(181c) Stimuli-Responsive, Hydrolysable Layer-By-Layer Nanoparticles Enhance Biofilm Penetration

Biofilm bacterial infections cause 65-80% of all human microbial infections, affect 17 million, cause approximately 550,000 deaths, and cost the healthcare system billions of dollars. Biofilm-forming bacteria withstand high concentrations of antibiotics, resulting in chronic infections. The extracellular matrix­ plays a critical role in the antibiotic recalcitrance, in part by impeding antibiotic penetration due to its mechanical and physicochemical properties, including electrostatic and hydrophobic forces. To date, there is an urgent need for new strategies to deliver high local concentrations of antibiotics into the biofilm. Nanoparticle (NP) based therapeutics delivery is a promising solution, and surface chemistry is a key player in their design. It governs the interactions at the interface between the nanomaterial and biological systems (nano-bio), influencing targeting, binding, cargo unloading, and pharmacokinetics. Interactions at the nano-bio interface are a complex interplay between matrix composition, NP characteristics, and the microenvironment. Moreover, a key structure-function relationship has been identified for NP surfaces: cationic, positively charged NPs are superior compared to neutral or anionic NPs in entering into the negatively charged microenvironment. However, when administrated systemically, cationic NPs are toxic and rapidly cleared. Thus, a critical gap in the field exists: how can we conserve the positive surface charge required for biofilm penetration while mitigating the accompanying toxicity and rapid systemic clearance? To address this challenge, we will: design a NP drug delivery platform utilizes the layer-by-layer (LbL) assembly approach, a versatile method for generating libraries of surface chemistries for controlled release of therapeutics; employ stimuli-responsive principles of NP surface design; and leverage the acidic biofilm microenvironment for switching the NP surface charge at the nano-bio interface. We have synthesized an anionic polymer with hydrolysable amide side-chains responsive to moderate acidic pHs (6.5), known to be present within the biofilm. After hydrolysis, the resulting amine provides a net positive charge, resulting in a cationic polymer. By modifying the polymer backbone, as well as the flexibility of side-chain reaction partners, we can tune the cleavage rates, ranging from hours to days. A panel of these polymers were then layered as the outermost surface of an LbL NP, and probed for biofilm penetration with myriad assays. Nanoparticle permeation and penetration through both wild-type, and overproducing matrix, Pseudomonas aeruginosa strains will be quantified using a Transwell assay and visualized with confocal microscopy. Furthermore, efficacy of nanoparticle-associated antibiotics will be assessed in vitro and potentially in vivo. From these experiments, we identify structure-property relationships that can be used to maximize the delivery of nano-encapsulated antimicrobials throughout biofilms.