Surface Porosity and Core Interconnectivity in Small Diameter PCL/PLA Vascular Scaffolds Prepared by Ultrasonic Irradiation Enhanced Foaming

Highly interconnected porous structure and bionic mechanical performance are important challenges to the successful fabrication of small-diameter vascular scaffolds. This article describes an effective approach to prepare the outer and inner tubular porous poly(ε-caprolactone) (PCL)/polylactic acid (PLA) scaffolds by ultrasonic irradiation (UI)-assisted supercritical CO2 (scCO2) microcellular foaming technology. The pore structures, mechanical properties, and cytocompatibility are investigated with respect to the introduction of UI at various foaming moments. As expected, a tubular porous scaffold with an inner diameter of 4 mm, a nonuniform pore gradient distribution in the core, and a smooth surface is fabricated based on a 280 μm foaming gap. By introducing UI at the end of the saturation process, the resultant foams exhibit a significant increase in surface porosity: pore density increases near 2 orders of magnitude, compared to samples without UI. A denser inner pore structure is obtained, and the corresponding open-pore content increases from 68% to 78%. The Pre-UI scaffolds possess radial tension strength of 2.5 MPa, longitudinal tension strength of 3 MPa, sufficient tensile elastic, high compressive recovery performance, and burst pressure of 250 kPa to maintain human blood flow. Furthermore, suture strength of 2.5 N for Pre-UI scaffolds exceeds the strength of some human veins, which fulfill transplantation requirements. Human endothelial cell culture and proliferation tests for Pre-UI scaffolds reveal good biocompatibility and high capacity for intramural to extramural cell growth. The results gathered in this study may provide a theoretical basis and data to support research into small-diameter vascular tissue engineering of porous scaffolds.