instruction: Based on the following paragraph on the current use of obsidian, what's the difference between obsidian scalpels and steel scalpels?
context: Obsidian can be used to make extremely sharp knives, and obsidian blades are a type of glass knife made using naturally occurring obsidian instead of manufactured glass. Obsidian is used by some surgeons[who?][example needed] for scalpel blades, although this is not approved by the US Food and Drug Administration (FDA) for use on humans. Well-crafted obsidian blades, like any glass knife, can have a cutting edge many times sharper than high-quality steel surgical scalpels: the cutting edge of the blade is only about three nanometers thick. All metal knives have a jagged, irregular blade when viewed under a strong enough microscope; however, obsidian blades are still smooth, even when examined under an electron microscope. One study found that obsidian incisions produced fewer inflammatory cells and less granulation tissue in a group of rats after seven days but the differences disappeared after twenty-one days. Don Crabtree has produced surgical obsidian blades and written articles on the subject. Obsidian scalpels may currently[when?] be purchased[by whom?] for surgical use on research animals.
response: Obsidian scalpels have a cutting edge that is many times sharper than a steel scalpel. In addition, obsidian scalpels have a smooth blade surface whereas all metal knifes have a jagged, irregular blade surface.