Y.X. Leng

Hemocompatibility of titanium oxide films.

Hemocompatibility is a key property of biomaterials that come in contact with blood. Surface modification has shown great potential for improving the hemocompatibility of biomedical materials and devices. In this paper, we describe our work of improving hemocompatibility with Ti-O thin films prepared by plasma immersion ion implantation and deposition and by sputtering. The structure and surface chemical and physical properties of the films were characterized by X-ray diffraction, Auger electron spectroscopy, atomic force microscopy (AFM), contact angle measurement, and Hall effect measurement. The behavior of fibrinogen adsorption was investigated by 125I radioactive isotope labeling and AFM. Systematic evaluation of hemocompatibility, including in vitro clotting time, thrombin time, prethrombin time, platelet adhesion, and in vivo implantation into dogs ventral aorta or right auricle from 17 to 90 days, proved that Ti-O films have excellent hemocompatibility. It is suggested that the significantly lower interface tension between Ti-O films and blood and plasma proteins and the semiconducting nature of Ti-O films give them their improved hemocompatibility.

Activation of platelets adhered on amorphous hydrogenated carbon (a-C:H) films synthesized by plasma immersion ion implantation-deposition (PIII-D)

Amorphous carbon films have attracted much attention recently due to their good biocompatibility. Diamond-like carbon (DLC), one form of amorphous carbon that is widely used in many kinds of industries, has been proposed for use in blood contacting medical devices. However, the blood coagulation mechanism on DLC in a biological environment is not well understood. Platelet adhesion and activation are crucial events in the interactions between blood and the materials as they influence the subsequent formation of thrombus. In this work, the behavior of platelets adhered onto hydrogenated amorphous carbon films (a-C:H) is investigated. Hydrogenated amorphous carbon films with different hydrogen contents, structures, and chemical bonds were fabricated at room temperature using plasma immersion ion implantation-deposition (PIII-D). The wettability of the films was investigated by contact angle measurements using several common liquids. Platelet adhesion experiments were conducted to examine the interaction of blood with the films in vitro and the activation of adherent platelets. The results show that the behavior of the platelets adhered on the a-C:H films is influenced by their structure and chemical bond, and it appears that protein interaction plays a key role in the activation of the adherent platelets.

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.

Structure and properties of passivating titanium oxide films fabricated by DC plasma oxidation

Abstract Titanium oxide layers have been synthesized on commercially pure titanium and TiN using direct current plasma oxidation. X-ray diffraction analyses reveal that the titanium oxide layers have the rutile structures. Micro-hardness, nano-hardness test, ball-on-plate wear experiment, scratch adhesion test and platelet adhesion investigation were conducted to evaluate the mechanical properties and blood compatibility of the titanium oxide layers. The results show that the commercial purified titanium sample micro-hardness increased by approximately 70% and the TiN sample micro-hardness increased by approximately 30% after plasma oxidation. It is believed that the increase in the film hardness is due to the development of TiO2 phases. The nano-hardness of titanium oxide layer reached 11 GPa. The wear resistance of the titanium oxide layer increased by a factor of 200 in Hanks solution. The adhesion strength between the titanium oxide layer and titanium matrix was as high as 25 N. Our results thus indicate that titanium oxide layers fabricated by this method have good blood compatibility and mechanical properties.

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.

In vivo study of Ti-O thin film fabricated by PIII

Over the past decade, much attention has been paid to anti-thrombotic materials applied in artificial organs. Surface modification has shown potential to improve the anti-coagulation of blood-contacting biomedical devices and materials w1-3x. Our in vitro study of Ti-O thin films has recently shown that Ti-O thin films possess superior blood compatibility to low temperature isotropic pyrolytic carbon (LTI-carbon) w1x. In this work, we have focussed our attention onto the in vivo evaluation of Ti-O thin films ,