Papers by Author: Bram Neirinck

Abstract: Magnesium and magnesium alloys are gaining considerable attention for use in biomedical applications due to their capability to completely resorb in the human body without noticeable side effects. For structural biomedical applications however, the resorption rate is too large. In order to decrease this rate researchers are investigating magnesium alloys with an increased corrosion resistance and/or biodegradable coatings, such as dense protein layers, which retard the resorption.In this work, we demonstrate the electrophoretic deposition of Bovine Serum Albumin (BSA) directly onto pure magnesium substrates using unbalanced alternating fields (AC-EPD). The effect of the obtained coatings on the corrosion behavior of the substrates was evaluated by potentiodynamic polarization. The results show that an albumin layer deposited by AC-EPD from a 50/50 ethanol/H₂O medium significantly reduces the corrosion rate.

Abstract: A new powder metallurgical processing route for porous Ti coatings on Ti-6Al-4V substrates based on the electrophoretic deposition (EPD) of TiH₂ suspensions is presented. After dehydrogenation and sintering in vacuum, coatings with a fully interconnected porosity (up to 51%, interconnective pore channels (IPC) of 2-50 µm) and high adhesion strength (up to 47 MPa) are obtained. Further evaluation of these coatings for potential use in biomedical implants shows that EPD Ti coatings are significantly less prone to bacterial adhesion compared to state-of-the-art vacuum plasma sprayed (VPS) coatings, while still allowing substantial bone ingrowth. Using EPD, the coating process can easily be transferred to complex-shaped implant components.

Abstract: Electrophoretic deposition is a promising method for the near net shaping of ceramics if deposit damage during removal from the electrode can be prevented. The latter can be achieved by providing a lubricated interface between electrode and deposit. During application of such a lubricant care must be taken that none of the electrode surface details are lost. Hence thins layers which closely represent the original electrode surface are needed. In the present work electrophoretic deposition of alumina powder on a thin layer of ionic liquid applied on polymer electrodes is described. After deposition this ionic liquid layers serves as a shear plane during the deposit removal. The resulting deposits exhibit a smooth surface quality and high green density. Furthermore experiments show that the ionic liquid can be used as a means for producing electrodes with areas at which deposition is locally prevented.

Abstract: The surface chemistry of a suspended particle greatly affects it behavior during electrophoretic deposition. The type and amount of surface groups determines whether the particles can be charged by interaction with the solvent. Furthermore, it is suspected that the surface chemistry plays a prominent role in the mechanisms governing the actual deposition of the particles. In the present work the surface chemistry of as-received and surface modified alumina powder is characterized by means of contact angle measurements and Diffuse Reflectance Infrared Fourier Transform spectroscopy. The wetting is measured using a modified Washburn method which yields quantitative contact angle values. The acid-base and dispersive surface energy components are calculated from these values using the surface tension component theory. Infrared spectroscopy was used to compare the surface groups of the treated and untreated powders and confirm the trends in surface properties as calculated from the contact angles.

Abstract: The recent development of the alternating current electrophoretic deposition (AC-EPD) technique has rendered it possible to deposit material from aqueous suspensions while preventing the electrochemical reactions associated with the application of high voltages on such systems. This does not only allow for more economical and ecological processes but also opens up electrophoretic deposition as a processing technique to a whole range of materials sensitive to either electrochemical reactions or non-aqueous solvents. Living cells can be considered as one class of such materials. In this paper the deposition of two types of bacteria, the Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli, and one type of yeast cells, Saccharomyces cerevisiae, is demonstrated.

Abstract: Recent developments demonstrated that liquid templates in the form of solid particles stabilized emulsions can be used to produce porous materials. The use of such emulsions offers the possibility to control the porous properties over a wide range of pore sizes and porosities for a variety of materials. In addition, the liquid nature of the template enables the formed products to be sintered without a low temperature debinding step. In this work, the electrophoretic deposition (EPD) of these liquid templates for the production of porous alumina is reported. The experimental parameters needed to obtain stable emulsions, their influence on the final porous properties, as well as the influence of the deposition parameters are discussed.

Abstract: From an environmental, safety and economic perspective water should be the solvent of choice for electrophoretic deposition under industrial circumstances. However, because of the electrolytic decomposition of water under the influence of direct current, the majority of EPD is carried out in non-aqueous solvents. In this work, experiments prove that deposits can be obtained from aqueous alumina suspensions while avoiding electrolysis of the medium by using unbalanced alternating current fields [1]. In addition it is shown that the formed deposits have a green density which is intrinsically higher than those formed by traditional DC EPD from ethanol based suspensions. A theoretical basis for both electrophoretic deposition by means of unbalanced alternating fields and the higher density of deposits formed by application of such fields is provided.

Abstract: The deposit can induce an extra potential drop near the electrode, depending on the suspension composition. This can result in a levelling off of the deposition rate in a constant-voltage deposition process. The magnitude of the extra voltage drop determines the uniformity of the deposit as function of the uniformity of the electric field present at the deposition electrode. It was experimentally proven that a uniform Al2O3 coating thickness was obtained in a non-homogeneous electrical field in ethanol with addition of HNO3, while the coating thickness varied uniformly with the E-field strength for a MEK with n-butylamine based suspension. The uniformity of the coating deposited from these suspensions was related to the measured potential drop over the deposit during electrophoretic deposition.

Abstract: A model was developed to explain the magnitude of the potential drop over the deposit for non-conductive powders during electrophoretic deposition (EPD). The magnitude of the potential drop over the deposit is explained in terms of a reduced ion transport through the deposit, as controlled by the pore potential that is related to the thickness of the electrostatic double layer relative to the pore radius and the magnitude of the surface potential of the powder particles. This model was validated for EPD of Al2O3 powder from ethanol-based suspensions with HNO3 addition. The specific resistivity of the deposit could be related to the calculated potential in the pores of the deposit.

Abstract: The electrical field drop over a deposit during electrophoretic deposition (EPD) determines the deposition rate and the uniformity of the deposit when a non-uniform electrical field is present. Due to the large practical consequences of a potential drop over the deposit, a procedure was developed to calculate the electrical field strength at the deposition front from currentconductivity measurements during EPD. The evolution of the electrical field strength during EPD was calculated for MEK and ethanol based suspensions. It was found that the suspension composition determines whether a potential drop over the deposit is present or not. EPD experiments on a membrane revealed that the extra potential drop is over the deposit and not caused by electrode polarization for the ethanol-acid based suspensions.