Poly(L-lactic acid) foams with cell seeding and controlled-release capacity

A synthetic porous three-dimensional structure that can mimic the architecture of actual tissues, provide sustained release of nutrients or growth factors, and serve as a template for cell seeding would be an ideal substrate for tissue engineering. Poly(l-lactic acid) (PLLA) foams were fabricated for this purpose, based on the principle of phase separation from homogeneous naphthalene solutions. Complex shapes could be readily fabricated, and resulting foams had relatively uniform, open cells throughout the matrix. Densities and total pore-surface areas were in the range of 0.05-0.1 g/cm3 and 0.8-1.3 m2/g, respectively. The loss tangent of these foams ranged from 0.07 to 0.128, as measured by thermomechanical analysis. Naphthalene residue in the resulting foams went below 0.2 wt% after extensive vacuum sublimation. Feasibility of incorporating drugs or nutrients into such a highly porous structure was demonstrated by the dispersion of two model compounds, bromothymol blue (BTB) and sulforhodamine B (SD), in the matrix. Sustained release of BTB from the foam with a porosity as high as 87% was observed for more than 2 months. Alkaline phosphatase, as a model protein to be incorporated, lost approximately 30% of its bioactivity during the fabrication. As a cell-culture substrate, the PLLA foams performed as well as the flat PLLA surface in supporting the growth of rat osteosarcoma cells (ROS 17/2.8) and in maintaining their functions such as alkaline phosphatase activity and osteocalcin synthesis. UMR-106 cells cultured in the foam also expressed a higher degree of mineralization than those cultured on the flat PLLA substrate.