Surface Characterization and Antimicrobial Capability Evaluation of Medical-Grade Titanium Modified by Facile Immersion in the Solution of Novel Catechol-Terminated Compounds Having Cationic Quaternary Ammonium Functionality with Different Alkyl Chain Lengths

Reducing hospital-acquired infections, especially those related to medical devices, is essential not only to improve patients’ well-being but also to reduce healthcare costs. Among various antibacterial approaches, creating bactericidal device surfaces has been advocated as it reduces the likelihood of antibiotic-resistant strains emerging when antibiotics are used. Functionalizing the device surface with cationic groups, such as quaternary ammonium terminal groups, has been considered an effective approach for killing microbes upon contact. Nonetheless, multiple steps, some of which may require harsh chemical reactions and toxic solvents, are generally required to attach the cationic quaternary ammonium functionalities to the surface. Inspired by the mussel’s capability to bind to various substrates, various novel biomimetic cationic catechol-terminated small molecules having the quaternary ammonium functionality with different alkyl chain lengths were synthesized for the first time. These compounds were used for surface modification of medical-grade titanium using simple immersion approaches: a single-layer procedure or a two-layer approach, in which the first layer was prepared by dopamine immersion, followed by a second immersion in the compound of interest. The surface characteristics and antimicrobial capability against the Gram-negative E. coli and Gram-positive S. aureus were assessed. The likely effects of the alkyl chain length and modification schemes on the surface properties and antibacterial activity are discussed and compared. The highest antimicrobial activity against E. coli was noted on the modified surfaces prepared by the two-layer approach with the cationic compound having the shortest alkyl chain, C1, at 2 mg/mL (DA_C1-2) and 8 mg/mL (DA_C1-8). The DA_C1-8 surface also exhibited the highest antimicrobial activity against S. aureus. These findings indicated that the antibacterial activity of titanium can be greatly improved by selecting the appropriate compound and a proper, facile immersion procedure.