Preclinical in vivo evaluation of human amniotic membrane in peripheral nerve injury reconstruction.

Background. Peripheral Nerve Injuries (PNIs) are among the most common traumatic lesions affecting the upper limbs, often leading to long-term functional deficits and significant impact on patients’ quality of life. While direct end-to-end neurorrhaphy remains the gold standard for PNIs without nerve gap, outcomes are often suboptimal. For this reason, the development of novel strategies to enhance nerve regeneration remains a major focus of current medical research. Aim of the study. This thesis presents a preclinical study aimed at evaluating the regenerative potential of human Amniotic Membrane (hAM) in peripheral nerve repair. Specifically, it was investigated whether the application of hAM at the suture site could improve morpho-structural outcomes following sciatic nerve transection in animal model of disease, in comparison with standard neurorrhaphy and neurorrhaphy combined with a commercially available nerve wrap (Reaxon® Direct). Materials and methods. Twelve eight-week-old Sprague-Dawley rats were randomly assigned to three experimental groups (n = 4/group) and all underwent surgical transection of the left sciatic nerve without loss of substance, uniformly followed by direct end-to-end neurorrhaphy. In Group 1, no further repair strategies were applied. Group 2 received neurorrhaphy with a Reaxon® Direct wrap, Group 3 was treated with neurorrhaphy in combination with a hAM wrap. Following surgery, the animals were evaluated for their wellbeing. After 6 weeks, the euthanasia was administered and the sciatic nerve was exposed: the surgery site was carefully observed (adhesions, neuromas, inflammation) and the sciatic nerves were than excised and adequately fixed for subsequent analyses (histology, immunohistochemistry, transmission electron microscopy). Thus, the gastrocnemius muscle was dissected, compared for macroscopic appearance with the contralateral, weighted and fixed for histological analyses. Results. During surgical procedures, no intraoperative complications occurred. Postoperative monitoring did not reveal any significant variation in animals’ weight and overall well-being, suggesting that all animals well-tolerated both the procedure and the wrap materials. All animals survived until the 6-week study endpoint, and at the time of explantation no neuroma formation or wrap dislocation was observed. At the repair site, hAM was associated with minimal perineural adhesions, compared to other experimental groups. Nerves wrapped with hAM also showed negligible inflammatory infiltration and preserved nerve regeneration, as demonstrated through histological and immunohistochemical analyses. Evaluation of the gastrocnemius muscle revealed a more balanced ipsilateral/contralateral muscle trophism, both macroscopically and histologically, in the group treated with hAM wrap. Conclusion. The hAM wrap provided superior outcomes not only in terms of nerve regeneration and perineural immunomodulation, but also regarding target reinnervation and preservation of muscle trophism, compared to other experimental groups. Although its clinical translatability is yet to be completely established, these preclinical results frame this nerve wrap as a promising and appealing solution for peripheral nerve repair.