BIODEGRADABLE AND MACROPOROUS POLYLACTIDE IMPLANTS FOR CELL TRANSPLANTATION .1. PREPARATION OF MACROPOROUS POLYLACTIDE SUPPORTS BY SOLID-LIQUID PHASE-SEPARATION

Freeze-drying of polylactide solutions in 1,4-dioxane has been studied as a way to produce microcellular foams. The thermally induced phase separation has been studied in relation to several processing and form ulation parameters. The effects of polymer concentration, chain stereo regularity, polymer molecular weight and cooling rate have been invest igated in connection with the porous morphology and the physico-mechan ical characteristics of the final foams. As a rule, bundles of channel s are formed with a diameter of similar to 100 mu m. They have a prefe rential orientation that fits the cooling direction. A porous substruc ture (similar to 10 mu m) is observed in the internal walls of the tub ular macropores. Variations in this general porous morphology-and part icularly in the porosity, density, solvent residue, mechanical resista nce and degree of regularity in the spatial organization of pores-have been observed when polymer concentration in 1,4-dioxane and polylacti de stereoregularity are changed. As expected, cooling rate has a stron g effect on the foam morphology, which is essentially controlled by th e solvent crystallization. Pores are nothing but the fingerprints of 1 ,4-dioxane crystallites.