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Highly Crystalline Poly(L-lactic acid) Porous Films Prepared with CO2-philic, Hybrid, Liquid Cell Nucleators

Supercritical CO2 (scCO(2)) foaming of poly(L-lactic acid) composite films with liquid polyhedral oligomeric silsesquioxanes (PLLA-POSS) was carried out to obtain polymer matrices for drug delivery applications. Highly crystalline (>45%) PLLA generally requires high supercritical processing (saturation) temperatures close to its melting temperature (similar to 450 K) and pressures about or over 20 MPa for foaming with scCO(2). To decrease the saturation temperature and obtain ductile PLLA films with uniform and homogeneous porosity, we used two different, novel CO2-philic organic-inorganic hybrid liquid POSS as cell nucleators. The solvent-casting of the polymer with these additives resulted in porous thin films. ScCO2 processing at 313 K and 21 MPa increased the pore density and enhanced the mechanical and thermal properties such as elastic modulus and T-g of the highly crystalline PLLA porous films. ScCO2 processing led to the extraction of the cell nucleators, allowing the recovery of these additives from the porous films. Drug release studies with a model antibiotic (Ceftriaxone Sodium) showed that the porous films exhibit burst release characteristics, which is suitable for local antibiotic applications.