Biofilm-associated bacterial infection brings serious threats to global public health owing to serious antibiotic resistance. It is urgently needed to develop innovative strategies to combat biofilm-associated bacterial infections. Polymyxins stand out as the last line of defense against Gram-negative bacteria. However, serious nephrotoxicity of polymyxins severely limits their clinical utility. Herein, a hypoxia-responsive liposome is designed as the nanocarrier of polymyxin B (PMB) to combat biofilms developed by Gram-negative bacteria. A metronidazole modified lipid (hypoxia-responsive lipid (HRLipid)) is synthesized to fabricate hypoxia-responsive liposomes (HRLip). PMB loaded hypoxia-responsive liposomes (HRL-PMB) is then prepared to mitigate the nephrotoxicity of PMB while preserving its excellent bactericidal activity. HRL-PMB shows very low hemolysis and cytotoxicity due to liposomal encapsulation of PMB. PMB can be readily released from HRL-PMB in response to hypoxic biofilm microenvironment, exerting its bactericidal activity to realize biofilm eradication. The excellent in vivo antibiofilm ability of HRL-PMB is confirmed by a Pseudomonas aeruginosa infected zebrafish model and a P. aeruginosa pneumonia infection model. Meanwhile, HRL-PMB can greatly reduce the nephrotoxicity of PMB after intravenous injection. The hypoxia-sensitive liposomes held great promise to improve the biosafety of highly toxic antibiotics while preserving their intrinsic bactericidal ability, which may provide an innovative strategy for combating biofilm-associated infections.

Hypoxia, an important characteristic of bacterial biofilms, can hinder the generation of reactive oxygen species (ROS) in photodynamic therapy (PDT), leading to reduced therapeutic efficacy of PDT. In order to address this issue, fluorinated liposome was fabricated as an oxygen-sufficient nanoplatform for enhanced photodynamic eradication of bacterial biofilms. The liposomes (denoted as Lip-Ce6-PFH@O₂) were prepared by co-encapsulation of O₂ carrier perfluorohexane (PFH) and photosensitizer chlorin e6 (Ce6). Lip-Ce6-PFH@O₂ could achieve efficient biofilm penetration due to the positively charged surface. The hypoxic microenvironment of biofilms would then be relieved, leading to the generation of more ROS under laser irradiation. Therefore, the bactericidal capability of PDT could be significantly improved because of the co-delivered O₂ carrier PFH. Lip-Ce6-PFH@O₂ exhibited much better antibiofilm ability than that of Lip-Ce6 both in vitro and in vivo. Meanwhile, Lip-Ce6-PFH@O₂ also effectively alleviated inflammation symptoms and accelerated wound healing in the mice model. In general, this study provides a new paradigm to enhance the therapeutic efficacy of PDT for efficient biofilm eradication.