Green technology actively seeks new solvents to replace common organic solvents that present inherent toxicity and have high volatility, leading to evaporation of volatile organic compounds to the atmosphere. Over the past two decades, ionic liquids (ILs) have gained enormous attention from the scientific community, and the number of reported articles in the literature has grown exponentially. Nevertheless, IL "greenness" is often challenged, mainly due to their poor biodegradability, biocompatibility, and sustainability. An alternative to ILs are deep eutectic solvents (DES). Deep eutectic solvents are defined as a mixture of two or more components, which may be solid or liquid and that at a particular composition present a high melting point depression becoming liquids at room temperature. When the compounds that constitute the DES are primary metabolites, namely, aminoacids, organic acids, sugars, or choline derivatives, the DES are so called natural deep eutectic solvents (NADES). NADES fully represent green chemistry principles. Can natural deep eutectic solvents be foreseen as the next generation solvents and can a similar path to ionic liquids be outlined? The current state of the art concerning the advances made on these solvents in the past few years is reviewed in this paper, which is more than an overview on the different applications for which they have been suggested, particularly, biocatalysis, electrochemistry, and extraction of new data. Citotoxicity of different NADES was evaluated and compared to conventional imidazolium-based ionic liquids, and hints at the extraction of phenolic compounds from green coffee beans and on the foaming effect of NADES are revealed. Future perspectives on the major directions toward which the research on NADES is envisaged are here discussed, and these comprised undoubtedly a wide range of chemically related subjects.

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a b s t r a c tThis paper presents a novel approach toward the production of hybrid alginate-lignin aerogels. The key idea of the approach is to employ pressurized carbon dioxide for gelation. Exposure of alginate and lignin aqueous alkali solution containing calcium carbonate to CO 2 at 4.5 MPa resulted in a hydrogel formation. Various lignin and CaCO 3 concentrations were studied. Stable hydrogels could be formed up to 2:1 (w/w) alginate-to-lignin ratio (1.5 wt% overall biopolymer concentration). Upon substitution of water with ethanol, gels were dried in supercritical CO 2 to produce aerogels. Aerogels with bulk density in the range 0.03-0.07 g/cm 3 , surface area up to 564 m 2 /g and pore volume up to 7.2 cm 3 /g were obtained. To introduce macroporosity, the CO 2 induced gelation was supplemented with rapid depressurization (foaming process). Macroporosity up to 31.3 ± 1.9% with interconnectivity up to 33.2 ± 8.3% could be achieved at depressurization rate of 3 MPa/min as assessed by micro-CT. Young's modulus of alginate-lignin aerogels was measured in both dry and wet states. Cell studies revealed that alginate-lignin aerogels are non-cytotoxic and feature good cell adhesion making them attractive candidates for a wide range of applications including tissue engineering and regenerative medicine.

Engineering metabolically demanding tissues requires the supply of nutrients, oxygen, and removal of metabolic byproducts, as well as adequate mechanical properties. In this work, we propose the development of chitosan (CHIT)/alginate (ALG) freestanding membranes fabricated by layer-by-layer (LbL) assembly. CHIT/ALG membranes were cross-linked with genipin at a concentration of 1 mg·mL(-1) or 5 mg·mL(-1). Mass transport properties of glucose and oxygen were evaluated on the freestanding membranes. The diffusion of glucose and oxygen decreases with increasing cross-linking concentration. Mechanical properties were also evaluated in physiological-simulated conditions. Increasing cross-linking density leads to an increase of storage modulus, Young modulus, and ultimate tensile strength, but to a decrease in the maximum hydrostatic pressure. The in vitro biological performance demonstrates that cross-linked films are more favorable for cell adhesion. This work demonstrates the versatility and feasibility of LbL assembly to generate nanostructured constructs with tunable permeability, mechanical, and biological properties.