ICMCTF2004 Session TS4-2: Coatings and Thin Films for Biomedical Applications

Monday, April 19, 2004 1:30 PM in Room Royal Palm 1-3

Monday Afternoon

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1:30 PM TS4-2-1 Interfactin Live Cells with Inorganic Materials
S. Bhatia (University of California, San Diego)
The ability to engineer highly functional tissue has applications in the development of both cell-based therapies and in vitro models of organs that can be used to study in vivo responses. In order to improve cell-based therapies (i.e. implantable tissues and bioartificial devices), we are interested in understanding the structure/function relationship of a particular tissue, the liver. Of particular interest is how the microenvironment around hepatocytes (the functional cell of the liver) affects cell fate and function. Microtechnology tools are utilized to control and study the role of cell-cell interactions, cell-extracellular matrix interactions, and soluble stimuli (e.g. oxygen tension) on hepatocyte function. Novel systems have also been developed to extend our findings in two-dimensional model tissues to three-dimensional constructs using photopatterned hydrogels. In order to develop in vitro models of liver tissue, live cells would be used as ‘sensors’ of in vivo responses. Our focus in this area has therefore been on the development of micro and nanotechnology tools to integrate cellular arrays with inorganic platforms. The combination of robust tools to manipulate live hepatocytes with insight on the role of their microenvironment should have broad clinical and technological implications.
2:10 PM TS4-2-3 Towards the Deposition of Tetrahedral Diamond-like Carbon Films on Hip Joints by Femtosecond Pulsed Laser Ablation
A.S. Loir, F. Garrelie, C. Donnet, F. Rogemond (Université Jean Monnet, France); B. Forest (Centre Sciences des Materiaux et des Structures, France); M. Belin (Laboratoire de Tribologie et Dynamique des Systemes, France); P. Laporte (Universite Jean Monnet, France)
Compared to conventional nanosecond laser ablation, femtosecond pulsed laser deposition (PLD) allows the production of higher energy ions (up to a few keV) in the plasma plume, which strongly affect the structure and properties of the deposited films. In this work, tetrahedral diamond-like carbon films (ta-C) have been deposited by femtosecond PLD on various substrates, including 316L stainless steel and ultra-high molecular weight polyethylene, in order to extend the wear resistance of materials used for hip joints replacement. The deposition process has been optimized to obtain smooth and wear resistant carbon films by ablating a graphite target in ultra-high vacuum conditions at room temperature, the laser fluence (energy density) ranging from 1 to 5J.cm-2. The films exhibit high wear resistance (in the 10-8 mm3.N-1.m-1 range) with moderate hardness (in the 20-30 GPa range), which may be favorable for the accommodation motion between contacting surfaces in a hip joint. Sputter cleaning of the substrates in an argon atmosphere prior to carbon deposition is widely investigated : tensile tests show that the adhesion of the films onto stainless steel substrates is remarkably enhanced by removing the contamination and oxidized top-coats. The capacity of these films to satisfy the biomedical requirements is discussed and the possibility of depositing homogeneous ta-C films on a 22.2 mm diameter hemispherical surface is examined. Finally homogeneous films have been deposited on a 316L stainless steel femoral head, the wear of which will be quantified using a walking simulator during one million cycles (one year of the human activity approximately).
2:30 PM TS4-2-4 Osteoblast Attachment on Amorphous Carbon Films
S.E. Rodil, C. Ramírez, R. Olivares, H. Arzate, J. Réyes-Gasga, C. Magaña (Universidad Nacional Autónoma de México, Mexico)
In this work we studied the osteoblasts response to amorphous carbon (a-C) films deposited on stainless steel substrates with different surfaces textures. For osteoblasts cells, attachment to the substrate is the first step in the process of cell/surface interactions and affects subsequent cellular and tissue response. Amorphous carbon films are characterized by very smooth surfaces that imaged the surface roughness of the substrate and many of their applications rely on this property. However, in the biomedical field, cell response is strongly influenced by the topography and for osteoblast cells it has been shown that rough surfaces enhance cellular attachment and differentiation. Therefore, during this work we modified the surface roughness of the substrate in order to obtain carbon films with different values of average roughness. The substrates were abraded or fine-polished to obtain four different average roughness; 0.01, 1, 2 and 3 microns. Surface topography before and after deposition of the a-C films was evaluated by profilometry and scanning electron microscopy (SEM), while chemical composition was determined by X-ray photoelectron spectroscopy. Human osteoblast cells were used to evaluate the effect of the different surface finishes on the adhesion. The number of attached cells after 24h of incubation was determined by enzyme linked inmunoabsorbance assay (ELISA), while morphological and cytoskeletal changes were monitored using SEM. Relations between surface composition, morphology, contact angle and cellular adhesion are discussed.
2:50 PM TS4-2-5 The Effect of Multilayer Filtered Arc Coatings on Mechanical Properties, Corrosion Resistance and Performance of Periodontic Dental Instruments
V.I. Gorokhovsky (Arcomac Surface Engineering, LLC.); B. Heckerman (American Eagle Instruments, Inc.); P. Watson (University of Toronto, Canada); N. Bekesch (Dental Clinic, Canada)

A large area filtered arc deposition (LAFAD) process was used to deposit a multi-layer cermet coatings on various dental scalers made of martensitic stainless steel1. A custom mechanical stroking device was used to include features capable of simulating the load and motion of dental scalers against enamel or dentin tooth surfaces in an aqueous environment. The abrasion resistance of the coating was tested by subjecting the coated instruments to vibratory tumbling. The working edge wear was than investigated by means of optical and electron spectroscopy as well as metallurgical cross-section profile analysis. Coating adhesion was characterized by Rockwell testing. Corrosion resistance of dental instruments with multi-layer coatings was studied by subjecting the instruments to conventional autoclave sterilization procedure. Comparison of the laboratory tests with the field testing results in dental clinical practice is presented. The mass production yield of high quality scalers with LAFAD coatings is discussed.

1 Vladimir I. Gorokhovsky, Rabi Bhattacharya and Deepak G. Bhat, Surface and Coating Technology, 140 (2) 2001, pp. 82-92.

3:10 PM TS4-2-6 ICP Assisted Sputter Deposition of TiC/CaO Nanocomposite Films for Biomedical Applications
W. Kulisch, P. Colpo, P.N. Gibson, G. Ceccone (Institute for Health and Consumer Protection, Italy); D.V. Shtansky, E.A. Levashov (Moscow State Institute of Steel and Alloys, Russia); F. Rossi (Institute for Health and Consumer Protection, Italy)
TiC/CaO nanocomposite films for biomedical applications have been deposited by a hydrid PVD/PACVD set-up from a TiC0.5 + 10% CaO target, which has been fabricated by self-propagating high-temperature synthesis. The deposition system combines dc magnetron sputtering in an Ar atmosphere with a high density inductively coupled plasma (ICP). The influence of the three major deposition parameters, i.e. the target current (power), the ICP power and the rf substrate bias voltage, which determine the flux of neutrals, the flux of ions, and the ion energy, respectively, on the growth rate, the composition and nature of the coatings was investigated. To meet this end, the films (with thicknesses between 1 and 3 µm) were characterized with respect to their morphology and structure, composition, crystallinity and bonding environment by e.g. scanning electron microscopy, atomic force microscopy, x-ray photoelectron spectroscopy, and x-ray diffraction. First tests were carried out in order to investigate the suitability of these films for biomedical applicationsn (e.g. surface roughness, adhesion, hardness, biocompatibility), and to establish correlations between these application relevant properties and the basic film properties.
3:30 PM TS4-2-7 Crystallization of CaTiO3 by Sol-Gel Synthesis and Rapid Thermal Processing
S.G. Holliday, A.V. Stanishevsky (University of Alabama at Birmingham)
In a number of studies, the formation of perovskite CaTiO3 (CTO) phase was observed at the interface layer when depositing hydroxyapatite coatings onto biomedical titanium alloys. Recently, CTO itself has been proposed as a suitable candidate for biocompatible coatings for medical implants, particularly Ti implants. At present, few studies have been conducted on the synthesis and characterization of physical properties of CTO for biomedical applications in load-bearing implants. In this study, we report on CaTiO3 coatings prepared on silicon, titanium, and TiO2 substrates by a sol-gel technique from an inexpensive stable precursor solution followed by rapid thermal processing (RTP) in oxygen or nitrogen. The structure, composition, and surface morphology of polycrystalline CTO coatings fabricated by RTP in the range of 500°C - 800°C for 30 s to 180 s were investigated by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Crystallization of smooth single-phase CTO coatings with thickness of up to 0.5 µm was observed at 600°C on Si substrates, while an intermediate phase of CaCO3 was observed at 500°C. While similar crystallization behavior of CTO was found for Ti and TiO2 substrates, the cracking of the coatings on early stages of annealing often occurred. We discuss the role of the CTO gel drying procedure before RTP, and the optimization of RTP parameters for crystallization of stable CTO coatings.
3:50 PM TS4-2-8 TiO2 Layers on Commercial Dental Ti Implants
M.J. Iribarren (National Atomic Energy Commission (CNEA), Argentina); M.E. De Las Heras (National General San Martin University, Argentina); F. Dyment (National Atomic Energy Commission (CNEA), Argentina)

Dental implants constitute the best artificial replacement of natural teeth. They consist, essentially, in a porous titanium screw root part to allow anchoring by bone tissue in-growth and a solid smooth finished supercrestal secondary stage, which is abutted to the artificial root implant. The two stage implantation procedure employed has the advantage that the tooth root is isolated from the oral cavity during the critical early stages of bone repaired and bone ingrowths into the pores. In the case of a gum retraction, the metallic colour of the Ti pillar can be seen, with the negative aesthetic consequence. In order to avoid this problem, a simple solution consisting in a white (or similar teeth colour) TiO2 layer which covers completely the pillar surface has been developed.

The advantage of this solution stems from: a) no new material is added to the implant, so, the adequate inert characteristic of Ti is maintained; b) mechanical properties remain basically unaffected; c) the process is applied after the complete manufacturing of the whole device; d) no special equipment is required, this means that no important costs are to be added to the final price of the implant.

The growth of the layer is produced by oxygen diffusion in Ti. The phase transformations involved in Ti matrix during the heat treatments do not affect the basic characteristics of the core of the implant. Thickness and adherence measurements were performed in order to determine the layer characteristics. Composition and homogeneity were determinate by X-ray diffraction and EMP techniques. The layers were developed firstly on flat samples and then, onto commercial implants showing similar characteristics in both.

4:10 PM TS4-2-9 Characteristics of Microfabricated Flexural Plate Wave (FPW) Device Based on PZT Thin Film for Biosensors
Y.S. Lee, J.Y. Kang, D.S. Yoon, T.S. Kim (KIST, South Korea)
Recently acoustic signals propagating on thin membrane, so called Lamb waves or flexural plate wave, have been explored as chemical gas sensor, protein molecule sensor, fluidic sensor, micro pump, particle transfer, pressure sensor and so on. This paper presents fabrication and characterization of microfabricated flexural plate wave device based on the piezoelectric PZT(Zr/Ti=52/48) thin films for biosensors. The device consists of interdigital transducers(IDT) patterned on a thin film composite membrane of silicon nitride, platinum electrode, and a sol-gel derived piezoelectric PZT thin film fabricated on a silicon substrate. The multilayer of 2µm thickness is released by the bulk micromachining technique to from a freestanding membrane. The flexural plate wave device is a solid-state, acoustic sensor. Acoustic waves are launched piezoelectrically, and propagate on the plate. The velocity of the acoustic wave is dependent upon the material properties of this thin plate. Thus, if we bind immunoglobulins directly to the device, the mass of the sensing plate is increased and a decrease in wave velocity, or resonant frequency, of the device results. The sensitivity of flexural plate wave device is about 1kHz/ng(-200 cm/g). This is characterized by Au deposition method which has the mass loading effect such as adsorption of protein. Also biotin-streptavidin binding shows the good linear response to streptavidin addition of the biotin coated Au on membrane. The FITC(Fluorescein Isothiocyanate) is labeled on streptavidin to check the binding between biotin and streptavidin. This is verified by using fluorescence microscopy.
4:30 PM TS4-2-10 In Vitro Studies of Coated and Surface Modified Metallic Materials by Employing Potentiodynamic Measurements in Thin Electrolyte Layers
M. Suaréz, L. Braganti, Z. Marcano, L. Agudo (Universidad Central de Venezuela); J.N. Feugeas (IFIR (CONICET-UNR), Argentian); M.H. Staia (Universidad Central de Venezuela)
The present work was carried out in order to set up a localized corrosion-monitoring test able to study the corrosion behavior in thin electrolyte layers of coated and surface modified 316L and 304 stainless steels, respectively as possible candidates for use as surgical materials. Magnetron sputtered PVD TiN coating on 316L stainless steel and pulsed ion nitrided 304 AISI stainless steel samples have been tested using a droplet of 5% NaCl solution. All the potential values were measured with respect to Hg/HgSO4 reference electrode. The results were compared with the substrate behavior in the same conditions and were correlated with the microstructural characteristics of the samples in each case. It has been shown that the corrosion monitoring technique employed is reproducible, easy to perform and is an excellent in vitro method for characterizing any surgical materials.
4:50 PM TS4-2-11 An Overview of DLC Coatings for Biological Applications
R. Hauert (EMPA, Switzerland)
Diamond-like carbon (DLC) is a class of materials with outstanding mechanical, tribological and biological properties. From in-vitro experiments it is known that by the incorporation of other elements into the DLC film, the ratios of the different proteins adsorbed on the surface can be changed. These proteins will then subsequently control cell attachment, cell proliferation and cell differentiation. Certain toxic elements such as Cu, Ag or V embedded in the DLC will, when exposed to a biological media, be released and cause toxic reactions. DLC has proven its outstanding tribological properties in many technical applications, mainly due to the build up of a transfer layer on the counterpart. In medical applications, i.e. the coating of load bearing joints that slide against UHMWPE, the different in vitro experiments apparently showed contradicting results, mainly due to the different experimental setups and especially the different liquids used as lubricants. However, when DLC slides against DLC in medical applications low wear rates could be demonstrated in different in vitro tests. DLC coatings have an excellent haemocompatibility, which is expressed in a decreased thrombus formation. When exposed to blood, an increased ratio of albumin to fibrinogen adsorption, as well as decreased blood platelet activation is observed on coated surfaces. A few DLC coated cardiovascular implants such as artificial heart valves, blood pumps and stents are already commercially available
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