Unfortunately, TNs are strictly available for the professions listed and described in the NAFTA agreeement. If your job title and tasks do not match the NAFTA description VERY closely, you will be rejected at the US border when you go request the TN. I would certainly NOT recommend applying for a
TN without being sure that your job is within the NAFTA schedule and you have the proper credentials... So you can either look for a job that is on the NAFTA schedule or keep trying for a H1.
In the science field which you are in, you can sometimes get lucky and find an employer wiling to sponsor you. So keep trying if you're really set on working in the US. It might take longer but dont give up.
Alternatively, you could get a job in Canada for a company that has offices in the US and after a year of being at the Canadian branch, you could ask them to transfer you. You'd be looking at an L-1.
Hope this helps!