MIT PhD candidate Nikolai Begg, who won a Lemelson-MIT Student Prize for Invention last year, was one of the special guests at the MIT Museum during school vacation week. On Wednesday, he helped 8-year-old Donny Azar build a device to remove an object stuck in a model lung. One of Begg’s specialities is medical device design.Mark Shanahan can be reached at email@example.com. Follow him on Twitter @MarkAShanahan. Meredith Goldstein can be reached at firstname.lastname@example.org. Follow her on Twitter @MeredithGoldste.