Biocompatibility testing ISO 10993 looks at how a substance works with living things to make sure it doesn't hurt them or make the immune system react. A lot of the time, chemicals, sterilization, and mechanical force are used to test things, which can change how well they work. Even after going through these steps, metals and some plastics can still be useful. On the other hand, biodegradable or porous materials may break down, making it unsafe or impossible to replace.