Liquid crystalline nanoparticles for co-delivery of gentamicin and cinnamaldehyde: enhancing antibiofilm efficacy against Pseudomonas aeruginosa via quorum sensing inhibition.

Biofilm-associated infections present a major therapeutic challenge due to reduced antibiotic susceptibility, altered bacterial physiology, and protection by the extracellular polymeric substance (EPS) matrix. In this study, liquid crystalline nanoparticles (LCNPs) were developed as a co-delivery platform for gentamicin (GEN) and the biofilm-modulating quorum sensing inhibitor cinnamaldehyde (CIN) to enhance antibiofilm activity against Pseudomonas aeruginosa PAO1. LCNPs were successfully fabricated using a hydrotrope dilution method, producing nanoparticles with mean diameters of approximately 200-230 nm and negative surface charge. Co-loading of GEN and CIN resulted in high encapsulation efficiency, particularly for CIN (∼90%), although increasing hydrophobic CIN loading influenced nanostructural organisation, particle size distribution, and colloidal stability. Release/recovery studies demonstrated distinct behaviours for the two compounds: GEN showed rapid initial release followed by a plateau in the recovered fraction, whereas CIN showed a non-linear apparent filtrate recovery profile, consistent with its hydrophobicity and association with lipid domains. Antimicrobial evaluation demonstrated that LCNP encapsulation enhanced GEN activity against planktonic P. aeruginosa PAO1 compared with unformulated GEN. CIN reduced biofilm formation at sub-inhibitory concentrations, supporting its role as a biofilm-modulating agent. GEN-CIN co-loaded LCNPs, particularly at a 1:100 ratio, produced enhanced antibiofilm activity compared with individual treatments and unformulated combinations, including marked reductions in biofilm biomass and viable biofilm-associated bacteria. This improved performance may arise from the complementary roles of GEN as a bactericidal antibiotic and CIN as a biofilm-modulating compound, together with LCNP-mediated co-delivery that supports concurrent presentation of both agents within the biofilm treatment environment. Overall, GEN-CIN co-loaded LCNPs improved antibiofilm activity against P. aeruginosa PAO1 under the tested conditions, supporting the potential of LCNP-mediated antibiotic-biofilm modulator co-delivery. However, the study was limited to a single laboratory strain, and higher CIN loading was associated with structural disruption and reduced colloidal stability. Further formulation optimisation, cytotoxicity and biocompatibility assessment, and evaluation against clinical and antibiotic-resistant P. aeruginosa isolates are required to establish broader translational relevance.