Understanding the interaction between metal nanoparticles and biological membranes

Project Information

BioMNP

Grant agreement ID: 677513

DOI

10.3030/677513

Project closed

EC signature date 23 March 2016

Start date 1 April 2016

End date 30 November 2021

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 131 250,00

EU contribution

€ 1 131 250,00

Coordinated by

UNIVERSITA DEGLI STUDI DI GENOVA
Italy

Periodic Reporting for period 4 - BioMNP (Understanding the interaction between metal nanoparticles and biological membranes)

Reporting period: 2020-10-01 to 2021-11-30

Summary of the context and overall objectives of the project

Nanomaterials are nowadays produced in large scale for the most diverse applications, such as catalysis, material mechanical reinforcement, data storage, cosmetics, biomedicine, food packaging. In most cases, their design has to take into account the prediction and assessment of their toxicity to the human body, as well as, of course, their functionality. In the field of biomedicine, inorganic nanoparticles are being studied as promising diagnostic, therapeutic and drug delivery agents. By encapsulating inorganic nanoparticles, such as metal or oxide nanoparticles, into shells of organic molecules that make them biocompatible, researchers are experimenting their use as contrast agents for optical and magnetic imaging of tissues, as photothermal agents for photothermal anticancer therapies, and as vehicles of drugs to specific target cells.
During its journey via intravenous route into our body, though, nanoparticles have to overcome a number of natural obstacles: they interact with the proteins of our blood, and need to overcome the plasma membrane to successfully enter the interior of our cells. Unfortunately, there is still poor understanding of the molecular processes that drive the interactions of metal NPs with proteins and cells. In this project we aim at comprehend, with molecular resolution, these mechanisms of interactions. We plan to achieve this objective by means of computational tools, such as Molecular Dynamics, which allow to simulate in silico the interaction of the nanoparticles with the biological environment, at atomistic and molecular resolution.
The BioMNP objective is the molecular-level understanding of the interactions between surface functionalized metal nanoparticles and biological membranes, by means of cutting- edge computational techniques and new molecular models. BioMNP aims at answering fundamental questions at the crossroads of physics, biology and chemistry.
The understanding and control of the interaction of nanoparticles with biological membranes is of paramount importance to understand the molecular basis of the NP biological effects and guide the rational design of nanoparticles with biomedical applications. BioMNP will go beyond the state of the art by rationalizing the complex interplay of NP size, composition, functionalization and aggregation state during the interaction with model biomembranes. Its results will have an impact on nanomedicine, toxicology, nanotechnology and material sciences.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Within the BioMNP project, we addressed the understanding of the molecular interactions between gold NPs and biological membranes from three main perspectives. We investigated
• the influence of the properties of the single NP, such as surface charge, hydrophobicity/hydrophilicity, ligand patterning, NP size… on its interaction with model lipid bilayers;
• the collective behavior of surface-functionalized NPs, both in the aqueous and membrane environments;
• the thermal response of the NPs, when irradiated by intense, short laser pulses, as it happens in photothermal and photoporation applications;

We demonstrated that the nature of the ligand-NP adsorption (covalent or not covalent), the ligand hydrophobicity, the ligand arrangement on the surface of the NP as well as the NP size are important physical parameters driving NP-lipid membrane interactions. We rationalized how collective NP behaviors – such as linear or planar aggregation – can sense and induce membrane deformations, often involving significant membrane reshaping and alterations of membrane curvature. While the general principles of membrane reshaping upon interaction with rigid spherical inclusions root in the Helfrich elastic theory for membranes, in BioMNP we showed that the molecular details of the NP soft, deformable interface can not be disregarded, as they dramatically influence NP-membrane interactions. It is only by including such details that we could explain several experimental findings, such as the unexpected aggregation of same-charge nanoparticles on supported bilayers and liposomes, the reduced NP uptake by cholesterol-rigidified and gel-phase membranes, the reshaping of liposomes.
We also addressed one specific in vitro application of ligand-protected gold NPs, which is photoporation. In photoporation applications, NPs are irradiated by short, intense laser pulses and convert radiation energy into heat, which in turn is released to the membrane. The local release of heat causes, in vitro, transient pores that allow for the translocation of macromolecules into the cytoplasm. The experimental characterization of temperature gradients around NPs is extremely challenging. Within BioMNP, we were able to use our computational tools to make predictions on the temperatures that can be reached in the biological environment around the irradiated NPs. We found, once more, that the nature of the ligands on the NP surface influences thermal transport through a mechanism that involves water diffusion at the ligand-water interface.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

All the achievements described in the previous section represent important advancements beyond the state of the art. The role of the NP surface charges and ligand patterning at shaping the interaction with model cell membranes was the object of some debate in the literature. We can now state that small nanoparticles, able to passively translocate through cell membranes, interact with zwitterionic lipid bilayers independently on the sign of their charged moieties (anionic or cationic). Moreover, we demonstrated that ligand patterning is an important factor influencing the kinetics of NP-membrane interaction, providing an interpretation to the puzzling experimental observation that different ligand patterning can cause, in vitro, different NP internalization pathways.
Concerning NP aggregation, our studies were the among the first considering, by means of MD simulations with sub-molecular resolution, the aggregation of NPs with a soft interface in a biological environment such as the lipid membrane. As remarked in the previous section, the aggregation of same-charge NPs was an unexpected observation. We have shown that only the nano-resolution offered by the computational approach allows to capture all the physico-chemical driving forces leading to such an aggregation. While membrane curvature and membrane deformations were known to cause the aggregation of transmembrane inclusions, as a result of the minimization of the membrane elastic free energy, it was not clear how these effects would couple to electrostatics effects, such as the ion-bridging phenomenon that we identified as one of the driving forces to NP aggregation.
Concerning heat transfer at the NP surface, instead, the main advancement with respect to the state of the art is that we developed a predictive tool to assess, by means of MD simulations, the temperature gradients around the NPs (in presence of short, intense laser pulses). Given that this measure is extremely challenging from the experimental point of view, we showed that MD simulations can really complement the experimental investigation in this field.

Overall, we expect our project to have an immediate impact on the researcher community dealing with nano-bio interfaces, and on a longer run to contribute to the rational design of nanoparticles with controlled interactions with proteins and cell membranes.

Fig.1 - A charged NP anchored to the hydrophobic core of a phospholipid membrane

Fig.2 - A Au NP irradiated by laser light can transfer heat to the surrounding biological medium