In vitro models for the development of peripheral nerve conduits, part I: Design of a fibrin gel-based non-contact test

Current clinical strategies to repair peripheral nerve injuries draw on different approaches depending on the extent of lost tissue. Nerve guidance conduits (NGCs) are considered to be a promising, off-the-shelf alternative to autografts when modest gaps need to be repaired. Unfortu-nately, to date, the implantation of an NGC prevents the sacrifice of a healthy nerve at the price of suboptimal clinical performance. Despite the significant number of materials and fabrication strategies proposed, an ideal combination has not been yet identified. Validation and comparison of NGCs ultimately requires in vivo animal testing due to the lack of alternative models, but in the spirit of the 3R principles, a reliable in vitro model for preliminary screening is highly desirable. Nevertheless, more traditional in vitro tests, and direct cell seeding on the material in particular, are not representative of the actual regeneration scenario. Thus, we have designed a very simple set-up in the attempt to appreciate the relevant features of NGCs through in vitro testing, and we have verified its applicability using electrospun NGCs. To this aim, neural cells were encapsulated in a loose fibrin gel and enclosed within the NGC membrane. Different thicknesses and porosity values of two popular polymers (namely gelatin and polycaprolactone) were compared. Results indicate that, with specific implementation, the system might represent a useful tool to characterize crucial NGC design aspects.