This is a DNA Double Helix structure that I modeled for a biology projec tin school. I would like to note that if you use supports on this you must be incredibly patient, and be willing to deal with the amount. You will also want to flip the model on its base before printing. (For some reason thingiverse likes to flip all my files on their sides) You will also want to use a relatively high infill to reinforce the structure, and I do NOT suggest using a filament type like ABS that supports do not come off of easily when printing. Enjoy and happy printing!
Disclaimer: The video included is not mine, and I am not taking credit for it. I used it for reference when making this, and if you need help when designing something like this use it as reference.
I used Solidworks in the entirety of its design process. It took a little bit of special tricks, using helix driven pattterns isn't exactly easy. I would just like to say if you need to ever make a helical pattern in Solidworks specifically, you must, and I can not stress this enough, use a surface sweep as the pattern requires it. If you need help, please reference this video (https://www.youtube.com/watch?v=l24NnDsRTT8), it is not mine but it should help in the design process.