Graphene[1] -a flat monolayer of carbon atoms tightly packed into a two-dimensional (2D) honeycomb lattice -is the basal building block in all graphitic materials. [2] Since it was first reported in 2004, [1] graphene has attracted great interest because of the unique electronic, [3][4][5][6][7][8][9][10] thermal, [11] and mechanical properties [12,13] arising from its strictly 2D structure, and to its potential technical applications. [2,[13][14][15][16] However, producing graphene on a large scale using existing mechanical methods is still unfeasible. Searching for alternative chemical approaches is an urgent matter. [17] However, the hydrophobic nature of graphene and its strong tendency to agglomerate in solvents [13] present a great challenge to the development of fabrication methods, and severely restrict its promising applications. Although the mechanism involved remains unproven, [18] the chemical reduction of readily available exfoliated graphite oxide (GO) with reducing agents such as hydrazine and dimethylhydrazine is a promising strategy in the large-scale production of graphene. [13,18,19] Unfortunately, the reducing agents involved are very hazardous, and the graphene obtained presents irreversibly agglomerated features in solvents that do not contain polymer surfactants.[13] Here, we report a new green route for the synthesis of processable graphene on a large scale. We observed that a stable graphene suspension could be quickly prepared by simply heating an exfoliated-GO suspension under strongly alkaline conditions at moderate temperatures (50-90 8C) (Figure 1a). Our initial purpose was to introduce functional groups to exfoliated GO by free-radical addition.[20] Surprisingly, the addition of NaOH to the GO suspension -to improve the solubility of the alkyl free-radical initiator, which is carboxyl-terminated -was accompanied by a fast, unexpected color change (from yellow-brown to homogeneous black). Careful experiments revealed that exfoliated GO can undergo fast deoxygenation in strongly alkaline solutions, resulting in stable aqueous graphene suspensions (Figure 1b). Typically, 150 mL of exfoliated-GO suspension (0.5-1 mL mg À1 ) and 1-2 mL NaOH or KOH solution (8 M) were loaded into a jacketed vessel, with hot water circulating through the outer chamber ( Figure 1S, Supporting Information). The temperature of the circulating water was constantly controlled by a temperature circulator, and the whole vessel was subjected to mild sonication (25 W, 40 KHz). The yellow-brown exfoliated-GO suspension became black after it was kept at the desired temperature (e.g. 80 8C) for a few minutes. The 13 C NMR spectrum of the GO (Figure 2a) confirms the presence of abundant epoxide and hydroxyl groups, [21] which should align perpendicular to the basal-plane carbon atoms. The carboxyl groups, which are located at the edges of the basal plane, are too few for 13 C NMR detection, in agreement with previous studies [21] on GO prepared by the Hummers method.[22] After the reaction, however, the exfoliated GO (...

Bottlebrush polymers are a type of branched or graft polymer with polymeric side-chains attached to a linear backbone, and the unusual architecture of bottlebrushes provides a number of unique and potentially useful properties. These include a high entanglement molecular weight, enabling rapid self-assembly of bottlebrush block copolymers into large domain structures, the self-assembly of bottlebrush block copolymer micelles in a selective solvent even at very low dilutions, and the functionalization of bottlebrush side-chains for recognition, imaging, or drug 2 delivery in aqueous environments. This review article focuses on recent developments in the field of bottlebrush polymers with an emphasis on applications of bottlebrush copolymers.Bottlebrush copolymers contain two (or more) different types of polymeric side-chains. Recent work has explored the diverse properties and functions of bottlebrush polymers and copolymers in solutions, films, and melts, and applications explored include photonic materials, bottlebrush films for lithographic patterning, drug delivery, and tumor detection and imaging. We provide a brief introduction to bottlebrush synthesis and physical properties and then discuss work related to: i) bottlebrush self-assembly in melts and bulk thin films, ii) bottlebrushes for photonics and lithography, iii) bottlebrushes for small molecule encapsulation and delivery in solution, and iv) bottlebrush micelles and assemblies in solution. We briefly discuss three potential areas for future research, including developing a more quantitative model of bottlebrush self-assembly in the bulk, studying the properties of bottlebrushes at interfaces, and investigating the solution assembly of bottlebrush copolymers.

Bottlebrush polymers are highly branched macromolecules with potential applications in antifouling coatings, rheological modifiers, and drug delivery systems. However, the solution conformation of bottlebrush polymers has been studied in only a limited set of materials made primarily by grafting-from polymerization. Here we present small-angle neutron scattering (SANS) measurements on a series of polystyrene bottlebrush polymers with varying side-chain and backbone lengths in d 8-toluene to analyze their size, shape, and conformation. Bottlebrush polymers with 2–7 kg mol–1 polystyrene side chains (degree of polymerization DP = 14–54) and poly(oxanorbornene) backbones (DP = 10–264) were synthesized using reversible addition–fragmentation chain transfer (RAFT) followed by a ring-opening metathesis polymerization (ROMP) grafting-through synthesis scheme. Analysis by Guinier–Porod, rigid cylinder, and flexible cylinder models provided estimates of the bottlebrush polymer length, radius, and stiffness. The bottlebrush polymer cross-sectional area depends primarily on side-chain DP, and the radius of gyration R g exhibits a power-law dependence with side-chain DP. We also observe a sphere-to-cylinder transition with increasing backbone DP, with the transition occurring at a backbone DP of approximately 120 for the polystyrene bottlebrush polymers studied. The maximum molecular dimension for the series studied varies from 25 to 350 nm.

Bottlebrush polymer thin films may be attractive for the preparation of antifouling and/or stimuli-responsive surface coatings due to the high grafting density and conformational flexibility of polymeric side chains, but bottlebrush polymer thin films have not been previously reported and their surface properties are unknown. Herein, we report a study of the surface properties of mixed bottlebrush polymer (MBBPs) films. MBBPs with hydrophobic polystyrene (PS) and hydrophilic poly(ethylene glycol) (PEG) side chains are synthesized using a "graftingthrough" ring-opening metathesis polymerization (ROMP) approach. Stimuli-responsive MBBPs films are prepared by spin-casting a solution of MBBPs onto a solid surface, and the resulting film morphology and surface properties are characterized using atomic force microscopy (AFM), grazing-incidence small-angle X-ray scattering (GISAXS), water contact angle measurements, and X-ray photoelectron spectroscopy (XPS). The water contact angles of MBBPs films decrease or increase upon exposure of the MBBPs films to selective solvents methanol or cyclohexane, respectively. This contact angle change is dependent on the length of the PEG side chain; longer PEG side chains result in greater contact angle changes with solvent exposure. Consistent with watercontact angle measurements, XPS indicates enrichment of PEG or PS chains at the film surface after exposure of the MBBPs film to methanol or cyclohexane solvent vapors, respectively. Finally, it is demonstrated that bottlebrush polymer films can be stabilized by the addition of a radical cross-linker and irradiation with UV light. This work demonstrates that bottlebrush polymers enable the preparation of stimuli-responsive, "brush-like" polymeric coatings using simple solution processing methods.

An intense stimulus can cause death of odontoblasts and initiate odontoblastic differentiation of stem/progenitor cell populations of dental pulp cells (DPCs), which is followed by reparative dentin formation. However, the mechanism of odontoblastic differentiation during reparative dentin formation remains unclear. This study was to determine the role of β-catenin, a key player in tooth development, in reparative dentin formation, especially in odontoblastic differentiation. We found that β-catenin was expressed in odontoblast-like cells and DPCs beneath the perforation site during reparative dentin formation after direct pulp capping. The expression of β-catenin was also significantly upregulated during odontoblastic differentiation of in vitro cultured DPCs. The expression pattern of runt-related transcription factor 2 (Runx2) was similar to that of β-catenin. Immunofluorescence staining indicated that Runx2 was also expressed in β-catenin–positive odontoblast-like cells and DPCs during reparative dentin formation. Knockdown of β-catenin disrupted odontoblastic differentiation, which was accompanied by a reduction in β-catenin binding to the Runx2 promoter and diminished expression of Runx2. In contrast, lithium chloride (LiCl) induced accumulation of β-catenin produced the opposite effect to that caused by β-catenin knockdown. In conclusion, it was reported in this study for the first time that β-catenin can enhance the odontoblastic differentiation of DPCs through activation of Runx2, which might be the mechanism involved in odontoblastic differentiation during reparative dentin formation.

Parenchymatous organs consist of multiple cell types, primarily defined as parenchymal cells (PCs) and nonparenchymal cells (NPCs). The cellular characteristics of these organs are not well understood. Proteomic studies facilitate the resolution of the molecular details of different cell types in organs. These studies have significantly extended our knowledge about organogenesis and organ cellular composition. Here, we present an atlas of the cell-type-resolved liver proteome. In-depth proteomics identified 6000 to 8000 gene products (GPs) for each cell type and a total of 10,075 GPs for four cell types. This data set revealed features of the cellular composition of the liver: (1) hepatocytes (PCs) express the least GPs, have a unique but highly homogenous proteome pattern, and execute fundamental liver functions; (2) the division of labor among PCs and NPCs follows a model in which PCs make the main components of pathways, but NPCs trigger the pathways; and (3) crosstalk among NPCs and PCs maintains the PC phenotype. This study presents the liver proteome at cell resolution, serving as a research model for dissecting the cell type constitution and organ features at the molecular level.

We explore the phase behaviour, solution conformation, and interfacial properties of bottlebrush polymers with side-chains comprised of poly(N-isopropylacrylamide) (PNIPAAM), a thermally responsive polymer that exhibits a lower critical solution temperature (LCST) in water. PNIPAAM bottlebrush polymers with controlled side-chain length and side-chain end-group structure are prepared using a "grafting-through" technique. Due to reduced flexibility of bottlebrush polymer side-chains, side-chain end-groups have a disproportionate effect on bottlebrush polymer solubility and phase behaviour. Bottlebrush polymers with a hydrophobic end-group have poor water solubilities and depressed LCSTs, whereas bottlebrush polymers with thiol-terminated side-chains are fully water-soluble and exhibit an LCST greater than that of PNIPAAM homopolymers. The temperature-dependent solution conformation of PNIPAAM bottlebrush polymers in D2O is analyzed by small-angle neutron scattering (SANS), and data analysis using the Guinier-Porod model shows that the bottlebrush polymer radius decreases as the temperature increases towards the LCST for PNIPAAM bottlebrush polymers with relatively long 9 kg mol(-1) side-chains. Above the LCST, PNIPAAM bottlebrush polymers can form a lyotropic liquid crystal phase in water. Interfacial tension measurements show that bottlebrush polymers reduce the interfacial tension between chloroform and water to levels comparable to PNIPAAM homopolymers without the formation of microemulsions, suggesting that bottlebrush polymers are unable to stabilize highly curved interfaces. These results demonstrate that bottlebrush polymer side-chain length and flexibility impact phase behavior, solubility, and interfacial properties.

No abstract