N24 - A Bacteria-Responsive Hydrogel for Treatment of Topical Infections

Saturday, October 11, 2025

10:00 AM - 11:00 AM PDT

Location: Exhibit Hall F, G & H

Presenting Author(s)

JS

Jared I. Sonkin

Undergraduate Student
Brown University
White Plains, New York, United States

Co-Author(s)

Alec Mccall, BSE

Graduate Student Researcher
Brown University
North Providence, Rhode Island, United States

Primary Investigator(s)

Anita Shukla, PhD

Elaine I. Savage Professor of Engineering
Brown University
Providence, Rhode Island, United States

Introduction: : Wound infections are a major clinical problem with 8.2 million cases in the United States in 2014.[1] Topical antibiotics are the most common treatment for these infections, but their effectiveness is becoming increasingly limited by the emergence of antibiotic resistance. The Centers for Disease Control and Prevention estimates that there are 2.8 million antibiotic resistant infections per year in the United States, resulting in approximately 35,900 deaths.[2] A more selective administration of antibiotics could potentially limit antibiotic resistance in wound infections. This controlled delivery can be accomplished through a wound dressing that releases therapeutics in response to an endogenous marker of infection. Hydrogels have been established as suitable materials for wound dressings due to their ability to hydrate wounds and absorb wound exudate.[3] These materials consist of a hydrophilic polymer network with the capacity for functionalization and drug loading, making them suitable for fabricating a responsive wound dressing.
Here, we designed a hydrogel-based wound dressing that degrades in the presence of esterase enzymes. Esterases are universally produced by bacteria have been studied as a biomarker for diagnosis of topical infection, but there has been limited research investigating their use as a trigger for responsive delivery of therapeutics. We hypothesized that degradation of this hydrogel by esterases could trigger the controlled release of encapsulated antimicrobial cargo for treatment of topical infections. The hydrogels were characterized for their elastic modulus and mesh size. Additionally, hydrogel degradation was evaluated in response to Staphylococcus aureus, a common bacterial pathogen found in skin wounds.

Materials and

Methods: : The design of the hydrogel was first validated by measuring the esterase activity of a library of bacterial strains. Intracellular fluid was extracted through cell lysis and assessed for esterase activity using the chromogenic substrate p-nitrophenyl acetate (PNPA). Additionally, a pH titration assay was conducted to verify that the responsive element of the hydrogel, poly(ethylene glycol) (PEG) diacrylate (PEGDA), was hydrolyzed by esterases and not by other enzymes.
PEG-based hydrogels were synthesized from 4-arm PEG thiol and PEGDA in a 5:4 molar ratio dissolved in 0.1x phosphate buffered saline (PBS) at pH 2.5. The photoinitiators triethanolamine, eosin Y (10 nM), and n-vinyl pyrrolidinone were also added, each at a concentration of 0.5% (v/v). Hydrogel formation was enabled by a light-initiated free radical polymerization. After crosslinking, the hydrogels were soaked in PBS, allowing them to swell to equilibrium.
The degradation of the hydrogels was evaluated with S. aureus grown on tryptic soy agar (TSA). A liquid culture containing 10^8 CFU/mL was spread on a TSA plate. Hydrogels were placed on the plates and then incubated at 37°C to assess the progress of hydrogel degradation.
The elastic modulus of the hydrogel was determined using the Instron 6800 Series universal testing system. Each hydrogel was preloaded with a force of 0.02 N. The hydrogels were compressed at a rate of 0.1 mm/s to a final displacement of half the hydrogel height. The mesh size was estimated based on swelling studies of the hydrogels.

Results, Conclusions, and Discussions:: Most of the tested strains showed significant esterase activity compared to the baseline level of PNPA hydrolysis, indicating that these strains produce measurable amounts of esterase enzymes (Figure 1A). Titration showed that PEGDA was hydrolyzed by esterase isolated from porcine liver. At a concentration of 1.96 U/mL, this esterase hydrolyzed PEGDA, our hydrogel crosslinker, at a rate of 1.13 μmol/min (Figure 1B).
The hydrogels were formed successfully, requiring approximately 8 minutes of exposure to white light to fully crosslink. The measured elastic modulus of the hydrogel was 2.56 ± 0.08 kPa, while an estimated mesh size of 6.98 ± 0.06 nm was determined from the swelling studies. Compared to previously reported hydrogels with a similar concentration of PEG thiol, this hydrogel exhibited a much lower stiffness and a slightly larger mesh size, suggesting that this hydrogel has a less dense polymer network.[4] We hypothesized that these matrix properties would enable esterase enzymes to permeate the gel more easily and also allow for efficient hydrogel degradation and drug release. Next, the hydrogels were loaded with silver nanoparticles (AgNPs). These AgNP-loaded hydrogels were considerably stiffer than non-loaded hydrogels, with an elastic modulus of 4.34 ± 1.03 kPa. The increase in stiffness may be a result of the formation of crosslinks between the vinyl groups in PEGDA or thiol groups in the 4-arm PEG thiol and the surface of the AgNPs, resulting in a more densely crosslinked matrix. The unloaded hydrogels degraded within one day of incubation with S. aureus (Figure 1C), indicating the potential for the hydrogels to release encapsulated cargo in a controlled manner. These hydrogels could be used to specifically deliver therapeutics in the presence of bacterial wound infections, providing rapid and effective treatment.

Acknowledgements and/or References (Optional): : 1. Nussbaum, S. R., Carter, M. J., Fife, C. E., DaVanzo, J., Haught, R., Nusgart, M., & Cartwright, D. (2018). An Economic Evaluation of the Impact, Cost, and Medicare Policy Implications of Chronic Nonhealing Wounds. Value in Health, 21(1), 27–32. https://doi.org/10.1016/j.jval.2017.07.007
2. Centers for Disease Control and Prevention (U.S.). (2019). Antibiotic resistance threats in the United States, 2019. Centers for Disease Control and Prevention (U.S.). https://doi.org/10.15620/cdc:82532
3. Liang, Y., He, J., & Guo, B. (2021). Functional Hydrogels as Wound Dressing to Enhance Wound Healing. ACS Nano, 15(8), 12687–12722. https://doi.org/10.1021/acsnano.1c04206
4. Alkekhia, D., LaRose, C., & Shukla, A. (2022). β-Lactamase-Responsive Hydrogel Drug Delivery Platform for Bacteria-Triggered Cargo Release. ACS Applied Materials & Interfaces, 14(24), 27538–27550. https://doi.org/10.1021/acsami.2c02614