A razor has a blade and thus can be turned into a weapon. So how do you make a razor that can't be turned into a shank? You make it bright orange so that it's very visible and build in 8 fragile points which break apart if you apply pressure. It can't be opened, so there's no way to hide contraband inside.
Rain Noe of Core77 perused the online store of Bob Barker, a company that sells products made specifically for prison and jail environments. There are many adaptations that you might never think of, such as soft silicone chess pieces (so they can't be used as weapons), transparent toothpaste tubes, and transparent wind-up radios.