# Sustained Release Varnish of Chlorhexidine for Prevention of Biofilm Formation on Non-Absorbable Nasal and Ear Sponges

## TL;DR

A new varnish coating with chlorhexidine can prevent bacterial growth on nasal and ear sponges for up to 39 days, reducing infection risk and antibiotic use.

## Contribution

A sustained-release chlorhexidine varnish coating for sponges that provides long-term antibacterial and anti-biofilm activity.

## Key findings

- SRV-CHX-coated sponges inhibited biofilm formation for up to 33 days against Staphylococcus aureus and 16 days against Pseudomonas aeruginosa.
- HR-SEM and confocal imaging showed sparse, non-viable biofilms on SRV-CHX-coated sponges compared to dense biofilms on controls.
- The coating provided bactericidal effects for up to 16 days against S. aureus and 5 days against P. aeruginosa.

## Abstract

Background: Non-absorbable polyvinyl alcohol sponges (Merocel) are widely used in otolaryngology for nasal and ear packing but are prone to bacterial colonization and biofilm formation, which may increase infection risk and drive frequent use of systemic antibiotics. Sustained-release drug delivery systems enable prolonged local antiseptic activity at the site of packing while minimizing systemic exposure. Methods: We developed a sustained-release varnish containing chlorhexidine (SRV-CHX) and coated sterile Merocel sponges. Antibacterial, in vitro, activity against Staphylococcus aureus and Pseudomonas aeruginosa was evaluated using kinetic diffusion assays on agar, optical density (OD600) measurements of planktonic cultures, drop plate, ATP-based viability assays, biofilm analysis by MTT metabolic assay, crystal violet bio-mass staining, high-resolution scanning electron microscopy (HR-SEM), and spinning disk confocal microscopy. Results: SRV-CHX-coated sponges produced sustained zones of inhibition on agar plates for up to 37 days against S. aureus and 39 days against P. aeruginosa, far exceeding the usual 3–5 days of clinical sponge use. Planktonic growth was significantly reduced compared with SRV-placebo, and a bactericidal effect persisted for up to 16 days for S. aureus and 5 days for P. aeruginosa before becoming predominantly bacteriostatic. Biofilm formation was markedly inhibited, with suppression of metabolic activity and biomass for at least 33 days for S. aureus and up to 16 days for P. aeruginosa. HR-SEM and confocal imaging confirmed sparse, discontinuous biofilms and predominance of non-viable bacteria on SRV-CHX-coated sponges compared with dense, viable biofilms on the placebo controls. Conclusions: Coating Merocel sponges with SRV-CHX provides prolonged antibacterial and anti-biofilm activity against clinically relevant pathogens. This strategy may reduce dependence on systemic antibiotics and improve infection control in nasal and ear packing applications in otolaryngology.