Lipid extraction by boron nitride nanosheets from liquid-ordered and liquid-disordered nanodomains

Molecular mechanisms of integrin αvβ8 activation regulated by graphene, boron nitride and black phosphorus nanosheets

Integrin αvβ8 is a heterodimeric transmembrane protein on macrophages. Nanosheets can activate the integrin and elicit immune responses, exhibiting adverse immunotoxicity. Understanding the mechanism of integrin activation regulated by nanosheets is crucial for safe and effective use of nanosheets in biomedical applications. Herein, we performed all-atom molecular dynamics simulations to clarify the interactions between integrin αvβ8 in the cell membrane and three types of nanosheets, graphene (GRA), hexagonal boron nitride (BN), and black phosphorus (BP). We observed that BP could adsorb the intracellular end of αv monomer and thus break the inner membrane clasp, an important hydrophobic cluster for maintaining the inactive state of integrin. The association between αv and β8 subunit is weakened, promoting the integrin activation. By contrast, GRA and BN exert little influence on the association state of the integrin. Interestingly, the puckered structure of BP affects the integrin activation, where BP with the armchair direction perpendicular to the membrane plane cannot unpack the integrin. Moreover, the perturbation effect of nanosheets on the membrane was also evaluated. BP shows a milder effect on membrane structures and lipid properties than GRA and BN. This work unravels the molecular basis on the activation of integrin mediated by three nanosheets, and suggests the toxicity and therapeutic effect of well-established nanomaterials in the immune system.

Molecular insights into the resistance of phospholipid heads to the membrane penetration of graphene nanosheets

The interaction between nanomaterials and phospholipid membranes underlies many emerging biological applications. To what extent hydrophilic phospholipid heads shield the bilayer from the integration of hydrophobic nanomaterials remains unclear, and this open question contains important insights for understanding biological membrane physics. Here, we present molecular dynamics (MD) simulations to clarify the resistance of phospholipid heads to the membrane penetration of graphene nanosheets. With 130 simulation trials, we observed that ∼22% graphene nanosheets penetrate the POPC bilayer. Sharp corners of the nanosheets should have a lower energy barrier than nanosheet edges, but interestingly, the membrane penetration mainly starts from the edge-approaching orientation. We thoroughly analyzed the pentration pathway and propulsion, indicating that the membrane penetration of graphene nanosheets is dominated by the joint effects of nanosheet edges and corners. Furthermore, the molecular origin of the resistance is clarified by evaluating the bilayers of different phospholipids, which successfully correlates the penetration resistance of phospholipid heads with the correlated motions of neighboring phospholipids for the first time. These results are expected to inspire future studies on the dynamic behavior of phospholipids, bio-nano interfaces, and design of biological nanomaterials.

Molecular mechanisms underlying the role of the puckered surface in the biocompatibility of black phosphorus

As a newly emerging two-dimensional material, black phosphorus (BP) has received broad attention in the field of biomedical applications. Prior to its clinical application, its cytotoxicity to cells should be carefully evaluated; however, this field is still in its infancy. Motivated by this, we performed molecular dynamics (MD) simulations to systematically investigate the potential mechanisms of the cytotoxicity of BP to the lipid membrane, including lipid extraction, penetration into the membrane, and the impacts of BP on the physical properties of the membrane. Surprisingly, we observed that BP could not extract lipid molecules from the membrane. The thermodynamic analyses suggested that the puckered surface structure could weaken the interactions between BP and lipid molecules, thus inhibiting the lipid extraction. Additionally, through simulating the spontaneous interaction modes between BP and the lipid membrane, we found that the "passivated" edges of BP prohibited it from penetrating into the membrane. As a result, BP could only spontaneously lie parallel on the surface of the membrane, in which manner BP exerted little influence on the properties of the lipid membrane. To comprehensively appraise the cytotoxicity, we even artificially inserted BP into the membrane and compared the effects of BP and graphene on the properties of the membrane. Simulation results showed that the influences of the inserted BP on the lipid properties were much milder than those of graphene. Overall, the present work suggests that BP possesses distinctive biocompatibility benefiting from its puckered surface structure. This work provides a better understanding of the interactions between BP and the membrane, which may offer some useful suggestions for exploring strategies to improve the biocompatibility of nanomaterials.