An Innovative Method to Produce Scaffolds with a Pore Size Gradient for Tissue Engineering Applications

Thermally Induced Phase Separation (TIPS) is a technique for the production of porous scaffold for Tissue Engineering applications. A wide range of microporous morphologies, in terms of pore size and distribution, can be obtained by tuning TIPS processing parameters, especially thermal history. The production of scaffolds for bone tissue regeneration is a challenging target: as a matter of fact, scaffolds must mimic the bone morphology, thus requiring a gradient of pore dimension and morphology along one dimension. To attain this goal, an experimental apparatus capable to impose different thermal histories on the two sides of a sample was designed, set up and tested. The sample (35x35 mm surface, 10 mm thickness) was located between two Peltier cells, employed to control temperature on sample surfaces. In that way each sample surface can be thermally controlled independently and anisotropic scaffolds were produced by following various thermal protocols on both sample surfaces. The system investigated in this study is the ternary solution poly-L-lactic acid (PLLA)-dioxane (solvent)-water (non-solvent). The as-obtained foams were inspected by Scanning Electron Microscopy (SEM), to verify the pore size and distribution. The results showed that via this technique, based on TIPS, is possible to produce scaffolds with a pore size increasing along sample thickness. The obtained pore dimension on one side of the sample was about 70 micron, whereas it was around 240 micron on the opposite surface. By moving along the sample thickness, the pore dimension increased steadily. Moreover, since pure PLLA does not show fully satisfactory mechanical properties for bone tissue engineering purposes, composite PLLA/hydroxyapatite (HA) scaffolds were produced, in order to improve foams’ mechanical performances. Compression tests showed a fourfold increase of Young module with respect to pure PLLA scaffold. All things considered, a reliable route for the production of scaffolds with a controlled pore size distribution was assessed, thus offering a valid support to tissue engineering applications, such as bone tissue engineering