Controlled preparation and properties of porous poly( l-lactide) obtained from a co-continuous blend of two biodegradable polymers

Abstract

This study prepares porous PLLA from a blend of two biodegradable polymers. This approach is based on a detailed and quantitative morphology control of the blends. Co-continuous blends comprised of poly( l-lactide)/poly( ε-caprolactone) PLLA/PCL, were prepared via melt processing. Through a judicious combination of concentration control and a subsequent annealing step it is possible to generate a wide range of sizes for the co-continuous phases. Subsequent extraction of the PCL porogen phase generates a fully interconnected porous PLLA material with a void volume between 50% and 60%. The volume average pore diameter is controlled from 1.5 to 88 μm as measured by mercury intrusion porosimetry. Through static annealing it is also possible to generate porous structures well beyond that upper limit of pore size. The upper limit of pore size reported above is in the range required for scaffolds for tissue engineering. Micrographs of porous polyglycolide and PCL derived from co-continuous blends of PLLA/polyglycolide and PCL/poly(ethylene oxide) are also shown and demonstrate the versatility and wide applicability of this preparation protocol. The porous structures produced from PLLA/PCL blends possess a high level of mechanical integrity and a degree of crystallinity between 25% and 38%. High values of both compressive modulus and strength at 10%-strain are obtained, greater than 190 and 11 MPa, respectively. The compressive modulus is found to be from 10% to 20% of that of the pure PLLA material. A series of loading studies were also carried out and it was shown that under a pressure of 40 atm applied for 1 h, the pores of a 1.5 μm porous PLLA structure were filled to approximately 80% by water. In addition, the loading of an aqueous solution of a model drug compound, bovine serum albumin (BSA), was carried out at 40 atm and the results indicate that large quantities of BSA (up to 25% of the weight of the original porous capsule) can be driven into the pores. These results indicate that the internal porous structure is accessible to aqueous solution and that this material also has potential as a substrate for controlled release applications.