Based on the following paragraph on the current use of obsidian, what's the difference between obsidian scalpels and steel scalpels?

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.[57] 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.[58] 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.[59] Don Crabtree has produced surgical obsidian blades and written articles on the subject.[57] Obsidian scalpels may currently[when?] be purchased[by whom?] for surgical use on research animals.

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.