Redi! Have you tried doing exactly that through the GUI and then right clicking the simulation and selecting 'To Python..' if I remember correctly that shows you how to assign materials to the database.
Just tried it and I get something like this:
import s4l_v1.materials.database as database
# Adding a new MaterialSettings
material_settings = acoustic.MaterialSettings()
components = [entity__block1]
mat = database["IT'IS 4.0"]["Brain (Grey Matter)"]
if mat is not None:
# Fallback if material is not found
material_settings.Name = "Brain (Grey Matter)"
material_settings.MassDensity = 1044.5, Unit("kg/m^3")
material_settings.AttenuationCoefficient = 1.2, Unit("Np/m")
Never tried it with the ViP model but should work.