Mussel‐Inspired Polydopamine Coating as a Universal Route to Hydroxyapatite Crystallization

TLDR

Bone tissue is a complex biocomposite with hierarchically organized organic proteins and inorganic hydroxyapatite crystals, and mimicking its unique mechanical properties requires controlling interfacial adhesion—a challenge that current surface modifications have not fully addressed. The study introduces a universal biomineralization route, polydopamine‑assisted hydroxyapatite formation (pHAF), that can be applied to virtually any scaffold material regardless of type or morphology. Inspired by mussel adhesion, the pHAF method deposits polydopamine on diverse substrates, where surface‑anchored catecholamine groups attract calcium ions and promote hydroxyapatite crystal growth aligned along the c‑axes parallel to the coating. This universal surface biomineralization offers an innovative foundation for future tissue engineering applications.

Abstract

Abstract Bone tissue is a complex biocomposite material with a variety of organic (e.g., proteins, cells) and inorganic (e.g., hydroxyapatite crystals) components hierarchically organized with nano/microscale precision. Based on the understanding of such hierarchical organization of bone tissue and its unique mechanical properties, efforts are being made to mimic these organic–inorganic hybrid biocomposites. A key factor for the successful designing of complex, hybrid biomaterials is the facilitation and control of adhesion at the interfaces, as many current synthetic biomaterials are inert, lacking interfacial bioactivity. In this regard, researchers have focused on controlling the interface by surface modifications, but the development of a simple, unified way to biofunctionalize diverse organic and inorganic materials remains a critical challenge. Here, a universal biomineralization route, called polydopamine‐assisted hydroxyapatite formation (pHAF), that can be applied to virtually any type and morphology of scaffold materials is demonstrated. Inspired by the adhesion mechanism of mussels, the pHAF method can readily integrate hydroxyapatites on ceramics, noble metals, semiconductors, and synthetic polymers, irrespective of their size and morphology (e.g., porosity and shape). Surface‐anchored catecholamine moieties in polydopamine enriches the interface with calcium ions, facilitating the formation of hydroxyapatite crystals that are aligned to the c ‐axes, parallel to the polydopamine layer as observed in natural hydroxyapatites in mineralized tissues. This universal surface biomineralization can be an innovative foundation for future tissue engineering.