Waltham-based Thermo Fisher Scientific Inc. said Tuesday that it has appointed Dr. David M. Sabatini to its Scientific Advisory Board. Sabatini is a member of the Whitehead Institute for Biomedical Research, where he studies the basic mechanisms of cell growth. He has several affiliations with MIT, including his position as an associate professor of biology. He is also an investigator at the Howard Hughes Medical Institute. Sabatini received his doctorate degrees from Johns Hopkins University in 1997 and has been awarded numerous academic distinctions.