Bioactive Coating of Titanium Surfaces with Recombinant Human β-Defensin-2 (rHuβD2) May Prevent Bacterial Colonization in Orthopaedic Surgery

Background: A promising strategy to prevent infections around orthopaedic titanium implants is to use naturally occurring cationic antimicrobial peptides (CAMPS) such as the human beta-defensin-2 as antibacterial coatings. Human antimicrobial peptides represent a part of the innate immune system and have a broad antimicrobial spectrum against bacteria, fungi, and viruses. Methods: In the present study, titanium surfaces were functionalized by four different self-assembled monolayers (SAMs) forming methoxy silanes: (1) hexadecyltrimethoxysilane, (2) dimethoxymethyloctylsilane, (3) allyltrimethylsilane, and (4) 3-aminopropyltrimethoxysilane. In addition, calf skin type-I collagen was cross-linked to the SAM surface 3-aminopropyltrimethoxysilane by means of two different treatments: (1) N-hydroxysuccinimide and (2) glutaraldehyde. The functionalized titanium surfaces were coated with recombinant human beta-defensin-2 (rHu beta D2), an antimicrobial peptide, and were tested for antibacterial activity against Escherichia coli. The release of rHu beta D2 was quantified by means of enzyme-linked immunosorbent assay (ELISA). Results: The coating of functionalized titanium surfaces with rHu beta D2 was successful. Recombinant Hu beta D2 was eluted from the titanium surfaces continuously, yielding antimicrobial activity up to several hours. Antimicrobial activity with a killing rate of 100% was observed for all functionalized titanium surfaces after two hours of incubation. The dimethoxymethyloctylsilane-functionalized titanium surface delivered 0.65 mu g of rHu beta D2 after six hours with a 60% bacterial killing rate. The silane-functionalized surfaces exhibited a faster release of antimicrobially active rHu beta D2 compared with collagen modifications. Conclusions: Natural antibiotics such as rHu beta D2 integrated into the metal surface of titanium implants may be a promising tool to prevent and control infections around orthopaedic implants.