A mechanical characterization of polymer scaffolds and films at the macroscale and nanoscale

Biomaterials should be mechanically tested at both the nano- and macro-scale under conditions simulating their working state, either in vitro or in vivo, in order to confirm their applicability in tissue engineering applications. In this paper, polyester-urethane-based films and porous scaffolds produced by hot pressing and thermally induced phase separation respectively, were mechanically characterised at both the macro- and nano-scale by tensile tests and indentation-type atomic force microscopy (IT-AFM). All tests were conducted in wet state with the final aim of simulating scaffold real operating conditions. The films showed two distinct Young Moduli populations which can be ascribed to polyurethane hard and soft segments. In the scaffold, the application of a thermal cooling gradient during phase separation was responsible for a nanoscale polymer chain organisation in a preferred direction. At the macroscale, the porous matrices showed a Young Modulus of about 1.5 MPa in dry condition and 0.3 MPa in wet condition. The combination of nano- and macro-scale values as well as the aligned structure are in accordance with stiffness and structure required for scaffolds used for the regeneration of soft tissues such as muscles.