Microfluidic-based skin-on-chip systems for safety assessment of nanomaterials.

The skin is the body's largest organ, continuously exposed to and affected by natural and anthropogenic nanomaterials (materials with external and internal dimensions in the nanoscale range). This broad spectrum of insults gives rise to irreversible health effects (from skin corrosion to cancer). Organ-on-chip systems can recapitulate skin physiology with high fidelity and potentially revolutionize the safety assessment of nanomaterials. Here, we review current advances in skin-on-chip models and their potential to elucidate biological mechanisms. Further, strategies are discussed to recapitulate skin physiology on-chip, improving control over nanomaterials exposure and transport across cells. Finally, we highlight future opportunities and challenges from design and fabrication to acceptance by regulatory bodies and industry.

Mechanistic study of the adjuvant effect of chitosan-aluminum nanoparticles.

The use of tailored particle-based adjuvants constitutes a promising way to enhance antigen-specific humoral and cellular immune responses. However, a thorough understanding of the mechanisms underlying their adjuvanticity is crucial to generate more effective vaccines. We studied the ability of chitosan-aluminum nanoparticles (CH-Al NPs), which combine the immunostimulatory effects of chitosan and aluminum salts, to promote dendritic cell activation, assess their impact on innate and adaptive immune responses, and compare the results to those reported for conventional chitosan particles (CH-Na NPs). All tested CH-NP formulations were capable of modulating cytokine secretion by dendritic cells. CH-Al NPs promoted NLRP3 inflammasome activation, enhancing the release of IL-1ß without significantly inhibiting Th1 and Th17 cell-polarizing cytokines, IL-12p70 or IL-23, and induced DC maturation, but did not promote pro-inflammatory cytokine production on their own. In vivo results showed that mice injected with CH-Al NPs generated a local inflammatory response comparable to that elicited by the vaccine adjuvant alum. Importantly, after subcutaneous immunization with CH-Al NPs combined with the hepatitis B surface antigen (HBsAg), mice developed antigen-specific IgG titers in serum, nasal and vaginal washes. Overall, our results established CH-Al NPs as a potential adjuvant to enhance both innate and adaptive immune responses.

Association of chitosan and aluminium as a new adjuvant strategy for improved vaccination.

The use of particulate adjuvants offers an interesting possibility to enhance and modulate the immune responses elicited by vaccines. Aluminium salts have been extensively used as vaccine adjuvants, but they lack the capacity to induce a strong cellular and mucosal immune response. Taking this into consideration, in this study we designed a new antigen delivery system combining aluminium salts with chitosan. Chitosan-aluminium nanoparticles (CH-Al NPs) exhibited a mean diameter of 280nm and a positive surface charge. The newly developed CH-Al NPs are more stable at physiological environment than classical CH NPs, showing no cytotoxic effects and revealing potential as a delivery system for a wide range of model antigens. In vivo studies showed that mice immunized with hepatitis B surface antigen (HBsAg)-containing CH NPs display high anti-HBsAg IgG titers in the serum, as well as the highest antigen-specific IgG on vaginal washes. Furthermore, in contrast to mice receiving antigen alone, mice immunized with the particulate adjuvant were able to elicit IgG2c antibody titers and exhibited higher antigen-specific IFN-γ levels in splenocytes. In conclusion, we established that CH-Al NPs, combining two immunostimulants to enhance both humoral and cellular immune responses, are a safe and promising system for antigen delivery. Our findings point towards their potential in future vaccination approaches.

Intranasal Administration of Novel Chitosan Nanoparticle/DNA Complexes Induces Antibody Response to Hepatitis B Surface Antigen in Mice.

The generation of strong pathogen-specific immune responses at mucosal surfaces where hepatitis B virus (HBV) transmission can occur is still a major challenge. Therefore, new vaccines are urgently needed in order to overcome the limitations of existing parenteral ones. Recent studies show that this may be achieved by intranasal immunization. Chitosan has gained attention as a nonviral gene delivery system; however, its use in vivo is limited due to low transfection efficiency mostly related to strong interaction between the negatively charged DNA and the positively charged chitosan. We hypothesize that the adsorption of negatively charged human serum albumin (HSA) onto the surface of the chitosan particles would facilitate the intracellular release of DNA, enhancing transfection activity. Here, we demonstrate that a robust systemic immune response was induced after vaccination using HSA-loaded chitosan nanoparticle/DNA (HSA-CH NP/DNA) complexes. Furthermore, intranasal immunization with HSA-CH NP/DNA complexes induced HBV specific IgA in nasal and vaginal secretions; no systemic or mucosal responses were detected after immunization with DNA alone. Overall, our results show that chitosan-based DNA complexes elicited both humoral and mucosal immune response, making them an interesting and valuable gene delivery system for nasal vaccination against HBV.