Cardiovascular Engineering and Technology

, Volume 5, Issue 3, pp 270–280 | Cite as

Influence of Thermal Annealing on the Mechanical Properties of PLLA Coiled Stents

  • Tré R. Welch
  • Robert C. Eberhart
  • Joan Reisch
  • Cheng-Jen Chuong


To investigate the influence of elevated annealing temperature (70–90 °C) on the mechanical properties of coiled helical PLLA stents. PLLA 0.10 mm fibers and Ø3 mm × 12 mm stents were fabricated and annealed at 70, 80 and 90 °C for 25 min. The mechanical properties of the fibers and the functional characteristics of the stents were measured and compared to a control group processed at 21 °C. The stents were mounted, expanded and relaxed using an Ø3 mm × 2 cm balloon catheter to a maximum balloon pressure of 12 atm. Measurements of stent diameter, length, and the balloon pressure were used to determine the effective circumferential strain, incremental stiffness, elastic recoil, and lengthening of the stents. Stents exhibited progressively higher incremental stiffness with annealing temperature, higher collapse resistance and a reduction in elastic recoil vs. controls. Single fiber mechanical properties decreased as annealing temperature increased. Differential scanning calorimetry revealed crystallinity increased within thermally annealed stent fibers compared with controls. SEM examination indicated thermally annealed stents underwent less twisting than controls during balloon-induced unfurling. Thermal annealing of PLLA fibers and stents between 70 and 90 °C induced changes in crystalline structure, thereby favorably influencing fiber stress–strain behavior and stent expansion characteristics.


Thermal annealing PLLA stent Bioresorbable polymer Crystallinity 


D12 atm

Stent diameter at a balloon pressure of 12 atm

D0 atm

Stent diameter when the balloon pressure is at 0 atm


Instantaneous stent diameter at each pressure level


Stent diameter for the unfurled state

Xc (%)

Percent crystallinity



We thank Ms. Martha Gracey and Dr. Howard Arnott of the Biology Department, UT Arlington, for their help in SEM image generation.

Conflict of Interest

Dr. Tré R. Welch, Dr. Robert C. Eberhart, Dr. Joan Reisch, and Dr. Cheng-Jen Chuong has no conflict of interest. No human and or animal studies were carried out by the authors for this article.


  1. 1.
    Barker G, Welch T, D’Souza N, Nugent A, Eberhart RC, editors. Influence of CO2 Blowing Agent on Porous Bioresorbable Stent Structure. ASME 2013 Summer Bioengineering Conference; 2013 June 26–29; Sunriver, Oregon, USA: ASME Proceedings.Google Scholar
  2. 2.
    Drumright, R. E., P. R. Gruber, and D. E. Henton. Polylactic acid technology. Adv. Mater. 12:1841–1846, 2000.CrossRefGoogle Scholar
  3. 3.
    Engelberg, I., and J. Kohn. Physico-mechanical properties of degradable polymers used in medical applications: a comparative study. Biomaterials 12(3):292–304, 1991.CrossRefGoogle Scholar
  4. 4.
    Grabow, N., C. M. Bunger, C. Schultze, K. Schmohl, D. P. Martin, S. F. Williams, et al. A biodegradable slotted tube stent based on poly(L-lactide) and poly(4-hydroxybutyrate) for rapid balloon-expansion. Ann. Biomed. Eng. 35(12):2031–2038, 2007.CrossRefGoogle Scholar
  5. 5.
    Grabow, N., C. M. Bünger, K. Sternberg, S. Mews, K. Schmohl, and K.-P. Schmitz. Mechanical Properties of a Biodegradable Balloon-expandable Stent From Poly(L-lactide) for Peripheral Vascular Applications. J. Med. Devices 1(1):84–88, 2006.CrossRefGoogle Scholar
  6. 6.
    Grizzi, I., H. Garreau, S. Li, and M. Vert. Hydrolytic degradation of devices based on poly(DL-lactic acid) size-dependence. Biomaterials 16(4):305–311, 1995.CrossRefGoogle Scholar
  7. 7.
    Kotsar, A., T. Isotalo, I. Uurto, J. Mikkonen, P. Martikainen, M. Talja, et al. Urethral in situ biocompatibility of new drug-eluting biodegradable stents: an experimental study in the rabbit. BJU Int. 103(8):1132–1135, 2009.CrossRefGoogle Scholar
  8. 8.
    Levy, Y., D. Mandler, J. Weinberger, and A. J. Domb. Evaluation of drug-eluting stents’ coating durability–clinical and regulatory implications. J. Biomed. Mater. Res. B 91(1):441–451, 2009.CrossRefGoogle Scholar
  9. 9.
    Li, S. M., H. Garreau, and M. Vert. Structure-property relationships in the case of the degradation of massive aliphatic poly-(a-hydroxy acids) in aqueous media, Part 1: poly(DL-lactic acid). J. Mater. Sci.: Mater. Med. 1:123–130, 1990.CrossRefGoogle Scholar
  10. 10.
    Lincoff, A. M., J. G. Furst, S. G. Ellis, R. J. Tuch, and E. J. Topol. Sustained local delivery of dexamethasone by a novel intravascular eluting stent to prevent restenosis in the porcine coronary injury model. J. Am. Coll. Cardiol. 29(4):808–816, 1997.CrossRefGoogle Scholar
  11. 11.
    Mani, G., M. D. Feldman, D. Patel, and C. M. Agrawal. Coronary stents: a materials perspective. Biomaterials 28(9):1689–1710, 2007.CrossRefGoogle Scholar
  12. 12.
    Nishio, S., K. Kosuga, K. Igaki, M. Okada, E. Kyo, T. Tsuji, et al. Long-Term (>10 Years) clinical outcomes of first-in-human biodegradable poly-l-lactic acid coronary stents: Igaki-Tamai stents. Circulation 125(19):2343–2353, 2012.CrossRefGoogle Scholar
  13. 13.
    Oberhauser JP, Hossainy S, Rapoza RJ. Design principles and performance of bioresorbable polymeric vascular scaffolds. EuroIntervention : journal of EuroPCR in collaboration with the Working Group on Interventional Cardiology of the European Society of Cardiology. 2009;5 Suppl F:F15-22.Google Scholar
  14. 14.
    Onuma, Y., and P. W. Serruys. Bioresorbable scaffold: the advent of a new era in percutaneous coronary and peripheral revascularization? Circulation 123(7):779–797, 2011.CrossRefGoogle Scholar
  15. 15.
    Palmerini T, Biondi-Zoccai G, Della Riva D, Mariani A, Genereux P, Branzi A, et al. Stent thrombosis with drug-eluting stents: is the paradigm shifting? Journal of the American College of Cardiology. 2013;62(21):1915-21.Google Scholar
  16. 16.
    Perego, G., G. Cella, and C. Bastioli. Effect of molecular weight and crystallinity on poly(lactic acid) mechanical properties. Polymer 59:37–43, 1996.Google Scholar
  17. 17.
    Sarasua, J. R., A. L. Arraiza, P. Balerdi, and I. Maiza. Crystallinity and mechanical properties of optically pure polylactides and their blends. Polym. Eng. Sci. 45:745–753, 2005.CrossRefGoogle Scholar
  18. 18.
    Sheth, M., R. Kumar, V. Dave, R. Gross, and S. McCarthy. Biodegradable polymer blends of poly(lactic acid) and poly(ethylene glycol). J. Appl. Polym. Sci. 66:1495–1505, 1997.CrossRefGoogle Scholar
  19. 19.
    Su, S. H., R. Y. Chao, C. L. Landau, K. D. Nelson, R. B. Timmons, R. S. Meidell, et al. Expandable bioresorbable endovascular stent. I. Fabrication and properties. Ann. Biomed. Eng. 31(6):667–677, 2003.CrossRefGoogle Scholar
  20. 20.
    Tamai, H., K. Igaki, E. Kyo, K. Kosuga, A. Kawashima, S. Matsui, et al. Initial and 6-month results of biodegradable poly-l-lactic acid coronary stents in humans. Circulation 102(4):399–404, 2000.CrossRefGoogle Scholar
  21. 21.
    Tsuji, H., and Y. Ikada. Properties and morphologies of poly(L-lactide), Part 1: annealing condition effects on properties and morphologies of poly(L-lactide). Polymer 36:2709–2716, 1995.CrossRefGoogle Scholar
  22. 22.
    Tsuji, T., and Y. Ikada. Crystallization from the melt of pLA with different optical purities and their blends. Macromol. Chem. Phys. 197:3483–3499, 1996.CrossRefGoogle Scholar
  23. 23.
    Tsuji, H., and Y. Ikada. Stereocomplex formation between enantiomeric poly(lactic acid)s. XI. Mechanical properties and morphology of solution cast films. Polymer 40:6699–6708, 1999.CrossRefGoogle Scholar
  24. 24.
    Turner, J. F. I. I., A. Riga, A. O’Connor, J. Zhang, and J. Collis. Charcterization of drawn and undrawn poly-L-lactide films by differential scanning calorimetry. J. Therm. Anal. Calorim. 76:257–268, 2004.CrossRefGoogle Scholar
  25. 25.
    van der Giessen, W. J., A. M. Lincoff, R. S. Schwartz, H. M. van Beusekom, P. W. Serruys, D. R. Holmes, Jr., et al. Marked inflammatory sequelae to implantation of biodegradable and nonbiodegradable polymers in porcine coronary arteries. Circulation 94(7):1690–1697, 1996.CrossRefGoogle Scholar
  26. 26.
    Weir NA, Buchanan FJ, Orr JF, Dickson GR. Degradation of poly-L-lactide. Part 1: in vitro and in vivo physiological temperature degradation. Proceedings of the Institution of Mechanical Engineers Part H, Journal of engineering in medicine. 2004;218(5):307-19.Google Scholar
  27. 27.
    Welch, T., R. C. Eberhart, and C. J. Chuong. Characterizing the expansive deformation of a bioresorbable polymer fiber stent. Ann. Biomed. Eng. 36(5):742–751, 2008.CrossRefGoogle Scholar
  28. 28.
    Welch, T. R., R. C. Eberhart, and C. J. Chuong. The influence of thermal treatment on the mechanical characteristics of a PLLA coiled stent. J. Biomed. Mater. Res. B 90(1):302–311, 2009.Google Scholar
  29. 29.
    Zilberman, M., R. C. Eberhart, and N. D. Schwade. In vitro study of drug-loaded bioresorbable films and support structures. J. Biomater. Sci. Polym. Ed. 13(11):1221–1240, 2002.CrossRefGoogle Scholar
  30. 30.
    Zilberman, M., K. D. Nelson, and R. C. Eberhart. Mechanical properties and in vitro degradation of bioresorbable fibers and expandable fiber-based stents. J. Biomed. Mater. Res. B. 74(2):792–799, 2005.CrossRefGoogle Scholar

Copyright information

© Biomedical Engineering Society 2014

Authors and Affiliations

  • Tré R. Welch
    • 1
  • Robert C. Eberhart
    • 2
    • 3
  • Joan Reisch
    • 4
  • Cheng-Jen Chuong
    • 3
  1. 1.Department of Pediatric Cardiovascular Thoracic SurgeryUniversity of Texas at Southwestern Medical Center of DallasDallasUSA
  2. 2.Department of SurgeryUniversity of Texas Southwestern Medical Center at DallasDallasUSA
  3. 3.Bioengineering DepartmentUniversity of Texas at ArlingtonArlingtonUSA
  4. 4.Department of BiostatisticsUniversity of Texas Southwestern Medical Center at DallasDallasUSA

Personalised recommendations