Papers by Author: H. Sun

Abstract: The magnetic filed arrangement of unbalance magnetron sputtering can be changed employed to expand the plasma region and induce more ions to bombard the films for fabricating excellent quality films. In this paper, four targets closed-filed unbalance magnetron sputtering was introduced, the effect of the different magnetic field arrangement on the titanium oxide films properties was investigated. By changing the distance from target to vacuum center, the different unbalance state of the magnetic field was formed around the substrate. The titanium oxide films were synthesized at different unbalance state of the magnetic field. The microstructure of the titanium oxide films was studied by X-Ray Diffraction (XRD), and the residual stress measurement for the films was determined by grazing incidence XRD. The results revealed that the higher unbalance of the magnetic field around the substrate, the higher ion current of the substrate. Comparing with increasing the substrate bias voltage, the ion current increased 2~4 times through changing magnetic field arrangement to induce higher unbalance of the magnetic field. Ion/atom ratio increase was in favor of rutile phase formation for titanium oxide film. The unbalance state increase resulted in more higher compressive stress in the films.

Abstract: CrN coatings were deposited on cemented carbide substrates by filtered cathodic vacuum arc technique (FCVA). The effect of different deposition parameters: nitrogen partial pressure, substrate-bias voltage and preheating of the substrate, on the structural and mechanical properties of the coating was investigated. X-ray diffraction analysis was used to determine the structure and composition of the coatings. The tribological behaviour and wear properties of the coatings against Si3N4 ball at different normal loads were studied under reciprocating sliding condition. The results showed that a smooth and dense CrN coating with good properties can be obtained provided a pure Cr interlayer was pre-deposited. The optimal deposition parameters were the nitrogen partial pressure of 0.1 Pa, substrate-bias voltage of -100 V. Preheating of the substrate was no good for improving the properties of the coating. The FCVA CrN coating showed high hardness and good wear resistance, which was probably attributed to its smooth surface and dense microstructure. The wear mechanism of the CrN coating was a combination of abrasion and oxidation. However, the coating flaked off at high normal load due to the deficient adhesion strength of the coating to the substrate.

Abstract: One of the most applications of HIPSN(Hot-Isocratic Pressed Silicon Nitride) ceramic ball bearings is applied to the high-speed spindle of numerical control machine tools and high-speed precise mechanics. However, it is very difficult to process the HIPSN ceramic ball bearing. In this paper, a new grinding process method, taper rubbing method, is applied to process the HIPSN ceramic ball. Mechanical analysis of taper rubbing method is given, and the influence of grinding parameters on the ceramic material excision rate, surface quality of ceramic ball and wear and tear ratio of diamond wheel is studied by taper rubbing method. The experimental results show that the HISPN ceramic balls of G3 and G5 are obtained with taper rubbing method by properly controlling the motion of HIPSN ceramic balls and selecting reasonable processing technological parameters.

Abstract: In this paper, polyethylene glycol (PEG) of various different molecular weights was grafted onto PET films using plasma surface grafting modification. The surface structure of PEG-grafted PET films was analyzed by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS), suggesting that the surface structure and composition of PET films changes due to the presence of PEG. Blood compatibility was characterized by in vitro platelet adhesion experiments and coagulation factors. The tests of platelet adhesion and coagulation factors in vitro suggest that PEG grafted onto polymer surfaces can improve the blood compatibility of PET films remarkably. The modified PET films were pre-coated with albumin and fibrinogen respectively; platelet adhesion tests in vitro then indicated that samples pre-coated with albumin have better blood compatibility than with fibrinogen, resulting in the conclusion that the albumin can improve blood compatibility. The contact angle of PEG-grafted films was measured by the sessile drop method and the surface free energy and interface free energy were induced. It is indicated that the PEG-grafted PET films have the characteristic of preferentially adsorbing albumin.

Abstract: Biomedical PET films were modified by the approach of chitosan-surface-grafting. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) revealed that chitosan molecules were successfully grafted on the PET surface. The bacterial adhesion on the modified surface was evaluated by bacteria plate counting in vitro and scanning electron microscopy (SEM). The results testified that chitosan did make the surface of PET become more antibacterial. The free energy of adhesion (∆Fadh) between the bacteria and the chitosan-immobilized surface of PET was calculated. The value of the ∆Fadh was positive, which suggests that the process of bacterial adhesion on the modified PET surface was not thermodynamically favorable, namely, not spontaneous.

Abstract: We report a study involving chitosan chains immobilized on poly (ethylene terephthalate) (PET) films by plasma and ultraviolet (UV) grafting modification. The surface structure of the modified PET is determined by means of attenuated total reflection Fourier transform infraed spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). The results show that the chains of chitosan are successfully grafted on the surface of PET. Platelet adhesion evaluation in vitro is conducted to examine the blood compatibility in vitro. Scanning electron microscopy (SEM) and optical microscopy reveal that the amounts of adhered, aggregated and morphologically changed platelets are reduced on the chitosan-immobilized PET films. The number of platelet adhered on the modified film is reduced by almost 48% compared to the amount of platelets on the untreated film. Our result thus shows that chitosan immobilized on the PET surface improves blood compatibility.

Abstract: Amorphous hydrogenated carbon (a-C:H) thin films were deposited on silicon wafers and Ti6Al4V substrate using plasma ion immersion implantation and deposition (PIII-D) at room temperature (R.T.). The composition and structure of a-C:H films were employed by X-ray photoelectron spectra (XPS) and Raman spectra. Nano-indenter tests measured the hardness of the films. In addition, wettability and bloodcompatibility were investigated. In this paper, the effects of hydrogen content on structure, mechanical properties, surface wettability and haemocompatibility were discussed.

Abstract: Surface modification has shown great potential for improving the hemocompatibility of biomedical materials and devices. In this paper we describe our work on improving blood compatibility with Ti–O thin films prepared by unbalanced DC magnetron sputtering. The structure and surface chemical and physical properties of the films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), SEM, sheet resistance tests, and Hall effect measurements. The sheet resistance of the titanium oxide samples increased with oxygen pressure and shows a sharp increase when only TiO2 exists in the films. The band gap, carrier density and sheet resistance of the titanium oxide films synthesized at different oxygen pressure are different. These properties affect blood compatibility significantly. We suggest that the semiconducting nature of n-type Ti–O films with bandgap 3.0~3.2 eV, sheet resistance greater than 1 Ω.cm and carrier density of about 1.17 x 1016cm-2 leads to their excellent blood compatibility.

Abstract: Aminopropyltriethoxysilane (APTE) was covalently interacted with hydroxyl on the surface of Ti-O films prepared by magnetron sputtering, and albumin and heparin were immobilized on the APTE-coated surface with addition of 1-ethyl-3- (3-dimethyl aminopropyl) carbodiimide (EDC) as cross-link agent. X-ray photoelectron spectroscopy (XPS) was used to investigate the modified surface. Contact angle results indicate that there was an increase in the contact angle to the surface of APTE-coated Ti-O films, and a decrease in the contact angle to the surface of albuminand heparin-immobilized surfaces. Blood platelet adhesion in vitro was improved significantly after immobilization of albumin and heparin on Ti-O films. Endothelial cell (EC) culture tests showed that EC could grow on the surface of Ti-O films immobilized with albumin and heparin, but the growth and proliferation behavior of endothelial cells was not as good as on naked Ti-O films. This investigation showed that the surface of bio-inert inorganic materials immobilized with biological molecules is feasible and effective for improving the blood compatibility.

Abstract: In the present paper, the scientific basis, technique approaches, the present status and the development trends of surface modification for blood contacting materials are discussed briefly. The work in authors’ Lab. is also presented.