Genipin crosslinking promotes biomechanical reinforcement and pro-regenerative macrophage polarization in bioartificial tubular substitutes

Traumatic nerve injuries are nowadays a significant clinical challenge and new substitutes with adequate biological and mechanical properties are in need. In this context, fibrin-agarose hydrogels (FA) have shown the possibility to generate tubular scaffolds with promising results for nerve repair. However, to be clinically viable, these scaffolds need to possess enhanced mechanical properties. In this line, genipin (GP) crosslinking has demonstrated to improve biomechanical properties with good biological properties compared to other crosslinkers. In this study, we evaluated the impact of different GP concentrations (0.05, 0.1 and 0.2% (m/v)) and reaction times (6, 12, 24, 72 h) on bioartificial nerve substitutes (BNS) consisting of nanostructured FA scaffolds. First, crosslinked BNS were studied histologically, ultrastructurally and biomechanically and then, its biocompatibility and immunomodulatory effects were ex vivo assessed with a macrophage cell line. Results showed that GP was able to improve the biomechanical resistance of BNS, which were dependent on both the GP treatment time and concentration without altering the structure. Moreover, biocompatibility analyses on macrophages confirmed high cell viability and a minimal reduction of their metabolic activity by WST-1. In addition, GP-crosslinked BNS effectively directed macrophage polarization from a pro-inflammatory (M1) towards a pro-regenerative (M2) phenotype, which was in line with the cytokines release profile. In conclusion, this study considers time and dose-dependent effects of GP in FA substitutes which exhibited increased biomechanical properties while reducing immunogenicity and promoting pro-regenerative macrophage shift. These tubular substitutes could be useful for nerve application or even other tissue engineering applications such as urethra.

A Novel In Vitro Pathological Model for Studying Neural Invasion in Non-Melanoma Skin Cancer

Neural Invasion (NI) is a key pathological feature of cancer in the colonization of distant tissues, and its underlying biological mechanisms are still scarcely known. The complex interactions between nerve and tumor cells, along with the stroma, make it difficult to reproduce this pathology in effective study models, which in turn has limited the understanding of NI pathogenesis. In this study, we have designed a three-dimensional model of NI squamous cell carcinoma combining human epidermoid carcinoma cells (hECCs) with a complete peripheral nerve segment encapsulated in a fibrine-agarose hydrogel. We recreated two vital processes of NI: a pre-invasive NI model in which hECCs were seeded on the top of the nerve-enriched stroma, and an invasive NI model in which cancer cells were immersed with the nerve in the hydrogel. Histological, histochemical and immunohistochemical analyses were performed to validate the model. Results showed that the integration of fibrin-agarose advanced hydrogel with a complete nerve structure and hECCs successfully generated an environment in which tumor cells and nerve components coexisted. Moreover, this model correctly preserved components of the neural extracellular matrix as well as allowing the proliferation and migration of cells embedded in hydrogel. All these results suggest the suitability of the model for the study of the mechanisms underlaying NI.