In-vitro biodegradation study of poly(ε-caprolactone) films using a 3D printed helical flow prototype to simulate the physiological conditions for cardiovascular implanted devices

Abstract

Current in-vitro biodegradation test methods for characterizing bioabsorbable polymer implants including ASTM F1635-11, focus on testing mechanical and chemical properties of samples under static conditions. These tests oversimplify the implant service environment and yield limited data due to the lack of fluid flow, stresses, and pressures. The effects of the helical or spiral blood flow observed in arterial vessels are of particular interest for biodegradable polymer cardiovascular stents due to its promising biomedical uses and relatively recent discovery. In this study, a novel 3D printed prototype flow device was designed and developed to simulate in-vivo conditions including flow rates, flow characteristics, pressures, temperatures, and chemical environment. The in-vitro biodegradation behavior of poly(ε-caprolactone) (PCL), in phosphate buffer solution (PBS) was used to study the influence of flow conditions compared to a standard static ASTM method over 5 weeks. Characterization of the polymer degradation was performed by evaluating changes in weight loss, molecular weight and the degree of crystallinity as a function of time. The number average molecular weight of the polymer showed the largest decline, decreasing linearly with time by 22% and 5% for the samples tested using the flow device and ASTM method, respectively. Similarly, the degree of crystallinity was found to increase linearly by 16% and 6% for the flow device and ASTM method, respectively. Helical/spiral flow at the flow rates as low as 1 cm3 s−1 were found to enhance the bulk degradation of PCL by up to 80% when compared to the static ASTM method. A combination of bulk and surface erosion mechanisms were proposed for the degradation behavior of the PCL in the flow prototype. This indicates that by more accurately mimicking physiological conditions, including blood dynamics, this 3D printed prototype can serve as an improved method for testing bioabsorbable and biodegradable polymers for implanted devices.