In this section, we discuss the specific molecular machine design. Our proposed molecular robot consists of a methane collection part and a self-assembly control part.

First, we clarify the requirements for the methane collection part and then describe its design, followed by the design of the DNA-RNA strand.

0. Methane Recovery System Requirements from Biological Perspectives

Biocompatibility, including low biotoxicity, is extremely important for early gas recovery utilizing the body environment. From this perspective, we examined the necessary conditions for the present system, i.e., the conditions that must be met when the goal is to recover methane and then discharge it.

①To ensure that particles are properly retained in the lumen for a period of time and are not inhaled into the lungs or passed through the lumen

Liquid feed, including milk, except for water, is known to pass through the esophageal groove and reach the fourth stomach directly by the esophageal groove reflex. Therefore, MOF should be administered with solid feed or water. Concerns such as inhalation into the lungs may be avoided by keeping the particles moist. [1]

②To achieve a vapor-liquid equilibrium-like situation for recovering methane.

This requires that the molecular robot, especially the MOF, always be in contact with the air surface, i.e., floating against the liquid in the cow's stomach.

③To prevent decomposition due to internal conditions of the cow.

The robots must endure three adverse conditions. 1.

1. pH of stomach acid: The pH in the first stomach of cattle is about 6~7, while the pH in the fourth stomach is about 2-3.
2. Temperature: The body temperature of cattle is about 38 degrees Celsius, and the gastrointestinal environment is expected to be the same.
3. Humidity: The rumen is kept at a very high humidity level to allow microbial fermentation to proceed.

④To be absorbed as little as possible from the intestinal tract[2][3]

In nutrient absorption in the intestinal tract, those with a molecular weight of 600 or less are generally absorbed.