Pluromed Inc. has received approval from the US Food & Drug Administration for its Backstop polymer gel plug, used during lithotripsy kidney stone treatments that use laser or other energy sources to break up the stones. The polymer gel plug uses Rapid Transition Polymers, which are liquid at low temperatures but gel at 98.6 degrees Fahrenheit. During the lithotripsy, the gel forms a plug above the stones, preventing them from moving during the procedure. Once they're broken up, saline is used to dissolve the plug. The Backstop product is already approved in Europe and Canada.