Weihong Jin

Antibacterial effects of titanium embedded with silver nanoparticles based on electron-transfer-induced reactive oxygen species

Although titanium embedded with silver nanoparticles (Ag-NPs@Ti) are suitable for biomedical implants because of the good cytocompatibility and antibacterial characteristics, the exact antibacterial mechanism is not well understood. In the present work, the antibacterial mechanisms of Ag-NPs@Ti prepared by plasma immersion ion implantation (PIII) are explored in details. The antibacterial effects of the Ag-NPs depend on the conductivity of the substrate revealing the importance of electron transfer in the antibacterial process. In addition, electron transfer between the Ag-NPs and titanium substrate produces bursts of reactive oxygen species (ROS) in both the bacteria cells and culture medium. ROS leads to bacteria death by inducing intracellular oxidation, membrane potential variation, and cellular contents release and the antibacterial ability of Ag-NPs@Ti is inhibited appreciably after adding ROS scavengers. Even though ROS signals are detected from osteoblasts cultured on Ag-NPs@Ti, the cell compatibility is not impaired. This electron-transfer-based antibacterial process which produces ROS provides insights into the design of biomaterials with both antibacterial properties and cytocompatibility.

Hydrothermal synthesis of perovskite-type MTiO3 (M = Zn, Co, Ni)/TiO2 nanotube arrays from an amorphous TiO2 template

Ordered perovskite-type MTiO3/TiO2 nanotube arrays (NTAs) (M = Zn, Co, Ni) are prepared by a general hydrothermal route based on amorphous TiO2 NTAs via electrochemical anodization of Ti foil. The as-anodized amorphous TiO2 is not stable and can react with H2O in solution producing soluble Ti(OH)62− to form anatase nanoparticles (NPs) via water-induced dissolution and recrystallization. The pH and salt content in the solution play important roles in the morphology and composition of the hydrothermal products. In the presence of a metal acetate, the reaction between Ti(OH)62− and H+ is dramatically restricted and the reaction proceeds preferentially between Ti(OH)62− and M2+ (M = Zn, Co, Ni) to produce insoluble MTiO3 NPs which adhere onto the original architecture in situ to form perovskite-type MTiO3/TiO2 NTAs. This study elucidates the role of the amorphous structure in the formation of MTiO3 and provides a general means of synthesizing nanostructured MTiO3.

Systematic Study of Inherent Antibacterial Properties of Magnesium-based Biomaterials

Magnesium-based materials are preferred in temporary orthopedic implants because of their biodegradability, mechanical properties, and intrinsic antibacterial properties. However, the fundamental mechanism of bacteria killing and roles of various factors are not clearly understood. In this study, we performed a systematic study of the antibacterial properties of two common Mg-based materials using a biofilm forming bacterium. Complete annihilation of the initial 3 × 10(4) bacteria is achieved with both materials in 0.1 mL LB medium in 24 h, whereas in the control, they proliferate to 10(10). The bacteria are killed more effectively in the solution than on the surface, and the bacteria killing efficiency depends more on the concentrations of the magnesium ions and hydroxyl ions than the corrosion rate. The killing process is reproduced using formula solutions, and killing is revealed to stem from the synergetic effects of alkalinity and magnesium ions instead of either one of them or Mg(OH)2 precipitate. Reactive oxygen species (ROS) are detected from the bacteria during the killing process but are not likely produced by the redox reaction directly, because they are detected at least 3 h after the reaction has commenced. The average cell size increases during the killing process, suggesting that the bacteria have difficulty with normal division which also contributes to the reduced bacteria population.

Competitive Reaction Pathway for Site‐Selective Conjugation of Raman Dyes to Hotspots on Gold Nanorods for Greatly Enhanced SERS Performance

Common methods to prepare SERS (surface-enhanced Raman scattering) probes rely on random conjugation of Raman dyes onto metal nanostructures, but most of the Raman dyes are not located at Raman-intense electromagnetic hotspots thus not contributing to SERS enhancement substantially. Herein, a competitive reaction between transverse gold overgrowth and dye conjugation is described to achieve site selective conjugation of Raman dyes to the hotspots (ends) on gold nanorods (GNRs). The preferential overgrowth on the nanorod side surface creates a barrier to prevent the Raman dyes from binding to the side surface except the ends of the GNRs, where the highest SERS enhancement factors are expected. The SERS enhancement observed from this special structure is dozens of times larger than that from conjugates synthesized by conventional methods. This simple and powerful strategy to prepare SERS probes can be extended to different anisotropic metal nanostructures with electromagnetic hotspots and has immense potential in in-depth SERS-based biological imaging and single-molecule detection.

Targeting ETS1 with RNAi-based supramolecular nanoassemblies for multidrug-resistant breast cancer therapy

&NA; Overexpression of erythroblastosis virus E26 oncogene homolog 1 (ETS1) gene is correlated with both tumor progression and poor response to chemotherapy in cancer treatment, and the exploitation of RNA interference (RNAi) technology to downregulate ETS1 seems to be a promising approach to reverse multidrug‐resistant cancer cells to chemotherapy. Hence, the RNAi‐based nanomedicine which is able to simultaneously downregulate ETS1 expression and to deliver chemotherapeutic agents may improve multidrug‐resistant cancer therapy synergistically. In this study, we developed a supramolecular nanoassembly that could deliver siRNA targeting ETS1 (siETS1) and doxorubicin (DOX) as an effective nanomedicine to achieve successful chemotherapy towards multidrug‐resistant breast cancer. The nanotherapeutic system was prepared by loading adamantane‐conjugated doxorubicin (AD) into polyethyleneimine‐modified (2‐hydroxypropyl)‐&ggr;‐cyclodextrin (HP) through the supramolecular assembly to form AD‐loaded HP (HPAD), followed by electrostatically‐driven self‐assembly between siETS1 and HPAD. When the HPAD/siETS1 nanoassemblies were delivered into drug‐resistant MCF‐7/ADR cells, the drug efflux was significantly reduced as a result of simultaneous silencing of ETS1 and MDR1 genes. Importantly, the HPAD/siETS1 nanoassembly could enhance drug residence time at tumor site, and effectively inhibit drug‐resistant tumor growth due to the inhibition of angiogenesis and necrosis in tumor tissues. Western blot analysis indicated that the gene expression of both ETS1 and MDR1 in vivo was considerably downregulated after the drug‐resistant tumor‐bearing mouse was treated with HPAD/siETS1 nanoassemblies. This study offers a new therapeutic delivery strategy targeting ETS1 for the effective multidrug‐resistant chemotherapy. Graphical abstract Figure. No caption available.

An antibacterial platform based on capacitive carbon-doped TiO2 nanotubes after direct or alternating current charging

Electrical interactions between bacteria and the environment are delicate and essential. In this study, an external electrical current is applied to capacitive titania nanotubes doped with carbon (TNT-C) to evaluate the effects on bacteria killing and the underlying mechanism is investigated. When TNT-C is charged, post-charging antibacterial effects proportional to the capacitance are observed. This capacitance-based antibacterial system works well with both direct and alternating current (DC, AC) and the higher discharging capacity in the positive DC (DC+) group leads to better antibacterial performance. Extracellular electron transfer observed during early contact contributes to the surface-dependent post-charging antibacterial process. Physiologically, the electrical interaction deforms the bacteria morphology and elevates the intracellular reactive oxygen species level without impairing the growth of osteoblasts. Our finding spurs the design of light-independent antibacterial materials and provides insights into the use of electricity to modify biomaterials to complement other bacteria killing measures such as light irradiation.Bacteria are known to be sensitive to electrical interactions with the environment. Here, the authors report on a study into how the antibacterial properties of carbon-doped titania nanotubes are affected by capacitance after charging with direct and alternating currents.

Unusual anti-bacterial behavior and corrosion resistance of magnesium alloy coated with diamond-like carbon

Magnesium and magneisum alloys are promising materials in degradable biomedical implants and also have inherent anti-bacterial ability. A surface coating can reduce the surface corrosion rate of magnesium-based materials without compromising the anti-bacterial properties. In this work, diamond-like carbon (DLC) coatings are deposited on the AZ31 Mg alloy by one-step plasma immersion ion implantation and deposition (PIII&D). After PIII&D, the corrosion current density diminishes largely from 3.17 × 10−4 A cm−2 to 6.53 × 10−5 A cm−2. The pH and amounts of leached magnesium ions are also significantly reduced. Meanwhile, 3 × 104 bacteria seeded on the AZ31-DLC are completely annihilated within 6 hours in contrast to 5 × 103 live ones left on the untreated AZ31 and more than 6 × 108 on Si-DLC (DLC deposited on Si). The favorable anti-bacterial behavior of AZ31-DLC is attributed to the combined effects of favorable bacteria adhesion on the DLC surface and local release of hydroxyl and magnesium ions from the magnesium substrate via defects in the DLC films.

Valence State Manipulation of Cerium Oxide Nanoparticles on a Titanium Surface for Modulating Cell Fate and Bone Formation

Abstract Understanding cell–biomaterial interactions is critical for the control of cell fate for tissue engineering and regenerative medicine. Here, cerium oxide nanoparticles (CeONPs) are applied at different Ce4+/Ce3+ ratios (i.e., 0.46, 1.23, and 3.23) to titanium substrate surfaces by magnetron sputtering and vacuum annealing. Evaluation of the cytotoxicity of the modified surface to cultured rat bone marrow mesenchymal stem cells (BMSCs) reveals that the cytocompatibility and cell proliferation are proportional to the increases in Ce4+/Ce3+ ratio on titanium surface. The bone formation capability induced by these surface modified titanium alloys is evaluated by implanting various CeONP samples into the intramedullary cavity of rat femur for 8 weeks. New bone formation adjacent to the implant shows a close relationship to the surface Ce4+/Ce3+ ratio; higher Ce4+/Ce3+ ratio achieves better osseointegration. The mechanism of this in vivo outcome is explored by culturing rat BMSCs and RAW264.7 murine macrophages on CeONP samples for different durations. The improvement in osteogenic differentiation capability of BMSCs is directly proportional to the increased Ce4+/Ce3+ ratio on the titanium surface. Increases in the Ce4+/Ce3+ ratio also elevate the polarization of the M2 phenotype of RAW264.7 murine macrophages, particularly with respect to the healing‐associated M2 percentage and anti‐inflammatory cytokine secretion. The manipulation of valence states of CeONPs appears to provide an effective modulation of the osteogenic capability of stem cells and the M2 polarization of macrophages, resulting in favorable outcomes of new bone formation and osseointegration.