Papers

ICMCTF2003 Session G6/TS4-2: Coatings and Thin Films for Biomedical Applications

Thursday, May 1, 2003 1:30 PM in Room Sunrise

Thursday Afternoon

Start	Invited?	Item
1:30 PM		G6/TS4-2-1 Process-phase-properties Relationship in Radio Frequency (rf) Plasma Synthesized Hydroxyapatite A.K. Khor, R. Kumar, P. Cheang (Nanyang Technological University, Singapore) This paper reports the radio-frequency (RF) plasma synthesis of ultra-fine bioceramic materials. A new processing technique called suspension plasma spraying (SPS) was used to synthesize ultra-fine (20nm-1µm)) hydroxyapatite (HA) and Zro₂-HA-CaP nano-composite powders. The ultra-fine powders were also consolidated using the spark plasma sintering method and in-vitro investigation of these sintered compacts revealed bioactive behaviour inherent in the original powder form. The influence of various plasma parameters feedstock and suspension concentration of HA in suspension on the characteristics of the as-sprayed powders were studied. The powders were characterised using particle size measurements, XRD analysis, SEM, FESEM, TEM, FTIR and DSC. It was realised from XRD and TEM analysis that a significant amount of amorphous material contributed to the overall phase composition after plasma spraying. With this information the XRD scans, from which relative decomposition values previously calculated, were more carefully scrutinised by the aid of an internal standard (Al₂O₃) and Rietveld analyses. The analyses were carried out for two sets of as-sprayed powders (plate power and suspension concentration variation) to fully quantify the phases (including amorphous phase) present after plasma spraying. Rietveld analysis was also utilised to determine structural changes to the HA lattice after the spraying process. The refinement of lattice parameters of HA in the as-sprayed powders indicated a large decrease in both a/c-axes corresponding to 15kW-plate power for both the concentrations of feedstock suspension. The amorphous content thus calculated was plotted against re-crystallisation peak areas obtained from DSC. The calculated amorphous content correlated well with the DSC peak areas giving a linear fit with R² value of 0.91. The correlation enabled the calculation of the heat of reaction (-85.84kJ/mol) for the crystallisation of the amorphous CaP into HA. The compacts consolidated from the ultra-fine HA powders by spark plasma sintering exhibited Young’s Modulus and hardness of around 103GPa and 550 HV, respectively, and fracture toughness (~1.2Mpam^-1/2) 1.5 times the values published in the literature for sintered HA. In-vitro results indicated that the compacts were highly bioactive revealing a re-precipitated layer of hydroxy-carbonated-apatite as early as one week after immersion.
2:10 PM		G6/TS4-2-3 Nitriding of Titanium Disks and Industrial Dental Implants using Hollow Cathode Discharge C. Alves Jr. (Universidade Federal do Rio Grande do Norte, Brazil); C.L.B. Guerra Neto, G.H.S. Morais, C.F. da Silva, V. Hajek (LabPlasma - Departamento de Fisica Teorica e Experimental - UFRN, Brazil) Hollow Cathode Discharge (HCD) was used in this work and the best temperature and pressure nitriding conditions, leading to higher surface contact area and an increased wettability of the surface of titanium disk samples and industrial dental implants, were searched. These surface properties are very important factors accelerating the osseointegration process. Samples were nitrided at pressures ranging from 1,5 to 2,5 mBar, temperatures ranging from 400 to 700°C, and exposing times between 1 and 2 hours. The samples were characterized by optical and electron microscopy and by X-ray diffraction. It has been observed that for temperatures above 500°C, the samples presented dark coloration and non-uniforms layers. Furthermore, these layers proved to be easily detached using ultrasound cleaning procedure. In contrary the best nitrided layer stability, increased surface roughness and better wettability has been observed for samples nitrided at 450 and 500°C, and at a lower pressure of 1,5 mBar. These conditions were used to nitride chosen industrially fabricated dental implants. Our results show increased surface roughness and superior wettability of the plasma treated dental implants over untreated. The starting clinical utilization of these dental implants is expected to prove faster osseointegration.
2:30 PM		G6/TS4-2-4 Investigation of Adhesion Between a Dielectric Layer and a Polymer Overcoat using a CV Measurement Technique V.D. Chiou, T.H. Wu, J.M. Ting (National Cheng Kung University, Taiwan, ROC) In recent years, the state-of-the-art molecular imprinting polymer (MIP) based sensor technology has received numerous attentions due to its high selectivity and high efficiency. This type of sensor uses field effect transistor (FET) as the sensing mechanism. The MIP layer is deposited on top of the gate material to immobilize the species that is to be detected. For successful sensing to occur, the adhesion between the MIP and the gate material is of great importance. In addition, the structure of MIP-based sensor calls for the use of polymeric encapsulant with a cavity for the exposure of the MIP and to host the liquid electrolyte. The polymeric encapsulant is therefore also in contact with the gate material. The adhesion between them is also critical to the integrity of the MIP-based sensor. As a result, we have investigated the adhesion between selected polymers, including both MIPs and encapsulation polymers, and different gate materials, including SiO₂, Si₃N₄, and TaN. In addition to conventional scratch test for the evaluation of adhesion, we have use a CV measurement technique to examine the adhesion in the presence of liquid electrolyte. Microstructure of the interface between polymer and gate materials was also examined using scanning electron microscopy.
2:50 PM		G6/TS4-2-5 Structure and Properties of Annealed Amorphous Hydrogenated Carbon (a-C:H) Films for Biomedical Applications P. Yang, R.K.Y. Fu, S. Kwok (City University of Hong Kong); Y. Leng (Southwest Jiaotong University, PR China); J. Wang (City University of Hong Kong); G.J. Wan, N. Huang, Y.X. Leng (Southwest Jiaotong University, PR China); P.K. Chu (City University of Hong Kong) When a biomaterial comes in contact with a biological body, biological substance denaturation will be concomitant with the physical interaction between the biomaterial surface and biological substance, such as blood protein denaturation resulting from electrical charge transfer. In this study, we focus on the relationship between the physical properties of amorphous hydrogenated carbon (a-C:H) and its blood compatibility. The films were fabricated using plasma immersion ion implantation - deposition (PIII-D), followed by annealing in vacuum between 200-600°C. A series of a-C:H films with different structures and chemical bonds were characterized by Raman, XPS, ERD and AFM. The blood compatibility of the films was evaluated employing in vitro platelet adhesion test. The adhesion, activation, and morphology of the platelets were investigated using scanning electron microscopy (SEM). The physical properties and surface characteristics of the films were also examined, including the carrier concentration and mobility, dielectric constant, resistivity, and surface wettability. The results were correlated with the biological data to elucidate the blood compatibility mechanism of a-C:H films.