The project, led by Dr. Kristian Wende at ZIK plasmatis in Greifswald, ran from 1 October 2020 to 31 December 2022 and was funded by the German Federal Ministry of Education and Research under grant 03Z22D511. Its central aim was to develop a label‑free detection method for plastic particles in biological tissues and to investigate how such particles are taken up by cells, how they interact with the immune system, and whether they contribute to chronic inflammatory diseases. Two complementary research arms were established: a biologically‑immunological arm focused on cellular uptake, immune responses, and protein modifications, and a physico‑biochemical arm that developed the analytical detection technique and studied the physicochemical properties of the particles.

The analytical breakthrough was the combination of atomic force microscopy (AFM) with micro‑infrared (IR) spectroscopy. By coupling the high spatial resolution of AFM with the chemical fingerprinting capability of micro‑IR, the team could identify plastic particles smaller than the wavelength of the IR light, thereby circumventing the classical Abbe diffraction limit. The method produced distinct fingerprint spectra that allowed unambiguous assignment of particle types to specific polymers such as polyethylene terephthalate (PET), polyvinyl chloride (PVC), polystyrene (PS), polymethyl methacrylate (PMMA), and polypropylene (PP). Although the project was delayed by late delivery of key components, the technique proved capable of detecting sub‑micrometer particles in complex biological matrices, including formalin‑fixed, paraffin‑embedded tissue sections, without the need for fluorescent or other labels. The detection limit was found to be below 1 µm, and the method could be applied to archived tissue banks, opening the possibility of retrospective studies on chronic inflammatory and neurodegenerative diseases.

Parallel investigations in the biologically‑immunological arm examined the cellular response to plastic exposure. In vitro experiments with lung epithelial cells, keratinocytes, and fibroblasts revealed only modest changes in the expression of adhesion molecules (e.g., focal adhesion kinase, vinculin, claudin‑1, connexin‑43, integrins α1‑6β1) after a single exposure to particles of various sizes. Fluorescence microscopy and quantitative PCR confirmed that the impact on cell‑cell junctions was generally weak and independent of the analytical method used. Reactive oxygen species (ROS) production was measured with H₂‑DCFDA staining and found to be low compared with a positive control, yet exposure time correlated with an up‑regulation of the oxidative‑stress marker GSTA1 at the mRNA level, indicating a delayed cellular oxidative response. Protein modification studies using human saliva as a surrogate for oral exposure demonstrated that smaller particles induced more extensive oxidative modifications of adsorbed proteins, whereas surface chemistry of the particles played a secondary role.

The project also documented transient disruption of the actin cytoskeleton in vitro, evidenced by loss of stress fibers after particle uptake. These findings suggest that plastic particles can perturb cellular architecture and signaling pathways, potentially influencing immune cell function and chronic inflammation. The collaborative framework involved mentors from the University of Greifswald and the Leibniz Institute for Astrophysics in Potsdam, as well as partners from ZIK HIKE and ZIK innoFSPEC. During the project, two doctoral theses, one master’s thesis, and two bachelor’s theses were completed, ensuring a strong training component. The results have been disseminated through peer‑reviewed publications and will inform future risk assessments of plastic exposure in human health.