Titanium Implant Functionalized with D-Amino Acid-Substituted Antimicrobial Peptides for Infection Resistance and Enhanced Biocompatibility

Antimicrobial peptide (AMP) coatings show potential in preventing implant-associated infections (IAI), but their effectiveness is frequently limited by enzymatic degradation and cytotoxicity at elevated densities. This study demonstrates that complete D-amino acid substitution of surface-grafted AMPs effectively addresses these shortcomings. Using a model antimicrobial peptide (DRAMP04195) covalently immobilized on titanium via strain-promoted azide-alkyne cycloaddition (SPAAC), we compared the L- and D-peptide variants. At a high grafting density, Ti-D-80 achieves near-complete eradication of both S. aureus and E. coli (>99.99%), outperforming Ti-L-80. Scanning electron microscopy confirms membrane disruption as the primary antibacterial mechanism for both surfaces. Importantly, Ti-D-80 retains over 90% of its antibacterial activity after protease treatment, whereas Ti-L-80 is almost completely inactivated. Moreover, Ti-D-80 exhibits excellent biocompatibility, supporting cell adhesion and proliferation comparable to that of pristine titanium, in contrast to the cytotoxicity observed with Ti-L-80. These findings establish D-amino acid substitution as an effective strategy to simultaneously enhance enzymatic stability, antibacterial potency, and biocompatibility of AMP-functionalized implants, providing a robust approach for designing durable and tissue-compatible antimicrobial interfaces.