Electroconductive Tantalum-Based Coatings for Bioelectronic Bone Implants: Fabrication, Characterisation, and Neural Interface Applications

Abstract

To improve the bioelectrical conductivity, bioactivity, and biocompatibility of titanium implants, an electroconductive tantalum (Ta) coating was fabricated on Ti6Al4V (TC4) substrates via the cold spray technique. Microstructural and phase characterizations were performed using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Fourier-Transform Infrared Spectroscopy (FTIR). Four-point probe resistivity, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) were used to characterize electrical and electrochemical properties relevant to neural interfaces. Mechanical and bioactivity evaluations included tensile adhesion, three-point bending, and Vickers microhardness tests, alongside simulated body fluid (SBF) immersion to assess osteointegration potential. Results show that the cold-sprayed Ta coating exhibits a bulk electrical conductivity of 6.8 × 106 S/m, approximately 40 % that of pure bulk Ta, due to the presence of inter-particle interfaces and porosity. The coating’s impedance at 1 kHz-a frequency range relevant to neural signal transmission was measured at ~8.2 kΩ•cm², indicating favorable charge transfer capability for neural electrode applications. The double-layer capacitance extracted from the EIS Nyquist plots was approximately 2.6 mF/cm², signifying strong electrochemical surface activity. Mechanically, the coatings exhibited an adhesive strength of 10.6 MPa, microhardness of 300 HV0.1, and Young’s modulus of 11.08 GPa, closely matching the modulus of natural cortical bone (10-30 GPa). Bioactivity assessment showed dense apatite layer formation within 14 days of immersion, while electrical stimulation (±100 μA, 1 Hz) significantly enhanced apatite nucleation rates, confirming electro-assisted biomineralization. These findings show improvement in bone-implant integration with emphasis on electrical performance suitable for bioelectronic and neural stimulation implants.