Effects of Secondary Structures and pH on the Self-Assembly of Poly(ethylene glycol)-b-polytyrosine.

Different from conventional synthetic polymers, polypeptides exhibit a distinguishing characteristic of adopting specific secondary structures, including random coils, α-helixes, and ß-sheets. The conformation determines the rigidity and solubility of polypeptide chains, which further direct the self-assembly and morphology of the nanostructures. We studied the effect of distinct secondary structures on the self-assembly behavior of polytyrosine (PTyr)-derived amphiphilic copolymers. Two block copolymers of enantiopure poly(ethylene glycol)-b-poly(l-tyrosine) (PEG-b-P(l-Tyr)) and racemic poly(ethylene glycol)-b-poly(dl-tyrosine) (PEG-b-P(dl-Tyr)) were synthesized through the ring-opening polymerization of l-tyrosine N-thiocarboxyanhydride (l-Tyr-NTA) and dl-tyrosine N-thiocarboxyanhydride (dl-Tyr-NTA), respectively, by using poly(ethylene glycol) amine as the initiator. PEG44-b-P(l-Tyr)10 adopts a ß-sheet conformation and self-assembles into rectangular nanosheets in aqueous solutions, while PEG44-b-P(dl-Tyr)9 is primarily in a random coil conformation with a tiny content of ß-sheet structures, which self-assembles into sheaf-like nanofibrils. A pH increase results in the ionization of phenolic hydroxyl groups, which decreases the ß-sheet content and increases the random coil content of the PTyr segments. Accordingly, PEG44-b-P(l-Tyr)10 and PEG44-b-P(dl-Tyr)9 self-assemble to form slender nanobelts and twisted nanoribbons, respectively, in alkaline aqueous solutions. The secondary structure-driven self-assembly of PTyr-derived copolymers is promising to construct filamentous nanostructures, which have potential for applications in controlled drug release.

Achiral substituent- and stoichiometry-controlled inversion of supramolecular chirality and circularly polarized luminescence in ternary co-assemblies.

Handedness inversion of supramolecular chirality and circularly polarized luminescence (CPL) in assembled systems containing more than two components with higher complexity is of prominent importance to simulate biological multicomponent species and design advanced chiral materials, but it remains a considerable challenge. Herein, we have successfully developed ternary co-assembly systems based on aromatic amino acids, vinylnaphthalene derivatives and 1,2,4,5-tetracyanobenzene with effective chirality transfer. Notably, the handedness of supramolecular chirality and CPL can be readily inverted by changing the residues of amino acids, the substituents of achiral vinylnaphthalene derivatives, or by adjusting the stoichiometric ratio. The hydrogen bonds, charge transfer interactions, and steric hindrance are proved to be the crucial factors for the chirality inversion. This flexible control over chirality not only offers insights into developing multicomponent chiral materials with desirable handedness from simple molecular building blocks, but also is of practical value for use in chiroptics, chiral sensing, and photoelectric devices.

Self-assembly of amphiphilic asymmetric comb-like copolymers with responsive rigid side chains.

Amphiphilic asymmetric comb-like copolymers (AACCs) exhibit distinct self-assembly behaviours due to their unique architecture. However, the synthetic difficulties of well-defined AACCs have prohibited a systematic understanding of the architecture-morphology relationship. In this work, we conducted dissipative particle dynamics simulations to investigate the self-assembly behaviours of AACCs with responsive rigid side chains in selective solvents. The effects of side chain length, number of branches, and spacers on the morphology of aggregates were investigated by mapping out morphology diagrams. Besides, the numbers and surface areas of aggregates clearly depicted the morphological transitions during the self-assembly process. Moreover, the rod-to-coil conformation transitions were simulated to explore the stimuli-responsive behaviour of the AACCs with responsive rigid side chains by adjusting the bond angle parameter of the rigid chains. The results indicated that without the support of the rigid chains, the assembly structure collapsed, leading to the tube-to-channelized micelles and one-compartment-to-multicompartment vesicle morphology transformations. The simulation results are consistent with earlier experimental results, which can provide theoretical guidance for assembly toward desired nanostructures.

Designable Photo-Responsive Micron-Scale Ultrathin Peptoid Nanobelts for Enhanced Performance on Hydrogen Evolution Reaction.

The development of high-reactive single-atom catalysts (SACs) based on long-range-ordered ultrathin organic nanomaterials (UTONMs) (i.e., below 3 nm) provides a significant tactic for the advancement in hydrogen evolution reactions (HER) but remains challenging. Herein, photo-responsive ultrathin peptoid nanobelts (UTPNBs) with a thickness of ≈2.2 nm and micron-scaled length are generated using the self-assembly of azobenzene-containing amphiphilic ternary alternating peptoids. The pendants hydrophobic conjugate stacking mechanism reveals the formation of 1D ultralong UTPNBs, whose thickness is dictated by the length of side groups that are linked to peptoid backbones. The photo-responsive feature is demonstrated by a reversible morphological transformation from UTPNBs to nanospheres (21.5 nm) upon alternative irradiation with UV and visible lights. Furthermore, the electrocatalyst performance of these aggregates co-decorated with nitrogen-rich ligand of terpyridine (TE) and uniformly-distributed atomic platinum (Pt) is evaluated toward HER, with a photo-controllable electrocatalyst activity that highly depended on both the presence of Pt element and structural characteristic of substrates. The Pt-based SACs using TE-modified UTPNBs as support exhibit a favorable electrocatalytic capacity with an overpotential of ≈28 mV at a current density of 10 mA cm-2. This work presents a promising strategy to fabricate stimuli-responsive UTONMs-based catalysts with controllable HER catalytic performance.

Morphologically Tunable Rectangular Platelets Self-Assembled from Diblock Molecular Brushes Containing Azopyridine Pendants.

Two-dimensional (2D) platelet structures are of growing importance as building blocks for the preparation of optical and electrical devices. However, the creation of morphologically tunable rectangular platelets through polymer self-assembly still remains a challenge. Herein, we describe a rational strategy for the fabrication of 2D rectangular platelets by stacking azopyridine-containing diblock molecular brushes in two dimensions in a selective solvent. Amphiphilic PEG-co-(PtBA-g-PAzoPy) DMBs with poly(ethylene glycol) (PEG) block, poly(t-butyl acrylate) (PtBA) backbone, and poly(6-(4-(4-pyridyazo)phenoxy)-hexyl methacrylate) (PAzoPy) brush were synthesized by sequential reversible addition-fragmentation chain transfer polymerization and atom transfer radical polymerization. Various rectangular platelets were obtained via the solution self-assembly of PEG-co-(PtBA-g-PAzoPy) through a heating-cooling-aging process in which the morphology and size of platelets could be controlled by adjusting the composition of DMBs as well as the solvent polarity. In addition, we investigated the metal chelation ability and H-bonding-assisted co-assembly capability of PEG-co-(PtBA-g-PAzoPy). The results displayed that 2D hybrids and flower-like platelets were formed, respectively. Our study presents an efficient method to fabricate rectangular platelets with tunable morphologies.

Assessment of the Adverse Health Effects of Aflatoxin Exposure from Unpackaged Peanut Oil in Guangdong, China.

Aflatoxins are liver carcinogens and are common contaminants in unpackaged peanut (UPP) oil. However, the health risks associated with consuming aflatoxins in UPP oil remain unclear. In this study, aflatoxin contamination in 143 UPP oil samples from Guangdong Province were assessed via liquid chromatography-tandem mass spectrometry (LC-MS). We also recruited 168 human subjects, who consumed this oil, to measure their liver functions and lipid metabolism status. Aflatoxin B1 (AFB1) was detected in 79.72% of the UPP oil samples, with levels ranging from 0.02 to 174.13 µg/kg. The average daily human intake of AFB1 from UPP oil was 3.14 ng/kg·bw/day; therefore, the incidence of liver cancer, caused by intake of 1 ng/kg·bw/day AFB1, was estimated to be 5.32 cases out of every 100,000 persons per year. Meanwhile, Hepatitis B virus (HBV) infection and AFB1 exposure exerted a synergistic effect to cause liver dysfunction. In addition, the triglycerides (TG) abnormal rate was statistically significant when using AFB1 to estimate daily intake (EDI) quartile spacing grouping (p = 0.011). In conclusion, high aflatoxin exposure may exacerbate the harmful effects of HBV infection on liver function. Contamination of UPP oil with aflatoxins in Guangdong urgently requires more attention, and public health management of the consumer population is urgently required.

NiCo2 O4 /Hollow Mesoporous Carbon Nanosphere Hybrids Enabling Super-Hydrophobicity, Thermal Insulation, and Highly Efficient Microwave Absorption.

The combination of 2D magnetic nanosheets and mesoporous carbon with unique interfaces shows considerable prospects for microwave absorption (MA). However, traditional assembly procedures make it impossible to accurately manage the assembly of magnetic nanosheets in carbon matrices. Herein, a reverse strategy for preparing complex magnetic nanosheet cores inside carbon-based yolk-shell structures is developed. This innovative approach focuses on controlling the initial crystallite formation sites in a hydrothermal reaction as well as the inflow and in situ growth behavior of 2D NiCo-layered double hydroxide precursors based on the capillary force induced by hollow mesoporous carbon nanospheres. Accordingly, the as-prepared YS-CNC-2 absorber exhibits remarkable MA performances, with an optimal reflection loss as low as -60.30 dB at 2.5 mm and an effective absorption bandwidth of 5.20 GHz at 2.0 mm. The loss of electromagnetic waves (EMW) depends on natural resonance loss, dipole polarization relaxation, and multiple scattering behavior. On top of that, the functionalized super-hydrophobic MA coating is produced in spraying and curing processes utilizing YS-CNC-2 nanoparticles and fumed silica additives in the polydimethylsiloxane matrix. The excellent thermal insulation, self-cleaning capability, and durability in diverse solutions of the coating promise potential applications for military equipment in moist situations.

Extracellular Matrix-Mimetic Immunomodulatory Hydrogel for Accelerating Wound Healing.

Macrophages play a crucial role in the complete processes of tissue repair and regeneration, and the activation of M2 polarization is an effective approach to provide a pro-regenerative immune microenvironment. Natural extracellular matrix (ECM) has the capability to modulate macrophage activities via its molecular, physical, and mechanical properties. Inspired by this, an ECM-mimetic hydrogel strategy to modulate macrophages via its dynamic structural characteristics and bioactive cell adhesion sites is proposed. The LZM-SC/SS hydrogel is in situ formed through the amidation reaction between lysozyme (LZM), 4-arm-PEG-SC, and 4-arm-PEG-SS, where LZM provides DGR tripeptide for cell adhesion, 4-arm-PEG-SS provides succinyl ester for dynamic hydrolysis, and 4-arm-PEG-SC balances the stability and dynamics of the network. In vitro and subcutaneous tests indicate the dynamic structural evolution and cell adhesion capacity promotes macrophage movement and M2 polarization synergistically. Comprehensive bioinformatic analysis further confirms the immunomodulatory ability, and reveals a significant correlation between M2 polarization and cell adhesion. A full-thickness wound model is employed to validate the induced M2 polarization, vessel development, and accelerated healing by LZM-SC/SS. This study represents a pioneering exploration of macrophage modulation by biomaterials' structures and components rather than drug or cytokines and provides new strategies to promote tissue repair and regeneration.

Supramolecular Polymerization of Polymeric Nanorods Mediated by Block Copolymers.

Introducing a second component is an effective way to manipulate polymerization behavior. However, this phenomenon has rarely been observed in colloidal systems, such as polymeric nanoparticles. Here, we report the supramolecular polymerization of polymeric nanorods mediated by block copolymers. Experimental observations and simulation results illustrate that block copolymers surround the polymeric nanorods and mainly concentrate around the two ends, leaving the hydrophobic side regions exposed. These polymeric nanorods connect in a side-by-side manner through hydrophobic interactions to form bundles. As polymerization progresses, the block copolymers gradually deposit onto the bundles and finally assemble into helical nanopatterns on the outermost surface, which terminates the polymerization. It is anticipated that this work could offer inspiration for a general strategy of controllable supramolecular polymerization.

Self-Assembly of Peapod-like Micrometer Tubes from a Planet-Satellite-type Supramolecular Megamer.

This study presents interesting self-assembly of peapod-like micrometer tubes from a planet-satellite-type supramolecular megamer, which was constructed through the specific host-guest molecular recognition between azobenzene (AZO)-functionalized hyperbranched poly(ethyl-3-oxetanemethanol)-star-poly(ethylene oxide) (HSP-AZO) and ß-cyclodextrin(CD)-based hydrophilic hyperbranched polyglycerol (CD-g-HPG). A peapod-like structure with micrometer-sized tube as the pod and vesicles encapsulated inside as the peas was formed through sequential vesicle entosis, linear association, and fusion processes. Dissipative particle dynamics (DPD) simulations support the structural possibility of the supramolecular peapod formation and its mechanism. UV light irradiation could lead to the disassembly of the peapod-like structure. This study expands the family of supramolecular polymers and opens a new avenue to develop bioinspired complex hierarchical nanoarchitectures at the microscopic level.

Electrical Signal Initiates Kinetic Assembly of Collagen to Construct Optically Transparent and Geometry Customized Artificial Cornea Substitutes.

Corneal transplantation is an effective treatment for reconstructing injured corneas but is very limited due to insufficient donors, which has led to a growing demand for development of artificial corneal substitutes (ACSs). Collagen is a potential building block for ACS fabrication, whereas technically there are limited capabilities to control the collagen assembly for creating highly transparent collagen ACSs. Here, we report an electro-assembly technique to kinetically control collagen assembly on the nanoscale that allows the yielding collagen ACSs with structure determined superior optics. Structurally, the kinetically electro-assembled collagen (KEA-Col) is composed of partially aligned microfibrils (∼10 nm in diameter) with compacted lamellar organization. Optical analysis reveals that such microstructure is directly responsible for its optimal light transmittance by reducing light scattering. Moreover, this method allows the creation of complex three-dimensional geometries and thus is convenient to customize collagen ACSs with specific curvatures to meet refractive power requirements. Available properties (e.g., optics and mechanics) of cross-linked KEA-Cols were studied to meet the clinical requirement as ACSs, and in vitro tests further proved their beneficial characteristics of cell growth and migration. An in vivo study established a rabbit lamellar keratectomy corneal wound model and demonstrated the customized collagen ACSs can adapt to the defective cornea and support epithelial healing as well as stroma integration and reconstruction with lower immunoreaction compared with commercial xenografts, which suggests its promising application prospects. More broadly, this work illustrates the potential for enlisting electrical signals to mediate collagen's assembly and microstructure organization for specific structural functionalization for regenerative medicine.

Morphology-Controlled Fabrication Strategy of Hollow Mesoporous Carbon Spheres@f-Fe2O3 for Microwave Absorption and Infrared Stealth.

The design and development of radar--infrared compatible stealth materials are challenging in the field of broadband absorption due to the contradiction of stealth requirements and mechanisms in different frequency bands. However, hollow structures show great promise for multispectral stealth because they can lengthen the attenuation path of electromagnetic waves (EMWs) for microwave absorption, interrupt the continuity of heat-transport channels, and lower the thermal conductivity to realize infrared stealth. Here, a new morphological fabrication strategy has been developed to efficiently prepare compatible stealth nanomaterials. In a specific hydrothermal process, the confined growth of flake α-Fe2O3 (f-Fe2O3) outside of hollow mesoporous carbon spheres (HMCS) is achieved using NH3·H2O as a shape-controlled reagent. The introduction of f-Fe2O3 helps to lower infrared emissivity and improve high-frequency impedance matching, which depends on the stable dielectric property of the specific flake shape. Moreover, the size of f-Fe2O3 can be regulated by changing the constituent proportion in the hydrothermal suspension to obtain excellent performance. The minimum reflection loss (RL) of the HMCS@f-Fe2O3-6 composite is -34.16 dB at 2.4 mm, and the effective absorption bandwidth (EAB) reaches 4.8 GHz. Furthermore, the lowest emissivities of the HMCS@f-Fe2O3-6-20 wt %/polyetherimide (PEI) film in the 3-5 and 8-14 µm infrared wavebands are 0.212 and 0.508, respectively. These discoveries may pave the way for the development of radar-infrared compatible stealth materials from the perspective of microstructural design.

Self-assembly of sequence-regulated amphiphilic copolymers with alternating rod and coil pendants.

We conducted a computational study on the self-assembly behavior of sequence-controlled amphiphilic copolymers with alternating rod and coil pendants. Complex self-assembled morphologies, such as onion-like vesicles with two layers, can be generated by introducing rod pendants. The amphiphilic alternating copolymers self-assemble into onion-like vesicles through a fusion process of tiny micelles and a bending operation of disk-like micelles with double layers. A stimuli-responsive simulation shows that the cylindrical vesicles can transform into onion-like vesicles by a rod-to-coil conformation transition of rigid pendants. Inspired by this finding, we conducted a drug-loading simulation by adding two reactive drugs at different stages and found that the onion-like vesicles can almost completely isolate two drugs. This work provides theoretical guidance on the self-assembly of amphiphilic alternating copolymers with rod and coil pendants for future experimental design.

Membrane Nanopores Induced by Nanotoroids via an Insertion and Pore-Forming Pathway.

The formation of membrane nanopores is one of the crucial activities of cells and has attracted considerable attention. However, the understanding of their types and mechanisms is still limited. Herein, we report a novel nanopore formation phenomenon achieved through the insertion of polymeric nanotoroids into the cellular membrane. As revealed by theoretical simulations, the nanotoroid can embed in the membrane, leaving a nanopore on the cell. The through-the-cavity wrapping of lipids is critical for the retention of the nanotoroid in the membrane, which is attributed to both a relatively large inner cavity of the nanotoroid and a moderate attraction between the nanotoroid and membrane lipids. Under the guidance of the simulation predictions, experiments using polypeptide toroids as pore-forming agents were performed, confirming the unique biophysical phenomenon. This work demonstrates a distinctive pore-forming pathway, deepens the understanding of the membrane nanopore phenomenon, and assists in the design of advanced pore-forming materials.

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.

Spiral- and meridian-patterned spheres self-assembled from block copolymer/homopolymer binary systems.

Spiral nanostructures, mainly in the 2D form, have been observed in polymer self-assembly, while well-defined 3D spirals are rarely reported. Here we report that a binary system containing polypeptide-based block copolymers and homopolymers can self-assemble into well-defined spiral spheres (3D spirals), in which the homopolymers form the core and the copolymers form the spirals. Upon increasing the preparation temperature, meridian spheres were obtained. Mixing polypeptide block copolymers with opposite backbone chirality also leads to the formation of meridian spheres. In the meridian patterns, a tighter packing manner of the phenyl groups appended to the polypeptide blocks was observed, which is responsible for the spiral-to-meridian transitions. This work enriches the research of spiral assemblies and provides a facile route to switch chiral/achiral nanostructures by regulating the packing manner of the pendant groups.

Branched Aggregates with Tunable Morphology via Hierarchical Self-Assembly of Azobenzene-Derived Molecular Double Brushes.

Hierarchical self-assembly is one of the most effective approaches to fabricate nature-inspired materials with subtle nanostructures. We report a distinct hierarchical self-assembly process of molecular double brushes (MDBs) with each graft site carrying a poly(azobenzene-acrylate) (PAzo) chain and a poly(ethylene oxide) (PEO) chain. Asymmetric tapered worm (ATW) nanostructures with chain-end reactivity assembling from the azobenzene-derived MDBs serve as primary subunits to prepare branched supermicelles by increasing water content (Cw ) in THF/water. Various natural Antedon-shaped multiarm worm-like aggregates (MWAs) can be created via the particle-particle connection of ATWs. Intriguingly, the azobenzene moieties undergo trans-cis isomerization upon UV irradiation and further promote a morphology evolution of MWAs. Multiscale supermicelles comprised of starfish shapes with differing central body and arm morphologies (e.g., compare to the biological specimens Luidia ciliaris and Crossaster papposus) were prepared by manipulating irradiation time.

Flying Squirrel-Inspired Motion Control of a Light-Deformed Pt-PAzoMA Micromotor through Drag Force Manipulation.

Micromotors require stable and precise motion control for complex tasks such as microsurgery, drug delivery in vivo, or environmental monitoring ex vivo. However, a continuous control signal is needed for micromotors to achieve motion control during their whole journey, which hinders their application in areas where external control stimuli are limited or unavailable. Fortunately, nature suggests an excellent solution that flying squirrel exhibits motion tuning capability by deforming itself when jumping off a tall tree. Inspired by this, we propose a Pt-PAzoMA Janus micromotor that precisely changes its shape (from a spherical shape to an elliptical shape) under a brief light signal (450 nm) and maintains this deformation until next signal reception. The deformed elliptical micromotor performs relatively low-speed motion compared to the spherical one, which is further confirmed by massive simulation results. In addition, by investigating motion behavior experimentally and theoretically, it is proved that the motion modulation is caused by the drag force changing brought from the deformation. This method represents a different route to regulate the motion of micromotors without a continuous signal, which is useful in application scenarios where the environmental control signal is inaccessible/limited or long-time operation with minimum energy input is required to maintain motion manipulation. With further function modification, this kind of shape-changing micromotor has potential in optimizing drug diffusion efficiency by speed altering and long-term monitoring at the diseased area by confining the active range of the micromotor in the targeted area through deformation.

Helical Self-Assembly of Amphiphilic Chiral Azobenzene Alternating Copolymers.

Imposing chirality to supramolecular architectures is an important step forward toward understanding and utilization of chiral nanomaterials. This article reports the self-assembly of amphiphilic chiral alternating copolymers of poly(binaphthyl azobenzene-alt-hexaethylene glycol) (P(BNPAzo-alt-EG6)) into helical supramolecular rods. Unlike conventional chiral assembly of copolymers largely through intermolecular organization, the intrachain stacking of chiral units along the main chain into single molecular micelles with amplified axial chirality of binaphthyl is key to the formation of helical supramolecular rods, which takes advantage of the particular chiral unit and soft unit alternating topological structure of the backbones. Moreover, the supramolecular self-assembly is light reversible because the azobenzene rings in the backbone scarcely execute trans- to cis-isomerization upon UV irradiation, and therefore the supramolecular rods keep their sublevel chirality even though the helical appearance was destroyed. This work paves an effective route to construct and regulate chiral supramolecular architectures and reveals an insight into natural and artificial chiral self-assembly.

Light-Induced Reversible Hierarchical Self-Assembly of Amphiphilic Diblock Copolymers into Microscopic Vesicles with Tunable Optical and Nanocarrier Properties.

In contrast to the conventional hierarchical self-assembly process, effective methods to enable reversible hierarchical self-assembly of block copolymers are comparatively few and limited in scope. Herein, we report, for the first time, a simple yet robust strategy for light-induced reversible hierarchical self-assembly of an amphiphilic diblock copolymer, poly(4-vinylpyridine)-block-poly[6-[4-(4-butyloxyphenylazo)phenoxy]hexyl methacrylate] (denoted P4VP-b-PAzoMA). The hierarchical structures are constructed via a two-step self-assembly process (first-level reverse micelles, second-level compound micelles, and rearrangement into micrometer-sized vesicles) driven by use of solvent. Intriguingly, because of reversible photoinduced trans-to-cis isomerization of azobenzene moieties in PAzoMA, the vesicles could disassemble into subunits upon UV light and then recover the nearly identical vesicular morphology upon visible light. Such a reversible hierarchical self-assembly process is accompanied by reversible fluorescence, encapsulation, and controlled release of dyes and can be used as a template for the synthesis of nanoparticles. Clearly, the ability to render the light-enabled reversible hierarchical self-assembly provides a unique platform for smart delivery vehicles and templates for nanomaterials.