WESTLAKE VILLAGE, Calif.--(BUSINESS WIRE)--Sienna Biopharmaceuticals, Inc., a privately held, clinical stage medical dermatology and aesthetics company, today announced that it completed a $40 million Series B financing led by existing investors ARCH Venture Partners and Venvest Capital. Additional investors participating included Partner Fund Management, Altitude Life Science Ventures, and Dr. David Pyott. New investors accounted for approximately half of the investments and