Preventing infections of hip joint prostheses: activity of an antimicrobial coating based on the LL-37 peptide

Details

Supervisors

Dupont-Gillain, Christine C. ; Vranckx, Cédric

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en chimie et bioindustries, à finalité spécialisée

Abstract

This Master’s thesis studies the activity of an antimicrobial coating designed for the battle against S. epidermidis biofilms, which are the leading cause for nosocomial infections related to implants and medical devices, including prosthetic joint infection, an important worldwide consideration nowadays. New strategies based on the design of antimicrobial coatings are under current research to prevent and treat such infections. The antimicrobial property of the investigated coating is conferred by LL-37, an antimicrobial peptide. The coating is constructed using the Layer-by-Layer self-assembly technique, allowing easy immobilization of proteins and other charged compounds on a surface. These multilayered films constitute a powerful tool for nanoscale surface functionalization. Here, LL-37 was immobilized together with chitosan and heparin, two bioactive PEs. Two different LL-37-based coatings were constructed. A first coating was made of bare, positively-charged, LL-37, alternately adsorbed with negatively-charged heparin ((bare LL-37-HEP)n). The second coating was made of LL-37 whose charges had been standardized by complexation with heparin to form Protein-Polyelectrolyte Complexes or PPCs, displaying a negatively-charged corona, and alternately adsorbed with positively-charged chitosan ((PPCs-CHI)n). Coatings activity was assessed through two approaches. The first objective was to study the secondary structure of LL-37 released from the coatings. The bactericidal activity of the peptide is conferred by its a-helical conformation, which could be revealed by circular dichroism (CD). To enable such analysis, the release protocol had to be optimized to maximize the concentration of the released peptide. Despite the use of different strategies to maximize this concentration, results showed that the concentration of LL-37 released by the coatings was not high enough for CD analysis. Secondly, activity of the coating with bare LL-37 was assessed by studying its potential synergistic effect with four routinely-used antibiotics. Results showed a potential synergistic activity with all four antibiotics regarding the reduction of the biofilm biomass. In contrast, no significant effect of the coating compared to antibiotics alone was revealed for the reduction of metabolic activity of the biofilm. This work brings a contribution to the understanding of the activity of LL-37-based antimicrobial coatings, that offer new ways to prevent prosthetic joint infections.