I applaud your effort to solicit feedback on this issue. It must have been hurtful to hear yourself described as "mean" and "rude" when you clearly strive to convey professionalism at work and take your work very seriously. I don't think you need to lower your standards to be more approachable.
Maybe you could try small things, like making a conscious effort to make eye contact and smile upon greeting your coworkers. Or just smiling when you walk by them in the halls. (I personally have what I call "b****face," meaning that, when I am thinking, or otherwise not speaking to or looking directly at someone, I have a sour look on my face. I only learned this recently when I caught myself looking angry and mean in the rear view mirror, so now I'm working on it!
Maybe you could join your colleagues for happy hour, bring a box of doughnuts in for the shift, or do some other thing that isn't strictly work-related (showing you have an "off-duty" side), but also doesn't force you to compromise your values pertaining to how a professional nurse should behave on the job.
And finally, when you say that you are blunt, if that means you don't filter as well as maybe you should (think Sophia from Golden Girls, minus the cute little old lady factor), then I would consider remembering that not everything that is true needs to be spoken (and that Sophia was that way as a result of a stroke!). I only add this because I had a friend years ago who considered herself "blunt," but what she was was rude and inappropriate. Just because one sees/thinks/feels something doesn't mean it is appropriate to speak about it. And if someone does have that foot-in-mouth problem, they should work on it -- not wear their rudeness and lack of decorum as a badge of honor, calling it being "blunt" or "no-nonsense." (NOTE: It doesn't sound to me like that describes you, but I have heard more than one rude, nasty person call themselves "blunt" and take pride in being what amounts to a total @$$. So, I'm just putting that out there just in case. No offense intended!)
Good luck; I hope things warm up at the workplace sooner rather than later.