Papers by Author: Paul K. Chu

Abstract: Diamond-like carbon (DLC) films were synthesized on a p-type silicon wafer using radio-frequency plasma composed of a mixture of Ar and C₂H₂ (ratio of 7 to 28). NH₃ plasma treatment of as-grown DLC substrate was carried out to generate surface-terminal amino groups while oxidation of as-grown DLC was performed in O₂ plasma. X-ray photoelectron spectroscopy (XPS) was used to characterize the different surface functions formed on DLC surfaces. Water contact angle measurements indicate different wetbility of modified surfaces. The cell (Mouse MC₃T₃-E₁ pre-osteoblasts) morphology and proliferation were monitored to evaluate the biocompatibility of the modified DLC surfaces. A cell count kit-8 (CCK-8 Beyotime) was employed to determine quantitatively the viable pre-osteoblasts. The cell viability assay shows that osteoblast proliferation are improved on NH₃ and O₂ plasma-treated DLC surface after culturing for 1day, 2days and 3 days. The cell-surface interactions are studied by fluorescence microscopy. There are more osteoblasts as well as better spreading on the aminated and oxidized surfaces after culturing for 3 days. In summary, compared to the as-grown sample, the modified DLC shows better biocompatibility.

Abstract: A simple synthesis route to high-quality ZnO nanorod is reported, utilizing ZnO thin films grown by Filtered Pulse Cathodic Vacuum Arc (FPCVA) deposition as seed layers and continuous growth by hydrothermal method. Depending upon the FPCVA deposited conditions, implanted voltages, thickness and annealing temperature of ZnO seed layer, the surface morphology of the ZnO nanorod on ZnO film was noticeably different. The average diameters of the nanorod on Al substrates varied from about 131.99 ± 23.87 to 418.17 ±75.50 nm. The grown ZnO nanorod showed a high crystallinity with energy gap of 3.37 eV and low defect density confirmed by UV/VIS Spectrometer and photoluminescence spectrum (PL). Large-area growth, quasi-aligned and high quality indicates that the ZnO nanorods produced have potential application in field emission and optoelectronic devices.

Abstract: Electro-Fenton process as a modified Fenton’s oxidation method in waster water treatment can provide a stable hydroxyl radical (·OH) source by continuous reaction of electrochemically generated H2O2 with Fe2+ ions for surface oxidation modification of NiTi shape memory alloy (SMA). In this work, effects of electro-Fenton process on blood compatibility and nickel suppression of NiTi SMA were investigated by SEM and XPS, inductively-coupled plasma mass spectrometry (ICPMS), hemolysis analysis and blood platelet adhesion test. It is found that electro-Fenton process is a notably effective way to impede out-diffusion of Ni from NiTi SMA in simulated body fluids during the entire ten week immersion period. It can also improve the hemolysis resistance and thromboresistance of biomedical NiTi SMA. The improvement of blood compatibility and nickel suppression of NiTi SMA can be attributed to the formation of surface titania film with a Ni-free zone near its top surface by electro-Fenton process.

Abstract: A graded titania film was formed on chemically polished NiTi shape memory alloy (SMA) by a novel deposition-assisted advanced oxidation method in a modified Fenton’s reagent containing titanium tetrachloride and then characterized by SEM and XPS. The effects of the titania film on leaching of harmful Ni ions from the NiTi substrate in simulated body fluids (SBF) is assessed by inductively-coupled plasma mass spectrometry (ICPMS). The results indicate that a thick and dense titania film was successfully fabricated in this in situ advanced oxidation reaction assisted with an additional deposition process by the hydrolysis of titanium tetrachloride on NiTi. The titania film can dramatically reduces Ni leaching from NiTi. XPS depth profiles show that the film possesses a smooth graded interfacial structure that boost mechanical stability.

Abstract: Ammonia implanted silicon was performed by using plasma immersion ion implantation (PIII) to form a silicon nitride films. Blood compatibility of the prepared samples was investigated by platelets adhesion testing. It showed less activation i.e. lower thrombosis risks occurs on the prepared silicon nitride films than control silicon sample. The enhanced blood compatibility of the material is attributed to the modified surface properties such as hydrophilicity from thermodynamic adsorption perspective, which is related to surface chemical bonding states achieved by PIII process.

Abstract: Cerium oxide films have been fabricated using dual plasma deposition. X-ray diffraction. (XRD) reveals a crystalline phase and X-ray photoelectron spectroscopy (XPS) shows that La exists predominantly in the +4 oxidation state. The activated partial thromboplastin time is longer than that of blood plasma and stainless steel. Furthermore, the numbers of adhered, aggregated and morphologically changed platelets are reduced compared to low-temperature isotropic carbon (LTIC). HUVEC cells exhibit good adhesion and proliferation behavior on cerium oxide films. This study suggests rare earth oxide films are potential blood-contacting biomedical materials.

Abstract: The long-term stability of plasma-sprayed dicalcium silicate (C2S) composite coatings is determined by the phase composition, crystallinity, and other properties. Zirconia reinforcement and post-spraying heat treatment are applied to C2S coatings simultaneously in this work. The stability of the coating increases evidently by reinforcement with 70wt% zirconia and heat treatment at 800oC for 4 hours. SEM reveals that the smooth glassy surface of the as-sprayed coatings is replaced by randomly dispersed crystals. Tris-HCl immersion test results show that the dissolution rate of the composite coatings decreases after the heat treatment.

Abstract: Nickel-titanium shape memory alloys (NiTi) have potential applications as orthopedic implants but out-diffusion of harmful Ni from the NiTi substrate during prolonged use inside a human body is a serious issue and the problem must be solved before the materials can be more widely used in orthopedics. In this work, we produce TiN and TiOx barrier layers by plasma immersion ion implantation (PIII) and study the effects of different working voltages (20kV, 30kV, and 40kV). The corrosion resistance of the plasma-treated materials is found to be much improved and the optimal processing windows are described in this paper.

Abstract: In-vitro evaluation of plasma sprayed wollastonite and dicalcium silicate coatings was carried out by SBF soaking test and osteoblasts seeding test. Apatite layers were formed on the surfaces of the two coatings indicative of the excellent bioactivity. The formation rate of apatite is higher on dicalcium silicate than on wollastonite. The cause is believed to be the presence of orthosilicate species in the dicalcium silicate coating promoting easier leaching by exchanging H3O+ ions from the solution with calcium ions concentrated in the orthosilicate positions. At the same time, loss of soluble silicon occurs, and it is supposed to enhance the repolymerization of the silica gel layer and provide the active sites for the nucleation of apatite. The outcome is that apatite forms faster on dicalcium silicate than on wollastonite. The data obtained from the osteoblasts seeding test indicate that the wollastonite and dicalcium silicate coatings promote the proliferation of osteoblasts and possess excellent biocompatibility.