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  • Advanced microscopy technique visualizes bactericidal effect on hydrogel patches in real time

Advanced microscopy technique visualizes bactericidal effect on hydrogel patches in real time


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Hydrogel with an encapsulated photosensitizer (methylene blue, MB) activated by light during photodynamic therapy, causes the release of reactive oxygen species that alter bacterial activity, resulting in a change in the oscillations of the Min system. Image: ACS.

  • The work of IMDEA Nanociencia’s Advanced Fluorescence Nanoscopy Group takes advantage of the high transparency of the hydrogel to investigate with light microscopy the response of bacteria to antimicrobial therapies.
  • The antimicrobial strategy is based on the activation and release of reactive oxygen species that cause bacterial death, by stimulating the hydrogel with light (photodynamic therapy).
  • The study carried out by researchers from IMDEA Nanociencia (Madrid) and the Leibniz Institute for Surface Engineering (Leipzig) reveals that the antibacterial mechanism depends on the hydrogel preparation method, and provides valuable information to improve this therapy.

Madrid, 3rd April, 2024. Hydrogel patches are commonly used for dermatology and cosmetic applications, due to their fluid retention capacity, adherent properties and elasticity. The porosity of hydrogels makes them ideal candidates in the context of drug delivery, as their 3D molecular structure allows for the encapsulation of drugs and photoactive molecules.

In particular, some hydrogels can encapsulate molecules -photosensitizers- that activate reactive oxygen species when illuminated with light of a certain wavelength. These reactive species can oxidize lipids, proteins, DNA, and other biomolecules, thus generating an antimicrobial action known as photodynamic therapy.  An important requirement for this strategy is that the hydrogel in which such photosensitizers are encapsulated is highly transparent so that light can activate them efficiently.

The high transparency of these patches has also been key in their study using optical microscopy techniques. The Advanced Fluorescence Nanoscopy Group at IMDEA Nanociencia, led by Dr. Cristina Flors, has managed to study and understand the effect of patches of PEGDA (poly(ethylene glycol) diacrylate), a highly transparent hydrogel, loaded with photoactive molecules, on E. coli bacteria. These experiments have captured the mechanisms of antimicrobial action and bacterial death at the single-cell level, and in real time, which has given them valuable information about the process and how it can be improved.

hydrogels2The researchers used the Min regulatory system to observe changes in the bacterium's physiology. Under normal conditions, the Min protein system oscillates from pole to pole of the bacterium in order to mark its centre and divide symmetrically.  Moreover, the frequency of oscillations can be altered if the bacterium is subjected to stress conditions, for example mechanical stress or the presence of antibiotics.

Using an advanced fluorescence microscopy technique, which could be applied thanks to the high transparency of the hydrogels, they observed the Min oscillations in individual bacteria, and in real time, for several minutes. Changes in the oscillation patterns of the Min system revealed the different mechanisms of bacterial death, from which it could be concluded that this mechanism depends on the method of hydrogel preparation. Differences were found between hydrogels that encapsulate the photoactive molecule reversibly or irreversibly, since the mobility of the photosensitizer towards the surface of the hydrogel is limited in the latter case.  This is a pioneer study in determining, in real time and at the single-cell level, the process of bacterial degradation and death with an unprecedented level of detail and in the real-world environment of a hydrogel patch.

Dr. Flors' lab results reveal details of the antibacterial process on the surface of the hydrogel, which may help provide design guidelines for next-generation antibacterial materials, such as wound dressings and patches for clinical treatment of skin conditions.

This work is a collaboration between researchers from the Leibniz Institute for Surface Engineering (Leipzig) and IMDEA Nanoscience. The research has been partially funded by the Severo Ochoa Award of Excellence to IMDEA Nanociencia.


Ingrid V. Ortega, Tuğçe Şener Raman, Agnes Schulze, and Cristina Flors. In situ single-cell bacterial imaging provides mechanistic insight into the photodynamic action of photosensitizer-loaded hydrogels. ACS Applied Materials & Interfaces 2024 16 (5), 5677-5682. DOI: 10.1021/acsami.3c17916B.




Dr. Cristina Flors
cristina.flors [at]imdea.org
Group webpage: Advanced Fluorescence Nanoscopy Group

Oficina de Divulgación y Comunicación en IMDEA Nanociencia
divulgacion.nanociencia [at]imdea.org
Twitter: @imdea_nano
Facebook: @imdeananociencia
Instagram: @imdeananociencia

Source: IMDEA Nanociencia.