The development of new materials based on hydroxyapatite has undergone a great evolution in recent decades due to technological advances and development of computational techniques. The focus of this review is the various attempts to improve new hydroxyapatite-based materials. First, we comment on the most used processing routes, highlighting their advantages and disadvantages. We will now focus on other routes, less common due to their specificity and/or recent development. We also include a block dedicated to the impact of computational techniques in the development of these new systems, including: QSAR, DFT, Finite Elements of Machine Learning. In the following part we focus on the most innovative applications of these materials, ranging from medicine to new disciplines such as catalysis, environment, filtration, or energy. The review concludes with an outlook for possible new research directions.

Membranes for guided bone regeneration should have a mechanical structure and a chemical composition suitable for mimicking biological structures. In this work, we pursue the development of periosteum-inspired bilayered membranes obtained by crosslinking alginate with different amounts of nanohydroxyapatite. Alginate-nanohydroxyapatite interaction was studied by rheology and infrared spectroscopy measurements. The membranes were characterized regarding their tensile strength, degradation and surface morphology. Finally, cell cultures were performed on each side of the membranes. The ionic bonding between alginate polysaccharide networks and nanohydroxyapatite was proven, and had a clear effect in the strength and microstructure of the hydrogels. Distinct surface characteristics were achieved on each side of the membranes, resulting in a highly porous fibrous side and a mineral-rich side with higher roughness and lower porosity. Moreover, the effect of amount of nanohydroxyapatite was reflected in a decrease of the membranes' plasticity and an increment of degradation rate. Finally, it was proved that osteoblast-like cells proliferated and differentiated on the mineral-rich side, specially when a higher amount of nanohydroxyapatite was used, whereas fibroblasts-like cells were able to proliferate on the fibrous side. These periosteum-inspired membranes are promising biomaterials for guided tissue regeneration applications.

Hydrogels exhibit excellent properties that enable them as nanostructured scaffolds for soft tissue engineering. However, single-component hydrogels have significant limitations due to the low versatility of the single component. To achieve this goal, we have designed and characterized different multi-component hydrogels composed of gelatin, alginate, hydroxyapatite, and a protein (BSA and fibrinogen). First, we describe the surface morphology of the samples and the main characteristics of the physiological interplay by using fourier transform infrared (FT-IR), and confocal Raman microscopy. Then, their degradation and swelling were studied and mechanical properties were determined by rheology measurements. Experimental data were carefully collected and quantitatively analyzed by developing specific approaches and different theoretical models to determining the most important parameters. Finally, we determine how the nanoscale of the system influences its macroscopic properties and characterize the extent to which degree each component maintains its own functionality, demonstrating that with the optimal components, in the right proportion, multifunctional hydrogels can be developed.