Principle of autoclave?

An autoclave is piece of equipment that is usually used to sterilize objects and supplies by subjecting them to high pressure saturated steam at 121 °C or more, typically for 15 to 20 minutes depending on the size of the load and the contents. The sterilization occurs by three mechanisms: temperature, pressure, and thermal oxidation.

The high temperature will kill most microorganisms because they cannot tolerate the temperature - essentially it "cooks" them. Viruses, which may not be considered "organisms" are also broken down by the temperature and proteins can be denatured.

The pressure will cause penetration of membrane walls of organisms, disrupting or breaking the walls, forcing the steam into them, and screwing up the osmotic pressure.

Some biological materials will also experience thermal oxidation - they react with residual air present in the autoclave or with other oxidizers present in the autoclave. As the reactions occur, the biological materials are broken down or destroyed.