First source of inspiration is “Fantastic Voyage”, the 1966 film where a submarine crew is shrinked and injected into a human body. I particulary love the scene in wich Pleasence is ingested by the white blood cell. I know that Cameron is planning a remake, maybe after a pair of Avatar clones. Unfortunately I’ve missed the animated sequel (1968) and Joe Dante’s “Innerspace” (1987). For oversized and undersized aliens, check also Voltaire’s “Micromégas”, written in 1752, and “Pictures can’t lie”, by Katherine MacLean (1955).