In recent years, the use of nanotechnology for drug delivery purposes has witnessed a very significant growth aiming to improve the efficacy and/or reduce toxicity of existing drugs. This project aimed to design hyaluronic acid (HA)-coated chitosan-triphosphate (TPP) nanoparticles applicable for the delivery of genetic payload, and predominantly focused on the study of chitosan molecular weight-dependent effects.Firstly, we explored the effect of chitosan molecular weight (MW) on the physico-chemical characteristics and morphology/structure of chitosan-TPP nanoparticles and their functional behaviour. Combining dynamic light scattering and atomic force microscopy analysis allowed to highlight the influence of chitosan MW on the porosity, environmental response and HA adsorption of the resulting particles. For example, increasing chitosan MW provided increasingly porous nanoparticles. Upon coating with HA, HA showed a different adsorption mode depending on the nanoparticle porosity (and therefore on chitosan MW), with deeper penetration in more porous nanoparticles and the formation of an HA corona for less porous ones. This different mode of HA adsorption on nanoparticles appears to largely influence the enzymatically triggered payload release from the nanoparticles, the protein adsorption on the surface of the nanoparticles and also to affect the overall stability of the nanoparticles.As a spin-off of this study, we became interested in the effect of the different mode of HA adsorption described earlier on the way HA is presented to phagocytic cells (264.7 RAW macrophages), and therefore on the kinetics and possibly also on the mechanism of nanoparticles uptake. Here, we provide conclusive evidence that HA-coated nanoparticle internalisation is a CD44-mediated phenomenon. Interestingly, our data suggest that a better presentation of HA, i.e. hyaluronic acid less tightly complexed on the nanoparticle surface, is linked to both higher affinity and lower capacity/uptake rate. Paradoxically, particles with a lower affinity for CD44 may allow a more efficient HA-mediated delivery of payloads.Finally, we investigated the feasibility of CD44-dependent therapeutic approaches using HA-coated nanoparticles made from different chitosan MWs with or without a nucleic acid payload. The physico-chemical characteristics and nucleic acid encapsulation efficiency were compared. Transfection efficiency in cells characterised by a significantly different expression of CD44 and the possibility for the HA-coated nanoparticles to exert a direct anti-inflammatory effect were also analysed. HA-coated nanoparticles allowed successful entrapment and delivery of both siRNA and pDNA, with significant effects of the nanoparticle bulk structure (i.e. chitosan MW). We also showed an unprecedented anti-inflammatory effect of HA-coated nanoparticles devoid of any payload, which was more potent than the effect resulting from soluble HA. We speculate that the different organisation and possibly different crowding and mobility of HA chains may give rise to significant effects on macrophage inflammatory activation possibly arising from clustered binding to HA receptors such as CD44. These results indicate the potentiality of CD44-mediated therapies using HA-coated nanoparticles.