Abstract: A device for preventing blood leakage during use of an intravenous catheter and needle using a stopper made of a material that is air permeable when dry; upon exposure to blood or other liquids bercomes rapidly liquid impermeable; is non-toxic and validated to use on humans; is inexpensive; is stable and withstands normal sterilization procedures such as heating and ionizing radiation; and is flexible and able to seal the hole when the needle is removed from the IV catheter during the cannulation process.