Receptor-Mediated Endocytosis of Two-Dimensional Nanomaterials Undergoes Flat Vesiculation and Occurs by Revolution and Self-Rotation.

Two-dimensional nanomaterials, such as graphene and transitional metal dichalcogenide nanosheets, are promising materials for the development of antimicrobial surfaces and the nanocarriers for intracellular therapy. Understanding cell interaction with these emerging materials is an urgently important issue to promoting their wide applications. Experimental studies suggest that two-dimensional nanomaterials enter cells mainly through receptor-mediated endocytosis. However, the detailed molecular mechanisms and kinetic pathways of such processes remain unknown. Here, we combine computer simulations and theoretical derivation of the energy within the system to show that the receptor-mediated transport of two-dimensional nanomaterials, such as graphene nanosheet across model lipid membrane, experiences a flat vesiculation event governed by the receptor density and membrane tension. The graphene nanosheet is found to undergo revolution relative to the membrane and, particularly, unique self-rotation around its normal during membrane wrapping. We derive explicit expressions for the formation of the flat vesiculation, which reveals that the flat vesiculation event can be fundamentally dominated by a dimensionless parameter and a defined relationship determined by complicated energy contributions. The mechanism offers an essential understanding on the cellular internalization and cytotoxicity of the emerging two-dimensional nanomaterials.

Construction of a linker library with widely controllable flexibility for fusion protein design.

Flexibility or rigidity of the linker between two fused proteins is an important parameter that affects the function of fusion proteins. In this study, we constructed a linker library with five elementary units based on the combination of the flexible (GGGGS) and the rigid (EAAAK) units. Molecular dynamics (MD) simulation showed that more rigid units in the linkers lead to more helical conformation and hydrogen bonds, and less distance fluctuation between the N- and C-termini of the linker. The diversity of linker flexibility of the linker library was then studied by fluorescence resonance energy transfer (FRET) of cyan fluorescent protein (CFP)-yellow fluorescent protein (YFP) fusion proteins, which showed that there is a wide range of distribution of the FRET efficiency. Dissipative particle dynamics (DPD) simulation of CFP-YFP with different linkers also gave identical results with that of FRET efficiency analysis, and we further found that the combination manner of the linker peptide had a remarkable effect on the orientation of CFP and YFP domains. Our studies demonstrated that the construction of the linker library with the widely controllable flexibility could provide appropriate linkers with the desirable characteristics to engineer the fusion proteins with the expected functions.

A Filled-Honeycomb-Structured Crystal Formed by Self-Assembly of a Janus Polyoxometalate-Silsesquioxane (POM-POSS) Co-Cluster.

Clusters with diverse structures and functions have been used to create novel cluster-assembled materials (CAMs). Understanding their self-assembly process is a prerequisite to optimize their structure and function. Herein, two kinds of unlike organo-functionalized inorganic clusters are covalently linked by a short organic tether to form a dumbbell-shaped Janus co-cluster. In a mixed solvent of acetonitrile and water, it self-assembles into a crystal with a honeycomb superstructure constructed by hexagonal close-packed cylinders of the smaller cluster and an orderly arranged framework of the larger cluster. Reconstruction of these structural features via coarse-grained molecular simulations demonstrates that the cluster crystallization and the nanoscale phase separation between the two incompatible clusters synergistically result in the unique nano-architecture. Overall, this work opens up new opportunities for generating novel CAMs for advanced future applications.

Highly stretchable and super tough nanocomposite physical hydrogels facilitated by the coupling of intermolecular hydrogen bonds and analogous chemical crosslinking of nanoparticles.

Highly stretchable and super tough nanocomposite physical hydrogels (NCP gels) were fabricated by a facile and one-pot process. NCP gels show superior mechanical properties with tensile strength of 73 kPa-313 kPa and elongation at break of 1210-3420%. This is due to the effective strengthening mechanism: under stretching, the intermolecular hydrogen bonds can dynamically break and recombine to dissipate energy and homogenize the gel network. In addition, vinyl hybrid silica nanoparticles (VSNPs) can work as stress transfer centres to transfer stress to the grafted polymer chains.

Entropy-mediated mechanical response of the interfacial nanoparticle patterning.

The precise organization of nano-objects into well-defined patterns at interfaces is an outstanding challenge in the field of nanocomposites toward technologically important materials and devices. Herein, by means of computer simulations we show novel mechanomutable nanocomposites designed by binary mixtures of tethered Janus nanoparticles at the interface of a binary fluid mixture under mechanical pressure. Our simulations demonstrate that the nanoparticle organization in the systems undergo reversible transition between random state and long-ranged intercalation state, controlled by various structural parameters of the tethered chains and the applied pressure. The dynamical mechanism during the transition is explored through examining the diffusion trajectories of the nanoparticles confined at the interfaces. We provide a theoretical analysis of the lateral pressure induced by the tethered chains, which is fully supported by simulation data and reveals that the compression-induced transition is fundamentally attributed to the entropic effect from the tethered chains. Our study leads to a class of interface-reactive nanomaterials in which the transfer and recovery of interfacial nanopatterning presents precise and tunable mechanical responses.

Predictive supracolloidal helices from patchy particles.

A priori prediction of supracolloidal architectures from nanoparticle and colloidal assembly is a challenging goal in materials chemistry and physics. Despite intense research in this area, much less has been known about the predictive science of supracolloidal helices from designed building blocks. Therefore, developing conceptually new rules to construct supracolloidal architectures with predictive helicity is becoming an important and urgent task of great scientific interest. Here, inspired by biological helices, we show that the rational design of patchy arrangement and interaction can drive patchy particles to self-assemble into biomolecular mimetic supracolloidal helices. We further derive a facile design rule for encoding the target supracolloidal helices, thus opening the doors to the predictive science of these supracolloidal architectures. It is also found that kinetics and reaction pathway during the formation of supracolloidal helices offer a unique way to study supramolecular polymerization, and that well-controlled supracolloidal helices can exhibit tailorable circular dichroism effects at visible wavelengths.

Fibril aggregates formed by a glatiramer-mimicking random copolymer of amino acids.

Amyloid formation is now considered a universal and intrinsic property of all proteins, irrespective of their sequences. Therefore, it is interesting to see whether random copolymers of amino acids can also form amyloid aggregates. Here we use a copolymer of 4 amino acids, mimicking the clinically used drug Glatiramer, and demonstrate that it does form amyloid-like fibrils in the aqueous solution despite its random sequence structure. The fibrillar aggregates show an alanine-rich ß-sheet secondary structure, proving the high tolerance of amyloid aggregates to the sequence irregularity in poly(amino acid)s, and suggesting the potential application of random copolymers as amyloid materials.

Simulation and analysis of cellular internalization pathways and membrane perturbation for graphene nanosheets.

Clarifying the mechanisms of cellular interactions of graphene family nanomaterials is an urgent issue to the development of guidelines for safer biomedical applications and to the evaluation of health and environment impacts. By combining large-scale computer simulations, theoretical analysis, and experimental discussions, here we present a systematic study on the interactions of graphene nanosheets having various oxidization degrees with a model lipid bilayer membrane. In the mesoscopic simulations, we investigate the detailed translocation pathways of these materials across a 56 × 56 nm(2) membrane patch which allows us to fully consider the role of membrane perturbation during this process. A phase diagram regarding the transmembrane translocation mechanisms of graphene nanosheets is thereby obtained in the space of oxidization degree and particle size. Then, we propose a theoretical approach to analyze the effects of various initial equilibrium states of graphene nanosheets with membrane on their following cellular uptake process. Finally, we demonstrate that the simulation and theoretical results reproduce some important experimental findings towards the mechanisms of cytotoxicity and antibacterial activity of graphene materials. These results not only provide new insight into the cellular internalization mechanism of graphene-based nanomaterials but also offer fundamental understanding on their physicochemical properties which can be precisely tailored for safer biomedical and environment applications.

Unique dynamical approach of fully wrapping dendrimer-like soft nanoparticles by lipid bilayer membrane.

Wrapping dendrimer-like soft nanoparticles by cell membrane is an essential event in their endocytosis in drug and gene delivery, but this process remains poorly elucidated. Using computer simulations and theoretical analysis, we report the detailed dynamics of the process in which a lipid bilayer membrane fully wraps a dendrimer-like soft nanoparticle. By constructing a phase diagram, we firstly demonstrate that there exist three states in the interaction between a dendrimer and a lipid bilayer membrane, i.e., penetration, penetration and partial wrapping, and full wrapping states. The wrapping process of dendrimer-like nanoparticles is found to take a unique approach where the penetration of the dendrimer into the membrane plays a significant role. The analysis of various energies within the system provides a theoretical justification to the state transition observed from simulations. The findings also support recent experimental results and provide a theoretical explanation for them. We expect that these findings are of immediate interest to the study of the cellular uptake of dendrimer-like soft nanoparticles and can prompt the further application of this class of nanoparticles in nanomedicine.

Computer simulation of cell entry of graphene nanosheet.

Recent studies suggest the great promise of functionalized nanosized graphene in biomedical applications, but the transmembrane translocation mechanisms of this two-dimensional nanomaterial have remained poorly understood. Understanding how graphene interacts with cell membrane is related to the fundamental biological responses and cytotoxicity, and is thereby one critical issue to be resolved before further applications of graphene in nanomedicine. Here, by using computer simulations, we explore the translocation of graphene nanosheet (GN) across lipid bilayer membrane and the roles of size and edge of GN in the process. We discover the permeation of small GN into bilayer center through insertion and rotation driven by transbilayer lateral pressure. For large GNs, the translocation undergoes a vesiculation process driven by complicated energetic contributions. Circular GNs with smooth edge show faster translocation but similar mechanisms with square GNs. Our results are fundamentally essential for optimized design of GNs towards extensively biological and biomedical applications.

Harnessing Dynamic Covalent Bonds in Patchy Nanoparticles: Creating Shape-Shifting Building Blocks for Rational and Responsive Self-Assembly.

Using computational modeling, we suggest and demonstrate a novel class of building blocks for nanoparticle self-assembly, that is, shape-shifting patchy nanoparticles. These nanoparticles are designed by harnessing dynamic covalent bonds between nanoparticles and patches decorated on them. The breaking and reforming of these bonds in response to their environment allow the patches to undergo a structural rearrangement that shifts the location or number of patches. Our simulations for the assembled superstructures and kinetic pathway of two types of these building blocks demonstrate that shape-shifting patchy nanoparticles delicately meet two emerging design concepts of next generation materials: rational self-assembly and responsive matter. In this context, these nanoparticles may enable new generations of materials with reconfigurable property as well as controllable topologies in a dynamical manner.

Length-Dependent Assembly of a Stiff Polymer Chain at the Interface of a Carbon Nanotube.

We perform computer simulations to explore the suprastructures and their formation mechanism in the length-dependent assembly of a stiff polymer chain on the carbon nanotube surface. Three types of local conformations, that is, helical wrapping along the nanotube threadline, nonhelical loop, and straight extension along the nanotube, are identified in the very stiff polymer, depending on its length. It is revealed that the high elastic energy penalty and the large length of a long stiff polymer hinder its conformation transition on the nanotube, which impairs the match between the polymer beads and the structural details of the underlying nanotube surface and thereby weakens the polymer-nanotube interaction. A preferred chain length with an energy minimum is documented for the first time in the self-assemble of a stiff polymer at the nanotube interface. These data significantly advance our understanding of the superstructure formation by self-assembly of various chain-like molecules (e.g., polymer, surfactants, DNA, peptides, etc.) on carbon nanotube.