A catheter assembly comprises a catheter shaft, a balloon and a pair of collars. The collars may be fixed or rotatable about a catheter shaft prior to exposure to an electric current. Where the collars are fixed to the shaft, the balloon is rotatable about the collars. When exposed to the electric current the collars expand to engage the waists of the balloon thereby sealing the balloon. Where the collars are rotatable about the shaft, the each waist of the balloon is engaged to a respective collars. When the rotatable collars are exposed to the electric current the collars expand to engage the shaft of the catheter thereby sealing the balloon.