Patent ID: 7524445

Claim:
A method for making an ePTFE structure, said method comprising the steps of: providing an unexpanded PTFE extrudate which is un-sintered; initially expanding the un-sintered extrudate to produce an ePTFE structure having an initial node and fibril micro-structure therein; heating the ePTFE structure to raise the temperature thereof for a time period of sufficient duration such that at least a portion of the ePTFE structure is partially sintered, said heating step providing for the ePTFE structure to retain at least a portion of the initial expansion, said heating step further providing for limiting the temperature and time duration such that the portion of the ePTFE structure in which at least a portion of the initial expansion is retained is not fully sintered; subsequently expanding the partially sintered ePTFE structure to produce a subsequent node and fibril micro-structure therein; and heating the partially sintered ePTFE structure to raise the temperature thereof for a time period of sufficient duration to fully sinter the subsequently expanded ePTFE structure to completely lock the subsequent node and fibril micro-structure therein.