Yesterday, The Backshop Academy of Sciences considered an idea for self-inflating inner tubes. Because most bike owners only inflate their tires (or have them inflated) when they get a tube replaced after a pinch flat from under-inflation, they would benefit greatly from a tire that maintains its pressure longer.
It occurred to us that if you put a dead rat in the tire, the gases of putrefaction would build up on their own until that phase of decomposition had ended. Then we realized that the weight of the rat carcass would cause the wheel to rotate unevenly. We would have to put the rat in a blender to create a rat slurry that would then decompose anaerobically inside the tube. We would use special apparatus to inject the slurry and change it for new mixture when the old batch was exhausted.
Larger tires would require a larger carcass, like a 'possum, or multiple rats. Of course, the use of slurry would simplify the process. A certain number of milliliters of any species of animal should suffice for a given volume of inner tube.
The idea of sticking a dead rat in someone's tire has a certain appeal for certain customers. Although the system needs quite a bit of work before it can be implemented widely, we may try some preliminary experiments.