There is no way to create a Simulink signal that is a character vector or a string array or a struct array (except for a timeseries.)
Therefore to use that function inside Simulink, you would need to create a MATLAB Function Block that brought in the inputs from non-signal sources as necessary, and then called your function, and disposed of the results in non-signal ways.
The only alternative to this is that you could encode the string array or struct array as numeric signals and pass those around, and then decode them inside a MATLAB Function Block and then call your function and encode the results as numeric signals. For example you could use the fast serialization contribution from the File Exchange. Remember, though, that if you try to do this in continuous time instead of discrete time, that your signals are likely to be interpolated...
