POLYLACTIDE MACROPOROUS BIODEGRADABLE IMPLANTS FOR CELL TRANSPLANTATION .2. PREPARATION OF POLYLACTIDE FOAMS BY LIQUID-LIQUID PHASE-SEPARATION

Potential of thermally induced phase separation as a porogen technique has been studied in an effort to produce a surgical implant suitable for cell transplantation. Emphasis has been placed on the liquid-liqui d phase separation of solutions of amorphous poly DL-lactide and semic rystalline poly L-lactide in an 87/13 dioxane/water mixture. The relat ed temperature/composition phase diagrams have been set up by turbidim etry, and the possible occurrence of a gel has been discussed. Freeze- drying of some phase-separated polylactide solutions can produce flexi ble and tough foams with an isotropic morphology. Interconnected pores of 1-10 mu m in diameter are expected to result from the spinodal dec omposition of the polylactide solutions with formation of co-continuou s phases. Thermodynamics of the polymer/solvent pair has a decisive ef fect on the final macroporous foams, as shown by the dependence of the ir porosity, density, porous morphology, and mechanical behavior on mo lecular weight and crystallinity of polylactide and concentration of t he original solutions. On the basis of the foam characteristics, poten tial of the liquid-liquid phase separation (spinodal decomposition) ha s been compared with the solid/liquid phase separation (solvent crysta llization) as a porogen technique. (C) 1996 John Wiley & Sons, Inc.