Zhengwei Wu

Mechanical and biological characteristics of diamond-like carbon coated poly aryl-ether-ether-ketone

Poly aryl-ether-ether-ketone (PEEK) is an alternative to metal alloys in orthopedic applications. Although the polymer provides many significant advantages such as excellent mechanical properties and non-toxicity, it suffers from insufficient elasticity and biocompatibility. Since the elastic modulus of diamond-like carbon (DLC) is closer to that of cortical bone than PEEK, the DLC/PEEK combination is expected to enhance the stability and surface properties of PEEK in bone replacements. In this work, PEEK is coated with diamond-like carbon (DLC) by plasma immersion ion implantation and deposition (PIII&D) to enhance the surface properties. X-ray photoelectron spectrometry (XPS), Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy demonstrate successful deposition of the DLC film on PEEK without an obvious interface due to energetic ion bombardment. Atomic force microscopy (AFM) and contact angle measurements indicate changes in the surface roughness and hydrophilicity, and nanoindentation measurements reveal improved surface hardness on the DLC/PEEK. Cell viability assay, scanning electron microscopy (SEM), and real-time PCR analysis show that osteoblast attachment, proliferation, and differentiation are better on DLC/PEEK than PEEK. DLC/PEEK produced by PIII&D combines the advantages of DLC and PEEK and is more suitable for bone or cartilage replacements.

Biocompatibility and bioactivity of plasma-treated biodegradable poly(butylene succinate).

Poly(butylene succinate) (PBSu), a novel biodegradable aliphatic polyester with excellent processability and mechanical properties, is a promising substance for bone and cartilage repair. However, it typically suffers from insufficient biocompatibility and bioactivity after implantation into the human body. In this work, H(2)O or NH(3) plasma immersion ion implantation (PIII) is conducted for the first time to modify the PBSu surface. Both the treated and control specimens are characterized by X-ray photoelectron spectroscopy, contact angle measurements and atomic force microscopy. The plasma treatments improve the hydrophilicity and roughness of PBSu significantly and the different PIII processes result in similar hydrophilicity and topography. C-OH and C-NH(2) functional groups emerge on the PBSu surface after H(2)O and NH(3) PIII, respectively. The biological results demonstrate that both osteoblast compatibility and apatite formability are enhanced after H(2)O and NH(3) PIII. Furthermore, our results suggest that H(2)O PIII is more effective in rendering PBSu suitable for bone-replacement implants compared to NH(3) PIII.

Dispersion of linear waves in quantum plasmas

The dispersion of linear waves in a uniform cold quantum plasma is derived using the quantum hydrodynamic equations with the magnetic field of the Wigner-Poisson system. The dispersion of the Langmuir wave becomes whistler-like due to quantum effects and, therefore, the Langmuir wave can propagate in a cold plasma. It is also found that quantum effects do not affect the dispersion of the left-handed, right-handed, and ordinary waves.

Osteoblast behavior on polytetrafluoroethylene modified by long pulse, high frequency oxygen plasma immersion ion implantation

Polytetrafluoroethylene (PTFE) is a commonly used medical polymer due to its biological stability and other attractive properties such as high hardness and wear resistance. However, the low surface energy and lack of functional groups to interact with the cellular environment have severely limited its applications in bone or cartilage replacements. Plasma immersion ion implantation (PIII) is a proven effective surface modification technique. However, when conducted on polymeric substrates, conventional PIII experiments typically employ a low pulsing frequency and short pulse duration in order to avoid sample overheating, charging, and plasma sheath extension. In this paper, a long pulse, high frequency O(2) PIII process is described to modify PTFE substrates by implementing a shielded grid in the PIII equipment without these aforementioned adverse effects. X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and contact angle measurements are carried out to reveal the surface effects of PTFE after long pulse, high frequency O(2) PIII and the results are compared to those obtained from conventional short pulse, low frequency O(2) PIII, O(2) plasma immersion, and the untreated control samples. Our results show that less oxygen-containing, rougher, and more hydrophobic surfaces are produced on PTFE after long pulse, high frequency O(2) PIII compared to the other 2 treatments. Cell viability assay, ALP activity test, and real-time PCR analysis are also performed to investigate the osteoblast behavior. It is clear that all 3 surface modification techniques promote osteoblast adhesion and proliferation on the PTFE substrates. Improvements on the ALP, OPN, and ON expression of the seeded osteoblasts are also obvious. However, among these treatments, only long pulse, high frequency O(2) PIII can promote the OCN expression of osteoblasts when the incubation time is 12 days. Our data unequivocally disclose that the long pulse, high frequency O(2) PIII technique is better than the other two types of traditional plasma treatment in the development of PTFE for bone or cartilage repair.

Equivalent Circuit Derivation and Performance Analysis of a Single-Sided Linear Induction Motor Based on the Winding Function Theory

A linear metro that is propelled by a single-sided linear induction motor (SLIM) has recently attracted much attention. Compared with the rotating-induction-machine drive system, the SLIM drive has advantages such as direct thrust without needing friction between the wheel and the railway track, small cross-sectional area, lack of gear box, and flexible line choice on account of the greater climbing capability and smaller turning circle. However, due to its cut-open primary magnetic circuit, the SLIM has a longitudinal end effect and half-filled slots on the primary ends, which can reduce the air-gap average flux linkage and thrust. Based on the winding function method, the SLIM is supposed to have the following three groups of windings: 1) primary windings; 2) secondary fundamental windings; and 3) secondary end effect windings. The proposed method considers the actual winding distribution and structure dimensions. It can calculate the mutual, self, and leakage inductance to describe the influence of the longitudinal end effect and half-filled slots. Moreover, a new equivalent model is presented to analyze the different dynamic and steady-state performance. Comprehensive comparisons between simulation and experimental results that were obtained from both one arc induction machine and one linear metro indicate that the proposed model can be applied to predict the SLIM performance and control scheme evaluation.

Quantum effects on Rayleigh–Taylor instability in magnetized plasma

The effects of the quantum mechanism and magnetic field on Rayleigh–Taylor (RT) instability in an ideal incompressible plasma are investigated. The explicit expression of the linear growth rate is obtained in the presence of fixed boundary conditions. It is shown that the magnetic field has a stabilizing effect on RT instability similar to the behavior in classical plasmas and RT instability is affected significantly by quantum effects. Quantum effects are also shown to suppress RT instability with the appropriate physical quantities. Some astrophysical parameters are discussed as an example to investigate the new effects.

Jeans instability in quantum magnetoplasma with resistive effects

The Jeans instability in dense quantum plasmas is investigated in the presence of two dimensional magnetic fields and resistive effects. The resistive effects are shown to introduce instability whether the perturbation is stable or not in the ideal magnetohydrodynamic model. The analytical expressions of the growth rate of Jeans instability are obtained for both the finite and remarkable resistive effects cases. The results are relevant to dense astrophysical objects, e.g., neutron stars and the interior of white dwarfs, as well as low-temperature laboratory plasmas.

Tailoring of Mesenchymal Stem Cells Behavior on Plasma-Modified Polytetrafluoroethylene

By altering the surface properties of polytetrafluoroethylene (PTFE) substrates using a special PIII technique, mesenchymal stem cells (MSCs) proliferation and osteogenesis can be promoted in culture without osteogenic supplements. The structures are created intrinsically in the PTFE for no risk of materials delamination. Large-scale features and locally different functions can also be readily produced on the same substrate by this technique.

Rat calvaria osteoblast behavior and antibacterial properties of O2 and N2 plasma-implanted biodegradable poly(butylene succinate)

Poly(butylene succinate), a novel biodegradable aliphatic polyester with excellent processability and mechanical properties, was modified by O(2) or N(2) plasma immersion ion implantation (PIII). X-ray photoelectron spectroscopy and contact angle measurements were carried out to reveal the surface characteristics of the treated and control specimens. The in vitro effects of the materials on seeded osteoblasts were detected by cell viability assay, alkaline phosphatase activity test, and real-time polymerase chain reaction analysis. Plate counting was performed to investigate the antibacterial properties. Our results show that both PIII treatments significantly improve the hydrophilicity of PBSu, and CO and nitrogen groups (CNH and CNH(2)) can be detected on the PBSu after O(2) and N(2) PIII, respectively. The modified samples exhibit similar compatibility to osteoblasts, which is better than that of the control, but O(2) PIII and N(2) PIII produce different effects according to the osteogenic gene expressions of seeded osteoblasts on the materials. Moreover, the N(2) plasma-modified PBSu exhibits anti-infection effects against Staphylococcus aureus and Escherichia coli but no such effects can be achieved after O(2) PIII.

Electrostatic drift modes in quantum dusty plasmas with Jeans terms

Electrostatic drift waves (EDWs) are investigated in nonuniform quantum magnetized dusty plasmas by taking into account dust gravitational effects with the help of the quantum hydrodynamic model. Ions and electrons are viewed as low-temperature Fermi gases, whereas quantum effects are neglected for the dust grains. The analytical dispersion relationship of the quantum EDWs is derived. Quantum effects are shown to affect the dispersion of EDW significantly. The Jeans terms induce a driftlike instability, which does not exist with the absence of gravitational effects. The criteria and growth rate of the kind of instability are presented. Our results are relevant to dense astrophysical objects such as the interiors of astrophysical compact objects (e.g., white dwarfs and neutron stars).