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EMAC 276

Polymers for Vascular Graft Applications Sean Arlauckas , Randy Birkenmeier , Rick Ditto, Alex Engel, & Joe Karas. EMAC 276. Application and Clinical Issues. Overview of vascular grafts. Vascular diseases create the need to replace diseased blood vessels with healthy grafts

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EMAC 276

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  1. Polymers for Vascular Graft ApplicationsSean Arlauckas, Randy Birkenmeier, Rick Ditto, Alex Engel, & Joe Karas EMAC 276

  2. Application and Clinical Issues

  3. Overview of vascular grafts • Vascular diseases create the need to replace diseased blood vessels with healthy grafts • Autologous grafts are desired, but not always possible • Polymers are best option for synthetic graft materials http://www.p2pays.org/ref/04/03837/perm/vascular_graft_files/Image2.jpg http://ristretto.ecn.purdue.edu/~sonusv/Frankel-webpage/plaque_image.gif

  4. Clinical issues with polymer grafts • Patency-- vessel being free from fibrin, platelet, and erythrocyte accumulation (thrombosis) • Patency rate-- percentage of clinical cases in which vessels remained patent • Polymer grafts are inferior to autologous grafts in terms of patency in numerous clinical studies • In the aorta, polymer grafts exhibited 90% patency over 2 years, autologous grafts exhibited 90% patency over 10 years • In the lower leg, polymer grafts showed 45% patency opposed to 77% for autologous grafts over 5 years Julio C. Palmaz, M. (1998). Review of Polymeric Graft Materials for Endovascular Applications. J VascIntervRadiol. , 9 (1), 7-13. Laube HR, Duwe J, Rutsch W, Konertz W. Clinical experience with autologous endothelial cell-seeded polytetrafluoroethylene coronary artery bypass grafts. J ThoracCardiovascSurg 2000;120(1):134—41.

  5. Clinical issues with polymer grafts • Polymer grafts have only been successful in large diameter blood vessels (diameter > 6mm) • In small vessels (diameter < 4mm) thrombosis occurs within months of grafting. • 75% thrombosis causes oxygen depravation, 90% results in cell death Lian X, Greisler P. Biomaterials in the development and future of vascular grafts. J Vasc Surg. 2003;37:472-80.

  6. Role of Polymers in Artificial Vasculature

  7. Why Polymers? • Wide range of chemical and physical properties • Lower risk of patient infection • Diameter and thickness control • No limit on available material • Elimination of off-site surgery www.greenfacts.org Laube HR, Duwe J, Rutsch W, Konertz W. Clinical experience with autologous endothelial cell-seeded polytetrafluoroethylene coronary artery bypass grafts. J ThoracCardiovascSurg 2000;120(1):134—41.

  8. Material Requirements--Mechanical • Durability in prolonged radial and proximal stresses • Suturability • Compliance close to that of the host vessel • Resistance to leakage • Tm above 37oC www.GoreMedical.com Morris, L., et al. A mathematical model to predict the in vivo pulsatile drag forces acting on bifurcated stent grafts used in endovascular treatment of abdominal aortic aneurysms (AAA). Journal of Biomechanics 2004; 37(7): 1087-1095.

  9. Material Requirements--Biological • Biologically stable (inert in blood) • Non-thrombogenic • Low porosity to prevent leakage Salacinski HJ, Goldner S, Giudiceandrea A, Hamilton G, Seifalian AM, Edwards A, et al. The Mechanical Behavior of Vascular Grafts: A Review. J Biomater Appl. 2001;15(3):241-278. Inder, Stephanie J., et al. Identification of dendritic cells in ePTFE grafts explanted from humans. Cardiovascular Surgery 2000;8(4): 265-273.

  10. Polymers Chosen • ePTFE (Goretex) • Tg=-100oC • Tm=330oC • Cost range= $1.6-6 /lb • PET (Dacron) • Tg=69oC • Tm=267oC • Cost range= $0.9-2.2/lb Omnexus Polymer Selector, SpecialChem. Accessed April 4, 2009. http://www.omnexus.com/tc/polymerselector/polymerprofiles.aspx. http://en.wikipedia.org/wiki/Polyethylene_terephthalate http://en.wikipedia.org/wiki/PTFE

  11. Synthesis, Processing, and Fabrication

  12. Synthesis of Dacron® + + 2n H2O Terephthalic Acid (TPA) Ethylene Glycol Dacron® http://en.wikipedia.org/wiki/Polyethylene_terephthalate http://en.wikipedia.org/wiki/Terephthalic_acid http://en.wikipedia.org/wiki/Ethylene_glycol http://www.biomed.metu.edu.tr/courses/term_papers/Blood-Vessel-Substitutes_durmus_files/image017.jpg

  13. Dacron® Processing (Helen E. Kambic, 1986)

  14. Dacron® Fabrication Knitted Graft Woven Graft Textured Textured Untextured Untextured • Velour/Looping • Crimping (Helen E. Kambic, 1986)

  15. Synthesis of ePTFE 2n Peroxide into Free Radical + Free Radical Polymerization of Tetrafluoroethylene http://en.wikipedia.org/wiki/Benzoyl_peroxide http://en.wikipedia.org/wiki/PTFE http://www.biomed.metu.edu.tr/courses/term_papers/Blood-Vessel-Substitutes_durmus_files/image025.jpg

  16. ePTFE Processing 18: Preformed “green tube” 22: Rotating die 26: Counter-rotating mandrel • Extrusion, Expansion, and Sintering • Crimping U.S. Patent no. 5,874,032

  17. Future Applications

  18. Problems with Current Materials • Dacron grafts must be pre-clotted to seal pores and prevent leakage • Possibility of harsh immunogenic responses still exists • Compliance issues • Permanent fixtures within vessel

  19. Polyurethane (PU) • Proven biocompatibility in spinal implants and artificial heart coatings • Versatile material properties allow PU to match the compliance of the native vessel • Theoretically reduces possibility of intimal hyperplasia • Pilot studies have shown in vitro effectiveness, but further research and clinical trials are needed

  20. Polylactic Acid (PLLA) • Several are in clinical trials in the EU • Bioabsorbable implants must meet three criteria: • Mechanical Strength • Degradation Profile • Biocompatibility • As PLLA and most other biopolymers degrade, acid is released at the implant site • This can create a harsh inflammatory response • No product in trials has met all three criteria yet

  21. Acknowledgements • John Blackwell, Ph.D., Department of Macromolecular Science & Engineering, Case Western Reserve University

  22. Questions?

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