Understanding the interaction of 2D particles with phospholipid membranes

The research being performed in this project will lead to a better understanding of the way small particles interact with membranes, both biological and non-biological, composed of lipid molecules. The specific particles that will be studied are graphene, and the membranes will be comprised of a lipid molecule naturally found in the lungs. The graphene is representative of a broader class of particles called two-dimensional particles, which are increasingly being utilized in consumer products such as batteries, concrete, various coatings, and even safety masks.

As the uses and availability of two-dimensional particles increases, their interaction with biological membranes in various capacities, including those within the lungs, will likely increase. In addition, two-dimensional particles can be incorporated into products where lipids similar in nature to those found in lungs are used to create emulsions such as paints, and cosmetics.

Although many two-dimensional particles such as graphene will not undergo chemical reactions with lipids, there is evidence that their interaction with lipid films can alter the structure of the film at a microscopic level in ways that are not understood. This research seeks to characterize those alterations in lipid film structure in the presence of two-dimensional particles with both experiments and computer simulations.

The results can lead to a better understanding of the way two-dimensional particles influence biological membranes, especially those found in the lungs, but they can also lead to a better understanding of the ways two-dimensional particles can be used in lipid-containing consumer products. The project also includes an outreach component with a local primary school where the principal investigator will work with students with specific learning disabilities using hands-on demonstrations that illustrate important physics concepts relevant to the work, including surface tension.

The goal is to increase the long-term interest in STEM careers of those students who may avoid technical fields because of a specific learning disability.

This work seeks to understand the interaction of two-dimensional particles with phospholipid monolayers using experiments and molecular dynamics simulations. Two-dimensional particles are a class of nanoparticle that is rapidly expanding in terms of the available chemistries. As the number of two-dimensional materials increases, and the applications expand, the intersection of these materials with biology, either intentionally or unintentionally, will become more prevalent.

Phospholipid membranes, including monolayers and bilayers, are ubiquitous in biology, and are influenced by the presence of nanoparticles, although the nature of the interaction between these membranes and two-dimensional particles is not understood. The central hypothesis is that lateral diffusion of two-dimensional particles in contact with phospholipid monolayers is dependent on a number of variables, including particle chemistry, the number of stacked particle layers, and the membrane area density, and that this is related to both the physical position of the particle in the membrane (e.g. surfing on lipid tails vs embedded), and the influence the particle has on the surrounding phospholipid structure.

The approach will be both experimental and computational, making use of particle synthesis techniques, various forms of microscopy, and molecular dynamics simulations. The materials utilized will be graphene, and the phospholipid dipalmitoylphosphatidylcholine. One significant contribution that this work will make is the generation of a large amount of experimental data on a model system with which to compare computational results, a limiting factor thus far in understanding the interaction of two-dimensional particles with biological membranes.

Another product of this work will be an improved understanding of how two-dimensional particles influence the structure of phospholipids that they interact with laterally, a behavior that can change the interfacial rheological properties of the membrane. A third contribution of this work will be to understand how multiple, stacked layers of two-dimensional particles interacts differently with membranes than single layers.

Although two-dimensional particles are often thought of as single monolayers, thermodynamics drive monolayers to stack. As a consequence, it is relevant to understand the interaction of multilayers with biological membranes, since this is likely to be physiologically relevant whether the interaction derives from an unintended exposure to two-dimensional particles, or from an intentional use of the particles in a future biotherapeutic application.

It is expected that what is learned in this work utilizing graphene as a model two-dimensional particle will likely be generalizable to two-dimensional particles of different chemistries since research involving spheroidal particles at interfaces indicates that particle shape is a major factor in predicting the dynamics of the particles at fluid-fluid interfaces. The project includes an outreach component where the investigator will visit a local primary school to perform hands-on demonstrations that illustrate basic concepts in interfacial phenomena such as surface tension for groups of students with specific learning disabilities.

Such students tend to avoid STEM fields because of a labeled learning disability. The goal is to increase their long-term interest in STEM careers by showing them that they are fully capable of understanding complex concepts in physics.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.