Confocal Microscopy and Competitive Adsorption: a New Look at Polymer-Enhanced Lung Surfactant Adsorption

Lung surfactant (LS) is a mixture of lipids and proteins that lines the air-liquid interface of the alveolar walls. It modulates the surface tension in the lungs which greatly reduces the mechanical work of breathing and also prevents the collapse of the alveoli upon expiration. Blood serum leaking into the alveoli as a result of trauma can lead to LS inhibition, which is one characteristic of acute respiratory distress syndrome (ARDS). One mode of LS inhibition, as observed during ARDS, is the competitive adsorption of albumin to the air-liquid interface of the alveoli which blocks LS from forming a functional monolayer.

The addition of hydrophilic polymers, such as polyethylene glycol (PEG) and chitosan, to the liquid subphase has been shown to enhance interfacial LS adsorption in vitro. Optimal amounts of polymer allow LS to form a functional monolayer in the presence of albumin, thus reversing inhibition. Albumin must be at least partially, if not completely, displaced from the air-liquid interface in order for a functional monolayer of LS to form. Imaging of the competitive adsorption process with confocal microscopy has allowed us to better understand the mechanisms behind forming an interfacial LS monolayer under inhibitory conditions. We can simultaneously track LS, polymer, and albumin, as well as separately visualize phenomena occurring at the interface from those occurring in the bulk. As a result of these capabilities, we have studied how changes to various system components affect the transport of LS to the interface and the subsequent displacement of interfacial albumin in order to form a function surfactant monolayer.