Surface Topography and Oxide Layer Enhance Initial Adhesion of Isolated Coral Polyps on Titanium Substrates: A Biomaterials Approach to Coral Restoration

Coral reef degradation is a critical global issue, demanding innovative restoration strategies. Drawing inspiration from biomedical engineering, this study investigates the potential of surface-modified titanium (Ti) as a scaffold for coral restoration starting from single, isolated polyps. Commercially pure Ti substrates were modified by sandblasting with different alumina grit sizes (#24, #36, #46) to create varying micro-scale topographies, with some subsequently undergoing anodic oxidation to form a titanium dioxide (TiO2) layer. Polyps of Pocillopora damicornis, isolated via a stress-induced bailout response, were seeded onto these substrates. The initial adhesion fraction was quantified over an 8-hour period. Results showed a strong positive correlation between surface roughness and polyp adhesion; the coarsest surface (#24, Ra ≈ 4.5 µm) exhibited the highest adhesion rate. Furthermore, the presence of the TiO2 layer consistently enhanced polyp adhesion across all topographies. These findings demonstrate that the principles of contact guidance and surface chemistry, well-established in mammalian cell-biomaterial interactions, are also applicable to coral polyps. This work establishes a scientific basis for designing engineered scaffolds to improve the efficacy of novel, single-polyp-based coral propagation techniques.