There are some textbooks out there on device design, like this one. I honestly think you're best served by learning about the design process overall, for which there are a ton of great open source resources. I'd look into IDEO, which is a real force in that area. Alternatively, you can take a case-study-style approach, where you take one device, like a pacemaker or a surgical stapler or the artificial hip, and learn everything you can about the evolution of that device, from the time it was invented in its most basic form all the way up to today.