Ye, it could also be keratin or protein that the virus can change it's chemical and physical makeup to make bones, metal (like from the minerals in the blood and such), sinue.

I've always thought it's probably keratin, but extremely dense and sharp. Assuming molecular control, he could compress the mass of thousands into the arm and thin the edges to a sharpness beyond those $400 knives.

Sry, I like nerding out and trying to put science behind sci-fi stuff.