Xiubo Tian

Blood compatibility and sp3/sp2 contents of diamond-like carbon (DLC) synthesized by plasma immersion ion implantation-deposition

Diamond-like carbon (DLC) is an attractive biomedical material due to its high inertness and excellent mechanical properties. Using plasma immersion ion implantation-deposition (PIII-D), DLC films are fabricated on silicon substrates at room temperature. By changing the C2H2 to Ar (FC2H2/FAr) flow ratio during deposition, the effects of the reactive gas pressure and flow ratio on the characteristics of the DLC films are systematically examined to correlate to the blood compatibility. The thickness, surface morphology, composition, structure, sp3/sp2 content, as well as carbon–hydrogen bonding are studied using alpha-step profilometry, atomic force microscopy (AFM), Rutherford backscattering spectrometry (RBS), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR), respectively. The blood compatibility of the film is evaluated using in vitro platelet adhesion investigation, and the quantity and morphology of the adherent platelets are investigated employing optical microscopy and scanning electron microscopy (SEM). The Raman D-band to G-band intensity ratio is consistent with the adherent platelet quantity. Both first increase and then decrease with higher FC2H2/FAr flow ratios. This implies that the blood compatibility of the DLC films is influenced by the ratio of sp3 to sp2, not by the absolute sp3 or sp2 content. Our study suggests that DLC films with the proper sp3 to sp2 ratio and good blood compatibility can be fabricated by C2H2–Ar PIII-D using a suitable C2H2/Ar gas ratio.

Antithrombogenic investigation of surface energy and optical bandgap and hemocompatibility mechanism of Ti(Ta(+5))O2 thin films.

Recent improvements in the antithrombogenic properties of blood contacting biomaterials permit a hybrid design of layers for biomedical applications such as artificial heart valves and stents. Using magnetron sputtering and thermal oxidation, titanium oxide thin films containing tantalum. Ti(Ta(+5))O2, are fabricated to meet the challenge of enhanced hemocompatibility. The blood compatibility is evaluated in vitro by clotting time and platelet adhesion measurement, and in vivo experiments are also conducted. The Ti(Ta(+5))O2 films exhibit attractive blood compatibility exceeding that of low isotropic pyrolytic carbon. Physical properties such as surface energy and semiconductivity are found to play important roles. Our calculated results reveal that the smaller surface force gamma(s) of the film and the smaller blood film interfacial tension gamma(c,blood) are partially responsible for the enhancement of the blood compatibility. Based on the optical bandgap model, the film possesses better hemocompatibility because its optical bandgap of 3.2 eV is wider than that of fibrinogen having a bandgap of 1.8 eV. These factors result in thinner protein layers on the film surface, less protein denaturing, and overall excellent antithrombogenic properties.

Biomedical properties of tantalum nitride films synthesized by reactive magnetron sputtering

The biomedical properties of tantalum nitride thin films synthesized by reactive magnetron sputtering employing orthogonal design technology are investigated. The adhesion properties between the film and substrate can be enhanced by optimizing the sputtering gas pressure and substrate temperature. The hardness of the tantalum nitride films is greatly affected by the nitrogen partial pressure, and our results show that films deposited under the optimal conditions can achieve a hardness value of approximately 40 GPa. The blood compatibility of the tantalum nitride films, as evaluated by clotting time measurement and platelet adhesion tests, is compared to that of TiN, Ta and low-temperature isotropic pyrolytic carbon (LTIC). Our data reveal that the blood compatibility of our tantalum nitride films is better, and tantalum nitride is thus an excellent material for the fabrication of commercial artificial heart valves.

Fabrication of Ti–O/Ti–N duplex coatings on biomedical titanium alloys by metal plasma immersion ion implantation and reactive plasma nitriding/oxidation

Abstract Ti–O/Ti–N duplex coatings were fabricated on titanium alloys by metal plasma immersion ion implantation and reactive plasma nitriding/oxidation. The purpose of Ti–O is to improve the blood compatibility, and that of Ti–N is to improve the mechanical properties. X-Ray diffraction (XRD), microhardness tests, pin-on-disk wear experiments, and platelet adhesion investigation were conducted to evaluate the properties and blood compatibility of the coatings. The results reveal that the blood compatibility of the Ti–O/Ti–N duplex coatings is better than that of low temperature isotropic pyrolytic carbon (LTIC). The microhardness of Ti–O/Ti–N duplex coatings can reach 14 GPa. The wear resistance is also much better than that of Ti6Al4V alloy. The semiconductor nature of non-stoichiometric titanium oxide may be responsible for the observed improvement in the blood compatibility.

Corrosion resistance of titanium ion implanted AZ91 magnesium alloy

Degradable metal alloys constitute a new class of materials for load-bearing biomedical implants. Owing to their good mechanical properties and biocompatibility, magnesium alloys are promising in degradable prosthetic implants. The objective of this study is to improve the corrosion behavior of surgical AZ91 magnesium alloy by titanium ion implantation. The surface characteristics of the ion implanted layer in the magnesium alloys are examined. The authors’ results disclose that an intermixed layer is produced and the surface oxidized films are mainly composed of titanium oxide with a lesser amount of magnesium oxide. X-ray photoelectron spectroscopy reveals that the oxide has three layers. The outer layer which is 10nm thick is mainly composed of MgO and TiO2 with some Mg(OH)2. The middle layer that is 50nm thick comprises predominantly TiO2 and MgO with minor contributions from MgAl2O4 and TiO. The third layer from the surface is rich in metallic Mg, Ti, Al, and Ti3Al. The effects of Ti ion implantation...

Corrosion resistance and cytocompatibility of biodegradable surgical magnesium alloy coated with hydrogenated amorphous silicon

The fast degradation rates in the physiological environment constitute the main limitation for the applications of surgical magnesium alloys as biodegradable hard-tissue implants. In this work, a stable and dense hydrogenated amorphous silicon coating (a-Si:H) with desirable bioactivity is deposited on AZ91 magnesium alloy using magnetron sputtering deposition. Raman spectroscopy and Fourier transform infrared spectroscopy reveal that the coating is mainly composed of hydrogenated amorphous silicon. The hardness of the coated alloy is enhanced significantly and the coating is quite hydrophilic as well. Potentiodynamic polarization results show that the corrosion resistance of the coated alloy is enhanced dramatically. In addition, the deterioration process of the coating in simulated body fluids is systematically investigated by open circuit potential evolution and electrochemical impedance spectroscopy. The cytocompatibility of the coated Mg is evaluated for the first time using hFOB1.19 cells and favorable biocompatibility is observed.

Electrochemical Behavior Al2O3 ∕ Al Coated Surgical AZ91 Magnesium Alloy in Simulated Body Fluids

Magnesium alloys are potential materials for use in biodegradable hard-tissue implants, but the fast degradation rate in a biological environment limits their applications. In order to improve the corrosion resistance, a dense, adhesive, and biocompatible Al 2 O 3 /Al bilayered coating is fabricated on AZ91 magnesium alloy by means of filtered cathodic arc deposition. The electrochemical behavior is systematically studied in simulated body fluids using a potentiodynamic polarization test, open-circuit potential evolution, as well as electrochemical impedance spectroscopy. Our results indicate that the corrosion resistance of the coated alloy is significantly enhanced. The deterioration mechanism and corrosion process of the coating during immersion are discussed.

Structure and properties of biomedical TiO2 films synthesized by dual plasma deposition

Abstract Titanium metal and titanium alloys are among the most widely used materials in biomedical devices because of their relatively high corrosion resistance and good biocompatibility. It has been suggested that the physiochemical and dielectric properties of the surface native oxide play a crucial role in the biocompatibility. There is increasing evidence that titanium may be extensively released in vivo and, under certain conditions, accumulated in adjacent tissues or transported to distant organs. Therefore, it is necessary to synthesize thicker and denser TiO 2 films on titanium to enhance its biomedical properties. In this paper, we discuss our fabrication technique utilizing dual plasma generated by metal vacuum arc and radio frequency. The films fabricated consist of rutile crystal, although the substrates are not heated. As the oxygen partial pressure is raised, the intensity of the (101) and (110) diffraction peaks increases, and that of the (002) diffraction peak decreases. The preferred orientation of the TiO 2 film shifts from (002) to (110) as a result of the competition between the surface free energy and ion bombardment. At low oxygen pressure, the TiO 2 grain growth is mainly affected by ion bombardment, whereas thermodynamic factors affect the film growth at higher oxygen partial pressure. When the oxygen partial pressure reaches 0.93×10 −2 Pa, further increase in the oxygen flow rate does not change the film composition. The film is completely oxidized and only comprises the TiO 2 phase. The microhardness of the TiO 2 films increases with the oxygen partial pressure and reaches a maximum value of 19 GPa at 1.7×10 −2 Pa.

Properties of titanium oxide biomaterials synthesized by titanium plasma immersion ion implantation and reactive ion oxidation

Abstract As an artificial heart valve material, titanium oxide is superior to low temperature isotropic pyrolytic carbon in terms of mechanical properties and biocompatibility. The irregular shape of a heart valve makes conventional fabrication techniques like beam-line ion implantation and ion beam enhanced deposition (IBED) difficult. Plasma immersion ion implantation (PIII) does not suffer from the line-of-sight limitation and is an excellent technique for this purpose. In this work, titanium oxide thin films are synthesized on Ti6Al4V by titanium metal PIII and oxygen PIII. By controlling the deposition/implantation rate of titanium and oxygen plasma density, TiO x films with different compositions and properties can be fabricated. The film properties are evaluated by techniques including atom force microscopy (AFM), X-ray diffraction (XRD), and various mechanical testing methods. AFM results reveal that the TiO x film surface is quite dense without gross voids. The microhardness is enhanced with increasing oxygen partial pressure between the range of 0–3×10 −2 Pa and reaches a maximum value of 17 GPa at an oxygen partial pressure of 3×10 −2 Pa. The wear resistance is also much better than that of Ti6Al4V. In spite of our encouraging results, the TiO x films synthesized in our experiments are still too thin. In order to exploit its full potential as an artificial heart valve material, the films must be thicker. It can be achieved by using a more efficient metal arc source or by increasing the PIII duty cycle.

Special modulator for high frequency, low-voltage plasma immersion ion implantation

Plasma immersion ion implantation is a burgeoning surface modification technique and not limited by the line-of-sight restriction plaguing conventional beam-line ion implantation. It is therefore an excellent technique to treat interior surfaces as well as components of a complex shape. To enhance the implant uniformity and increase the thickness of the modified layer, we are using a high frequency, low-voltage process to achieve high temperature and dose rate to increase the thickness of the modified layer. The low voltage conditions also lead to a thinner sheath more favorable to conformal implantation. In this article, we will describe our special modulator consisting of a single ended forward converter with a step-up transformer. The modulator is designed to operate from 5 to 35 kHz and the output voltage is adjustable to an upper ceiling of 5000 V that is deliberately chosen to be our voltage limit for the present experiments. We will also present experimental data on SS304 stainless steel materials ...