a process is provided wherein a laser is used to shape and / or trim a polymer tubular catheter material while in situ on a metal insertion needle or cannula . the laser process seals the interface between the polymer catheter material and the metal cannula to prevent the flow of blood between the tubular catheter and the introducing cannula during insertion into a patient . the interface is of sufficient strength to resist such blood flow , but still sufficiently weak to prevent the removal of the cannula needle after insertion into a patient .