What happened I won't say, "I told you so." In fact, I didn't tell you so -- not outright at least. But in discussing Proto Labs' (NYSE: PRLB) remarkable 12.3% jump in stock price yesterday, I think I at least implied that there wasn't any good reason for it and that investors were lumping in Proto Labs stock with a much different story. So what Specifically, the story of how 3-D printer-maker 3D Systems (NYSE: DDD) is getting into the human body-parts-printing business. To refresh your memory, yesterday, 3D announced that it is expanding its partnership with United Therapeutics Corporation (NASDAQ: UTHR), whereby 3D uses a "Print to Perfusion" process to 3D print scaffoldings that United Therapeutics then uses to grow human tissue, essentially creating artificial human organs for medical research and surgical transportation. Image source: Getty Images. Now what This is cutting edge biotech stuff, folks, and 3D thinks it could be "an exciting growth driver" for its business over the next decade or so. It does not, however, have a whole lot to do with Proto Labs' business, which consists of using 3D printers to manufacture prototypes and small batches of products for primarily industrial customers. I think today other investors may have come to the same conclusion. After running up 12.3% in share price yesterday, today, Proto Labs stock ran back down 12.6% and closed Thursday trading below where they had begun trading on Wednesday. 10 stocks we like better than Proto LabsWhen investing geniuses David and Tom Gardner have a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* David and Tom just revealed what they believe are the ten best stocks for investors to buy right now... and Proto Labs wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of November 20, 2020 Rich Smith has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Proto Labs. The Motley Fool recommends 3D Systems. The Motley Fool has a disclosure policy.Source