Morphology transformation of hybrid micelles self-assembled from rod-coil block copolymer and nanoparticles

Dynamic Processes and Mechanical Properties of Lipid-Nanoparticle Mixtures

In this study, we investigate the dynamic processes and mechanical properties of lipid nanoparticle mixtures in a melt via dissipation particle dynamic simulation. By investigating the distribution of nanoparticles in lamellar and hexagonal lipid matrices in equilibrium state and dynamic processes, we observe that the morphology of such composites depends not only on the geometric features of the lipid matrix but also on the concentration of nanoparticles. The dynamic processes are also demonstrated by calculating the average radius of gyration, which indicates the isotropic conformation of lipid molecules in the x-y plane and that the lipid chains are stretched in the z direction with the addition of nanoparticles. Meanwhile, we predict the mechanical properties of lipid-nanoparticle mixtures in lamellar structures by analyzing the interfacial tensions. Results show that the interfacial tension decreased with the increase in nanoparticle concentration. These results provide molecular-level information for the rational and a priori design of new lipid nanocomposites with ad hoc tailored properties.

Current State-of-the-Art and New Trends in Self-Assembled Nanocarriers as Drug Delivery Systems

Self-assembled nanocarrier drug delivery has received profuse attention in the field of diagnosis and treatment of diseases. These carriers have proved that serious life-threatening diseases can be eliminated evidently by virtue of their characteristic design and features. This review is aimed at systematically presenting the research and advances in the field of self-assembled nanocarriers such as polymeric nanoparticles, dendrimers, liposomes, inorganic nanocarriers, solid lipid nanoparticles, polymerosomes, micellar systems, niosomes, and some other nanoparticles. The self-assembled delivery of nanocarriers has been developed in recent years for targeting diseases. Some of the innovative attempts with regard to prolonging drug action, improving bioavailability, avoiding drug resistance, enhancing cellular uptake, and so on have been discussed. The discussion about various delivery systems included the investigation conducted at the preliminary stage, i.e., preclinical trials and assessment of safety. The clinical studies of some of the recently developed self-assembled products are currently at the clinical trial phase or FDA approved.

DPD Modelling of the Self- and Co-Assembly of Polymers and Polyelectrolytes in Aqueous Media: Impact on Polymer Science

This review article is addressed to a broad community of polymer scientists. We outline and analyse the fundamentals of the dissipative particle dynamics (DPD) simulation method from the point of view of polymer physics and review the articles on polymer systems published in approximately the last two decades, focusing on their impact on macromolecular science. Special attention is devoted to polymer and polyelectrolyte self- and co-assembly and self-organisation and to the problems connected with the implementation of explicit electrostatics in DPD numerical machinery. Critical analysis of the results of a number of successful DPD studies of complex polymer systems published recently documents the importance and suitability of this coarse-grained method for studying polymer systems.

Anchorage-Dependent Living Supramolecular Self-Assembly of Polymeric Micelles

Anchorage-dependent contact-inhibited growth usually refers to on-surface cell proliferation inhibited by the proximity of other cells. This phenomenon, prominent in nature, has yet to be achieved with polymeric micelles. Here, we report the control living supra-macromolecular self-assembly of elongated micelles with a liquid crystalline core onto a hydrophobic substrate via the synergetic interactions between the substrate and aggregates dispersed in solution. In this system, seed formation is a transient phenomenon induced by the adsorption and rearrangement of the core-swollen aggregates. The seeds then trigger the growth of elongated micelles onto the substrate in a living controllable manner until the contact with the substrate is disrupted. Brownian dynamic simulations show that this unique behavior is due to the fusion of the aggregates onto both ends of the anchored seeds. More important, the micelle length can be tuned by varying the substrate hydrophobicity, a key step toward the fabrication of intricate structures.

Engulfing Behavior of Nanoparticles into Thermoresponsive Microgels: A Mesoscopic Simulation Study

The engulfing of nanoparticles into microgels provides a versatile platform to design nano- and microstructured materials with various shape anisotropies and multifunctional properties. Manipulating the spontaneous engulfment process remains elusive. Herein, we report a mesoscopic simulation study on the engulfing behavior of nanoparticles into thermoresponsive microgels. The effects of the multiple parameters, including binding strength, temperature, and nanoparticle size, are examined systematically. Our simulation results disclose three engulfing states at different temperatures, namely full-engulfing, half-engulfing, and surface contact. The engulfing depth is determined by the complementary balance of interfacial elastocapillarity. Specifically, the van der Waals interaction of hybrid microgel-nanoparticle offers the capillary force while the internally networked structure of microgel reinforces the elasticity repulsion. Our study, validated by relevant experimental results, provides a mechanistic understanding of the interfacial elastocapillarity for nanoparticle-microgels.

Self-assembly of rod-coil diblock copolymer-nanoparticle composites in thin films: dissipative particle dynamics

In this study, the assembled structures of rod-coil diblock copolymer and nanoparticle blends were studied via dissipative particle dynamics (DPD). Thin films were composed of soft confinement DPD fluid beads and the fluctuating film structure was maintained during the simulation process. Analysis of the position of nanoparticles was done in the smectic lamellar phase of the rod-coil polymer matrix, and density distributions of rods, coils, and nanoparticles were obtained as functions of the size of the nanoparticle and the DPD repulsion constant between the rod and the nanoparticle. The distribution of nanoparticles was explained by using the concept of translational entropy of nanoparticles, stretching energy of the polymer chain, relative repulsion enthalpy of nanoparticles to rods or coils, and the effect of the liquid crystalline rod.

2D Chiral Stripe Nanopatterns Self-Assembled from Rod-Coil Block Copolymers on Microstripes

Chiral nanoarchitectures usually possess unique and intriguing properties. However, the construction of 2D chiral nanopatterns through polymer self-assembly is a challenge. Reported herein is the formation of chiral stripe nanopatterns through surface self-assembly of polypeptide-based rod-coil block copolymers on microstripes. The nanostripes align oblique to the boundary of the microstripes, resulting in the chirality of the nanopatterns. The chirality of the nanopatterns is closely related to the width of the microstripes, i.e., a narrower width results in higher chirality. Besides, the chiral sense of the nanopatterns can be regulated by the chirality of the polypeptide blocks. This work demonstrates the transmission of chirality from polymer to nanoarchitecture on a confined surface, which can guide the preparation of nanopatterns with tuned chiral features.

A Versatile Strategy for Unimolecular Micelle-Derived Hollow Polymer Nanoparticles as General Nanoreactors

We reported the synthesis of a well-defined hollow polymer nanoparticle derived from star-shaped unimolecular micelles. β-Cyclodextrin was first applied as an efficient macroinitiator to prepare a star-shaped PCL via ring-opening polymerization (ROP). Then, the star-shaped PCL was modified to be a macro-RAFT agent for photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of S-Cl monomers. The prepared unimolecular micelles can be photocross-linked under UV irradiation after a simple nucleophilic substitution reaction, which made -Cl groups to be -N₃ groups. After the selective removal of the PCL core, hollow polymer nanoparticles were achieved and exhibited to be a general nanoreactor strategy for the fabrication of nanocrystals with well-controlled architectures. Compared with unimolecular micelle templates, the nanocrystals prepared by hollow templates are absolutely pure as no polymer chains are embedded in the inorganic nanocrystals. In addition, by changing the concentration of the precursor, the structure of the nanocrystal can be changed from a normal spherical structure to a hollow structure.

Morphological transition of amphiphilic block copolymer/PEGylated phospholipid complexes induced by the dynamic subtle balance interactions in the self-assembled aggregates

Recently, there has been an increasing interest in the control of morphological transition of block copolymer aggregates. Here, we report how to control the morphological transition of methoxy polyethylene glycol–poly(d,l-lactic acid) (PDLLA–MPEG) by adding 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)] (DSPE–PEG). In the aggregates formed by dialyzing DSPE–PEG/PDLLA–MPEG mixed solutions against water, the two hydrophobic fatty acid tails of DSPE–PEG will preferentially anchor to the hydrophobic segment end of PDLLA–MPEG by interdigitating between these two tails and PDLLA segments. Consequently, DSPE–PEG and PDLLA–MPEG will form “ABA” temporary supra-amphiphiles in which A represents a poly(ethylene glycol) (PEG) chain segment and B is a mixed hydrophobic segment composed of PDLLA and DSPE segments; the repulsive force derived from the PEG segments of DSPE–PEG can affect the stability of “ABA” temporary supra-amphiphiles. Our results show that the dynamic subtle balance between the number of “ABA” temporary supra-amphiphiles formed and the strength of repulsive force between the PEG segments of DSPE–PEG drives the morphological structure of DSPE–PEG/PDLLA–MPEG aggregates to change from micelles to vesicles, then to semi-vesicles and finally to mixed micelles, with increasing DSPE–PEG additions.

Self-assembly of rod-coil block copolymers on a substrate into micrometer-scale ordered stripe nanopatterns

Micrometer-scale ordered stripe nanopatterns are readily constructed through an adsorption-assembly of rod-coil block copolymers on the substrate.

Polypeptide self-assemblies: nanostructures and bioapplications

Polypeptide copolymers can self-assemble into diverse aggregates. The morphology and structure of aggregates can be varied by changing molecular architectures, self-assembling conditions, and introducing secondary components such as polymers and nanoparticles. Polypeptide self-assemblies have gained significant attention because of their potential applications as delivery vehicles for therapeutic payloads and as additives in the biomimetic mineralization of inorganics. This review article provides an overview of recent advances in nanostructures and bioapplications related to polypeptide self-assemblies. We highlight recent contributions to developing strategies for the construction of polypeptide assemblies with increasing complexity and novel functionality that are suitable for bioapplications. The relationship between the structure and properties of the polypeptide aggregates is emphasized. Finally, we briefly outline our perspectives and discuss the challenges in the field.

Controllable multicompartment morphologies from cooperative self-assembly of copolymer-copolymer blends

Multicompartment nanostructures, such as microcapsules with clearly separated shell and core, are not easily accessible by conventional block copolymer self-assembly. We assess a versatile computational strategy through cooperative assembly of diblock copolymer blends to generate spherical and cylindrical compartmentalized micelles with intricate structures and morphologies. The co-assembly strategy combines the advantages of polymer blending and incompatibility-induced phase separation. Following this strategy, various nanoassemblies of pure AB, binary AB/AC and ternary AB/AC/AD systems such as compartmentalized micelles with sponge-like, Janus, capsule-like and onion-like morphologies can be obtained. The formation and structural adjustment of microcapsule micelles, in which the shell or core can be occupied by either pure or mixed diblock copolymers, were explored. The mechanism involving the separation of shell and core copolymers is attributed to the stretching force differences of copolymers which drive the arrangement of different copolymers in a pathway to minimize the total interfacial energy. Moreover, by adjusting block interactions, an efficient approach is exhibited for regulating the shell or core composition and morphology in microcapsule micelles, such as the transition from the "pure shell/mixed core" morphology to the "mixed shell/pure core" morphology in the AB/AC/AD micelle. This mesoscale simulation study identifies the key factors governing co-assembly of diblock copolymer blends and provides bottom-up insights towards the design and optimization of new multicompartment micelles.

Cellular Internalization of Rod-Like Nanoparticles with Various Surface Patterns: Novel Entry Pathway and Controllable Uptake Capacity

The cellular internalization of rod-like nanoparticles (NPs) is investigated in a combined experimental and simulation study. These rod-like nanoparticles with smooth, abacus-like (i.e., beads-on-wires), and helical surface patterns are prepared by the cooperative self-assembly of poly(γ-benzyl-l-glutamate)-block-poly(ethylene glycol) (PBLG-b-PEG) block copolymers and PBLG homopolymers. All three types of NPs can be internalized via endocytosis. Helical NPs exhibit the best endocytic efficacy, followed by smooth NPs and abacus-like NPs. Coarse-grained molecular dynamics simulations are used to examine the endocytic efficiency of these NPs. The NPs with helical and abacus-like surfaces can be endocytosed via novel "standing up" (tip entry) and "gyroscope-like" (precession) pathways, respectively, which are distinct from the pathway of traditional NPs with smooth surfaces. This finding indicates that the cellular internalization capacity and pathways can be regulated by introducing stripe patterns (helical and abacus-like) onto the surface of rod-like NPs. The results of this study may lead to novel applications of biomaterials, such as advanced drug delivery systems.

Co-assembly behaviour of Janus nanoparticles and amphiphilic block copolymers in dilute solution

This work not only provides insights into assembly behaviors of Janus nanoparticle solutions, but also offers strategies for permeable membranes.

Chemo-Enzymatic Synthesis of Perfluoroalkyl-Functionalized Dendronized Polymers as Cyto-Compatible Nanocarriers for Drug Delivery Applications

Among amphiphilic polymers with diverse skeletons, fluorinated architectures have attracted significant attention due to their unique property of segregation and self-assembly into discrete supramolecular entities. Herein, we have synthesized amphiphilic copolymers by grafting hydrophobic alkyl/perfluoroalkyl chains and hydrophilic polyglycerol [G2.0] dendrons onto a co-polymer scaffold, which itself was prepared by enzymatic polymerization of poly[ethylene glycol bis(carboxymethyl) ether]diethylester and 2-azidopropan-1,3-diol. The resulting fluorinated polymers and their alkyl chain analogs were then compared in terms of their supramolecular aggregation behavior, solubilization capacity, transport potential, and release profile using curcumin and dexamethasone drugs. The study of the release profile of encapsulated curcumin incubated with/without a hydrolase enzyme Candida antarctica lipase (CAL-B) suggested that the drug is better stabilized in perfluoroalkyl chain grafted polymeric nanostructures in the absence of enzyme for up to 12 days as compared to its alkyl chain analogs. Although both the fluorinated as well as non-fluorinated systems showed up to 90% release of curcumin in 12 days when incubated with lipase, a comparatively faster release was observed in the fluorinated polymers. Cell viability of HeLa cells up to 95% in aqueous solution of fluorinated polymers (100 μg/mL) demonstrated their excellent cyto-compatibility.

Nanoparticle Loading Induced Morphological Transitions and Size Fractionation of Coassemblies from PS-b-PAA with Quantum Dots

Inorganic nanoparticles play a very important role in the fabrication and regulation of desirable hybrid structures with block copolymers. In this study, polystyrene-b-poly(acrylic acid) (PS48-b-PAA67) and oleic acid-capped CdSe/CdS core/shell quantum dots (QDs) are coassembled in tetrahydrofuran (THF) through gradual water addition. QDs are incorporated into the hydrophilic PAA blocks because of the strong coordination between PAA blocks and the surface of QDs. Increasing the weight fraction of QDs (ω = 0-0.44) leads to morphological transitions from hybrid spherical micelles to large compound micelles (LCMs) and then to bowl-shaped structures. The coassembly process is monitored using transmission electron microscopy (TEM). Formation mechanism of different morphologies is further proposed in which the PAA blocks bridging QDs manipulates the polymer chain mobility and the resulting morphology. Furthermore, the size and size distribution of assemblies serving as drug carriers will influence the circulation time, organ distribution and cell entry pathway of assemblies. Therefore, it is important to prepare or isolate assemblies with monodisperse or narrow size distribution for biomedical applications. Here, the centrifugation and membrane filtration techniques are applied to fractionate polydisperse coassemblies, and the results indicate that both techniques provide effective size fractionation.

Nanoparticle-Induced Ellipse-to-Vesicle Morphology Transition of Rod-Coil-Rod Triblock Copolymer Aggregates

Cooperative self-assembly behavior of rod-coil-rod poly(γ-benzyl-l-glutamate)-block-poly(ethylene glycol)-block-poly(γ-benzyl-l-glutamate) (PBLG-b-PEG-b-PBLG) amphiphilic triblock copolymers and hydrophobic gold nanoparticles (AuNPs) was investigated by both experiments and dissipative particle dynamics (DPD) simulations. It was discovered that pure PBLG-b-PEG-b-PBLG copolymers self-assemble into ellipse-like aggregates, and the morphology transforms into vesicles as AuNPs are introduced. When the hydrophobicity of AuNPs is close to that of the copolymers, AuNPs are homogeneously distributed in the vesicle wall. While for the AuNPs with higher hydrophobicity, they are embedded in the vesicle wall as clusters. In addition to the experimental observations, DPD simulations were performed on the self-assembly behavior of triblock copolymer/nanoparticle mixtures. Simulations well reproduced the morphology transition observed in the experiments and provided additional information such as chain packing mode in aggregates. It is deduced that the main reason for the ellipse-to-vesicle transition of the aggregates is attributed to the breakage of ordered and dense packing of PBLG rods in the aggregate core by encapsulating AuNPs. This study deepens our understanding of the self-assembly behavior of rod-coil copolymer/nanoparticle mixtures and provides strategy for designing hybrid polypeptide nanostructures.

Revealing the morphological architecture of a shape memory polyurethane by simulation

The lack of specific knowledge of the network structure in shape memory polymers (SMPs) has prevented us from gaining an in-depth understanding of their mechanisms and limited the potential for materials innovation. This paper firstly reveals the unit-cell nanoscale morphological architecture of SMPs by simulation. The phase separated architecture of a segmented shape memory polyurethane (SMPU) with a 30 wt% hard segment content (HSC, 4,4’-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BDO)) showing good shape memory properties was investigated by dissipative particle dynamics (DPD) simulations. A linked-spherical netpoint-frame phase of MDI, a matrix-switch phase of polycaprolactone (PCL) and a connected-spider-like interphase for BDO were obtained for this SMPU. The BDO interphase can reinforce the MDI network. Based on these simulation results, a three-dimensional (3D) overall morphological architectural model of the SMPU can be established. This theoretical study has verified, enriched and integrated two existing schematic models: one being the morphological model deduced from experiments and the other the frame model for SMPs reported before. It can serve as a theoretical guide for smart polymeric materials design. This method for the simulation of polymer structure at the nanoscale can be extended to many areas such as photonic crystals where nanoscale self-assembly plays a vital role.

Computational and experimental approaches for investigating nanoparticle-based drug delivery systems

Most therapeutic agents suffer from poor solubility, rapid clearance from the blood stream, a lack of targeting, and often poor translocation ability across cell membranes. Drug/gene delivery systems (DDSs) are capable of overcoming some of these barriers to enhance delivery of drugs to their right place of action, e.g. inside cancer cells. In this review, we focus on nanoparticles as DDSs. Complementary experimental and computational studies have enhanced our understanding of the mechanism of action of nanocarriers and their underlying interactions with drugs, biomembranes and other biological molecules. We review key biophysical aspects of DDSs and discuss how computer modeling can assist in rational design of DDSs with improved and optimized properties. We summarize commonly used experimental techniques for the study of DDSs. Then we review computational studies for several major categories of nanocarriers, including dendrimers and dendrons, polymer-, peptide-, nucleic acid-, lipid-, and carbon-based DDSs, and gold nanoparticles. This article is part of a Special Issue entitled: Membrane Proteins edited by J.C. Gumbart and Sergei Noskov.

Controllable hierarchical microstructures self-assembled from multiblock copolymers confined in thin films

Hierarchical microstructures self-assembled from A(BC)n multiblock copolymers confined between two solid surfaces were explored by dissipative particle dynamics simulations. The strategy using confinement allows us to generate hierarchical microstructures with various numbers and different orientations of small-length-scale lamellae. Except for the hierarchical lamellar microstructures with parallel or perpendicular arrangements of small-length-scale lamellae, the coexistence of two different hierarchical lamellae was also discovered by varying the film thickness. The dynamics of hierarchical microstructure formation was further examined. It was found that the formation of the hierarchical microstructures exhibits a stepwise manner where the formation of small-length-scale structures lags behind that of large-length-scale structures. The present work could provide guidance for controllable manufacture of hierarchical microstructures.

Colloidal micelles of block copolymers as nanoreactors, templates for gold nanoparticles, and vehicles for biomedical applications

Target drug delivery methodology is becoming increasingly important to overcome the shortcomings of conventional drug delivery absorption method. It improves the action time with uniform distribution and poses minimum side effects, but is usually difficult to design to achieve the desire results. Economically favorable, environment friendly, multifunctional, and easy to design, hybrid nanomaterials have demonstrated their enormous potential as target drug delivery vehicles. A combination of both micelles and nanoparticles makes them fine target delivery vehicles in a variety of biological applications where precision is primarily required to achieve the desired results as in the case of cytotoxicity of cancer cells, chemotherapy, and computed tomography guided radiation therapy.

Nano-pipette directed transport of nanotube transmembrane channels and hybrid vesicles

Using computational modeling, we simulate the interactions between a nanopipette and transmembrane, end-functionalized nanotubes that are localized within flat bilayers or nanoscopic vesicles. The functional groups (hairs) provide a "handle" for the moving pipette to controllably pick up and move the nanotubes to specific locations in the flat membrane, or the hybrid vesicle to specified regions on a surface. The ability to localize these hybrid vesicles on surfaces paves the way for creating nanoreactor arrays in fluidic devices.

Mechanical properties of designed multicompartment gels formed by ABC graft copolymers

In the present work, we designed a multicompartment gel by taking advantage of the ABC graft copolymer with a solvophilic A backbone and solvophobic B and C grafts. The mechanical properties of such designed gels were investigated by a combination of dissipative particle dynamics simulation and a nonequilibrium deformation technique. The extensional moduli of multicompartment gels were found to be dependent on polymer concentration and architectural parameters of the graft copolymers (the sequence of graft arms and the position of the graft points). The graft copolymer solutions undergo a sol-gel transition as the polymer concentration increases. This leads to an abrupt increase in the extensional modulus. The studies also revealed that the multicompartment gels of graft copolymers exhibit higher extensional moduli than those of nonmulticompartment gels of graft copolymers and triblock copolymer gels. The position of graft points plays another important role in determining the extensional moduli of the multicompartment gels. The effects of graft positions on the gel modulus were found to be associated with the bridging fraction of graft copolymer chains. The results gained through the present work may provide useful guidance for designing high-performance gels.

Toroid formation through self-assembly of graft copolymer and homopolymer mixtures: experimental studies and dissipative particle dynamics simulations

Self-assembly of mixture systems containing poly(acrylic acid)-g-poly(γ-benzyl-L-glutamate) graft copolymers (PAA-g-PBLG) and PBLG homopolymers in aqueous solution was investigated by both experiments and computer simulations. It was found that the aggregate morphologies, such as rods, curved rods, and toroids, could be tuned by the homopolymer content. The toroidal micelles with uniform size were formed when the homopolymer content in the hybrid aggregates is higher. The effect of added water content on the toroid formation process was studied. Rods and curved rods were observed sequentially before formation of toroids. We also performed dissipative particle dynamics (DPD) simulations to verify the structure transition and explore the formation mechanism of the toroidal aggregates. The DPD results are in good agreement with the experimental findings and provide additional information such as chain distribution in aggregates, which is difficult to be gained through experiments. On the basis of the experimental and simulation results, the formation mechanism of the toroidal micelles was suggested.

Tuning self-assembly and photo-responsive behavior of azobenzene-containing triblock copolymers by combining homopolymers

The self-assembly behavior of azobenzene-based triblock copolymers poly(ethylene oxide)-block-polystyrene-block-poly[6-(4-methoxy-4'-oxy-azobenzene) hexyl methacrylate] (PEO-b-PS-b-PMMAZO) and their mixtures with PS or PMMAZO homopolymers was studied by means of transmission electron microscopy, scanning electron microscopy, laser light scattering and UV-vis spectrophotometry. It was found that pure block copolymers self-assembled into spherical micelles with core-shell structures. The addition of PS or PMMAZO homopolymers can not only increase the aggregate size but also have a significant influence on the photo-isomerization behavior and photo-deformation behavior of the aggregate. The photo-isomerization study revealed that a complete trans-cis or cis-trans isomerization of azobenzene chromophores can be acquired when irradiated with UV or visible light for polymers both in organic solutions and in micelles. The photo-isomerization rate of azobenzene chromophores increases when PS homopolymers were incorporated into micelles, while with the addition of PMMAZO homopolymers, it decreases. The photo-induced elongation of the aggregates by irradiation of a linearly polarized laser was observed for all the samples, and the deformation degree increases with the weight fraction of azobenzene groups in the parent copolymers, as well as the PMMAZO content for the mixture micelles.