Three-dimensional printer makers 3D Systems (DDD) and Stratasys (SSYS) are falling after a third company in the space disclosed in a regulatory filing earlier today that it would carry out an initial public offering, or IPO. ExOne, which sells 3D printers to industrial customers, stated that it expects to trade on Nasdaq under the symbol XONE. The IPO price will be $14-$16, the company added. In addition, an article on Seeking Alpha by one of the website’s contributors may also be weighing on shares of 3D Systems and Stratasys. The article compared 3D systems to a 1990s tech bubble stock and noted that it has several competitors in the 3D printing space. In mid-afternoon trading, 3D Systems plunged 12% to $60.59 while Stratasys sank 10% to $78.48.