MECHANICAL CHARACTERISTICS OF DILATED POLYTETRAFLOUROETHYLENE USED FOR TRANSLUMINALLY PLACED ENDOVASCULAR GRAFTS

This study was conducted to assess the mechanical characteristics of d ilated polytetraflouroethylene (PTFE) for use in transluminally placed endovascular grafts (TPEGs). Ten-centimeter lengths of 3- and 4-mm th inwalled PTFE were dilated to 8, 10, 12, and 15 mm diameters (3 mm) an d 10-, 14-, 16-, and 20-mm diameters (4 mm), respectively (n = 6 for e ach size). The dilated PTFE segments were evaluated for leakage, furth er dilation, structural changes (with electron microscopy), and change s in wall thickness occurring after 24 hours of perfusion at pressures of 300-350 mmHg. Both 3- and 4-mm thinwalled PTFE could be dilated to five times their initial diameter before rupture occurred. Three-mill imeter grafts dilated to 12- and 4-mm grafts dilated to 14 mm remained resistant to leakage at perfusion pressures up to 350 mmHg. When 3-mm grafts were dilated to 15 mm, the PTFE leaked saline at a rate of 20. 3 +/- 9.3 cc per hour at 300 mmHg. pressure. Four-millimeter grafts di lated to 16- and 20-mm diameters leaked saline at 8.4 +/- 7.8 and 52.8 +/- 22 cc per minute, respectively, at the same pressure. No grafts w ere found to increase in diameter after 24 hours of pressure perfusion . Electron microscopy revealed that PTFE node size was significantly s maller in dilated grafts than in undilated grafts, but there was no si gnificant change in internodal distance. This data suggests that thinw alled PTFE can be dilated to large diameters and retain sufficient str ength to resist supraphysiologic pressures. Long-term studies are need ed to determine the late structural integrity of dilated PTFE.