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Graphene and its derivatives attract extensive research interests in the biomedicine field due to their outstanding physiochemical properties. Lots of studies have reported that graphene materials exhibit antibacterial activities. However, antibacterial mechanisms of graphene materials still remain controversial and need further investigation. Herein, graphene oxide (GO) with and without nitrogen-doping were fabricated on the titanium surface by cathodic electrophoretic deposition and antibacterial activities were systematically investigated. Results showed that GO on the titanium surface presented antibacterial activity, while nitrogen-doped GO lost the antibacterial activity. The reason is that antibacterial mechanisms for the GO-metal system contain two steps. First, electron transfer occurs from bacterium’s cell membrane to GO surface which destroys the bacterial respiratory chain; subsequently, electrons on GO surface induce the production of reactive oxygen species (ROS) that damage the membrane structure and eventually lead to bacterial death. For nitrogen-doped GO, nitrogen atoms denote electrons into GO leading to n-type doping. Nitrogen-doped GO as an electron donor cuts off the electron transfer from the cell membrane to GO and subsequently inhibits the production of ROS. This is why nitrogen-doped GO exhibits no antibacterial activity. This work confirms the antibacterial mechanisms for the GO-metal system with a synergistic effect of non-oxidative electron transfer and ROS mediated oxidative stress.

Implant failures still happen because of bacterial infections and inferior osteogenic properties. Graphene oxide (GO) could induce osteogenic differentiation as well as exhibit superior antibacterial activity which may provide an answer for this issue. In this work, GO films loaded with minocycline hydrochloride (MH) were fabricated on titanium implant surfaces, and the antibacterial activity and osteogenic properties were studied in the presence of S. aureus and rat bone mesenchymal stem cells (rBMSCs) in in vitro and in vivo environments, respectively. The results indicated that the MH loaded GO films on titanium surfaces (MH&GO@Ti) exhibited enhanced osteogenic activity in vitro with improved alkaline phosphatase (ALP) activity and enhanced osteogenic related gene expressions including ALP, collagen-I, osteocalcin, and osteopontin. The in vitro results of the co-culture of rBMSCs and S. aureus indicated that the rBMSCs grew well on the MH&GO@Ti sample with a higher coverage of cells and the bacteria were almost unobservable on the surface. In the in vivo experiments, the MH&GO@Ti exhibited excellent antibacterial and osteogenic activities in the presence of bacteria. No inflammatory cells for example neutrophils were found and superior bone–implant integration was obtained. This study offers a new proposal for the clinical application of drug-loaded graphene coating.

Excellent antibacterial property of graphene oxide makes it an important antibacterial material. However, in some cases, a synergistic combination of materials with different antibacterial mechanisms is desired. In this work, we developed a simple two-step protocol to prepare ornidazole (ONZ), a nitroimidazole antiprotozoal drug, loaded graphene-based paper for combined antibacterial materials. Graphene oxide (GO) and reduced graphene oxide (rGO) were used as carriers in antibacterial materials. After mixed with ONZ directly in aqueous media and filtrated under vacuum, the freestanding GO/ONZ and rGO/ONZ were peeled off from the filtrate membrane. The ONZ loading contents in the paper was determined by UV/vis spectroscopy and the surface properties were investigated by measuring their contact angle, which will have an important impact on the antibacterial effects of the papers. Keywords: Ornidazole, Graphene oxide, Antibacterial material

To investigate protein-resistant surfaces with heterogeneous nanopatterns, V-shaped polymer brushes composed of a hydrophilic methoxypoly(ethylene glycol) (mPEG) arm and a hydrophobic polystyrene (PS) or fluorinated poly(methyl methacrylate) (PMMA-b-PFMA) arm were prepared, in which the surface structure and phase-separation behavior were controlled by altering the relative lengths of the two arms. The protein resistance of these amphiphilic brushes was better than that of pure poly(ethylene glycol) (PEG) brushes, and when the domain size of the phase-separated structures was about twice the size of the protein molecules, the surfaces exhibited optimal protein repellence. At the same time, the amount of protein adsorption was well related to both the adhesion and the relative friction coefficient of the protein on the brush surface. A heterogeneous surface with phase-separated domains twice the size of protein molecules may be beneficial for minimizing protein adsorption through the synergistic effect of ...

Thin polymer films with well-assembled fluorinated groups on their surfaces are not easily achieved via spin-coating film-fabrication methods because the solution solidifies very rapidly during spin-coating, which hinders the fluorinated moieties from segregating and organizing on the film surface. In this contribution, we have proposed a comprehensive strategy toward achieving well-ordered fluorinated thin films surfaces by optimizing the molecular organization at air/liquid interface of the film-formation solutions. To validate such a route, poly(methyl methacrylate) (PMMA) end-capped with several 2-perfluorooctylethyl methacrylate (FMA) units was employed as the model polymer for investigations. The air/solution interfacial structures were optimized by systematically changing the polymer chain structures and properties of the casting solvents. It was found that the polymers that form loosely associated aggregates (e.g., FMA1- ec-PMMA65- ec-FMA1) and a solvent with better solubility to FMA while having not too low surface tension (i.e., toluene) can combine to produce solutions with well-assembled FMA at the interfaces. By spin-coating the solutions with well-organized interfaces, an ultrathin film with perfluorinated groups that were highly oriented toward the film surface was readily achieved, exhibiting surface energies as low as 7.2 mJ/m2, which is among the lowest reported so far for the spin-coated thin films, and a very high F/C ratio (i.e., 0.98).

Titanium and its alloys have been widely used in orthopedic and dental implants because of their excellent properties. However, implant failures still occur due to implant-associated bacterial infections. Therefore, proper surface modification of titanium and its alloys is necessary. In this work, commercial pure titanium plates were modified with graphene oxide (GO) which was used to load minocycline hydrochloride. Gram-positive Staphylococcus aureus (S. aureus) and Streptococcus mutans (S. mutans) and Gram-negative Escherichia coli (E. coli) were used to investigate the antibacterial activity of the samples. Human gingival fibroblast (HGF) cells were applied to assess the cytocompatibility of the various samples. To investigate cell adhesion and cell surface coverage in the presence of bacteria, the coculture of HGF cells and S. aureus was performed. The results indicated that the GO-modified titanium surface could inhibit the growth of the bacteria which had direct contact with GO, while it could not affect the bacteria without direct contact of GO. Minocycline hydrochloride on the GO-modified titanium surface (M@GO-Ti) showed a slow release behavior and exhibited excellent antibacterial activity with the synergistic effect of contact-killing and release-killing by GO and minocycline hydrochloride, respectively. In the coculture process with the presence of S. aureus, HGF cells on M@GO-Ti demonstrated the best cell viability and cell surface coverage among all the samples.

Currently, graphene and its derivatives, used for surface modification of orthopedic and dental implants, are mainly in the form of two-dimensional planar structure. There is little information of three dimensional porous graphene nanosheets used as coating materials of titanium and its alloys. In the present study, three dimensional porous graphene nanosheets were first synthesized on the pure titanium surface. The physicochemical properties and osteogenic activity of the three dimensional porous graphene nanosheets-modified titanium (rGO@Ti) were systematically investigated. The results suggested that rGO@Ti showed super hydrophilicity, rough surface and excellent biocompatibility, and could enhance alkaline phosphatase (ALP) activity, extracellular matrix (ECM) mineralization and collagen secretion of rat bone mesenchymal stem cells (rBMSCs). Meanwhile, the expressions of osteogenesis related genes containing ALP, bone morphogenic protein-2 (BMP-2), osteocalcin (OCN), and osteopontin (OPN) on rGO@Ti were improved. The osteogenic differentiation of rBMSCs on rGO@Ti may be ascribed to both its superior protein adsorption ability and physical stimulation induced by the unique structure of three dimensional porous graphene nanosheets.

Polymer monolayers at liquid surfaces have attracted considerable attention as tools to construct molecular devices with unique properties. The aggregation states of chains within the monolayers must be understood as the first benchmark to establish molecular designs for the devices. It has been reported that large differences exist in surface pressure–area isotherms of polyacrylates and polymethacrylates at the water surface, although they differ chemically only by the absence of an alpha methyl group (α-CH3) in the former. Herein, we carried out experiments using sum-frequency generation vibrational spectroscopy, atomic force microscopy and infrared reflection absorption spectroscopy to explore the changes of the aggregation state and interaction of four poly(acrylates) (i.e., poly(methyl acrylate), PMA; poly(ethyl acrylate), PEA; poly(methyl methacrylate), PMMA; poly(ethyl methacrylate), PEMA) at the water surface during compression. In the case of PMA and PEA without α-CH3, the polymer chains adopt an...

Graphene oxide has attracted widespread attention in the biomedical fields due to its excellent biocompatibility. Herein we investigated the layer-number dependent antibacterial and osteogenic behaviors of graphene oxide in biointerfaces. Graphene oxide with different layer numbers was deposited on the titanium surfaces by cathodal electrophoretic deposition with varied deposition voltages. The initial cell adhesion and spreading, cell proliferation, and osteogenic differentiation were observed from all the samples using rat bone mesenchymal stem cells. Both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus were used to investigate the antibacterial effect of the modified titanium surfaces. Cocultures of human gingival fibroblasts (HGF) cells with Escherichia coli and Staphylococcus aureus were conducted to simulate the conditions of the clinical practice. The results show that the titanium surfaces with graphene oxide exhibited excellent antibacterial and osteogenic effects. Increasing the layer-number of graphene oxide resulted in the augment of reactive oxygen species levels and the wrinkling, which led to the antibacterial and osteogenic effects, respectively. Compared to pure titanium surface in the cells-bacteria coculture process, the modified titanium surfaces with graphene oxide exhibited higher surface coverage percentage of cells.

A well-defined amphiphilic graft copolymer comprising a hydrophilic poly(acrylic acid) (PAA) backbone and hydrophobic poly(lactic acid) side chains was synthesized by a combination of reversible addition–fragmentation chain transfer (RAFT) polymerization, ring open polymerization (ROP), and the grafting-from strategy. A well-defined PtBHBMA homopolymer having pendant hydroxyls in every repeated unit was first obtained by RAFT homopolymerization of a OH-containing tert-butyl 2-((4-hydroxybutanoyloxy)methyl)acrylate (tBHBMA) monomer. ROP of lactide was directly initiated by the pendant hydroxyls of PtBHBMA to provide a well-defined poly(tert-butyl acrylate)-g-poly(lactic acid) (PtBA-g-PLA) graft copolymer via the grafting-from strategy without post-polymerization functionality transformation. The hydrophobic PtBA backbone was selectively hydrolyzed into the hydrophilic PAA backbone so as to afford the targeted well-defined PAA-g-PLA amphiphilic graft copolymer (Mw/Mn = 1.17) having equally-distributed carboxyls along the backbone. PAA-g-PLA amphiphilic graft copolymer shows pH-responsive micellization behavior and it can self-assemble into spheres under certain conditions. Doxorubicin (DOX) can be loaded by non-toxic micelles self-assembled by the PAA-g-PLA graft copolymer and its in vitro accumulative release characteristics were investigated by fluorescence spectroscopy. In comparison with free DOX, the DOX-loading nanoparticles display decreased cytotoxicity against SMMC-7721 and SH-SY5Y cells in 48 h because of a sustained release profile of DOX.

Biotrophic pathogens, such as wheat rust fungi, survive on nutrients derived from host cells. Sugar appears to be the major carbon source transferred from host cells to various fungal pathogens; however, the molecular mechanism by which host sugar transporters are manipulated by fungal pathogens for nutrient uptake is poorly understood. TaSTP6, a sugar transporter protein in wheat (Triticum aestivum), was previously shown to exhibit enhanced expression in leaves upon infection by Puccinia striiformis f. sp. tritici (Pst), the causal agent of wheat stripe rust. In this study, we found that Pst infection caused increased accumulation of abscisic acid (ABA) and that application of exogenous ABA significantly enhanced TaSTP6 expression. Moreover, knockdown of TaSTP6 expression by barley stripe mosaic virus-induced gene silencing reduced wheat susceptibility to the Pst pathotype CYR31, suggesting that TaSTP6 expression upregulation contributes to Pst host sugar acquisition. Consistent with this, TaSTP6 overexpression in Arabidopsis (Arabidopsis thaliana) promoted plant susceptibility to powdery mildew and led to increased Glc accumulation in the leaves. Functional complementation assays in Saccharomyces cerevisiae showed that TaSTP6 has broad substrate specificity, indicating that TaSTP6 is an active sugar transporter. Subcellular localization analysis indicated that TaSTP6 localizes to the plasma membrane. Yeast two-hybrid and bimolecular fluorescence complementation experiments revealed that TaSTP6 undergoes oligomerization. Taken together, our results suggest that Pst stimulates ABA biosynthesis in host cells and thereby upregulates TaSTP6 expression, which increases sugar supply and promotes fungal infection.

Background Apical periodontitis (AP) is essentially an inflammatory disease of microbial etiology primarily caused by infection of the pulp and root canal system. Variation of the bacterial communities caused by AP, as well as their changes responding to dental therapy, are of utmost importance to understand the pathogensis of the apical periodontitis and establishing effective antimicrobial therapeutic strategies. This study aims to uncover the composition and diversity of microbiota associated to the root apex to identify the relevant bacteria highly involved in AP, with the consideration of root apex samples from the infected teeth (with/without root canal treatment), healthy teeth as well as the healthy oral. Methods Four groups of specimens are considered, the apical part of root from diseased teeth with and without root canal treatment, and wisdom teeth extracted to avoid being impacted (tooth healthy control), as well as an additional healthy oral control from biofilm of the buccal mucosa. DNA was extracted from these specimens and the microbiome was examined through focusing on the V3-V4 hypervariable region of the 16S rRNA gene using sequencing on Illumina MiSeq platform. Composition and diversity of the bacterial community were tested for individual samples, and between-group comparisons were done through differential analysis to identify the significant changes. Results We observed reduced community richness and diversity in microbiota samples from diseased teeth compared to healthy controls. Through differential analysis between AP teeth and healthy teeth, we identified 49 OTUs significantly down-regulated as well as 40 up-regulated OTUs for AP. Conclusion This study provides a global view of the microbial community of the AP associated cohorts, and revealed that AP involved not only bacteria accumulated with a high abundance, but also those significantly reduced ones due to microbial infection. Electronic supplementary material The online version of this article (10.1186/s12864-019-5474-y) contains supplementary material, which is available to authorized users.

Surface enhanced Raman spectroscopy (SERS) has been proposed as a promising technique in biological and chemical sample detection. Herein, with nanographene oxide (nGO) as substrate, we firstly prepared facile platforms (PAMAMG1-nGO-PEG and PAMAMG3-nGO-PEG) through the functionalization of nGO with biocompatible poly(ethylene glycol) (PEG) and hyperbranched polyamidamine (PAMAM) dendrimer. nGO/gold nanoparticle nanocomposites (Au@PAMAMG1-nGO-PEG and Au@PAMAMG3-nGO-PEG) were aptly fabricated through in situ covering of gold nanoparticles on PEG/PAMAM-functionalized nGO. A series of techniques were employed to confirm the covalent modification of nGO with different functional polymers and the uniformity of gold nanoparticles scattered over the nGO sheets in the as-prepared nanocomposites. Evidently, taking advantages of inherent electrochemical property of gold nanoparticles and their good dispersity on polymers and functionalized nGO, Au@PAMAMG1-nGO-PEG and Au@PAMAMG3-nGO-PEG both displayed sensitive and efficient SERS detection towards p-phenylenediamine, flavin adenine dinucletide and crystal violet (CV) molecules. It is foreseen that these nanocomposites can meet diverse SERS sensing applications with good dispersity, especially for environmental and clinical samples.

A series of well-defined amphiphilic brush polymers containing hydrophilic poly(ethylene glycol) (PEG) and hydrophobic poly(lactic acid) segments was synthesized by the combination of reversible addition–fragmentation chain transfer (RAFT) polymerization, ring opening polymerization (ROP), and the grafting-from strategy. tert-Butyl 2-((4-hydroxybutanoyloxy)methyl)acrylate (tBHBMA) monomer containing a ROP initiation group (–OH) was first RAFT block copolymerized using a PEG-based chain transfer agent to form two well-defined PEG-b-PtBHBMA diblock copolymers (Mw/Mn ≤ 1.10) bearing pendant hydroxyls in every repeated unit of PtBHBMA segment. Both diblock copolymers directly initiated ROP of lactide by the pendant hydroxyls to provide well-defined poly(ethylene glycol)-b-(poly(tert-butyl acrylate)-g-poly(lactic acid)) (PEG-b-(PtBA-g-PLA)) brush polymers (Mw/Mn ≤ 1.16) without post-polymerization functionality transformation. The target well-defined poly(ethylene glycol)-b-(polyacrylic acid)-g-poly(lactic acid) (PEG-b-(PAA-g-PLA)) amphiphilic brush polymers were achieved by the selective acidolysis of hydrophobic PtBA backbone (tert-butyoxycarbonyls) into hydrophilic PAA backbone (carboxyls) using trifluoroacetic acid. PEG-b-(PAA-g-PLA) brush polymers could self-assemble into spheres with a size of ca. 70–110 nm in aqueous media as evidenced by DLS and TEM. The drug (doxorubicin) loading ability of PEG-b-(PAA-g-PLA) brush polymers was investigated preliminarily by measuring the in vitro cell (SMMC-7721 and SH-SY5Y) viabilities, which showed higher cytotoxicity compared to free DOX.