Enhanced Corrosion Resistance and Biofilm Inhibition of Functionally Graded TC4/TC4-5Cu Fabricated by Selective Laser Melting against Streptococcus mutans

Ti–6Al–4V (TC4) used in dentistry and orthopedics as implant biomaterial faces the risk of microbiologically influenced corrosion (MIC) owing to the residence of diverse oral microorganisms. Hereinto, Streptococcus mutans is a critical pathogenic microorganism that causes dental caries. This work investigated the corrosive effects of S. mutans on TC4 and functional gradient TC4/TC4-5Cu coupons fabricated by selective laser melting (SLM) through various electrochemical measurements, surface examination, observation of biofilm and corrosion analysis. The results indicated that the Cu-bearing alloy showed an inhibitory effect on the biofilms due to the release of Cu element, thereby reducing the corrosion rate of MIC. The corrosion current density (icorr) of TC4 (11.7 ± 0.8) nA cm−2 is higher than that of TC4/TC4-5Cu (7.4 ± 0.4) nA cm−2 in the presence of S. mutans, while the maximum pit depth of TC4 is 1.6 times that of TC4/TC4-5Cu. Therefore, metal modification through Cu alloying is an effective strategy to improve the MIC resistance.