Photodegradation of poly(ether-b-amide) catalyzed by bismuth radiopaque additive

Abstract

Bismuth compounds (e.g., bismuth subcarbonate and bismuth oxychloride) are often used as radiopaque additives in poly(ether-b-amide) (PEBA) for medical catheter applications to enhance the visibility of the catheter tips during fluoroscopy-guided minimally invasive surgeries. However, there is an increasing number of reports on bismuth-based photocatalysts in other fields; yet the impact of bismuth additives on the shelf life of PEBA has never been studied/reported. In this work, the stability of PEBA containing bismuth subcarbonate was tested against PEBA containing other radiopaque additives, barium sulfate and tungsten, in several real-life-relevant lighting conditions. It was found bismuth-containing PEBA degraded significantly faster than these counterpart materials under light exposure conditions including indoor fluorescent light, daylight-simulating xenon light and high-flux visible blue light. The extents of photodegradation of bismuth-containing PEBA were characterized by optical imaging, tensile test, FTIR analysis, Raman imaging and ESR radical analysis. The results showed material surface cracking, material hardening, surface oxidation and radical concentration increase over the course of light exposure. Various environmental factors were studied; it was found PEBA containing bismuth not only degraded under lights containing UV light but also degraded under high intensity visible blue light. Larger doses of light exposure and higher environmental temperatures led to more material degradation. Additional shelf aging studies on light-exposed samples were performed, which showed latent aging with continued degradation shortening the shelf life after the initial light exposure, due to the formation of persistent free radicals. Finally, several design and use considerations were discussed in the context of catheter material photodegradation.