What are the most important patents for 3D printing in the US?

Hello. I'm a patent attorney in private practice (I don't work for a company), and I'm doing some research on patents covering 3D printing in the US. More specifically, I'm trying to develop a list of the patents that people in the 3D printing field believe are holding back growth or preventing the introduction of new, lower-priced products. I'm not working for a client on this. It is just a matter of personal interest to me, and I'm thinking of writing an article on the topic. If you have any patent numbers or other information that you would like to share, please post a reply. If you wish to respond privately, you can email me at sross@rossjoynerlaw.com. Many thanks!

It's really hard to say which patents are holding things up. Each technology has many patents. For example, the Selective Laser Sintering Patent is supposed to be a huge one. It has just recently expired (I think at the end of last month). However, there are still plenty of other patents surrounding SLS that make it hard for other companies to enter the market. I do know that when some of the major patents on FDM technology expired, we say an influx of new FDM printers. However, I am not so sure that will be the case with the SLS tech. Same goes for SLA. I don't know which patents on Stereolithography are still active. I know the technology is very old, so I'm assuming most of the major ones have already expired.

They are all important in different ways, would be the best answer. The most valuable patents are probably the SLA patents since it seems like SLA technology will eventually be catching on in consumer oriented 3d printers. In my opinion, SLA jetting technology will replace a lot of the FDM devices in people's garages.
I also feel that there are new technologies which will emerge in the coming years ahead which may in fact make many of the patents that still exist, null and void to some extent. Here is an example of what I mean: http://3dprint.com/2236/entirely-new...ic-deposition/