Preparation of Poly(l-lactic acid) Scaffolds by Thermally Induced Phase Separation: Role of Thermal History

Poly-L-Lactic Acid (PLLA) scaffolds for tissue engineering were prepared via thermally induced phase separation of a ternary system PLLA/dioxane/tetrahydrofurane. An extension to solution of a previously developed method for solidification from the melt was adopted, the technique being based on a Continuous Cooling Transformation (CCT) approach, consisting in recording the thermal history of rapidly cooled samples and analysing the resulting morphology. Different foams were produced by changing the thermal history, the dioxane to THF ratio (50/50, 70/30, 90/10 v/v) and the polymer concentration (2, 2.5, 4% wt) in the starting ternary solution. Pore size, porosity, melting and crystallization behavior were studied, together with a morphological and kinetic analysis of the foams produced. A large variety of morphologies was achieved, the largest pore size (20 mu m) was achieved at the highest polymer concentration (4% wt) and the lowest dioxane concentration (50/50 dioxane/THF v/v), whereas the largest porosity (90%) was attained at the highest dioxane concentration (90/10). The average pore size is related to cooling rate, with a 1/3 power law exponent at low polymer concentrations and low dioxane content for thermal histories driven by low undercoolings. At high undercoolings, the growth of the demixed domains significantly departs from the diffusive-like regime.