In vivo biodegradation of polyurethane foams in the rat animal model

Polymer foams are among the most studied scaffold for tissue engineering. Among them, cross-linked polyurethane foams (PUFs) with slow degradation rate can be used as scaffolds for soft tissue engineering or as matrices of porous composites containing inorganic salts for hard tissue engineering. The foaming process has been set up using polymeric MDI, 2% water as expanding agent and Fe-acetyl acetonate as catalyst. On the whole, two families of foams (EC and EF) were developed using two different polyether-polyol formulations, the EF-type being more hydrophilic and more flexible than the EC-one. In vitro cytocompatibility tests with different cell lines demonstrated the ability of these matrices to stimulate cell adhesion and proliferation. In this work we investigated the in vivo behaviour of both EC and EF PU foams in the rat animal model to evaluate the extent of inflammatory reaction and the biodegradation rate. Discs of the EC- and EF-type foams were implanted in the dorsal subcutaneous tissue of male rats up to 42 weeks, explanted and histologically inspected together with the surrounding tissues by haematoxylin and eosin staining. The obtained results indicated a good biocompatibility of both foam types, the evoked inflammatory response being physiological. In particular, for the EF-based foams, at the material/tissue interface neovascularization and formation of new peripheral nerves were noticed. Moreover, the EF PUFs seem to promote the formation of mesenchimal tissue that, under particular stimuli, could promote the regeneration of the intended tissue.