PASADENA, Calif.--(BUSINESS WIRE)--Jan. 25, 2006--Arrowhead Research Corporation (NASDAQ:ARWR), a diversified nanotechnology company, today announced that it has received $19.6 million and closed its previously announced private placement. In the offering, institutional investors received 5,590,000 shares of restricted common stock and 1,397,500 warrants to purchase common stock.