Plasticization of polylactide foams for tissue engineering
Supercritical CO2 foaming of amorphous and semicrystalline polylactides plasticized by blending with 20 wt% polyethylene glycol has been investigated as a means of producing low-stiffness bioresorbable scaffolds for tissue engineering. For a given set of foaming parameters, the presence of polyethylene glycol generally resulted in a significant reduction in foam density and increased cell diameters, effects that could be accounted for by a large decrease in melt viscosity with respect to that of the pure polylactides. The compression moduli of plasticized foams under simulated physiological conditions (immersion in deionized water at 37 degrees C)were also substantially lower than those of the neat foams. This was attributed primarily to a decrease in the glass transition temperature from about 60 degrees C for the pure polylactides to about 30 degrees C on addition of the polyethylene glycol, implying the blends to be in the rubbery state at the test temperature of 37 degrees C. Under the conditions investigated, the processing window for homogeneous foams was found to be wider for blends based on semicrystalline polylactides than for blends based on amorphous polylactides. However, by tailoring the processing parameters, open cell architectures with porosities of more than 75% and cell diameters in the range 200 to 700 mu m could be achieved in both types of blend. Such morphologies have already been shown to be suitable for bone repair and, when combined with a low-stiffness matrix, may offer exciting new possibilities for applications in soft tissue engineering, such as cartilage repair.