An NDA is most certainly not a patent. An NDA is basically two parties agreeing that they will not tell anyone about the information in questions. It is more akin to a trade secret than a patent. A patent is you telling the world how you did something but the government then telling everyone that they cannot copy what you did for a set period of time. An NDA is much more fitting for early in the research stage, during the pre-clinical research phase. At this point there isn’t enough information generated yet to warrant a patent, but the company doing the development will not want others finding out about it, so they will ask those involved to sign an NDA. A patent is needed once the project hit clinical trials, as the company will need to disclose the information about the device, but they will be afforded legal protections in doing so.