Ageing Affects the Mechanical Interaction between Microplastics and Lipid Bilayers

Plastic pellets are the building blocks and pre-production form of many plastic products. Exposure to oxygen and sunlight leads to oxidation and photodegradation of the pellets, which results in a visible change in color. We investigate the effect of pellet-derived microplastics' aging on their mechanical interaction with lipid bilayers. For that purpose, polyethylene pellets were collected at the beach La Pineda near Tarragona, Spain. Pellets were sorted by chemical composition and a yellowing index, which was used as an indicator of aging. The hydrophilicity of the pellets was estimated through contact angle measurements. We produced microplastics from these pellets by grinding and filtering. Then, microplastics were dispersed around a free-standing bilayer formed in a 3D microfluidic chip to study interactions between microplastics and lipid bilayers. Our findings indicate that as the microplastics aged, the bilayer was stretched more significantly due to its increased adhesive interaction with the lipid bilayer. Interestingly, our theoretical model shows that the extracted adhesive interaction increases linearly with the measured pellet contact angle (e.g., pellet hydrophilicity). These findings raise concerns about the toxic risks that aged microplastics may pose to living organisms.