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Layered double hydroxides (LDH) consist of brucite-like layers containing di- and trivalent metal ions with interchangeable counter anions and solvation molecules that are present between the layers [1]. LDH find several applications in the pharmaceutical field due to their chemical stability, biocompatibility and high mechanical strength, and they are well known to support cellular processes, such as cell differentiation and viability [2]. LDH have very high potentialities for industrial applications, but their synthesis often requires a high number of steps, which could also lead to the production of great amounts of waste [3]. Given these premises, the goal of the work is the design of sustainable strategies for the synthesis of LDH in view of a continuous manufacturing process. LDH were produced through two well-known methods using new green synthesis conditions and their properties were compared to investigate the differences given by the LDH compositions. In particular, their biological properties were considered for a future application in the biomedical field, especially in tissue engineering. Nitrate salts of Mg2+, Zn2+, Cu2+, Al3+, and Fe3+, chosen as bio-enabling cations, were used. First, a co-precipitation method through a fast addition of salts and reduced aging time was developed, using ammonia as an alkaline agent. Few studies are reported using this chemical for the synthesis of LDH. Being a volatile molecule, the excess of ammonia could be easily removed and trapped, together with some of the byproducts that might be formed during the process. Second, the urea hydrolysis through microwave and hydrothermal treatment was considered. The synthesis parameters were adjusted to minimize the waste production. In all cases, the LDH were characterized both as prepared and upon centrifugation/washing, in view of a single step synthesis without water and components waste. The XRD patterns showed that LDH phases represent the major part in the unwashed samples

Skin wound healing is a multiphase process that involves a series of biological responses following an injury. However, if its progression is altered or if an underlying disease (e.g. metabolic disorders, infections) is present, the wound could become chronic, posing significant health problems [1]. Three-dimensional structures, such as microfibers and microparticles, could act as scaffold which stimulate skin reparation [2]. Clay minerals are well known additives in the development of such scaffolds [3]. Among these, anionic clays like layered double hydroxides (LDH) have already been reported as drug delivery systems or as polymer additives in materials science for biomedical purposes. The combination of their peculiar structure and chemical composition should contribute to support cellular processes [4]. Therefore, the aim of this work was the development of spray-dried microparticles based on ZnAl LDH doped sodium alginate, to enhance the skin tissue regeneration. LDH based on Zn2+ were selected since Zn2+ proved to enhance wound healing and to be effective as antimicrobial. LDH containing Zn and Al were synthesized via co-precipitation using ammonia as an alkaline agent. The LDH were then isolated upon centrifugation and dispersed, without further washing, in water under stirring. Sodium alginate was added to the dispersion, which was then spray dried. The microparticles were then crosslinked with CaCl2 [5]. The spray drying process leads to the formation of smooth microparticles with a spheroidal shape. The presence of LDH slightly alters their morphology, which is evident by the hexagonal lamellar platelets visible on their surface. The crosslinking step with CaCl2 allows to obtain water insoluble microparticles without changes in morphology, dimensions as well as LDH loading. In all cases, the mean diameters of the microparticles range from 6 to 8 ¿m and the LDH doping slightly increases the diameters. To conclude, it was possible to manufacture sodium algin

A combination of original, powerful characterization techniques was used to make a thorough description of solid geopolymers and of the associated effect of varying the alkali cation source - NaOH, KOH, or CsOH - and aging for up to several years. More specifically, the local and pore structures were progressively determined from atomic local scale up to several nanometers by pair distribution function analysis (PDF), small-angle X-ray scattering (SAXS), and longer correlation concerning the pore network, and possible diffusion and accumulation phenomena were unraveled by thermoporosimetry and electrochemical impedance spectroscopy (EIS), respectively. These complementary observations resulted in a picture of an interface between the mineral and the porous network that was correlated to the solvated alkali cation present in the porous solution. After a short time of a few months, the Na-based geopolymer was found to exhibit a smooth interface built up from small "elementary"particles. This contrasted with the K- and Cs-based geopolymers, which presented developed interfaces arising from hierarchically organized smooth particles forming aggregates of fractal outer surface. This striking difference unraveled by SAXS and EIS is ascribed for the Na geopolymer to the contact of the solvated Na(H2O)x+ cations with the amorphous mineral surface. The K(H2O)x+ and Cs(H2O)x+ solvated cations were an integral part of the porous solution, without direct contact with the mineral surface, thus leading to apparently rough interfaces. Dewatering occurred with time, mostly impacting the Na series. Overall, we obtained a detailed picture of the geopolymer series and their changes in time. The environment generated around the kosmotropic (order-making) Na+ alkali cation was more prone to change upon aging toward a non-Debye type relaxation than the initially developed interface supplied by the chaotropic Cs+ alkali cati