sizes to be beyond several micrometers.

2nd generation: Slime Mold robots

The second generation molecular robots, called slime mold robots, increase the scale of their sizes by means of functionalized polymer gels that work as both reaction field and actuator at the same time. Their sizes expand to the range of several millimeters. Polymer gels also create a heterogeneous spatio-temporal reaction field that causes macroscopic anisotropy in shape. As a result, the robots move like slime molds.* (Footnote: A corresponding organism with similar characteristics is Physarum polycephalum.) However, slime mold robots are similar to amoeba robots in the sense that both of them are categorized as unicellular organisms.

3rd generation: Multi-cellular Robots

The third generation molecular robots, multi-cellular robots, can remark-ably increase their complexity by means of a combination of heterogeneous cells like organs and tissues. There are two ways to create multi-cellular robots: the cell aggregation method and the cell division method. The cell aggregation method develops a multi-cellular robot by fabricating various molecular robot cells separately and then assembling them later. The cell division method re-quires higher technologies, including cell-replication and spontaneous symmetric breaking, to name but a few. These technologies enable us to develop various kinds of multi-cellular molecular robots and accelerate the diversity of molecular robots, so to speak, a Cambrian explosion of molecular robots. In this genera-tion, we might be able to say that artifacts have selfness. However, multi-cellular robots cannot surpass living systems in performance and complexity due to the intrinsic limitations of bio-molecular reactions.

4th generation: Hybrid Molecular robots

The fourth generation molecular robots, hybrid molecular robots, can make use of electronic devices to go beyond the limitations of molecular re-actions. The fusion of electronic and molecular devices makes it possible for molecular robots to use advanced information processing technologies, such as high performance computation and high-speed communication. There is no such living system that corresponds to hybrid molecular robots. From this stage, the boundary between traditional artifacts and molecular robots gradually begins to blur.