Freeze-cast Mg-Fe-CO₃ nano-layered double hydroxide/alginate composite scaffolds for bone substitution: porous architecture and mechanical properties

Layered Double Hydroxides (LDH) are relevant inorganic materials for biomedical application thanks to both their tunable chemical composition and their lamellar structure allowing molecules or ions intercalation in the interlayer spaces. However, their brittleness and thermal sensibility limit the fabrication of 3D materials based on LDH, making it challenging, especially to prepare scaffolds for bone tissue engineering that require a macroporous structure for cell colonization and sufficient mechanical properties to be handled/cut by surgeons. To overcome these drawbacks, this study describes the preparation of 3D scaffolds based on the association of fully biocompatible LDH with an alginate matrix processed by freeze-casting, and leading to macroporous materials with a porosity compatible with cell colonization. To the best of our knowledge, the fabrication of such composite scaffolds by freeze-casting associated with a fine multiscale and systematic characterization was never described in the literature. Thus, this work first focused on the successful synthesis of Mg-Fe-CO3 layered double hydroxide nanoparticles, as confirmed by physicochemical characterizations (XRD, FTIR, SEM, DLS). Then, the resulting nano-LDH were associated with an alginate matrix to generate 3D composite scaffolds by freeze-casting. In order to evaluate the effect of nano-LDH content on the scaffold porous structure and mechanical properties, various compositions (nano-LDH/alginate ratio) were tested, and the structure and mechanical properties of the resulting scaffolds were characterized (SEM, X-Ray microtomography, compression tests). Results allowed us to identify an optimal nano-LDH/alginate composition (ratio 1:1) leading to 3D macroporous scaffolds combining suitable anisotropic microporosity for cell colonization and sufficient mechanical properties for non-bearing bone applications, while allowing for their manipulation without risks of collapse.