It was a rough week for nearly all of the publicly traded names in 3-D printing.

3D Systems (NYSE:DDD), ExOne (NASDAQ:XONE), and voxeljet (NYSE:VJET) tumbled 12%, 12%, and 10%, respectively, on the week.

Even the always-volatile Organovo (NASDAQ:ONVO) -- the 3-D bio-printing pioneer with the ambitious goal of bio-engineering a proxy for human tissue and eventually organs that could be used, at the very least, for drug testing -- took a huge 18% hit last week. 

Citron Research played a hand in the niche's slide. Citron's Andrew Left was talking down Organovo on CNBC's Fast Money on Tuesday. He drew attention to accusations of Japan's Kanagawa cold-calling investors to hype the stock. Organovo countered with a statement to CNBC refuting the claims, but the damage was done. 

Later in the week, Citron published another negative note on 3D Systems. It didn't help that 3D Systems had been the subject of a Credit Suisse downgrade to kick off the trading week. Citron's latest note argues that its shares can fall to $56 in the near term, but this isn't the first time that it has gone after 3D Systems. 

Citron issued a bearish report on 3D Systems last Valentine's Day. 

"When it comes to calling out a bubble stock, we are yet to be wrong," it noted early in the piece. Well, even after last week's slide, 3D Systems is kicking off this new trading week 83% higher. 

The big gains in 3-D printing stocks last year can't be ignored. ExOne and voxeljet went public in 2013, and the stocks closed well above their initial prices. 3D Systems and Organovo moved 161% and 326% higher, respectively, last year. All four of the stocks have moved sharply lower this month, but not to the point of eradicating most of last year's gains.

Now, I did mention that it was a rough week for nearly all of the 3-D printing names. Stratasys (NASDAQ:SSYS) was the lone holdout on the week. It rose modestly during a down week for the market. Naturally, it helped that as Credit Suisse was downgrading 3D Systems -- a move that sent smaller players ExOne and voxeljet lower -- that it also upgraded Stratasys. It was singled out as the more attractively valued 3-D printing play, and Credit Suisse even boosted its price target on Stratasys from $128 to $144.

The one thing that is certain is that all five of these stocks will continue to be volatile. Organovo will be feast or famine for investors until it proves the viability of its ambitious goals. It's a different scene for traditional 3-D printing. ExOne is expected to join voxeljet, 3D Systems, and Stratasys in profitability this year, but they all still trade at lofty income multiples. The premium is the result of the upside potential of 3-D printing in the years to come, but that faraway goal is going to create wild price swings along the way. It's been a bad week -- and a bad month -- for 3-D printing. These stocks won't be standing still in the weeks and months to come.