pH-Responsive, Charge-Reversing Layer-by-Layer Nanoparticle Surfaces Enhance Biofilm Penetration and Eradication

Microbes entrenched within biofilms can withstand 1000-foldhigherconcentrations of antibiotics, in part due to the viscous extracellularmatrix that sequesters and attenuates antimicrobial activity. Nanoparticle(NP)-based therapeutics can aid in delivering higher local concentrationsthroughout biofilms as compared to free drugs alone, thereby enhancingthe efficacy. Canonical design criteria dictate that positively chargednanoparticles can multivalently bind to anionic biofilm componentsand increase biofilm penetration. However, cationic particles aretoxic and are rapidly cleared from circulation in vivo, limiting theiruse. Therefore, we sought to design pH-responsive NPs that changetheir surface charge from negative to positive in response to thereduced biofilm pH microenvironment. We synthesized a family of pH-dependent,hydrolyzable polymers and employed the layer-by-layer (LbL) electrostaticassembly method to fabricate biocompatible NPs with these polymersas the outermost surface. The NP charge conversion rate, dictatedby polymer hydrophilicity and the side-chain structure, ranged fromhours to undetectable within the experimental timeframe. LbL NPs withan increasingly fast charge conversion rate more effectively penetratedthrough, and accumulated throughout, wildtype (PAO1) and mutant overexpressingbiomass (& UDelta;wspF) Pseudomonasaeruginosa biofilms. Finally, tobramycin, an antibioticknown to be trapped by anionic biofilm components, was loaded intothe final layer of the LbL NP. There was a 3.2-fold reduction in & UDelta;wspF colony forming units for the fastest charge-convertingNP as compared to both the slowest charge converter and free tobramycin.These studies provide a framework for the design of biofilm-penetratingNPs that respond to matrix interactions, ultimately increasing theefficacious delivery of antimicrobials.