Morphological study on the pore growth profile of poly(ε-caprolactone) bi-modal porous foams using a modified supercritical CO2 foaming process

Fabrication of open‐porous PCL/PLA tissue engineering scaffolds and the relationship of foaming process, morphology, and mechanical behavior

“…With an increase in the CO 2 dissolution time, the dissolution of carbon dioxide in the composites increased before foaming, which increased the number of nucleation points inside the blends, and the nucleation efficiency increased, so that the cell density increases and the average cell diameter was reduced . Also, as the amount of dissolved gas in the polymer increases and the interaction of carbon dioxide and the polymer leaded to an increase in the motion of molecular chains, so the melt viscosity of the composite materials decreased, and the resistance to the process of cell nucleation and growth was reduced, which promoted the nucleation and growth of bubbles, so that it was easier to obtain cells with a uniform size and cell structure …”

“…As the number of nucleation increased, the more amount of gas dissolved in the polymer was used for nucleation, and the amount used for bubble growth was relatively reduced, so the driving force for cell growth was relatively small, but the driving force at this time is sufficient to cause collision between the bubbles to form an open‐cell structure. When the effect of increasing nucleation amount was greater than that of the reduction of the driving force, the collision between the bubbles was relatively reduced, so the porosity decreased …”

“…When the cell was less than the critical size, the cell structure in the polymer tended to be stable and the bubble needed to be dense enough to cause the cell impact to occur. When the process parameter changed beyond the condition of critical nucleation density, the cell collision occurred and then formed the opening structure …”

“…When the effect of increasing nucleation amount was greater than that of the reduction of the driving force, the collision between the bubbles was relatively reduced, so the porosity decreased. 21 It can be seen from the Figure 8B that the porosity of the PCL/PLA (7/3) blend material increased from 62.4% to 68.9%, and then decreased to 58.4% with the increase of CO 2 dissolution time, and the PCL/PLA (3/7) blend material increased from 53.3% to 55.6%…”

“…20 3.1.3 | Influence of CO 2 dissolution time on cell morphologies of PCL/PLA blends With an increase in the CO 2 dissolution time, the dissolution of carbon dioxide in the composites increased before foaming, which increased the number of nucleation points inside the blends, and the nucleation efficiency increased, so that the cell density increases and the average cell diameter was reduced. 21 Also, as the amount of dissolved gas in the polymer increases and the interaction of carbon dioxide and the polymer leaded to an increase in the motion of molecular chains, so the melt viscosity of the composite materials decreased, and the resistance to the process of cell nucleation and growth was reduced, which promoted the nucleation and growth of bubbles, so that it was easier to obtain cells with a uniform size and cell structure. 22 3.2 | Influence of foaming process parameters on the porosity Figure 8A shows that the effect of foaming pressure on the porosity of different blends ratio has the same trend, with the increase of foaming pressure, the porosity increased first and then decreases, and the rate of increase of porosity increased more slowly.…”