Incorporation of tetracarboxylate ions into octacalcium phosphate for the development of next-generation biofriendly materials

Abstract

Octacalcium phosphate (OCP; Ca8(HPO4)2(PO4)4 ∙ 5H2O) is a precursor of hydroxyapatite found in human bones and teeth, and is among the inorganic substances critical for hard tissue formation and regeneration in the human body. OCP has a layered structure and can incorporate carboxylate ions into its interlayers. However, studies involving the incorporation of tetracarboxylic and multivalent (pentavalent and above) carboxylic acids into OCP have not yet been reported. In this study, we investigate the incorporation of pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), a type of tetracarboxylic acid, into OCP. We established that pyromellitate ions could be incorporated into OCP by a wet chemical method using an acetate buffer solution containing pyromellitic acid. The derived OCP showed a brilliant blue emission under UV light owing to the incorporated pyromellitate ions. Incorporation of a carboxylic acid into OCP imparted new functions, which could enable the development of novel functional materials for biomedical applications.

Fluorescent properties of octacalcium phosphate with incorporated isophthalate ions

“…5) For OCP with incorporated 1,2,4,5-benzenetetracarboxylate ions, fluorescence was at 450 nm with excitation at 260 and 320 nm. 6) Therefore, in contrast to the previously reported OCP-based fluorescent materials that exhibit visible light emission, in this study, we obtained the first OCP-based fluorescent material that exhibits ultraviolet light emission.…”

“…The second paper about fluorescent OCPs was an OCP with incorporated 1,2,4,5-benzenetetracarboxylate ions reported by our research group in 2021. 6) The chemical structure of 1,2,4,5-benzenetetracarboxylic acid is shown in Fig. 1(b).…”

Formation of octacalcium phosphate with incorporated dicarboxylate ions containing disulfide bonds

“…In previous studies, we successfully incorporated carboxylate ions containing aromatic rings into OCP, resulting in the creation of fluorescent OCP materials. [20][21][22] This material development serves as an excellent example where the selection of guest molecules based on their chemical bonding contributes to the expression of desired functionalities. Hence, the selection of guest molecules by focusing on their chemical bonds is effective for developing new functional materials.…”

Preparation of antimicrobial calcium phosphate/protamine composite powders with fluoride ions using octacalcium phosphate

“…However, OCP as a bone substitute exhibits distinctive properties that differ from those of HAp in terms of osteoconductivity and biodegradability [ 2 ]. The OCP is known as an interlayer compound containing a HAp layer with a dicalcium phosphate dihydrate layer, and incorporates organic compounds within its interlayer [ 3 , 4 ]. Composite materials such as OCP/collagen and OCP/HAp have been reported to be safe and useful as bone substitutes in clinical studies [ 5 , 6 ].…”