Junqi Chen

Graphene sheets as anode materials for Li-ion batteries: preparation, structure, electrochemical properties and mechanism for lithium storage

Varied graphene sheets were prepared from the graphite oxide (GO) with different degrees of oxidation and furthermore their structural characteristics and electrochemical properties as anode materials for Li-ion batteries were investigated. From the expandable graphite with a low oxidation level, the obtained graphene sheets had a thick and intact sheet structure with good crystallinity. Its specific surface area was quite low and no porous structure was detected. The graphene sheets prepared from the GO precursor with a high degree of oxidation were quite thin and disordered, along with high specific surface area and plenty of pores. These ultrathin graphene sheets demonstrated high reversible capacity mainly in the way of lithium absorption, where the specific surface area was the key structural parameter. The thick graphene sheets prepared from the expandable graphite had good crystallinity with few defects and pores, and had a similar lithium storage mechanism to graphite, whereby lithium storage is carried out by intercalation reactions.

Concentration ranges of antibacterial cations for showing the highest antibacterial efficacy but the least cytotoxicity against mammalian cells: implications for a new antibacterial mechanism.

Antibacterial metal ions, such as Ag(+), Zn(2+) and Cu(2+), have been extensively used in medical implants and devices due to their strong broad spectrum of antibacterial activity. However, it is still a controversial issue as to whether they can show the desired antibacterial activity while being toxic to mammalian cells. It is very important to balance their antibacterial effectiveness with minimal damage to mammalian cells. Toward this end, this study is to identify the suitable concentrations of these three ions at which they can effectively kill two types of clinically relevant bacteria (Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli)) but show no obvious cytotoxicity on fibroblasts. Such concentration ranges are found to be 2.5 × 10(-7) M-10(-6) M, 10(-5) M-10(-4) M, and 10(-5) M-10(-4) M for Ag(+), Zn(2+), and Cu(2+), respectively. Investigation of their antibacterial mechanism shows that these three metal ions all show antibacterial property through a mechanism of damaging bacterial cell membranes by the generation of reactive oxygen species but surprisingly preserving the integrity of bacterial genomic DNA. The encouraging results indicate that antibacterial metal ions with controlled concentrations can bring considerable benefits to biomedical applications.

Reversibly Controlling Preferential Protein Adsorption on Bone Implants by Using an Applied Weak Potential as a Switch

A facile method is needed to control the protein adsorption onto biomaterials, such as, bone implants. Herein we doped taurocholic acid (TCA), an amphiphilic biomolecule, into an array of 1D nano-architectured polypyrrole (NAPPy) on the implants. Doping TCA enabled the implant surface to show reversible wettability between 152° (superhydrophobic, switch-on state) and 55° (hydrophilic, switch-off state) in response to periodically switching two weak electrical potentials (+0.50 and -0.80 V as a switch-on and switch-off potential, respectively). The potential-switchable reversible wettability, arising from the potential-tunable orientation of the hydrophobic and hydrophilic face of TCA, led to potential-switchable preferential adsorption of proteins as well as cell adhesion and spreading. This potential-switchable strategy may open up a new avenue to control the biological activities on the implant surface.

Nanostructured Conducting Polymers as Intelligent Implant Surface: Fabricated on Biomedical Titanium with a Potential-Induced Reversible Switch in Wettability

Conducting polypyrrole (PPy) nanotube arrays, nanotube networks and irregular films are deposited on biomedical titanium. By in situ application of weak periodic potentials, the nanostructured conducting polymers undergo a reversible switch in wettability, which is a redox process of dopant molecules (as hydrophilic groups) immobilized and de-immobilized on the surface of the conducting polymers.

Taurine-induced fabrication of nano-architectured conducting polypyrrole on biomedical titanium.

In this article, taurine, one of the small biomolecules associated with bone metabolism, is firstly utilized to induce the fabrication of nano-architectured conducting polypyrrole (NCPPy) on biomedical titanium in diverse pH values of phosphate buffer solution (PBS). Accordingly, the possible mechanism for the fabrication of NCPPy is proposed, which is dependent on the states of polytaurine from the polymerization of taurine, i.e., the inability of forming polytaurine and unordered restricted space results in taurine-incorporated and polytaurine-incorporated tightly packed nanoparticles (pH 6.2 and 8.0), respectively, and however, ordered restricted space constructed by polytaurine chains induces the fabrication of polytaurine-incorporated nanopillars (pH 6.8) and polytaurine-incorporated nanowire networks (pH 7.4).

Surface-Selective Preferential Production of Reactive Oxygen Species on Piezoelectric Ceramics for Bacterial Killing

Reactive oxygen species (ROS) can be used to kill bacterial cells, and thus the selective generation of ROS from material surfaces is an emerging direction in antibacterial material discovery. We found the polarization of piezoelectric ceramic causes the two sides of the disk to become positively and negatively charged, which translate into cathode and anode surfaces in an aqueous solution. Because of the microelectrolysis of water, ROS are preferentially formed on the cathode surface. Consequently, the bacteria are selectively killed on the cathode surface. However, the cell experiment suggested that the level of ROS is safe for normal mammalian cells.

Chondroitin sulphate-guided construction of polypyrrole nanoarchitectures.

Nanospheres, nanocones, and nanowires are three typical polypyrrole (PPy) nanoarchitectures and electrochemically polymerized with the dope of chondroitin sulphate (CS) in this study. CS, a functional biomacromolecule, guides the formation of PPy nanoarchitectures as the dopant and morphology-directing agent. Combined with our previous reported other PPy nanoarchitectures (such as nanotube arrays and nanowires), this work further proposed the novel mechanism of the construction of PPy/CS nanoarchitectures with the synergistic effect of CS molecular chains structure and the steric hindrance. Compared to the undoped PPy, MC3T3-E1 cells with PPy/CS nanoarchitectures possessed stronger proliferation and osteogenic differentiation capability. This suggests that PPy/CS nanoarchitectures have appropriate biocompatibility. Altogether, the nanoarchitectured PPy/CS may find application in the regeneration of bone defect.

Spatial charge manipulated set-selective apatite deposition on micropatterned piezoceramic

Mineralization plays a crucial role in the formation and remodeling of bone and charge has a positive influence on the mineralization by manipulating apatite deposition. In this paper, micropatterned piezoelectric K0.5Na0.5NbO3 (MPK) was constructed via laser-irradiation induced micro-zonal phase transition to manipulate set-selective apatite deposition. Two types of piezoelectric micro-zones on polarized MPK showed different charge densities, namely, higher charge density zone (H-zone) and lower charge density zone (L-zone). The micro-zonal piezoelectric difference on negatively polarized MPK (N-MPK) was ascertained by scanning Kelvin probe force microscopy (SKPM). With the manipulation of spatial charge, apatite selectively deposited on H-zone rather than L-zone, forming stripped zonal distribution. The furry platelet morphology of apatite was observed by scanning electron microscopy (SEM). Energy-dispersive spectroscopy (EDS) mapping observation indicated selective distribution of Ca and P elements in apatite. Phase composition of deposited apatite also can be regulated effectively via X-ray diffraction (XRD), which confirmed the existence of hydroxyapatite phase. Meanwhile, the apatite was further identified as carbonated hydroxyapatite by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The feasible and convenient way of manipulating apatite deposition selectively with spatial charge realized by micro-zonal piezoelectric materials will inspire future development in biomimetic materials designation for biomedical applications.

Nanomaterials as photothermal therapeutic agents

Curing cancer has been one of the greatest conundrums in the modern medical field. To reduce side-effects associated with the traditional cancer therapy such as radiotherapy and chemotherapy, photothermal therapy (PTT) has been recognized as one of the most promising treatments for cancer over recent years. PTT relies on ablation agents such as nanomaterials with a photothermal effect, for converting light into heat. In this way, elevated temperature could kill cancer cells while avoiding significant side effects on normal cells. This theory works because normal cells have a higher heat tolerance than cancer cells. Thus, nanomaterials with photothermal effects have attracted enormous attention due to their selectivity and non-invasive attributes. This review article summarizes the current status of employing nanomaterials with photothermal effects for anti-cancer treatment. Mechanisms of the photothermal effect and various factors affecting photothermal performance will be discussed. Efficient and selective PTT is believed to play an increasingly prominent role in cancer treatment. Moreover, merging PTT with other methods of cancer therapies is also discussed as a future trend.

A built-in electric field with nanoscale distinction for cell behavior regulation

To mimic the electrical properties of collagen fibrils on a bone surface, a built-in nanoscale electric field is formed on the surface of a polypyrrole (PPy) coating-decorated potassium-sodium niobate (KNN) piezoceramic. With the fabrication strategy, the piezoelectricity of KNN after polarization results in the formation of an electric field on the surface, which could be regulated by adjusting the polarization process. Then, conductive PPy nanoarrays (CPNAs) are obtained on the surfaces of the KNN piezoceramics. The conductive PPy transports the electric field to the coating surface, and the nanoarray morphology results in variations in the surface potential, leading to a built-in nanoscale electric field. Biological characterization indicates that CPNAs exhibit acceptable biocompatibility. Moreover, the nanoscale electric field regulates cell behavior, and the relatively high surface potential promotes cell proliferation, cell attachment and osteogenic differentiation.