Hongqin Zhu

Antibacterial activity of large-area monolayer graphene film manipulated by charge transfer

Graphene has attracted increasing attention for potential applications in biotechnology due to its excellent electronic property and biocompatibility. Here we use both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) to investigate the antibacterial actions of large-area monolayer graphene film on conductor Cu, semiconductor Ge and insulator SiO2. The results show that the graphene films on Cu and Ge can surprisingly inhibit the growth of both bacteria, especially the former. However, the proliferation of both bacteria cannot be significantly restricted by the graphene film on SiO2. The morphology of S. aureus and E. coli on graphene films further confirms that the direct contact of both bacteria with graphene on Cu and Ge can cause membrane damage and destroy membrane integrity, while no evident membrane destruction is induced by graphene on SiO2. From the viewpoint of charge transfer, a plausible mechanism is proposed here to explain this phenomenon. This study may provide new insights for the better understanding of antibacterial actions of graphene film and for the better designing of graphene-based antibiotics or other biomedical applications.

Osteogenic activity and antibacterial effect of zinc ion implanted titanium

Titanium (Ti) and its alloys are widely used as orthopedic and dental implants. In this work, zinc (Zn) was implanted into oxalic acid etched titanium using plasma immersion ion implantation technology. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to investigate the surface morphology and composition of Zn-implanted titanium. The results indicate that the depth profile of zinc in Zn-implanted titanium resembles a Gaussian distribution, and zinc exists in the form of ZnO at the surface whereas in the form of metallic Zn in the interior. The Zn-implanted titanium can significantly stimulate proliferation of osteoblastic MC3T3-E1 cells as well as initial adhesion, spreading activity, ALP activity, collagen secretion and extracellular matrix mineralization of the rat mesenchymal stem cells. The Zn-implanted titanium presents partly antibacterial effect on both Escherichia coli and Staphylococcus aureus. The ability of the Zn-implanted titanium to stimulate cell adhesion, proliferation and differentiation as well as the antibacterial effect on E. coli can be improved by increasing implantation time even to 2 h in this work, indicating that the content of zinc implanted in titanium can easily be controlled within the safe concentration using plasma immersion ion implantation technology. The Zn-implanted titanium with excellent osteogenic activity and partly antibacterial effect can serve as useful candidates for orthopedic and dental implants.

Antimicrobial activity and cytocompatibility of Ag plasma-modified hierarchical TiO2 film on titanium surface.

To improve the antimicrobial ability and cytocompatibility of biomedical titanium implants, many efforts have been made to modify their surface topography and chemical composition. In this work, Ag plasma-modified hierarchical TiO2 film was fabricated on titanium surface via acid etching to produce micropit, hydrothermal treatment to generate TiO2 nanorod and subsequent plasma immersion ion implantation process to impregnate Ag into TiO2 surface. In view of the potential clinical applications, their antimicrobial activity, bioactivity and cytocompatibility were systematically evaluated. The hierarchical TiO2 film showed enhanced bioactivity and bacteriostatic effect on both microbes due to more negative zeta potential, constructing the first defense line against microbial adhesion by electrostatic repulsion. Addition of embedded Ag remarkably enhanced the antimicrobial efficiency toward both microbes based on Schottky contact without Ag(+) release, establishing the second defense line targeting microbial membrane. Furthermore, the addition of Ag degraded the bioactivity very little and exerted nearly no adverse or even promoted effect on MG63 cell functions, including adhesion, spreading and proliferation. This work illustrates a two-defense-line antimicrobial activity in darkness with both prior electrostatic repulsion to inhibit most microbes adhesion and posterior biocidal action to kill residual ones that luckily infiltrated through the first defense line, and provide proof of concept using both clinically relevant human pathogens. In conclusion, the Ag-embedded hierarchical TiO2 film with excellent antimicrobial activity, bioactivity and cytocompatibility provides a promising candidate for orthopedic and dental implants.

Chemically regulated bioactive ion delivery platform on a titanium surface for sustained controlled release

The efficacy of biomedical titanium implants mainly depends on their surface characteristics such as surface morphology, microstructure, and components, and the resulting performances. In this work, hierarchical hybrid micro/nanotip films incorporated with bioactive Sr2+/Mg2+ ions were prepared on a titanium surface by combining acid etching, hydrothermal treatment and a subsequent ion exchange process with Sr2+ and Mg2+ ions respectively. A Sr/Mg delivery platform is thus successfully obtained on a titanium surface and can allow for sustained release of Sr2+/Mg2+ ions at a slow rate for a period of time. In vitro SBF tests confirm that the Sr/Mg loaded titanate films possess good bioactivity accompanying the controlled release. Meanwhile, cell experiments further demonstrate that the Sr/Mg loaded micro/nanostructured titanium surfaces possess good biocompatibility and osteogenic activity. This is a successful attempt to apply an ion exchange technique to the surface modification of biomedical titanium materials and the strategy described here offers a general, facile, and straightforward chemical approach to functionalize various titanium-based material surfaces by constructing micro/nanostructures and using ion exchange with bioactive ions under mild synthetic conditions, and provides insight into the design of better biomedical implant surfaces for the future.

CVD Growth of Graphene on NiTi Alloy for Enhanced Biological Activity.

From the perspective of surface modification of biomaterials, graphene is very promising because of its unique physical and chemical properties. Herein, we report direct in situ fabrication of graphene on nitinol (NiTi) shape memory alloy by chemical vapor deposition (CVD) and investigate both the growth mechanism as well as surface bioactivity of the modified alloy. Growth of the graphene layer is independent of Ni but is rather correlated with the formation of the TiC phase on the surface. Graphene nucleates and grows on this carbide layer during exposure to CH4. The graphene layer is observed to promote the osteogenesis differentiation of mesenchymal stem cells and surface bioactivity. The use of graphene as a bioactive layer is a viable approach to improving the surface properties of NiTi-based dental and orthopedic implants and components.

Enhanced bioactivity and bacteriostasis effect of TiO2 nanofilms with favorable biomimetic architectures on titanium surface

To improve the bioactivity and antibacterial properties of biomedical titanium implants, many efforts have been made to modify its surface composition and topography. In this work, biomimetic hierarchical micro/nanostructured titania films were formed on titanium surfaces via acid etching to generate microtopography and subsequent hydrothermal treatment to produce titania nanopetals or nanorod layers on it. In view of the potential clinical applications, the apatite-forming ability of the hierarchical micro/nano-textured TiO2 films was evaluated by simulated body fluid (SBF) immersion tests, and Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were used to estimate the bacteriostatic effect. Meanwhile, the osteoblast-like cell line MG63 was cultured on the surface of the films to investigate their cytocompatibility. Compared to the microtopography, the hierarchical micro/nano-textured surfaces exhibit better apatite-forming ability and bacteriostatic effect on S. aureus, as well as enhancing the proliferation of MG63. The results obtained in this work suggest that the hierarchical micro/nano-textured TiO2 films on titanium may be a potential candidate for bone tissue engineering and biomedical implants. Our study reveals a synergistic effect on bioactivity and bacteriostasis as well as cell responses exerted by the titania nanofilms with biomimetic micro/nanotopographies and provides insight into the design of better biomedical implant surfaces.

Selective Tumor Cell Inhibition Effect of Ni-Ti Layered Double Hydroxides Thin Films Driven by the Reversed pH Gradients of Tumor Cells.

Nitinol is widely fabricated as stents for the palliation treatment of many kinds of cancers. It is of great importance to develop nitinol stents with selective tumor cell inhibition effects. In this work, a series of pH sensitive films composed of Ni(OH)2 and Ni-Ti layered double hydroxide (Ni-Ti LDH) with different Ni/Ti ratios were prepared on the surface of nitinol via hydrothermal treatment. The films with specific Ni/Ti ratios would release a large amount of nickel ions under acidic environments but were relatively stable in neutral or weak alkaline medium. Cell viability tests showed that the films can effectively inhibit the growth of cancer cells but have little adverse effects to normal cells. Besides, extraordinarily high intracellular nickel content and reactive oxygen species (ROS) level were found in cancer cells, indicating the death of cancer cells may be induced by the excessive intake of nickel ions. Such selective cancer cell inhibition effect of the films is supposed to relate with the reversed pH gradients of tumor cells.

Existence, release, and antibacterial actions of silver nanoparticles on Ag–PIII TiO2 films with different nanotopographies

Nanotopographical TiO2 films (including nanorod, nanotip, and nanowire topographies) were successfully fabricated on the metallic Ti surface via hydrothermal treatment and then underwent Ag plasma immersion ion implantation to incorporate Ag with TiO2. The surface morphology, phase component, and chemical composition before and after Ag–PIII were characterized. In view of the potential clinical applications, both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus were used to estimate their antimicrobial effect. The nanostructured TiO2 films on a Ti surface exhibit a better bacteriostatic effect on both microbes compared to the pristine Ti. The nanotopographies of the TiO2 films affect the nucleation, growth, and distribution of Ag nanoparticles in the films during Ag–PIII process. The Ag nanoparticles are completely embedded into the nanorod film while partially exposed out of the nanotip and nanowire films, which account for the significant differences in the release behaviors of Ag ions in vitro. However, no significant difference exists in their antimicrobial activity against both microbes. The antimicrobial actions of the Ag@TiO2 system described here consist of two methods – the contact-killing action and the release-killing action. Nevertheless, based on the observed results, the contact-killing action should be regarded as the main method to destroy microbes for all the Ag plasma-modified TiO2 nanofilms. This study provides insight to optimize the surface design of Ti-based implants to acquire more effective antimicrobial surfaces to meet clinical applications.

Layer-Number Dependent Antibacterial and Osteogenic Behaviors of Graphene Oxide Electrophoretic Deposited on Titanium

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.

“Petal effect”-inspired superhydrophobic and highly adhesive coating on magnesium with enhanced corrosion resistance and biocompatibility

With properties of complete degradation and favorable mechanical behavior, Mg and its alloys are regarded as the next generation medical metal materials. However, fast degradation and poor surface biocompatibility hinder their clinical applications. Inspired by the “petal effect”, we successfully constructed a superhydrophobic and highly adhesive coating on pure Mg via a simple hydrothermal treatment in a solution containing sodium oleate. The superhydrophobicity of the fabricated coating results from its flake-like micro-nanostructure and the low-surface-energy oleate group. Water droplet on the superhydrophobic coating cannot roll off even when the sample is turned upside down, owing to the sealed air-pockets and the van der Waals’ attraction at the solidliquid interface, indicating a highly adhesive force. The chemical and mechanical stability of the superhydrophobic coating were measured. Potentiodynamic polarization and electrochemical impedance spectroscopy measurements suggest enhanced corrosion resistance of the as-prepared sample. Furthermore, cell cytotoxicity, migration and adhesion data of human umbilical vein endothelial cells (HUVECs) reveal an improved cytocompatibility of the modified surface. Finally, hemolysis assay and platelet adhesion assay suggest an improved hemocompatibility. It is believed that the facile and low-cost method can expand the new application of superhydrophobic surface with highly adhesive on Mg in biomedical fields.摘要由于具有完全可降解性和良好的机械性能, 镁及其合金被誉为“下一代生物医用金属材料”. 然而, 过快的降解速率和较差的生物相容性制约着它们在临床上的应用. 受“花瓣效应”启发, 本文利用含有油酸钠的溶液, 通过水热法在纯镁表面制备了超疏水且具有高粘附力的涂层. 涂层表面的片状微纳结构和低表面自由能的油酸根赋予涂层超疏水性. 水滴与涂层表面之间封存的空气以及固液界面间的范德华力, 使水滴在涂层表面显示出高粘附性(即使倒置180°, 水滴也不会从材料表面脱落). 本工作评价了所制备超疏水涂层的化学稳定性和机械稳定性. 动电位极化曲线和阻抗谱测试都表明所制备涂层具有良好的抗腐蚀性. 此外, 细胞(人脐静脉内皮细胞)毒性、 细胞迁移以及细胞粘附等结果都表明超疏水涂层具有良好的细胞相容性. 最后, 溶血率和血小板粘附测试表明超疏水涂层的血液相容性也有明显提升. 利用超疏水高粘附力涂层改善纯镁抗腐蚀性和生物相容性的思路有望拓展镁在生物医用领域的应用.