Biomechanical Characterization of a Micro/Macroporous Polycaprolactone Tissue Integrating Vascular Graft

Abstract

The objective of the present study was to characterize the short-term biomechanical properties of cast micro/macroporous poly(caprolactone) (PCL) tubes intended for application as tissue integrating blood vessel substitutes. Micro/macroporous PCL vascular grafts (5. 5 mm internal diameter, 7.5 mm external diameter) with defined macropore structures were produced by rapidly cooling PCL solutions containing dispersed gelatin particles in dry ice, followed by solvent and gelatin extraction. A Bose-Enduratec BioDynamic chamber configured for cardiovascular applications was used to measure the diametrical stability (dilation) of tubular samples under hydrodynamic flow conditions at 37 °C. Microporous PCL tubes withstood the hydrodynamic stresses induced by short, 2-min duration flow rates up to 1000 mL/min, which resulted in estimated internal pressures in excess of arterial pressure (80-130 mmHg). Micro/macroporous PCL tubes having a maximum macroporosity of 23% accommodated the hydrodynamic stresses generated by short duration, flow rates up to 1000 mL/min, which resulted in estimated internal pressures similar to venous pressure (30 mmHg). The dilation of microporous PCL tubes under short, (5 min) pulsatile flow conditions (1 Hz) increased from 10 to 100 μm with increasing mean flow rate from 50 to 500 mL/min. Both microporous and macroporous tubes exhibited a burst strength higher than 900 mmHg under hydrostatic fluid pressure, which is in excess of arterial pressure (80-130 mmHg) by a factor of approximately 7. Quantitative analysis of the macropore structure was performed using micro-computed tomography for correlation with mechanical properties and cell growth rates. Mouse fibroblasts efficiently colonized the external surface of macroporous PCL materials over 8 days in cell culture and cell numbers were higher by a factor of two compared with microporous PCL. These findings demonstrate that micro/macroporous PCL tubes designed for vascular tissue engineering can accommodate the hydrodynamic stresses generated by short duration, simulated blood flow conditions and exhibit good potential for integration with host tissue. © 2010 Biomedical Engineering Society.