The effect of foaming process with supercritical <scp> CO ₂ </scp> on the morphology and properties of <scp>3D</scp> porous polylactic acid scaffolds

A systematic study was carried out in order to identify the optimum processing conditions for the preparation of PLA 3D porous structures applying foaming with supercritical CO2 (sc-CO2). Both the depressurization rate and the CO2 saturation pressure had a significant effect on the obtained sc-CO2 PLA structures. When sc-CO2 was instantaneously depressurized, a thin wall pore structure was formed, characterized by anisotropy with pores diameter ranging from 100 to 650 μm, whereas the scaffold porosity varied between 85% and 95%. In this case, a decrease in the porosity percentage was observed with increasing saturation pressure. A trend of increase in the pores' size was recorded from 150 to 200 bar, followed by a decrease at 300 bar. Highly organized pore structures with thicker pore walls and pores with diameters within the range of 10–350 μm and porosity and 74%–77% were fabricated when a slow depressurization rate was applied. An optimum porous structure, with average pore diameter 340 μm and porosity 88% was prepared when Psat was maintained at 200 bar, followed by instantaneous depressurization. Although this scaffold included the biggest number of closed pores in its structure, it presented the highest degree of pore interconnectivity due to CO2 bubbles' coalescence.