Amphiphilic hydrogels functionalized with antimicrobial peptides for wound care

Doctoral thesis, 2023

Bacteria have the potential to cause significant harm to us when found in places where we do not want them, such as in wounds. Through the last century, the gold standard of eradicating bacteria in these cases has been with antibiotics. However, this treatment is at the risk of being severely impeded by antibiotic resistance, requiring alternative ways of dealing with bacteria. Antimicrobial peptides (AMPs) have shown promise as such an alternative with its broad-spectrum and rapid antibacterial activity, with a lower risk of inducing resistance.
The aim of this thesis was to investigate the covalent attachment of AMPs to the surface of Pluronic F127 based amphiphilic hydrogels and validate the same in vitro, in vivo, and clinically for wound care applications. A few variants of the material were created, with hydrogel discs being the most common as a convenient base for evaluation. The material was also prepared as a wound dressing where it was evaluated in a human intact skin study for a clinically relevant investigation. Furthermore, the material was also made into particles as a platform for treating deeper wounds as well as in liquid formulation or as a coating.
Overall, the AMP-functionalized hydrogels showed a potent antibacterial activity against both gram-negative and gram-positive bacteria, and some antibiotic resistant strains among them. At the same time, the materials did not show any signs of cytotoxicity against fibroblasts or erythrocytes. Furthermore, the AMP-functionalized hydrogels showed a potential to reduce the endotoxin levels released by Pseudomonas aeruginosa, a property that might assist further with combating the adverse effects of a wound infection and improve healing outcomes. The material also showed a significant antibacterial effect against the bacteria naturally present on our skin when evaluated clinically on healthy volunteers.
A main limitation behind the clinical use of AMPs is that they have a low biostability and are rapidly degraded by proteolytic enzymes. By covalently attaching the AMPs to a solid substrate they should gain steric protection against degradation. That was also the case observed for the AMPs when covalently attached to the hydrogels, as they retained their antibacterial activity for several days, both in serum, and implanted in an infected rat model. The covalent attachment of the AMPs also resulted in a contact killing mechanism, suitable for a local antibacterial effect.