Self-assembly Characteristics Research Articles

Controlled Self-Assembly of Amphiphilic Random Copolymers into Folded Micelles and Nanostructure Materials.

In this review, we report controlled self-assembly systems of amphiphilic random copolymers in aqueous or organic media and the solid state to produce folded micelles, related nanoaggregates, vesicles, and microphase separation materials. The key features of random copolymer self-assemblies are 1) self-folding of polymer chains, 2) precision self-assembly of side chains, and 3) dynamic self-sorting and selective recognition. Typically, random copolymers bearing hydrophilic poly(ethylene glycol) and hydrophobic alkyl groups folded into small unimer micelles (~10 nm) via the association of the hydrophobic groups in water. Importantly, those random copolymers afforded precision intermolecular self-assembly into multichain micelles; the size, aggregation number, and thermoresponsive properties can be controlled as desired by tuning their molecular weight, composition, and side chains. The binary mixture of different random copolymers further self-sorted via chain exchange in water to simultaneously form discrete micelles. Namely, amphiphilic random copolymers can dynamically recognize themselves in complex media like natural biomolecules and proteins. Amphiphilic random copolymers opened new ways to create self-assembled materials with well-defined nanostructures and compartments, dynamic recognition properties, and functions.

Proanthocyanidin-crosslinked collagen/konjac glucomannan hydrogel with improved mechanical properties and MRI trackable biodegradation for potential tissue engineering scaffolds.

Collagen (Col) has been intensively exploited as a biomaterial for its excellent biocompatibility, biodegradation and bioactivity. However, the poor mechanical properties and rapid biodegradation of reconstituted collagen hydrogels have always been the bottlenecks for their further development especially for vascular tissue engineering. Herein, based on the self-assembly characteristics of collagen, a ternary hydrogel scaffold, comprising rigid collagen molecules, flexible konjac glucomannan (KGM) chains and biocompatible crosslinkers of proanthocyanidin (PA), has been designed to achieve a synergistic interaction for essentially optimizing the mechanical properties of the so-obtained Col/KGM/PA hydrogel, which possesses not only substantially improved strength but also good elasticity. PA endows these scaffolds with controllable biodegradation and anti-calcification and antioxidant activities. TEM discovered the co-existence of two types of fibrils with distinctly different arrangement patterns, explaining the contribution of KGM macromolecules to elasticity generation. The in vivo variations of Col/KGM/PA implants are visualized in real-time by magnetic resonance imaging (MRI). Moreover, a quantitative technique of MRI T2-mapping combined with histology is designed to visualize the in vivo biodegradation mechanism of layer-by-layer erosion for these hydrogels. Simultaneously, three different relationships between the respective processes of in vivo degradation and in vivo dehydration of these controlled hydrogel implants were clearly revealed by this technique. Such a designed Col/KGM/PA composite hydrogel realizes the essential integration of good biocompatibility, controllable biodegradation and improved mechanical properties for developing a desired scaffold material for tissue engineering applications.

Enzyme mimics based on self-assembled peptides for di(2-ethylhexyl)phthalate degradation.

Enzyme mimics have been developed by imitating and incorporating specific features of native enzymes to achieve catalytic activity, and are expectedly comparable to that of native enzymes. Here, inspired by the "catalytic triad" in serine proteases, a series of peptide-based enzyme mimics were designed to follow the rational design principle of peptides via self-assembly, and were further applied in the degradation of di(2-ethylhexyl)phthalate (DEHP). The relationship of the structure of enzyme mimics with their degradation activity was analyzed by transmission electron microscopy, fluorescence spectroscopy, circular dichroism, Raman spectroscopy, X-ray diffraction spectroscopy, and computational modeling. These results show that the hydrophobic skeleton, amino acid sequence, species, and periodic distribution have important effects on the structure of the peptide sequence and the number of hydrogen bonds; in addition, pH can also affect the self-assembly characteristics of peptides and the formation of stable fibers, which are all closely linked to the catalytic activity of the enzyme mimics. The self-assembled peptides had a stable fibrous morphology and secondary structure after the DEHP degradation assay. The enzyme mimics with high catalytic activity constructed from the self-assembled peptides may provide guidance for the future degradation of DEHP in food packaging or water treatment, and also give insights into the design of enzyme mimics in other related fields.

Metal self-assembly mimosine peptides with enhanced antimicrobial activity: towards a new generation of multitasking chelating agents.

Mimosine is a non-protein amino acid with various properties, such as antibacterial, anti-inflammatory, anti-cancer and anti-virus among others. Due to its structural similarity with deferiprone (DFP), mimosine is a potential excellent metal chelator. In the present work, we combine experimental and theoretical (DFT) approaches in order to investigate the properties of mimosine peptides. Six different peptides were synthesized and their complex stoichiometry and stability were characterized by means of UV-Vis spectrophotometry. Then, the binding mode and self-assembly features of the peptides were evaluated using a DFT approach, taking into account different number of mimosine amino acids and varying the length of the spacer between the mimosine residues, and there was good agreement between experimental data and computational calculations. Further elucidations of the structural properties of these peptides allowed us to propose improvements in the structure of the mimosine moiety which can lead to enhanced affinity for high-valent metals. Moreover, we demonstrate that these peptides show an anti-microbial activity against Gram positive bacteria that is enhanced by the formation of a complex with iron(iii) ions. The mimosine peptides could be an alternative to antimicrobial peptides (AMPs), which are expensive and susceptible to proteolytic degradation. In summary, in the present work, we propose a new generation of multipurpose mimosine-based peptides as new metal self-assembly chelators which could be a turning point in biomedical and nanotechnological applications.

A first-principle mechanism for particulate aggregation and self-assembly in stratified fluids

An extremely broad and important class of phenomena in nature involves the settling and aggregation of matter under gravitation in fluid systems. Here, we observe and model mathematically an unexpected fundamental mechanism by which particles suspended within stratification may self-assemble and form large aggregates without adhesion. This phenomenon arises through a complex interplay involving solute diffusion, impermeable boundaries, and aggregate geometry, which produces toroidal flows. We show that these flows yield attractive horizontal forces between particles at the same heights. We observe that many particles demonstrate a collective motion revealing a system which appears to solve jigsaw-like puzzles on its way to organizing into a large-scale disc-like shape, with the effective force increasing as the collective disc radius grows. Control experiments isolate the individual dynamics, which are quantitatively predicted by simulations. Numerical force calculations with two spheres are used to build many-body simulations which capture observed features of self-assembly.

Polymerization-Induced Polymersome Fusion.

The dynamic interactions of membranes, particularly their fusion and fission, are critical for the transmission of chemical information between cells. Fusion is primarily driven by membrane tension built up through membrane deformation. For artificial polymersomes, fusion is commonly induced via the external application of a force field. Herein, fusion-promoted development of anisotropic tubular polymersomes (tubesomes) was achieved in the absence of an external force by exploiting the unique features of aqueous ring-opening metathesis polymerization-induced self-assembly (ROMPISA). The out-of-equilibrium tubesome morphology was found to arise spontaneously during polymerization, and the composition of each tubesome sample (purity and length distribution) could be manipulated simply by targeting different core-block degrees of polymerization (DPs). The evolution of tubesomes was shown to occur via fusion of “monomeric” spherical polymersomes, evidenced most notably by a step-growth-like relationship between the fraction of tubular to spherical nano-objects and the average number of fused particles per tubesome (analogous to monomer conversion and DP, respectively). Fusion was also confirmed by Förster resonance energy transfer (FRET) studies to show membrane blending and confocal microscopy imaging to show mixing of the polymersome lumens. We term this unique phenomenon polymerization-induced polymersome fusion, which operates via the buildup of membrane tension exerted by the growing polymer chains. Given the growing body of evidence demonstrating the importance of nanoparticle shape on biological activity, our methodology provides a facile route to reproducibly obtain samples containing mixtures of spherical and tubular polymersomes, or pure samples of tubesomes, of programmed length. Moreover, the capability to mix the interior aqueous compartments of polymersomes during polymerization-induced fusion also presents opportunities for its application in catalysis, small molecule trafficking, and drug delivery.

Self-Assembled Nanomaterials for Enhanced Phototherapy of Cancer.

Following the wisdom of nature to assemble functional candidates into exquisite nanoarchitectures is emerging as a promising field of research and has been widely applied in biomedical sciences. Owing to their excellent properties of structural controllability, functional diversity, dynamic adjustability, and prominent biocompatibility, the self-assembled nanoarchitectures come to play a pivotal role in fighting against cancer. This review outlines the most up-to-date developments in constructing phototherapeutic nanomaterials for photodynamic and photothermal therapy (PDT and PTT) of tumors, with emphasis on design ideas, building blocks, and advantageous characteristics of self-assembly. The prominent activities of cancer therapy obtained by these photoinduced nanotheranostics are also explored in-depth, together with the connections between the specific nanostructures and unique features, providing a comprehensive understanding of the self-assembled nanomaterials in improving the outcomes of PDT and PTT. This review aims to highlight the significance of self-assembled nanomaterials in enhancing phototherapeutic efficacy and to promote its development in various research interests ranging from material science and nanoscience to biomedicine and clinical medicine.

Controlling the Periodically Ordered Nanostructures in Ceramics: A Macromolecule-Guided Strategy.

Microscopic structures have a significant influence on the properties of ceramics. The development of macromolecular self-assembly has allowed for control over microscopic structures of ceramics to prepare ceramics with diverse compositions and ordered nanostructures. Herein, recent progress in the preparation of ceramics with periodically ordered nanostructures guided by phase-separated macromolecules are reviewed, which can be summarized as a general strategy termed the "macromolecule-guided strategy." Moreover, two different subcategories, namely, the macromolecule-templated method and the macromolecule-precursor method, are illustrated. In the former method, amphiphilic macromolecules are used as templates to guide the assembly of inorganic species into ordered nanostructures, which are subsequently converted into ceramics; in the latter method, amphiphilic macromolecules containing non-volatile elements are used as the single-source precursors for ordered ceramics. It is believed that the unique diversity and tunable features of macromolecular self-assembly might offer unprecedented opportunities in the development of functional ceramics for various applications.

Metal-based surface active ionic liquids: Self-assembling characteristics and C[sbnd]C bond functionalization of tertiary amines with TMSCN in aqueous micellar solutions

Metal-based surface active ionic liquids (MSAILs), 1-alkyl-3-methyl imidazoliumtetrachloromanganate [Cnmim][MnCl4]2− (n= 8,10,12) have been synthesized and characterized for self-assembling behavior in aqueous solution using tensiometry, fluorescence, conductivity, dynamic light scattering (DLS) and transmission electron microscopy (TEM) techniques. MSAILs have exhibited 4 to 5 fold higher surface activity as compared to the non-metal based surface active ionic liquids. MSAILs micellar solutions have been successfully used for C(sp3)-H functionalized oxidative cyanation of the tertiary amines. Oxidative Strecker reaction was carried out with different concentrations of the MSAILs, cyanide source (TMSCN) and substrate, and moderate to very high yields (up to 95%) could be achieved in 3–4 h. Usually, cyanation of tertiary amines is carried out in organic solvents under harsh conditions without recycling of the catalyst. Herein aqueous MSAILs micellar solutions have been used as a solvent, catalyst as well as template with a good recycling ability, thus making the approach simpler, greener, and sustainable.

Consecutive Supramolecular Polymerization of a Rylene-Based Twistacene.

The synthesis and self-assembling features of twistacene 1 are reported. The supramolecular polymerization of 1 displays a consecutive pathway to afford slipped (AggI) and rotationally displaced (AggII) aggregates conditioned by the formation of intramolecularly H-bonded pseudocycles. In methylcyclohexane, both AggI and AggII are highly stable and the interconversion of the kinetically controlled AggI into the thermodynamically controlled AggII takes several weeks to occur. The utilization of toluene as solvent changes the energetic level for both aggregates and favors a faster conversion of AggI into AggII within a period of minutes. This conversion can be accelerated by the addition of seeds. Furthermore, concentration dependent kinetic studies demonstrate the consecutive character of the supramolecular polymerization of 1.

Promoting Dendrimer Self-Assembly Enhances Covalent Layer-by-Layer Encapsulation of Pancreatic Islets.

For type 1 diabetics, islet transplantation can induce beneficial outcomes, including insulin independence and improved glycemic control. The long-term function of the grafted tissue, however, is challenged by host inflammatory and immune responses. Cell encapsulation can decrease detrimental host responses to the foreign implant, but standard microencapsulation imparts large transplant volumes and impaired metabolite and nutrient diffusion. To mitigate these effects, we developed an efficient covalent Layer-by-Layer (cLbL) approach for live-cell nanoencapsulation, based on oppositely charged hyperbranched polymers functionalized with complementary Staudinger ligation groups. Reliance on cationic polymers for cLbL, however, is problematic due to their poor biocompatibility. Herein, we incorporated the additional feature of supramolecular self-assembly of the dendritic polymers to enhance layer uniformity and decrease net polymer charge. Functionalization of poly (amino amide) (PAMAM) with triethoxysilane decreased polymer charge without compromising the uniformity and stability of resulting nanoscale islet coatings. Encapsulated pancreatic rat islets were viable and functional. The implantation of cLbL islets into diabetic mice resulted in stable normoglycemia, at equivalent dosage and efficiency as uncoated islets, with no observable alterations in cellular engraftment or foreign body responses. By balancing multi-functionality and self-assembly, nano-scale and stable covalent layer-by-layer polymeric coatings could be efficiently generated onto cellular organoids, presenting a highly adaptable platform for broad use in cellular transplantation.

Biomineralization synthesis of HBc-CuS nanoparticles for near-infrared light-guided photothermal therapy

Transition metal sulfide nanoparticles provide efficient tumor photothermal therapy under near-infrared light, while suffering from poor chemical stability and biocompatibility. Protein scaffolds are attractive templates to fabricate various inorganic nanostructures, due to their inherent capabilities of molecular recognition and self-assembly characteristics. Herein, a straightforward method is demonstrated for efficiently synthesizing CuS nanoparticles inside the inner cavity of the genetically modified hepatitis B core protein virus-like particles (HBc VLPs) via the affinity of histidine tags to copper ions. The monodispersed and well-defined HBc-CuS VLPs have been yielded with high efficiency and used as a potential photothermal agent for cancer therapy due to their excellent photothermal conversion efficiency, high cellular uptake and biocompatibility.

Graphene oxide foam fabricated with surfactant foaming method for efficient solar vapor generation

Solar vapor generation is emerging as a reliable way to directly transfer solar illumination to vapor evaporation. Graphene-based porous photothermal materials are considered as promising absorbers in this system owing to the broadband absorption and excellent photothermal properties. In this paper, we construct a three-dimensional (3D) graphene oxide foam with a convenient surfactant foaming method for solar vapor generation. Abundant porous channels and good hydrophilicity are simultaneously achieved by means of the self-assembly and hydrophilic characteristics of the foaming agents. Detailed light absorption and vapor generation tests reveal that the foam monolith possesses an absorption rate at ~ 89% and a considerable solar vapor efficiency of ~ 81% under a solar intensity of 1 kW m−2.

A rational comparison of the effects of halogen atoms incorporated into the polymer donors on the performance of polymer solar cells

Despite the high performance polymer solar cells obtained by the fluorinated or chlorinated polymer donors, there is no effective guideline for how to choose a reasonable halogen atom incorporated into copolymer donors when designing organic photovoltaic materials. Two polymers of PBDT-F-3T2C containing F atom and PBDT-Cl-3T2C containing Cl atom are designed and synthesized. A direct comparison of the effects of fluorine and chlorine atom on the properties of the copolymer and resulting device performance is systematically studied. It can be found that both of the chlorine and fluorine atoms can effectively reduce the HOMO and LUMO levels, but chlorine atom is revealed to possess stronger downshifting ability for energy levels than fluorine atom in the copolymers. On the other hand, compared with the chlorine atom with larger atomic radius, the smaller fluorine atom possess strong self-assembly feature and negligible steric hindrance, enable the PBDT-F-3T2C with higher crystallinity and solution temperature-dependent aggregation behavior than PBDT-Cl-3T2C. The higher absorption coefficient, more favorable morphology, higher and more balanced charge mobilies endow the PBDT-F-3T2C with higher device performance than PBDT-Cl-3T2C (11.67% vs 10.19%). In addition, the performance of the 1,2,4-trimethylbenzene (TMB) solvent processed devices is also sensitive to halogenate atoms. An expressive PCE of 10.04% is obtained for F-containing devices, which is almost double higher than the Cl-containing devices. These results would provide a guideline for rational incorporation of halogen atoms into the polymer donors for high performance polymer solar cells. • Two polymer donors of PBDT-F-3T2C and PBDT-Cl-3T2C are designed and synthesized. • The effects of F and Cl atom on the properties of the polymers and PSCs. • A PCE of 11.67% obtained for halogenated solvent processed device. • Non-halogenated solvent processed devices yield a PCE over 10%.

Amino acid conformations control the morphological and chiral features of the self-assembled peptide nanostructures: Young investigators perspective

HypothesisA variety of nanostructures with different chiral features can be self-assembled from short peptides with highly similar sequences. We hypothesize that these supramolecular nanostructures are ruled by the constituent amino acid residues which adopt their conformations under the influence of intra-/inter-molecular interactions during peptide self-assembly. ApproachThrough reviewing recent advances in the self-assembly of short peptides and focusing on the relationship between amino acid conformations, peptide secondary structures and intra-/inter-molecular interactions within the supramolecular architectures, we aim to rationalize the complex interactive processes involved in the self-assembly of short, designed peptides. ResultsGiven the highly complexing interactive processes, the adoption of amino acid conformations and their control over peptide self-assembly consist of 4 main steps: (1) Each amino acid residue adopts its unique conformation in a specific sequence; (2) The sequence exhibits its own main chain geometry and determines the propensity of the intermolecular alignment within the building block; (3) The structural propensity of the building block and the packing mode between them determine the self-assembled structural features such as twisting, growth and chirality; (4) In addition to intra-/inter-molecular interactions, inter-sheet and inter-building block interactions could also affect the residue conformations and nanostructures, causing structural readjustment.

3D Graphene-Oil Absorbent Resin Hybrid Gel as High Efficiency Oil Absorbent Material

A new type of high oil absorbent resin (OAR) was synthesized by emulsion polymerization with lauryl methacrylate (LMA) and butyl methacrylate (BMA) as soft monomers, and methyl methacrylate (MMA) as hard monomer. A graphene-oil absorbent resin hybrid aerogel (G-OAR aerogel) was therefore prepared through the hydrothermal reduction of graphene oxide colloidal solution and the oil absorbent resin emulsion. The self-assembly characteristics of graphene oxide in hydrothermal treatment resulted in the formation of 3D porous structure for G-OAR aerogel. The component, morphology and hydrophobicity of G-OAR aerogel were characterized by FTIR, XRD, SEM and contact angle, and its absorption capacities to different kinds of organic solvents and oils were also been investigated. The results indicate that the absorption capacities of G-OAR aerogel reach up to 40-50 g/g for low density organic solvents, like acetone, anhydrous alcohol, cyclohexane, toluene, ethyl acetate and diesel. The absorption capacities are 80-90 g/g for high density and weak polarity organic solvents, like phenixin and castor oil. The good oil absorption property makes it show high potential in the application of wastewater treatment and oil leakage.

Salt and phytochemical assisted modulation of self-assembly characteristics of Polysorbate-80 in aqueous medium

Polysorbate 80 is one of the most widely used solubilizing agents in food, cosmetic and pharmaceutical industries. Influences of different classes of solubilizates and additives on its self-assembly characteristics are however, not sufficiently understood yet. In this manuscript, we show how common water structure making salt NaCl, and lipophilic phytochemicals like curcumin and lavender oil help in modulating the structure of Polysorbate 80 micelles in aqueous medium. Our DLS, SANS and rheological studies show that NaCl induces sphere-to-rod growth of polysorbate 80 micelles at the room temperature. Micellar solubilizations of the phytochemicals, which were found to be facilitated with increase in temperature, induce only a marginal growth of the micelles up to the highest level of solubilization. Their presence however, helps in modulating the NaCl induced micellar growth behavior in the tween 80 solutions leading to observation of micelle-to-vesicle structural transition at 2% lavender oil concentration. The phytochemical solubilized micellar solutions could be converted to alginate based hydrogel beads and patches that can freely release micellar phytochemical in aqueous medium. Our results shed light on possible ways of modulating the solubilization behavior, self-assembly characteristics and rheological properties of aqueous system of polysorbate 80, which could be important for their applications.

Modification of block copolymer lithography masks by O2/Ar plasma treatment: insights from lift-off experiments, nanopore etching and free membranes

Block copolymer lithography allows for the large-area patterning of surfaces with self-assembled nanoscale features. The created nanostructured polymer films can be applied as masks in common lithography processing steps, such as lift-off and etching for pattern replication and transfer. In this work, we discuss an approach to improve the pattern replication efficiency by modification of the polymer mask prior to lithographical use by means of an O2/Ar plasma treatment. We present a much better quality of pattern replication without loss of features, along with a precise tunability of feature sizes, that can be achieved by short mask treatment. We point out a correlation between nanopore position within the ordered arrays, expressed by its coordination number, the nanopore shape and the replication efficiency. Our experimental strategy to explain these correlations combines the indirect investigation of patterns replicated from the modified polymer masks and direct investigation of the mask top and bottom. Pattern replication is performed either in the form of gold nanodot arrays created via lift-off or nanopores transferred into a SiO2 substrate by reactive ion etching. The direct analysis of free polymer membranes released from the substrate reveals the nanopore shape at the mask top and bottom surfaces.

2-Deoxyglucose-Modified Folate Derivative: Self-Assembling Nanoparticle Able to Load Cisplatin.

Folic acid has been widely introduced into nano-drug delivery systems to give nanoparticle-targeted characteristics. However, the poor water solubility of folic acid may hinder the exploitation of its ability to load antineoplastic drugs. In the present study, we designed a new folate derivative (FA-2-DG) synthesized from folic acid and 2-Deoxyglucose (2-DG). The aim of this study was to evaluate the self-assembly characteristics of FA-2-DG, and its ability of loading cisplatin. The critical micelle concentration was 7.94 × 10−6 mol L−1. Fourier transform infrared spectroscopy indicated that hydrogen bonding interaction is a main driving force for the self–assembly of FA-2-DG. The particle was stable in pure water or 0.5% bovine serum albumin dispersions. By forming a coordination bond, the particles assembled from FA-2-DG can load cisplatin. The loading efficiency was maximal when the molar ratio of FA-2-DG to cisplatin was 2:1.

Catalyst: Size Distribution in Self-Assembly Matters

Dafni Moatsou completed her PhD in chemistry at the University of Warwick in 2015, was a Marie Sklodowska-Curie fellow at the Adolphe Merkle Institute until 2017, and is a junior research group leader at the Karlsruhe Institute of Technology, where she focuses on sequence control and self-assembly of polymers. Rachel O’Reilly completed her PhD in 2003 at Imperial College London. She currently holds a chair in chemistry within the College of Engineering and Physical Sciences at the University of Birmingham. In August 2018 she became the head of the School of Chemistry. Her research targets the design, synthesis, and application of polymeric materials, where control over architecture, functionality, and reactivity are central to their application.