Thermo-mechanical analysis of a compliant poly(carbonate-urea)urethane after exposure to hydrolytic, oxidative,
Henryk J Salacinski1, Marianne Odlyha, George Hamilton
1University Department of Surgery, Royal Free and University College Medical School, University College London, UK.
Aims:
To date, there is still a great need for a fully viable small diameter (< 6 mm) polymeric vascular graft. Currently in such low flow locations, non-elastic expanded polytetrafluoroethylene (ePTFE) is the best available but it is quite inferior to autologous saphenous vein since it fails due to intimal hyperplasia caused by compliance mismatch between the graft and elastic host artery. Recently, a novel compliant poly(carbonate-urea)urethane vascular graft whose trade name is MyoLink has been developed. In this article, we report the findings of a thermo-mechanical analysis of the polymers chemistry postexposure to in vitro solutions comprised of hydrolytic, oxidative, peroxidative and biological media.
Methods And Materials:
The following degradative solutions were used in vitro: plasma fractions I-IV; phospholipase A2 (PLA); cholesterol esterase (CE) and solutions of H2O2/CoCl2, t-butyl peroxide/CoCl2 (t-but/CoCl2) and glutathione/t-butyl peroxide/ CoCl2 (glut/t-but/CoCl2). The MyoLink graft was compared against a conventional poly(ether)urethane (Pulse-Tec). All the graft specimens were 100 mm in length (5.0 mm ID) and were incubated in the latter solutions at 37 degrees C for 70 days in total. The following thermo-mechanical methods were used to analyse both graft types: thermo-mechanical analysis (TMA) and dynamic mechanical thermal analysis (DMTA).
Results:
Incubation of Pulse-Tec in plasma fractions I-IV, PLA and CE reveals only one observable modification: an increase in the size of the low temperature, melting phase. But incubation in H2O2/CoCl2, and t-but/CoCl2 leads to an increase in the polymeric phase separation coupled with an enlargement in the size of the low temperature melting crystalline phase in Pulse-Tec. The glut/t-but/CoCl2 solution leads to a phase separation between the hard and soft segment domains, coupled with an increase of the internal order within the hard segment domains in Pulse-Tec. The only system in which MyoLink degraded was glut/t-but/CoCl2. In this system, an increase of the phase separation coupled with a simultaneous increase of the crystal size of the low-temperature melting crystalline phase occurred.
Conclusion:
This study shows dramatic changes in the chemistry of the soft and hard segments occurred in the case of the conventional poly(ether)urethane Pulse-Tec graft material. Such changes were not manifested in the majority of solutions in the case of MyoLink but a hydrolytic-led degradation of the carbonate soft segment was evidenced only in the glut/t-but/CoCl2 system.
