Development and preclinical evaluation of bioactive nerve conduits for peripheral nerve regeneration: A comparative study.

In severe peripheral nerve injuries, nerve conduits (NCs) are good alternatives to autografts/allografts; however, the results the available devices guarantee for are still not fully satisfactory. Herein, differently bioactivated NCs based on the new polymer oxidized polyvinyl alcohol (OxPVA) are compared in a rat model of sciatic nerve neurotmesis (gap: 5 mm; end point: 6 weeks). Thirty Sprague Dawley rats are randomized to 6 groups: Reverse Autograft (RA); Reaxon®; OxPVA; OxPVA + EAK (self-assembling peptide, mechanical incorporation); OxPVA + EAK-YIGSR (mechanical incorporation); OxPVA + Nerve Growth Factor (NGF) (adsorption). Preliminarily, all OxPVA-based devices are comparable with Reaxon® in Sciatic Functional Index score and gait analysis; moreover, all conduits sustain nerve regeneration (S100, ß-tubulin) without showing substantial inflammation (CD3, F4/80) evidences. Following morphometric analyses, OxPVA confirms its potential in PNI repair (comparable with Reaxon®) whereas OxPVA + EAK-YIGSR stands out for its myelinated axons total number and density, revealing promising in injury recovery and for future application in clinical practice.

Development and In Vitro/In Vivo Comparative Characterization of Cryopreserved and Decellularized Tracheal Grafts.

Tracheal reconstruction represents a challenge when primary anastomosis is not feasible. Within this scenario, the study aim was to develop a new pig-derived decellularized trachea (DecellT) to be compared with the cryopreserved counterpart (CryoT) for a close predictive analysis. Tracheal segments underwent decellularization by a physical + enzymatic + chemical method (12 cycles); in parallel, cryopreserved samples were also prepared. Once decellularized (histology/DNA quantification), the two groups were characterized for Alpha-Gal epitopes/structural proteins (immunohistochemistry/histology/biochemical assays/second harmonic generation microscopy)/ultrastructure (Scanning Electron Microscopy (SEM))/mechanical behaviour. Cytotoxicity absence was assessed in vitro (extract-test assay/direct seeding, HM1SV40 cell line) while biocompatibility was verified in BALB/c mice, followed by histological/immunohistochemical analyses and SEM (14 days). Decellularization effectively removed Alpha-Gal epitopes; cartilage histoarchitecture was retained in both groups, showing chondrocytes only in the CryoT. Cryopreservation maintained few respiratory epithelium sparse cilia, not detectable in DecellT. Focusing on ECM, preserved structural/ultrastructural organization and collagen content were observed in the cartilage of both; conversely, the GAGs were significantly reduced in DecellT, as confirmed by mechanical study results. No cytotoxicity was highlighted by CryoT/DecellT in vitro, as they were also corroborated by a biocompatibility assay. Despite some limitations (cells presence/GAGs reduction), CryoT/DecellT are both appealing options, which warrant further investigation in comparative in vivo studies.

Compressive Mechanical Behavior of Partially Oxidized Polyvinyl Alcohol Hydrogels for Cartilage Tissue Repair.

Polyvinyl alcohol (PVA) hydrogels are extensively used as scaffolds for tissue engineering, although their biodegradation properties have not been optimized yet. To overcome this limitation, partially oxidized PVA has been developed by means of different oxidizing agents, obtaining scaffolds with improved biodegradability. The oxidation reaction also allows tuning the mechanical properties, which are essential for effective use in vivo. In this work, the compressive mechanical behavior of native and partially oxidized PVA hydrogels is investigated, to evaluate the effect of different oxidizing agents, i.e., potassium permanganate, bromine, and iodine. For this purpose, PVA hydrogels are tested by means of indentation tests, also considering the time-dependent mechanical response. Indentation results show that the oxidation reduces the compressive stiffness from about 2.3 N/mm for native PVA to 1.1 ÷ 1.4 N/mm for oxidized PVA. During the consolidation, PVA hydrogels exhibit a force reduction of about 40% and this behavior is unaffected by the oxidizing treatment. A poroviscoelastic constitutive model is developed to describe the time-dependent mechanical response, accounting for the viscoelastic polymer matrix properties and the flow of water molecules within the matrix during long-term compression. This model allows to estimate the long-term Young's modulus of PVA hydrogels in drained conditions (66 kPa for native PVA and 34-42 kPa for oxidized PVA) and can be exploited to evaluate their performances under compressive stress in vivo, as in the case of cartilage tissue engineering.