Manufacturing and Characterization of Controlled Foaming of Single Layers in Bilayer Constructs Differing in Pore Morphology

Abstract

Bilayer porous constructs from degradable polymers are considered as scaffold materials with beneficial elastic properties for cell culture application in tissue engineering. Here, we explored whether such bilayer constructs, in which only one layer was porous while the other layer enhanced the compressive mechanical properties, could be created by specific foaming of one layer with supercritical carbon dioxide (scCO2). The bilayer constructs of a poly(L-lactide) (PLLA) and a poly(ϵ-caprolactone) (PCL) layer were prepared by sequential injection molding and subsequent specific foaming with scCO2. Foaming conditions of T = 45 °C and P = 100 bar resulted in the formation of a porous PCL layer and a non-porous PLLA layer. When the time intervals of the foaming process were increased the pore size was increased and the shape of the pores was changed from a circular to an unidirectional lamellar shape, which reduced the compressive elastic modulus of the porous PCL layer. Furthermore, the foaming process increased the adhesion force between the PLLA and PCL layers, which was attributed to a higher degree of diffusion of molten PCL into the PLLA layer. In summary, it was demonstrated that scCO2 foaming is a suitable method for the creation of layered scaffolds with only one foamed layer, in which the compressive elastic modulus and pore morphology of single porous layers can be controlled by the time interval of scCO2 process.