(6fp) Mechanism of non-disruptive membrane fusion by amphiphilic, monolayer-protected gold nanoparticles

The cellular membrane is the biological interface responsible for controlling the transport of material into the cell. Thus, it is a critical barrier that must be overcome to successfully deliver desired molecules to the cell interior. Recently, gold nanoparticles (NPs) protected by a binary mixture of purely hydrophobic and anionic end-functionalized alkanethiol ligands were observed to spontaneously penetrate cell membranes via a non-endocytic, non-disruptive mechanism. This direct penetration process is highly promising for applications in drug delivery, bioimaging, and biosensing as NPs can reach the cytosol without being trapped in endosomal compartments or inducing cytosolic leakage. However, no mechanism has yet emerged to explain the experimental observations, limiting the ability to rationally engineer NPs for optimal internalization.

Inspired by these findings, I present here research conducted at MIT with Prof. Alfredo Alexander-Katz in close collaboration with Prof. Darrell Irvine at MIT and Prof. Francesco Stellacci at EPFL. I used a combination of coarse-grained and atomistic simulation methodologies to show that these amphiphilic NPs can spontaneously insert into and fuse with lipid bilayers to obtain configurations resembling transmembrane proteins. The full insertion pathway is remarkably similar to the mechanism of vesicle-vesicle fusion due to the physicochemical similarity between these synthetic and biological systems, allowing us to take cues from biology to understand NP behavior. Predictions from my simulations were confirmed experimentally leading to the development of design guidelines to optimize fusion efficacy. Furthermore, experimental results demonstrated that the same NPs predicted to fuse with bilayers are internalized by the non-endocytic process described above, establishing a link between favorable bilayer interactions and intracellular localization. These findings yield significant physical insight into behavior at this important nano-bio interface and illustrate the power of such simulations in guiding NP design for biomedical applications.

In my future research, I will utilize detailed simulations across multiple time and length scales to generalize this strategy to the study of various membrane-active biological and synthetic systems in close collaboration with experimentalists. In particular, I am interested in understanding mechanisms of post-translational membrane protein insertion, capturing the role of lipid interfaces in membrane binding, and using novel optimization algorithms to tune NP-membrane interactions. My goal is thus to both study fundamental questions in membrane biophysics and develop novel engineered nanomaterials for biomedical applications.