Fanhao Meng

Biological actions of silver nanoparticles embedded in titanium controlled by micro-galvanic effects.

Titanium embedded with silver nanoparticles (Ag NPs) using a single step silver plasma immersion ion implantation (Ag-PIII) demonstrate micro-galvanic effects that give rise to both controlled antibacterial activity and excellent compatibility with osteoblasts. Scanning electron microscopy (SEM) shows that nanoparticles with average sizes of about 5 nm and 8 nm are formed homogeneously on the titanium surface after undergoing Ag-PIII for 0.5 h and 1 h, respectively. Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) indicate that those nanoparticles are metallic silver produced on and underneath the titanium surface via a local nucleation process from the solid solution of α-Ti(Ag). The Ag-PIII samples inhibit the growth of both Staphylococcus aureus and Escherichia coli while enhancing proliferation of the osteoblast-like cell line MG63. Electrochemical polarization and Zeta potential measurements demonstrate that the low surface toxicity and good cytocompatibility are related to the micro-galvanic effect between the Ag NPs and titanium matrix. Our results show that the physico-chemical properties of the Ag NPs are important in the control of the cytotoxicity and this study opens a new window for the design of nanostructured surfaces on which the biological actions of the Ag NPs can be accurately tailored.

Influences of ionic dissolution products of dicalcium silicate coating on osteoblastic proliferation, differentiation and gene expression

This work aims to explore the influence of the ionic products of dicalcium silicate coating on osteoblastic proliferation and differentiation, as well as on the expression of BMP2 and its signal transducers Smad1, 6 and 7 in MG-63 osteoblast-like cells. Plasma-sprayed dicalcium silicate coatings were soaked in DMEM to obtain culture media containing the ionic dissolution products of dicalcium silicate coating (Ca2SiO4-DMEM). MG63 osteoblast-like cells were cultured in Ca2SiO4-DMEM (experimental group) for 3-12 days, while those cultured in normal DMEM served as control (control group). MTT assay was used to evaluate cell viability and proliferation. Alkaline phosphatase activity (ALP), osteocalcin (OC) and type I collagen (COLI) were investigated as differentiation markers. Gene expression of BMP2 and Smad1, 6, 7 was also detected. BMP2 protein was examined by ELISA assay. Alizarin Red-S (AR-S) assay was used to detect mineralization. The results demonstrated that Si concentration in Ca2SiO4-DMEM is markedly higher than that in normal DMEM. Compared to the control group, MG63 cells of the experimental group exhibited upregulated proliferation on day 3, and markedly upregulated gene expression of the differentiation markers, especially on days 9 and 12 for OC and on days 3, 6 and 9 for ALP. Gene expression of BMP2 and Smad1, as well as BMP2 protein secreted into culture media, was also upregulated in the experimental group, while gene expression of Smad6 and 7 was not influenced. AR-S assay indicated a higher calcium mineral content deposition in cells of the experimental group. In conclusion, the ionic products of plasma-sprayed dicalcium silicate coating are beneficial to the proliferation and differentiation of MG63 osteoblast-like cells.

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.

Microstructure, bioactivity and osteoblast behavior of monoclinic zirconia coating with nanostructured surface

A monoclinic zirconia coating with a nanostructural surface was prepared on the Ti-6Al-4V substrate by an atmospheric plasma-spraying technique, and its microstructure and composition, as well as mechanical and biological properties, were investigated to explore potential application as a bioactive coating on bone implants. X-ray diffraction, transmission electron microscopy, scanning electron microscopy and Raman spectroscopy revealed that the zirconia coating was composed of monoclinic zirconia which was stable at low temperature, and its surface consists of nano-size grains 30-50 nm in size. The bond strength between the coating and the Ti-6Al-4V substrate was 48.4 + or - 6.1 MPa, which is higher than that of plasma-sprayed HA coatings. Hydrothermal experiments indicated that the coating was stable in a water environment and the phase composition and Vickers hardness were independent of the hydrothermal treatment time. Bone-like apatite is observed to precipitate on the surface of the coating after soaking in simulated body fluid for 6 days, indicating excellent bioactivity in vitro. The nanostructured surface composed of monoclinic zirconia is believed to be crucial to its bioactivity. Morphological observation and the cell proliferation test demonstrated that osteoblast-like MG63 cells could attach to, adhere to and proliferate well on the surface of the monoclinic zirconia coating, suggesting possible applications in hard tissue replacements.

Electron storage mediated dark antibacterial action of bound silver nanoparticles: smaller is not always better.

Size tunable silver nanoparticles (Ag NPs) are synthesized and incorporated into titanium oxide coatings (TOCs) by manipulating the atomic-scale heating effect of silver plasma immersion ion implantation (Ag PIII). The resulting Ag NPs/TOC composite coatings possess electron storage capability that gives rise to both controlled antibacterial activity and excellent compatibility with mammalian cells. The precipitation behavior of these Ag NPs is qualitatively constrained by the classical nucleation theory. Both photoluminescence (PL) spectra and fluorescence microscopy results demonstrate that larger Ag NPs (5-25 nm) are better at reserving electrons than smaller ones (∼4 nm). The antibacterial activities of the as-sprayed and Ag PIII treated TOCs show that Ag NPs with a different size act distinctively to bacteria: large particles induce serious cytosolic content leakage and lysis of both Staphylococcus aureus and Escherichia coli cells while small ones do not. The excellent activity of larger Ag NPs against bacteria is highly related to their stronger electron storage capability, which can induce accumulation of adequate valence-band holes (h⁺) at the titanium oxide side, arousing oxidation reactions to bacterial cells in the dark. Moreover, the in vitro cell culture assay (using both MG63 and MC3T3 cells) reveals no significant cytotoxicity and even good cytocompatibility on the Ag PIII treated samples. Our results show that, by taking advantage of the boundary property between Ag NP and titanium oxide, the antibacterial activity of Ag NPs can be accurately controlled. This study provides a distinct criterion for the design of nanostructured surfaces such that their osteoblast functions and antibacterial activity are perfectly balanced.

Enhanced apatite-forming ability and cytocompatibility of porous and nanostructured TiO2/CaSiO3 coating on titanium.

To improve the bioactivity and cytocompatibility of biomedical titanium dioxide coating, many efforts have been made to modify its surface composition and topography. Meanwhile, CaSiO(3) was commonly investigated as coating material on titanium implants for fast fixation and firm implant-bone attachment due to its demonstrated bioactivity and osteointegration. In this work, gradient TiO(2)/CaSiO(3) coating on titanium was prepared by a two-step procedure, in which porous and nanostructured TiO(2) coating on titanium was prepared by plasma electrolytic oxidation in advance, and then needle and flake-like CaSiO(3) nanocrystals were deposited on the TiO(2) coating surface by electron beam evaporation. In view of the potential clinical applications, apatite-forming ability of the TiO(2)/CaSiO(3) coating was evaluated by simulated body fluid (SBF) immersion tests, and MG63 cells were cultured on the surface of the coating to investigate its cytocompatibility. The results show that deposition of CaSiO(3) significantly enhanced the apatite-forming ability of nanostructured TiO(2) coating in SBF. Meanwhile, the MG63 cells on TiO(2)/CaSiO(3) coating show higher proliferation rate and vitality than that on TiO(2) coating. In conclusion, the porous and nanostructured TiO(2)/CaSiO(3) coating on titanium substrate with good apatite-forming ability and cytocompatibility is a potential candidate for bone tissue engineering and implant coating.

Antibacterial activity and cytocompatibility of titanium oxide coating modified by iron ion implantation

In this work, zero valent iron nanoparticles (Fezero-NPs) and iron oxide nanoparticles (Feox-NPs) were synthesized at the subsurface and surface regions of titanium oxide coatings (TOCs) by plasma immersion ion implantation. This novel Fe-NPs/TOC system showed negligible iron releasing, great electron storage capability and excellent cytocompatibility in vitro. Importantly, the system showed selective antibacterial ability which can kill Staphylococcus aureus under dark conditions but has no obvious antibacterial effect against Escherichia coli. Owing to a bipolar Schottky barrier between Fezero-NPs/TOC and Fezero-NPs/Feox-NPs, electrons could be captured by the Fezero-NPs bounded at the subsurface region of the coating. This electron storage capability of the Fe-NPs/TOC system induced extracellular electron transportation and accumulation of adequate valence-band holes (h(+)) at the external side, which caused oxidation damage to S. aureus cells in the dark. No obvious biocide effect against E. coli resulted from lack of electron transfer ability between E. coli and substrate materials. This work may open up a novel and controlled strategy to design coatings of implants with antibacterial ability and cytocompatibility for medical applications.

Positive Role of Surface Defects on Carbon Nanotube Cathodes in Overpotential and Capacity Retention of Rechargeable Lithium-Oxygen Batteries

Surface defects on carbon nanotube cathodes have been artificially introduced by bombardment with argon plasma. Their roles in the electrochemical performance of rechargeable Li-O2 batteries have been investigated. In batteries with tetraethylene glycol dimethyl ether (TEGDME)- and N-methyl-N-propylpiperidinium bis(trifluoromethansulfonyl)imide (PP13TFSI)-based electrolytes, the defects increase the number of nucleation sites for the growth of Li2O2 particles and reduce the size of the formed particles. This leads to increased discharge capacity and reduced cycle overpotential. However, in the former batteries, the hydrophilic surfaces induced by the defects promote carbonate formation, which imposes a deteriorating effect on the cycle performance of the Li-O2 batteries. In contrast, in the latter case, the defective cathodes promote Li2O2 formation without enhancing formation of carbonates on the cathode surfaces, resulting in extended cycle life. This is most probably attributable to the passivation effect on the functional groups of the cathode surfaces imposed by the ionic liquid. These results indicate that defects on carbon surfaces may have a positive effect on the cycle performance of Li-O2 batteries if they are combined with a helpful electrolyte solvent such as PP13TFSI.

Spacing-Dependent Antimicrobial Efficacy of Immobilized Silver Nanoparticles.

Silver nanoparticles (Ag NPs) with a similar mean particle diameter (∼5.0 nm) but distinguished dispersion densities were in situ fabricated and immobilized on plasma-sprayed titanium oxide coatings by a silver plasma immersion ion implantation process (Ag PIII). Experiments and theoretical predictions demonstrated that the efficacy of these Ag NPs against bacteria relies on their electron storage capability, which is the interparticle distance associated in the dark, and it is inversely dose-dependent. A particle population with a relatively large spacing distance is superior in concentrating the electrons extruded by bacterial cells, activating oxidative reactions, and disrupting the bacterial cells. The finding opens up a new window leading to active design and control of the interactions between materials and biological systems.

Hierarchical micro/nanostructured titanium with balanced actions to bacterial and mammalian cells for dental implants

A versatile strategy to endow dental implants with long-term antibacterial ability without compromising the cytocompatibility is highly desirable to combat implant-related infection. Silver nanoparticles (Ag NPs) have been utilized as a highly effective and broad-spectrum antibacterial agent for surface modification of biomedical devices. However, the high mobility and subsequent hazardous effects of the particles on mammalian cells may limit its practical applications. Thus, Ag NPs were immobilized on the surface of sand-blasted, large grit, and acid-etched (SLA) titanium by manipulating the atomic-scale heating effect of silver plasma immersion ion implantation. The silver plasma immersion ion implantation-treated SLA surface gave rise to both good antibacterial activity and excellent compatibility with mammalian cells. The antibacterial activity rendered by the immobilized Ag NPs was assessed using Fusobacterium nucleatum and Staphylococcus aureus, commonly suspected pathogens for peri-implant disease. The immobilized Ag NPs offered a good defense against multiple cycles of bacteria attack in both F. nucleatum and S. aureus, and the mechanism was independent of silver release. F. nucleatum showed a higher susceptibility to Ag NPs than S. aureus, which might be explained by the presence of different wall structures. Moreover, the immobilized Ag NPs had no apparent toxic influence on the viability, proliferation, and differentiation of rat bone marrow mesenchymal stem cells. These results demonstrated that good bactericidal activity could be obtained with very small quantities of immobilized Ag NPs, which were not detrimental to the mammalian cells involved in the osseointegration process, and promising for titanium-based dental implants with commercial SLA surfaces.