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During the last decades, great efforts have been devoted to design polymers for reducing the toxicity, increasing the absorption, and improving the release profile of drugs. Advantage has been also taken from the inherent multivalency of polymers and dendrimers for the incorporation of diverse functional molecules of interest in targeting and diagnosis. In addition, polymeric hydrogels with the ability to encapsulate drugs and cells have been developed for drug delivery and tissue engineering applications. In the long road to this successful story, pharmaceutical sciences have been accompanied by parallel advances in synthetic methodologies allowing the preparation of precise polymeric materials with enhanced properties. In this context, the introduction of the click concept by Sharpless and coworkers in 2001 focusing the attention on modularity and orthogonality has greatly benefited polymer synthesis, an area where reaction efficiency and product purity are significantly challenged. The purpose of this Expert Review is to discuss the impact of click chemistry in the preparation and functionalization of polymers, dendrimers, and hydrogels of interest in drug delivery.

The purpose of this Expert Review is to discuss the impact of click chemistry in nanosized drug delivery systems. Since the introduction of the click concept by Sharpless and coworkers in 2001, numerous examples of click reactions have been reported for the preparation and functionalization of polymeric micelles and nanoparticles, liposomes and polymersomes, capsules, microspheres, metal and silica nanoparticles, carbon nanotubes and fullerenes, or bionanoparticles. Among these click processes, Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) has attracted most attention based on its high orthogonality, reliability, and experimental simplicity for non-specialists. A renewed interest in the use of efficient classical transformations has been also observed (e.g., thiol-ene coupling, Michael addition, Diels-Alder). Special emphasis is also devoted to critically discuss the click concept, as well as practical aspects of application of CuAAC to ensure efficient and harmless bioconjugation.

Purpose: To design hyaluronic acid (HA) and chitosan-g-poly(ethylene glycol) (CS-g-PEG) nanoparticles intended for a broad range of gene delivery applications., Methods: Nanoparticles formulated at different HA/CS-g-PEG mass ratios were developed to associate either pDNA or siRNA. The physico-chemical characteristics, morphology, association efficiency and nuclease protection ability of the nanocarriers were compared for these two molecules. Their biological performance, including transfection effciency, nanoparticle cellular uptake and citotoxicity, was assesed., Results: The resulting nanoparticles showed an adequate size (between 130 and 180 nm), and their surface charge could be modulated according to the nanoparticle composition (from +30 mV to -20 mV). All prototypes exhibited a greater association efficiency and nuclease protection for pDNA than for siRNA. However, cell culture experiments evidenced that HA/CS-g-PEG nanoparticles were effective carriers for the delivery of both, siRNA and pDNA, eliciting a biological response with minimal cytotoxicity. Moreover, experiments performed in the HEK-EGFP-Snail1 cell line showed the potential of the HA/CS-g-PEG nanoparticles to silence the expression of the Snail1 transcription factor, an important mediator in tumor progression., Conclusions: HA/CS-g-PEG nanoparticles can be easily modulated for the delivery of different types of gene molecules, offering great potential for gene therapy applications, as evidenced by their biological performance.