# Ultrasound-Responsive Nanoparticles Enable Hydrophobic Antibiotic Release and Deep Penetration for Biofilm Treatment

## TL;DR

This study introduces ultrasound-responsive nanoparticles that effectively deliver hydrophobic antibiotics deep into bacterial biofilms, significantly improving treatment outcomes.

## Contribution

The novel design of nonporous silica nanoparticles enables controlled antibiotic release and deep biofilm penetration triggered by low-frequency ultrasound.

## Key findings

- Nonporous silica nanoparticles combined with ultrasound achieved 90% biofilm eradication compared to 20% without ultrasound.
- Confocal imaging showed ultrasound enabled nanoparticle penetration through all biofilm layers.
- Scanning electron microscopy confirmed nanoparticle presence and ultrasound's dual role in penetration and drug release.

## Abstract

Localized delivery of antibiotics is a promising strategy
that
leads to transformative treatment pathways of bacterial biofilms and
increases the effectiveness of their administration in contrast to
traditional delivery methods requiring high antibiotic doses. Hydrophobic
antibiotics have poor activity against bacterial biofilms due to their
limited penetration and are particularly challenging to deliver. Nanoparticles
are ideal drug delivery agents to achieve spatially controlled delivery,
but commonly their designs are either soft or porous, which limits
temporally triggered release, with the result that most of the antibiotic
does not reach deeply into the biofilm. In this study, we present
designs of nonporous silica nanoparticles that encapsulate a lipophilic
antibiotic, rifampicin, with noncovalent interactions and enable controlled
release triggered by Low-Frequency Ultrasound (LFUS). Staphylococcus aureus biofilms treated with the nonporous,
core@shell, rifampicin-encapsulated nanoparticles, RIF⊂PhSiO

2

@SiO

2
, combined with LFUS, achieved 90% biofilm eradication, compared
to 20% without ultrasound; treatment with free rifampicin and LFUS
resulted only in a 10% reduction. Nanoparticle penetration into biofilm
layers was visualized using fluorescent nanoparticles prepared with
coencapsulation of the Nile red fluorophore, RIF+NR⊂PhSiO

2

@SiO

2
. Confocal fluorescence imaging of the biofilms demonstrated penetration
of the nanoparticles throughout all the layers of the biofilm upon
LFUS application, in sharp contrast to their presence in only the
top few biofilm layers without LFUS. Scanning Electron Microscopy
of the biofilms confirmed the presence of nanoparticles and the dual
role of LFUS in promoting penetration and facilitating drug release
by disrupting molecular interactions within the nanoparticle. This
work introduces a design paradigm for nonporous nanoparticle agents
combined with ultrasound, enabling both temporal and spatial control
of drug release in bacterial biofilms. This will open transformative
therapeutic approaches for effective localized delivery of drugs that
have previously been challenging to deliver.