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nanocomplexes, [8,9] nanocomposites, [10,11] nanoassemblies [12] and coacervates. [13,14] Such colloidal systems, especially when prepared from biopolymers, have been extensively investigated due to their promising properties for numerous applications in biomedical fields. [1] Their merits come from the combination of three aspects: nanomedicine, biomaterials, and green chemistry. With the emergence of nanomedicine, the use of nanocarriers can offer tremendous advantages in drug encapsulation and delivery, namely enhancing the chemical stability of drugs and improving drug solubility and bioavailability. [15] Due to their small size and the possibility of surface modification with biological ligands or molecular imprinting, nanocarriers can easily cross biological barriers, which have limited pore sizes (fenestrations) under 1 micron in most cases, then target and enter the tissues or cells of interest. [16,17] Due to these aspects and the possibility of controlling drug distribution and release through particle engineering, nanocarriers can thus reduce systemic side effects and enhance the therapeutic efficacy of drugs. [15] Nanosystems can also offer unique advantages for biomedical imaging with their ability of sensing, image enhancement, and incorporating concomitantly therapeutic agents for theranostics, that is, simultaneous therapeutic and diagnostic applications. [18][19][20] When constructed from biomaterials, especially naturally occurring polysaccharides or proteins, PECs can become significantly biocompatible and biodegradable with much less immunogenicity and toxicity. [21] Besides such biorelevant aspects, the elaboration of biopolymerbased PECs is also in accordance with green chemistry principles since their preparation process usually requires only gentle mixing of polyelectrolyte solutions at room temperature, which is a simple and rapid procedure without the need for chemical agents, surfactants, organic solvents or high mechanical or thermal energy. [15] Beyond the above-mentioned basic advantages, the potential of colloidal PEC systems is increased by the inherent biological and chemical properties of individual constituent polymers. Hyaluronic acid (HA), also called hyaluronan to generally mention both its acid and salt forms, has been one of the most common polyanions among several biopolymers reported so far for the elaboration of colloidal PECs. The significant attention dedicated to HA in biomedical fields is associated with its unique advantages, stemming from not only its outstanding biocompatibility but also interesting biological activities. [22] Hyaluronic acid (HA) is a naturally occurring polysaccharide which has been extensively exploited in biomedical fields owing to its outstanding biocompatibility. Self-assembly of HA and polycations through electrostatic interactions can generate colloidal polyelectrolyte complexes (PECs), which can offer a wide range of applications while being relatively simple to prepare with rapid and "green" processes. The advantages of colloidal HA-base...

The lyophilization of nanogels is practical not only for their long-term conservation but also for adjusting their concentration and dispersant type during reconstitution for different applications. However, lyophilization strategies must be adapted to each kind of nanoformulation in order to minimize aggregation after reconstitution. In this work, the effects of formulation aspects (i.e., charge ratio, polymer concentration, thermoresponsive grafts, polycation type, cryoprotectant type, and concentration) on particle integrity after lyophilization and reconstitution for different types of polyelectrolyte complex nanogels (PEC-NGs) from hyaluronic acid (HA) were investigated. The main objective was to find the best approach for freeze-drying thermoresponsive PEC-NGs from Jeffamine-M-2005-functionalized HA, which has recently been developed as a potential platform for drug delivery. It was found that freeze-drying PEC-NG suspensions prepared at a relatively low polymer concentration of 0.2 g.L−1 with 0.2% (m/v) trehalose as a cryoprotectant allow the homogeneous redispersion of PEC-NGs when concentrated at 1 g.L−1 upon reconstitution in PBS without important aggregation (i.e., average particle size remaining under 350 nm), which could be applied to concentrate curcumin (CUR)-loaded PEC-NGs for optimizing CUR content. The thermoresponsive release of CUR from such concentrated PEC-NGs was also reverified, which showed a minor effect of freeze-drying on the drug release profile.