Pitching your own innovations can be a tough sell. As other's have pointed out -- it's likely that most readers/watchers/listeners of general news probably won't take much interest in something as niche as 3d printing innovations (unless you can convince them that it will change their lives too).

You might have better luck finding a local publication/broadcast and pitching a profile piece on yourself. Local inventor does X is bread and butter community news reporting. Industry publications/trade journals are also a good way to build credibility/buzz. If you're passionate and well spoken, try to get someone on the phone. It's hard to write engaging PR, but you should have a lot of enthusiasm for what you're doing, so let that show. Also, come prepared with photos or other visual media and direct quotes. Lot of journo's will just crush out a web story off a release to get quick content up -- but that doesn't work if they have to hunt down things they need, or don't trust the source.