Peripheral nerve injuries with substance loss: from current clinical approaches to new nerve conduits based on multi-walled carbon nanotubes

Background. Peripheral nerve injuries (PNI) are among the most common in upper limb trauma and can have serious consequences on patients ‘quality of life. When direct repair is not possible, current surgical options including autografts and nerve conduits (NCs) are not fully satisfactory. Aim of the study. This research thesis, divided into a clinical and preclinical study respectively, has a twofold aim: (i) evaluating the outcomes associated with treatment of severe PNI with substance loss to frame a representative clinical scenario and (ii) analyzing, through in vitro and in vivo studies, the effectiveness of vanguard electroconductive NC based on oxidized polyvinyl alcohol (OxPVA) with carbon nanotubes (CNT). Materials and Methods. Regarding the clinical study, a retrospective evaluation was carried out on a cohort of 15 patients (enrolled at Padova University Hospital) after surgery due to severe upper limb PNI. Cases were treated with autologous nerve transplantation or FDA approved NCs. Clinical examination was performed through Disability of the Arm, Shoulder and Hand (DASH) score, monofilament test, and 2-point discrimination test. Results suggest that although NCs are a valid option for treating PNI, they are still not fully comparable to autografts in large gaps or proximal lesion, implying there is still much to improve in the actual procedure. Taking these into account, our preclinical research is exploring new approaches to neuroconduits through OxPVA mixed with multiwalled CNT (0.1 wt.%) to prepare nanocomposite electroconductive hydrogels. OxPVA ± CNT scaffolds were assayed for ultrastructure, electroconductivity, in vitro cytotoxicity and in vivo biocompatibility. These conduits were then fabricated to be implanted in animal model of disease (Sprague Dawley rat; sciatic nerve injury, gap: 5 mm). 4 experimental groups were compared (reverse autograft/Reaxon® /OxPVA/OxPVA+CNT) and after 6 weeks, conduits effectiveness was verified through histological, immunohistochemical analyses and morphometric study. Results. According to in vitro data, potential CNT-related toxicity was excluded and the functionalization with CNTs conferred to OxPVA a rougher surface and an increased superficial electroconductivity. After 14-days of subcutaneous implant, 2 no thick fibrotic capsule was recognized, suggesting biocompatibility. Animals tolerated surgery well, at dissection all the guides were clearly identifiable (no dislocations/neuroma); additionally, axonal regeneration was observed in OxPVA+CNTs conduits comparable to OxPVA and Reaxon® , indicating their efficiency validated by morphometry. A certain atrophy of the operated-limb side gastrocnemius was evident in all groups. Conclusions. Both parts of this study highlight NCs as a suitable reconstructive alternative to autografts. Furthermore, incorporation of electroconductive CNT within OxPVA may be an appealing strategy to improve outcomes associated with tubular devices.