A few years back, I invested for a time in a blood testing company called Immucor (Ticker: BLUD). They followed the razor / razorblade model so popular today – sell your razor around or at cost while charging nice margins on the razorblades. The custom testing reagents had lofty profit margins.
One of the only drawbacks was the potential for “artificial blood” to come to market, something that sounds a bit further off based on this Wired article. Too bad I sold the stock, missing out on a fantastic run.