Optimizing Titanium Nanotube (TNT) Growth on Freeform Screw Profiles via Multi-Cathode–Anode (CA) Configuration: Simulation and Experimental Insights

Uniform TNT growth on complex geometries, such as screw-threaded surfaces, is challenging due to non-uniform electric fields in anodization. This study examines TNT growth on screw threads and dental implants, intending to determine the impact of geometry on the electric field distribution using Finite Element Analysis (FEA). Simulation results showed that the electric field intensity was highly variable, with increased values on teeth and decreased values on the root and flank, causing nonuniform growth of TNTs. Experimental anodization coupled with Field-Emission Scanning Electron Microscopy (FESEM) affirmed the findings with shorter TNTs on the root and more stable growth on the teeth and flanks. TNT diameter correlated with applied DC voltage, while TNT length, with variations of 6 μm, was highly sensitive to the cathode design. To solve the problem, a new multicathode anodization cell was developed to produce a uniform field distribution. By adjustment of the cathode-to-anode (CA) area ratio, it was discovered that a CA of 1 yielded the optimal results, and this resulted in uniform TNT growth in all regions. Lower CAs (e.g., 0.5:1) resulted in low field strength and incomplete TNT growth, and high CAs (2:1) led to over-dissolution and structural damage. Optimization on actual dental implants using the CA 1 setup and two-stage anodization process yielded a more controlled TNT length and diameter. The final TNT morphology on the dental implant had TNT length variations of 0.4 μm with a 100 nm diameter. These results reveal the importance of the electric field uniformity in anodizing implants with complex geometries. The proposed multicathode design presents an efficient and scalable solution for uniform TNT layer deposition on dental implants and similar freeform curved surfaces.