Low-temperature Isotropic Pyrolytic Carbon Research Articles

CFD-DEM study on mixing characteristics of ZrO2 particles using the fluidized bed-chemical vapor deposition method

Fluidized bed-chemical vapor deposition (FB-CVD) is the key method to prepare low-temperature isotropic pyrolytic carbon (LTIC) for artificial heart valve. In the process of FB-CVD of pyrolytic carbon, ZrO 2 hollow particles are not only the bed particles forming the fluidized bed, but also play the role of heat carrier in the pyrolysis reaction of carbon source gas. The mixing degree of particles directly affects the coating quality of pyrolytic carbon. In this paper, a coarse-grained CFD-DEM model is used to conduct 3D numerical simulation of fluidized bed to investigate the effect of fluidization wind speed on the mixing characteristics (particle distribution, particle motion and Lacey index) of ZrO 2 hollow particles from the particle perspective. The results show that the mixing process can be accelerated by increasing the fluidization wind speed within a reasonable range, and radial mixing is more sensitive to fluidization wind speed than axial mixing. In addition, due to the different densities of particles in the furnace along the radial direction, the number of particle collisions and the influence of traction also differ greatly, resulting in more significant changes of particle velocity in the fountain area, while the velocity distribution in the annular gap area near the wall is relatively smooth.

<i>In Vivo</i> Study of Carbon Artificial Femoral Head

Hip hemiarthroplasty is a popular method for curing hip joint diseases. Comparing with the total hip replacement (THR), hip hemiarthroplasty has some advantages, such as simpler operation, lower cost and less injury. However, inevitable acetabular cartilage wear, which leads to ultimately conversion to THR, has been reported by many authors. That limits its applications. To solve this problem, more suitable biomaterial should be chosen to make the femoral head. In this research, a kind of carbon femoral head, which was made of graphite coated with low temperature isotropic pyrolytic carbon, was studied in vivo. Nineteen New Zealand adult white rabbits were divided into 3 groups. Every rabbit was taken the replacement operation and time-dependently killed after certain periods. X-ray photographs of the hip joint, macroscopic apperarance and histological morphometry of the neocartilage around the prosthesis, were examined. The results proved that the coating material of the femoral head was biocompatible and the neocartilage tissue around the prothetic head might protect the acetabulum from wear. However, because of the complicated physiological environment, further research is needed.

Wettability and bloodcompatibility of a-C:N:H films deposited by PIII-D

Abstract Wettability of amorphous carbon films can be adjusted by doping with other elements, including F, Si, Ti, O and N. In this study, nitrogen-doped hydrogenated amorphous carbon (a-C:H:N) films were deposited on silicon wafers (100) by plasma immersion ion implantation–deposition (PIII-D) using C2H2 + N2 gas mixtures. Film composition and bonding structure were analyzed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Surface morphology of the films was characterized using an extended multimode nanoscope atomic force microscope (AFM). Wettability examination was performed using the sessile drop method. Bloodcompatibility of the films was assessed by in vitro platelet adhesion test. The results suggest that a-C:N:H film synthesized at the highest N2/C2H2 flux ratio of 2/1 presents better anti-thrombotic property than the low temperature isotropic pyrolytic carbon (LTIC) and this improvement of bloodcompatibility can owe to the increase of hydrophilicity of the film caused by N incorporation in the carbon network and additional increase of surface roughness.

Pyrolytic Carbon Endoprosthetic Replacement for Osteonecrosis and Femoral Fracture of the Hip: A Pilot Study

Hemiarthroplasty in young patients has the potential for eliminating bearing wear, but has the disadvantage of cartilage wear. Low-temperature isotropic (LTI) pyrolytic carbon reportedly reduces cartilage wear in canine hemiarthroplasties. We therefore initiated a study in humans when it was released for human use. However, we observed failures in some patients. We therefore document and report the high failure rate observed in a subset of patients treated with an LTI pyrolytic carbon femoral head for osteonecrosis. We conducted a prospective pilot study of 17 patients treated with a titanium stem and an LTI pyrolytic carbon femoral head bearing surface for unipolar hemiarthroplasty for either femoral neck fracture (10 patients) or osteonecrosis (seven patients). One of 10 patients in the fracture group underwent conversion to THA as a result of arthritic progression compared with six of seven patients with osteonecrosis who underwent conversion to THA as a result of acetabular wear and severe groin pain. In this small series, patients with osteonecrosis had a higher rate of revision compared with the patients treated for femoral neck fracture. Level III, therapeutic study.

Platelet activation behavior on nitrogen plasma-implanted silicon

To enhance the surface biocompatibility of silicon-based materials used in micro-biomedical devices, nitrogen plasma immersion ion implantation (PIII) was performed on single-crystal silicon wafers. The platelet activation behavior on the N-PIII silicon was investigated in vitro, and the results indicate that the nitrogen plasma-treated surface exhibits less platelets activation than low temperature isotropic pyrolytic carbon (LTIC) that is a common material used in blood-contacting implants such as artificial heart valves. Our results also indicate that Si–N bonds enhance the surface hydrophilicity and combined with good critical surface tension, activation of platelets is mitigated. The mechanism of the platelet activation reactions is discussed from the perspective of the surface energy.

Characteristics of phosphorus-doped diamond-like carbon films synthesized by plasma immersion ion implantation and deposition (PIII and D)

Plasma immersion ion implantation and deposition (PIII and D) is an effective approach to synthesize high quality thin films for different industrial applications. This dual implantation and deposition process can produce a graded layer that mitigates delamination and poor adhesion. In this work, phosphorus-doped diamond-like carbon (DLC) films were synthesized by PIII and D. Thin DLC films with various phosphorus concentrations were produced by using different experimental parameters. The chemical composition was determined by X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS). Micrographs obtained by cross-sectional transmission electron microscopy (X-TEM) reveal good adhesion between the films and substrates. The biocompatibility was evaluated using platelet adhesive tests. The results show that the sample doped with an optimal amount of phosphorus exhibits less platelet adhesive and activation, and the overall results are better than that observed on low-temperature isotropic pyrolytic carbon (LTIC). Phosphorus-doped DLC films thus have potential applications in blood contacting medical devices.

Si–N–O Films Synthesized by Plasma Immersion Ion Implantation and Deposition (PIII&D) for Blood-Contacting Biomedical Applications

Silicon-Oxynitride (Si-N-O) films were fabricated on silicon wafers by silicon cathodic arc combined with plasma immersion ion implantation and deposition. The blood compatibility of the films was assessed by platelet-adhesion test and fibrinogen conformational change measurements to evaluate the viability of the materials in biomedical engineering. Significantly, a better platelet-adhesion behavior, as manifested by a smaller number and weaker aggregation as well as pseudopodium, was observed on the Si-N-O samples compared to the low-temperature isotropic pyrolytic carbon, which is the most common material used in blood-contacting biomedical devices such as artificial heart valves. Enzyme-linked-immunoassay measurements that disclose fibrinogen conformational changes show results that are consistent with the platelets' behavior, which is believed to be involved in the activation process. The good blood compatibility of the films can be attributed to the high hydrophilicity and surface free energy arising from the Si-N, Si-N-O, and Si-O bonding states. The interfacial reactions between fibrinogen, platelets, and material surface are discussed from the perspective of thermodynamics. The promising blood compatibility of the Si-N-O films is of both scientific and commercial interests in biomedical engineering

Biocompatibility of calcium and phosphorus doped diamond-like carbon thin films synthesized by plasma immersion ion implantation and deposition

Diamond-like carbon has superior mechanical and chemical properties and has been widely studied as coatings in the optics, magnetic media, semiconductor and biomedical industry. In order to enhance the properties and performance of the materials, elemental doping and multi-layer deposition have been proposed. In cardiovascular biomedical applications such as artificial heart valves, low-temperature isotropic pyrolytic carbon (LTIC) is the most widely used material, but its blood compatibility is still not adequate. Diamond-like carbon (DLC) is a potential substitute due to its good biocompatibility and mechanical properties. In addition, the blood compatibility may be further enhanced by introducing some biologically friendly elements. In this work, calcium and phosphorus doped DLC films were fabricated by plasma immersion ion implantation and deposition (PIII and D). The structure and biological properties were assessed using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), contact angle measurement, and platelet adhesion test. Reduced platelet adhesion was obtained from the calcium or phosphorus doped DLC compared to LTIC, suggesting that doping DLC with calcium or phosphorus enhances its surface blood compatibility.

Hemocompatibility of nitrogen-doped, hydrogen-free diamond-like carbon prepared by nitrogen plasma immersion ion implantation-deposition.

Amorphous hydrogenated carbon (a-C:H) has been shown to be a potential material in biomedical devices such as artificial heart valves, bone implants, and so on because of its chemical inertness, low coefficient of friction, high wear resistance, and good biocompatibility. However, the biomedical characteristics such as blood compatibility of doped hydrogen-free diamond-like carbon (DLC) have not been investigated in details. We recently began to investigate the potential use of nitrogen-doped, hydrogen-free DLC in artificial heart valves. In our experiments, a series of hydrogen-free DLC films doped with nitrogen were synthesized by plasma immersion ion implantation-deposition (PIII-D) utilizing a pulsed vacuum arc plasma source and different N to Ar (FN/FAr) gas mixtures in the plasma chamber. The structures and properties of the film were evaluated by Raman spectroscopy, Rutherford backscattering spectrometry (RBS), and X-ray photoelectron spectroscopy (XPS). To assess the blood compatibility of the films and the impact on the blood compatibility by the presence of nitrogen, platelet adhesion tests were conducted. Our results indicate that the blood compatibility of both hydrogen-free carbon films (a-C) and amorphous carbon nitride films are better than that of low-temperature isotropic pyrolytic carbon (LTIC). The experimental results are consistent with the relative theory of interfacial energy and surface tension including both dispersion and polar components. Our results also indicate that an optimal fraction of sp2 bonding is desirable, but an excessively high nitrogen concentration degrades the properties to an extent that the biocompatibility can be worse than that of LTIC.

Influence of oxygen pressure on the properties and biocompatibility of titanium oxide fabricated by metal plasma ion implantation and deposition

Titanium oxide with a rutile structure has superior optical properties and blood compatibility and is thermodynamically more stable than other forms. Titanium oxide thin films are deposited on (1 0 0) silicon and SiO 2 wafers by metal plasma ion implantation and deposition. The substrates are DC biased during the film deposition and the influence of the oxygen pressure on the characteristics of the coatings is investigated. X-ray diffraction indicates the existence of Ti 4O 7 in the film when the oxygen pressure is lower than 2.0×10 −2 Pa. As the oxygen pressure increases, the preferred orientation of the as-deposited titanium oxide film changes to the (2 0 0) high-index plane from the (1 0 0) low-index plane. The as-deposited titanium oxide films are subsequently annealed at 750 °C for 60 min in vacuum. The microstructure, resistance, composition, and blood compatibility of the films are assessed. Before annealing, the sheet resistance of the titanium oxide increases with higher oxygen pressure, and after vacuum annealing, the sheet resistance of some of the titanium oxide films increases by approximately 60 times. The results of the platelet adhesion experiments acquired from the annealed samples are similar to those from low-temperature isotropic pyrolytic carbon.

Mechanical properties of titanium oxide film deposited on LTI-carbon by IBED

Titanium oxide films were deposited on low temperature isotropic pyrolytic carbon (LTI-carbon) by ion beam enhanced deposition, and its mechanical properties such as ultramicrohardness, adhesion strength and fatigue property were studied. The microhardness of titanium oxide films prepared at different experimental conditions is maintained between 900 and 1000 kg/mm 2, when measured by UMHT-3 ultramicrohardness tester installed in the scan electronic microscope. The adhesion strength measurement results show that the adhesion strength of titanium oxide films on LTI-carbon substrate is approximately 0.314–0.47 GPa. The deposition of Ti interlayer is beneficial to improve the adhesion strength of the film. Subsequently, the film with the highest adhesion strength was coated on mechanical heart valves, and the fatigue and wear resistance of the film was investigated in a simulated heart-valve-working environment. After 675 500 times of opening-and-closing cycles, a circular abrasion trail appeared, whereas titanium oxide was still present in this area. No peel of the film was observed. When the cycles increased to 1 617 000 times, a small part of the film located at the inboard boundary of the wear trail peeled off, however, Ti still could be detected in the wear trail region.

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 [1–3]. 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) [1]. In this work, we have focussed our attention onto the in vivo evaluation of Ti–O thin films fabricated by plasma immersion ion implantation (PIII). The samples of titanium coated by Ti–O thin films were implanted in dogs’ hearts for 1 month. The results of the implantation showed that no thrombus was found on the surfaces of the Ti–O thin film, although the coagulation occurred on the surfaces of LTI-carbon.

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

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.

In vivo and in vitro investigation of titanium oxide layers coated on LTI-carbon by IBED

A layer of titanium oxide layer was coated on low temperature isotropic pyrolytic carbon (LTI-carbon), a prevailing material used for artificial heart valves' fabrication, by ion beam enhanced deposition (IBED). Glancing angle x-ray diffraction (GAXRD), X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectroscopy (RBS), atomic force microscopy (AFM) and transmission electronic microscopy (TEM) were used to characterize the deposited titanium oxide layer. The results show that the layer is polycrystalline with TiO, Ti2O3 and TiO2 coexisting and the root-mean-square (RMS) roughness of the surface is measured to be 8.7 nm. Platelet adhesion experiments show that the adherent platelet on titanium oxide layer is about four times less than that on LTI-carbon. In vivo investigation was performed by implanting LTI-carbon and a titanium oxide layer coated LTI-carbon into the femoral artery of a dog for 4 weeks. By means of scan electron microscopy, coagulation, fibrin, deformed blood red cells and aggregation of adherent platelet were found on the surface of the uncoated LTI-carbon, whereas, nothing but a few normal-shaped blood red cells were found on the titanium oxide coated LTI-carbon. It can be concluded that titanium oxide coated LTI-carbon has a much better blood compatibility than that of the LTI-carbon.

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

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.

Haemocompatibility of tetrahedral amorphous carbon films

Tetrahedral amorphous carbon (ta-C) films have been prepared by filtered arc deposition (FAD). The structure of the ta-C films was characterised by Raman Spectroscopy. The haemocompatibility of the formed films was studied by measurement of haemolysis ratio and observation of platelet adhesion. Compared with low-temperature isotropic pyrolytic carbon (LTI-carbon), which is being used as the material for artificial heart valves in clinical use at present, the ta-C films showed improved anticoagulation property. In order to understand the observed haemocompatibility results, the surface energy of the films was evaluated to analyse surface adsorption of human serum albumin (HSA) and human fibrinogen (HFG). However, it was found that the ta-C films are identical to LTI-carbon with respect to protein adsorption. It is believed that effective work function could be a reason for the observed variation in haemocompatibility between the ta-C films and LTI-carbon.

In vivo investigation of blood compatibility of titanium oxide films.

Titanium oxide films were synthesized by ionbeam-enhanced deposition. The films were prepared by depositing titanium atoms and simultaneously bombarding them with Xe+ ions at an energy of 40 keV in an O2 environment. An in vivo investigation, which entailed implanting low-temperature isotropic pyrolytic carbon (LTI carbon) cylinders, widely used to fabricate artificial heart valves, and titanium-oxide-coated LTI carbon cylinders with diameters of 5 mm and thicknesses of 0.5 mm into the ventral aorta of dogs for 14 days, showed that the amount of thrombus on the titanium-oxide-coated LTI carbon was much less than that formed on the surface of LTI carbon alone. Scanning electron microscopy (SEM) was used to observe the morphology of thrombus. On the titanium oxide films no platelet aggregation was found, almost no red blood cells were damaged, and almost no fibrin was found on the surface. However, all three characteristics were found on the surface of LTI carbon alone, proving that the blood compatibility of titanium oxide films is better than that of LTI carbon and titanium-oxide-coated LTI carbon.

Synthesis and blood compatibility of rutile-type titanium oxide coated LTI-carbon

Titanium oxide films were synthesized by ion beam enhanced deposition, where the films were prepared by depositing titanium atoms and simultaneously bombarding with Xe(+) ions at an energy of 40 keV in an O(2) environment. The titanium oxide films exhibit rutile-type structure with (100) orientation and the O/Ti ratio is about 2:1. Ti(2+), Ti(3+) and Ti(4+) coexist in the films.In vitro andin vivo investigations were used to investigate the blood compatibility of titanium oxide films. The results show that the blood compatibility of rutile-type titanium oxide fi is better than that of low temperature isotropic pyrolytic carbon (LTI-carbon), which is widely used to fabricate artificial heart valve. It is thought that rutile-type titanium oxide coated LTI-carbon most probably becomes new biomaterial to fabricate artificial heart valves.

Artificial heart valves:: improved hemocompatibility by titanium oxide coatings prepared by ion beam assisted deposition

Titanium oxide films were prepared by ion beam assisted deposition on an Eaton Z-200 system, in which the deposition of titanium evaporated from an electron beam evaporator and the bombardment with xenon ions at an energy of 40 keV extracted from an arc discharge-type ion source proceeded simultaneously in an O 2 environment. X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectroscopy (RBS) and X-ray diffraction (XRD) were used to characterize the deposited films. It was found that the atomic ratio of O/Ti is about 1.85:1. XPS analysis shows that Ti 2+, Ti 3+ and Ti 4+ chemical states exist on the titanium oxide films. The films deposited are in principle crystalline TiO 2 with a rutile structure. The films exhibit a highly (100) orientation and increase the degree of (100) orientation with ion beam current density decreasing. The blood compatibility of titanium oxide films was studied by in vitro and in vivo investigation. In vitro investigation includes clotting time measurement and platelet adhesion. Clotting time measurements show that the clotting time of titanium oxide films is longer than that of low temperature isotropic pyrolytic carbon (LTI-carbon), which is widely used as artificial heart valves in clinics. There are also fewer platelets adhered to and deformed on the titanium oxide films compared to the LTI-carbon. In vivo investigation, implanting LTI-carbon and titanium oxide coated LTI-carbon into the ventral aorta of a dog for two weeks, shows that the amount of thrombus on titanium oxide coated LTI-carbon is only about 1/8 compared to that of LTI-carbon. The relationship between chemical states and blood compatibility was discussed. We think that the existence of Ti 2+ and Ti 3+ is beneficial for blood compatibility.