A Doubly Fmoc-Protected Aspartic Acid Self-Assembles into Hydrogels Suitable for Bone Tissue Engineering

Hydrogels have been used as scaffolds for biomineralization in tissue engineering and regenerative medicine for the repair and treatment of many tissue types. In the present work, we studied an amino acid-based material that is attached to protecting groups and self-assembles into biocompatible and stable nanostructures that are suitable for tissue engineering applications. Specifically, the doubly protected aspartic residue (Asp) with fluorenyl methoxycarbonyl (Fmoc) protecting groups have been shown to lead to the formation of well-ordered fibrous structures. Many amino acids and small peptides which are modified with protecting groups display relatively fast self-assembly and exhibit remarkable physicochemical properties leading to three-dimensional (3D) networks, the trapping of solvent molecules, and forming hydrogels. In this study, the self-assembling fibrous structures are targeted toward calcium binding and act as nucleation points for the binding of the available phosphate groups. The cell viability, proliferation, and osteogenic differentiation of pre-osteoblastic cells cultured on the formed hydrogel under various conditions demonstrate that hydrogel formation in CaCl₂ and CaCl₂-Na₂HPO₄ solutions lead to calcium ion binding onto the hydrogels and enrichment with phosphate groups, respectively, rendering these mechanically stable hydrogels osteoinductive scaffolds for bone tissue engineering.