After a few tough years, a California-based company called Ekso Bionics signed a promising deal with two Chinese firms in early 2019. The company designs robotic mechanical suits called exoskeletons, and it agreed to form a joint venture that would shift some of its production to China and help sell its equipment in Asia.  At the time, shares of the small, Nasdaq-listed company were depressed. And after years of working with the United States military, including participating in a failed project to build an “Iron Man” combat suit, the company was shifting its focus to produce outfits more suited to the medical market. China held out the promise of lots of new customers. But this month, the federal government told Ekso Bionics to call the deal off. The Committee on Foreign Investment in the United States, a federal inter-agency body that weighs whether business transactions are a threat to national security, blocked the joint venture after deciding that giving Chinese com