Supercritical Fluid Synthesis of Highly Porous Polylactide Matrices: Fundamental Features and Technology of Formation, Development and Stabilization of Polymer Foams

The paper studies the formation, development and stabilization of the structure of foamed amorphous D,L-polylactide after a slow (quasi-isothermal) and a fast (quasi-adiabatic) relief of the pressure of supercritical carbon dioxide used as a plasticizing/foaming agent. The following regularities have been established: (1) the values of the foam expansion factor in the process of quasi-adiabatic depressurization are significantly lower than in the quasi-isothermal regime because of significant dissipation of the "polymer-foaming agent" system internal energy due to the internal friction in the system; (2) an expansion-collapse effect is observed during the quasi-isothermal foaming; (3) at the intermediate stage between nucleation and intensive foam development, the pore nuclei growth in the plasticized polymer is self-similar. The results obtained are important for selecting foaming regimes that provide the synthesized highly porous matrices with the structural characteristics required for their use in regenerative medicine and tissue engineering.