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Hydroxyapatite represents the natural inorganic component of the bone and may be considered an essential element required for the development of bone substitutes in the field of regenerative medicine. Hydroxyapatite bone substitutes own biomimetic, osteoconductive, and osteoinductive properties thanks to their chemical-physical properties and nanostructure that play a critical role for the reconstruction of calcified tissues. Controlling the structure of hydroxyapatite nanocrystals is vital for obtaining a sustained product, and it should be an advantage on the final materials suitable for bone replacement, in terms of adsorptive activity, drug delivery system, etc. Compared to other synthesis techniques, hydrothermal processing (refers to a synthesis in aqueous solution at elevated pressure and temperature, in a closed system) has the ability to precipitate the hydroxyapatite from overheated solution, regulating the rate and uniformity of nucleation, growth, and maturation, which affect size, morphology, and aggregation of the crystals. This chapter wants to provide an overview of realization of nanosized hydroxyapatite-based bioceramics (e.g., powder and 3D structures) with desired morphology of crystallites, by hydrothermal processing. In this way, some critical hydrothermal parameters fundamental on the control of the crystal shape and dimension (pH, temperature, starting precursors, etc.) are discussed.

Today, as the need of new regenerative solutions is steadily increasing, the demand for new bio-devices with smart functionality is pushing material scientists to develop new synthesis concepts. Indeed, the conventional approaches for biomaterials fail when it comes to generate nano-biocomposites with designed biomimetic composition and hierarchically organized architecture mimicking biologically relevant tissue features. In this respect, an emerging concept in material science is to draw inspiration from natural processes and products, which we may consider as the most advanced examples of smart nanotechnology. Natural processes of supramolecular assembly and mineralization of organic macromolecules, known as biomineralization, generate complex hybrid 3D constructs that are the basis of skeletons, exoskeletons, nacre and shells. On the other hand, natural structures such as woods and plants exhibit multi-scale hierarchic organization that is the source of smart and anisotropic mechanical properties associated with high porosity and lightness. The association of nature-inspired nano-technological products with smart functionalization can provide new advanced solutions to critical and still unmet clinical needs. In this respect, magnetic activation of biomaterials by the use of a recently developed biocompatible, resorbable magnetic apatite promises to represent a new safe and effective switching tool, enabling personalized applications in regenerative medicine and theranostics that so far were not feasible, due to the cytotoxicity of the currently used magnetic materials.

Alkaly-aluminosilicate binders are synthetic inorganic polymers set at low temperature to produce ceramic type materials using an easier process than that usually required for ceramic production. Alkali-bonded devices can be produced by moulding while machining and finishing are generally not required. Additions of different inert fillers allow to reinforce or functionalize the materials for specific applications, such as thermal insulation and heat resistance in the field of building and infrastructures or transportation, etc. Actually, alkali-bonded composites have a high heat tolerance because they do not burn or ignite, they do not release gases or smokes and they do not "explode" because they do not incorporate waters of hydration within the structure as hydraulic cements do. Industrial wastes and by-products can be recycled as raw materials or inert fillers for this kind of application. An overview of composite materials prepared by exploiting the binder as a glue for other phases (SiC, Al2O3, non hazardous wastes) and showing porosity in the range nano-micro - ultramacro are presented for different applications.

In this feasibility study, the possibility to develop silicon carbide foams with a low temperature process such as chemically bonding was investigated. A coarse and re-crystallized ?-SiC was used as the main powder component. The important characteristics of R-SiC are ability to withstand high working temperatures, excellent corrosion resistance, good thermal shock resistance and high thermal conductivity. The binder for the chemical bonding was prepared using metakaolin as aluminosilicatic raw powder, while the alkali aqueous solution was KOH/K2SiO3. The surface reaction of the SiC particles in the alkaline solution leads to gas evolution that induces the foaming of the slurries. The foams were tested in inert and oxidative atmospheres up to 1300°C and characterized