Morphology and thermal properties of foams prepared via thermally induced phase separation based on polylactic acid blends

Blends of poly-l-lactic acid with two different types of polylactic acid with different average molecular weights (50,000 and 175,000 g/mol, respectively) in different proportions (90/10, 80/20 and 70/30) were utilized in order to produce biodegradable and biocompatible scaffolds for soft tissue engineering applications. The scaffolds were produced via thermally induced phase separation starting from ternary systems where dioxane was the solvent and water the non-solvent. Morphology (average pore size and interconnection) was evaluated by scanning electron microscopy. Foams apparent density was also evaluated (porosity ranges from 87% to 92%). Moreover, a differential scanning calorimetry analysis was carried out on the as-obtained scaffold, so as to obtain information about their thermal properties (enthalpy of melting and crystallization). The results showed that is possible to prepare scaffolds of poly-l-lactic acid/polylactic acid via thermally induced phase separation with both polylactic acids and to tune their average pore size (from 40 to 70 µm) by changing some experimental parameters (e.g. demixing temperature). Moreover, the average molecular weight of the polylactic acid in the blend seems to influence the thermally induced phase separation process in terms of demixing temperatures, which resulted higher than pure poly-l-lactic acid for the blends containing the high molecular weight polylactic acid, and lower for the blends containing the low molecular weight polylactic acid. Finally, a decrease in the crystallinity of the foams when increasing polylactic acid content in poly-l-lactic acid/polylactic acid blends was observed, as witnessed by a drop in the enthalpy of melting and crystallization. The results confirm that the morphology and the mechanical properties of the scaffold can be tuned up, starting from poly-l-lactic acid and blending it in different proportions with polylactic acid with different molecular weights.