Make it as ugly as possible, specify the most expensive materials you can find, use parametric tools to model it, and you're most of the way there.

Sounds like an efficient hospital.  Also make sure the ambulances need to circle the building twice before finding the emergency drop-off.

Hospital buildings are typically not expressionist in style or execution.  I think that term is a misnomer in architecture in general - expressionism is a painterly movement not an architectural one.  A Kandinsky painting is expressionist - fluid and spontaneous.  A building that required 50 sheets of construction drawings and engineering is not regardless of the final output - I think the closet you can get is a Gehry and those are craptastic leak machines.  Taut is not even close - alpine architecture and glass pavilion are way to crystalline and ordered to be considered expressionist.

Maybe your prof is hoping you will investigate brick expressionism.  Wiki it.  There are neo expressionists like Enric Miralles and Caruso St. John that are much more relevant to the continuity of architecture than the likes of Zaha/Schumacher/Gehry. 
 

extract the parts and programs that would not be less efficient/productive as a space if turned "expressive" over performance

actually i was also confused that hospital is a fully functional project..and in expressionism form is more important rather than function..
i want to design its elevation that looks like a expressionist building..not want to alter its function 

screw expressionists.. focus about the experience first.

anyways.. back to your question.  you could just design a monolithic concrete block.  that's expressionist