ICMCTF2012 Session DP: Symposium D Poster Session

Silver nanoparticles (NPs) have been extensively used to provide antibacterial properties to several commercial devices such as sportswear, toys and baby articles, among others. In fact, numerous reports have been published during the last few years regarding silver NPs attaining antimicrobial properties in countless kinds of materials and for a considerably good number of microorganisms. However, the durability of this effect is ignored in most of those reports, precluding their use in long term applications. Thus, this effect gains particular importance when dealing with applications involving the human body: the so-called biomaterials.

In this work ZrCN coatings doped with Ag NPs were produced on SS316L by unbalance magnetron sputtering using two targets, Zr and Zr/Ag in an Ar, C₂H₂, N₂ atmosphere. In order to investigate the evolution of silver dissolution and the corrosion resistance, these ZrCN with Ag NP’s were immersed for different periods of time, on three different electrolytes. 0.89% NaCl and phosphate buffer saline (PBS) with and without proteins ( 1.0 g/l bovine serum albumin ) were used to simulate the human body fluids. The former was selected due to its simplicity which permits to avoid the signal from other components in order to determine the kinetic mechanisms of the silver ions release. However, the latters were utilized in order to understand the influence of phosphates and proteins in this process. Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to determine the content of silver ions in the electrolytes, as a function of the immersion time. Electrochemical impedance spectroscopy (EIS) and potentiodynamics curves were used to evaluated the electrochemical response of the samples. A profile evaluation of the films before and after immersion was methodically carried out by means of glow discharge optical emission spectroscopy (GDOES). Structural and morphological characterizations were carried out by X-ray diffraction (XRD) and Scanning electron microscopy (SEM), respectively. Finally, morphological and structural characterization, silver content evolution and electrochemical response have been correlated, and a model containing information about morphology, structure and ions kinetics is performed.

In this study, plasma surface treatment was introduced as a method for controlling the drug release. Currently, the implantation of DES with surface coating of a drug-containing polymer, is the most powerful way to treat coronary artery disease. DES contains antithrombotic drugs that suppress the proliferation of smooth muscle cells in the stented segment of the artery. Although DES was remarkably successful in preventing restenosis, DES still has a disadvantage for not preventing restenosis at the implant site due to the relatively vast drug release from the stent surface in the early stage of the release.

To achieve the precise control of the drug release, we focused on plasma treatment which had no risk of damaging the fine surface of the stent. Oxygen and argon were selected as working gas. Several polymers were used as drug-reservoir materials, where it was necessary to achieve the controllable and sustainable drug release from the polymers. Three biocompatible polymer films were selected as base drug-reservoir materials: hydrophilic 2-metacryloyloxyethyl phosphorylcholine (MPC), hydrophobic poly (ethylene-co-vinyl acetate) (EVA), and less hydrophobic polyurethane (PU). These samples were soaked in 2mL of medium of phosphate-buffered saline with 10% ethanol. The drug release rate was measured by a spectrophotometer. By changing plasma treatment area of argon plasma at 0 %, 45%, 65%, and 100%, it was found that the initial burst release of drug, with EVA and PU films, was suppressed. These experimental results show that drug release could be effectively controlled by changing the plasma-treated area, which should be applicable to the next-generation DES system that would eventually prevent restenosis.

Different techniques are used to study protein adsorption on surfaces and each one of them present advantages and limitations. Thus, a combination of techniques allows a better understanding of the adsorption phenomenon.

Spectroscopic (SE) or Dynamic (DE) ellipsometry can be used to study protein adsorption in-situ in real time, i.e. the process kinetics, and the mass adsorbed on the surface at any time during the adsorption process. However, it does not allow chemical identification of the adsorbed material. X-Ray Photoelectron Spectroscopy (XPS) provide chemical identification of the adsorbed material but the studies are normally carried out ex-situ in a dry ambient after protein adsorption; thus, conformation of the proteins may differ from that in a wet ambient. Atomic Force Microscopy (AFM) can be used to monitor the adsorption in-situ or ex-situ. It does not allow chemical identification of the adsorbed material but it is possible to monitor the changes in surface morphology due to the adsorption.

In the present work, Ta₂O₅, Nb₂O₅ and TiO₂ thin films deposited on Si (100) substrates by Reactive Magnetron Sputtering were chosen as the study surfaces, mainly due to their potential as biocompatible coatings. Albumin (BSA) and Fibrinogen (Fib) were chosen as the study proteins. BSA is a small protein that readily adsorbs on surfaces and is the most abundant protein in serum; Fib is a bigger protein, highly abundant in blood and relevant for haemocompatibility.

The films were immersed in protein solutions and protein adsorption was monitored in-situ by DE during 2400 s; then, the protein layer adsorbed on the surface was studied using SE. After this, the films were rinsed and dried and the adsorbed protein layer was studied ex-situ using AFM and XPS.

The DE results showed adsorption occurring at different rates on the different surfaces, Ta₂O₅ showed the highest rate of adsorption for both proteins, leading to a surface mass density (Γ) of 0.9 and 1.2 mg/cm² for BSA and Fib, respectively. The lowest adsorption occurred on TiO₂ where Γ was 0.38 mg/cm² for BSA and 0.45 mg/cm² for Fib. The AFM results evidenced a change in the morphology and increasing of the roughness after protein adsorption; however, no trend, respect to the metal oxide films, was observed for these changes. The XPS results confirmed that the layer detected by SE was indeed adsorbed proteins. The analysis of the XPS spectra showed the same trend as SE; the highest N at. %, a signature of the protein adsorbed, corresponded to adsorption on Ta₂O₅, for BSA and Fib; while the lowest N at. % corresponded to TiO₂

Acknowledgements to L. Huerta and to CONACyT posdoctoral fellowship for PSB

Plasma-polymerized para-xylene (PPX), an alternative to biocompatible parylene coating for the surface treatment of medical devices has been developed in the previous study by adjusting the process parameters: pulse frequency of the input power (ω_p) and para-xylene monomer flow rate (f_p). PPX has an amorphous structure. It exhibits hydrophobicity, higher film growth rate and better cell proliferation than conventional parylene coating. In this study, in vitro (cell compatibility and platelet adhesion) tests and in vivo animal studies were done comparing PPX films deposited on industrial-grade silicone substrates and medical-grade silicone sheets.

Experimental results reveal that the PPX films deposited on industrial-grade silicone substrates at higher ω_p exhibit better cell proliferation in comparison with the medical-grade silicone sheets. However, PPX films show poor cell attachment regardless of the ω_p and f_p because of their hydrophobicity. Water contact angle of the deposited PPX films ranges from 98.5^o to 121.1^o, depending on the ω_p and f_p, This enables the deposited PPX films to exhibit a comparatively lower platelet adhesion ability than medical-grade silicone sheets. In the animal study, PPX-coated industrial silicone substrates result in similar local effects at 28 days (short-term) and 84 days (long-term) after implantation subcutaneously in the abdominal wall of rodents compared to medical-grade silicone sheets. These results suggest that the obtained PPX films are basically bio-inert and can be considered for application in the surface modification of biomedical devices where tissue fluids or blood will be encountered.

Keywords: plasma-polymerized para-xylene; biocompatability; in vitro; cell compatability; platelet adhesion; in vivo; animal study

Titanium and its alloys have been used successfully in several biomedical implants. However, they have certain disadvantages, such as poor osteoinductive properties and low corrosive-wear resistance. Several surface treatment techniques have been developed to overcome these drawbacks, such as alkaline and heat treatments, and microarc oxidation. There are also several techniques involving the application of bioactive coatings, such as dip coating, electrophoretic deposition, hot isostatic pressing, ion-beam sputtering, plasma spraying, conventional flame spraying and high velocity oxy-fuel combustion spraying. Among them, plasma spraying is the most popular method for coating implants. However, the deposition of these bioactive coatings is limited to the lacks in uniformity, mainly on implants with complex geometries. It results also on a poor adhesion of the coating due to the thermal expansion mismatch. To solve this problem, it is necessary to combine the biocompatibility of such coatings with the mechanical benefits of metal alloys, but with a surface that will serve as an anchor to the bioactive coating. The electrophoretic deposition technique has been studied as an alternative for the deposition of osteoinductive films on complex surface geometries by applying an electric field. Microarc oxidation is a simple and effective method to modify the surfaces of titanium implants and produce porous bioactive TiO₂ films. Our aim was to study the combination of the two techniques for surface modification of titanium, microarc oxidation and electrophoretic deposition, in order to obtain a bioactive homogeneous surface with good adhesion to the substrate. Bioactive glass-ceramic particles were deposited by electrophoresis on a porous film produced by anodic oxidation using a Ca-P containing electrolyte. X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) have been used to investigate the microstructure and morphology of the coatings. The adhesive strength between the TiO₂ films and substrate has been assessed using scratch test. Results indicate that a combination of micro-arc oxidation and electrophoretic deposition can provide a relatively thick and well adhered TiO₂ layer, with pores filled with bioactive glass-ceramic particles.

Ti and Ti alloys are widely used in many application. There are lots of studies about to improve their mechanical, structural, tribological and electrochemical properties e.g. by using Micro arc Oxidation (MAO) process. However, there is only a few study about improving the corrosion properties by using unipolar modes. In this study, MAO was used to produce oxide coatings on Cp-Ti alloy at both unipolar and bipolar voltage modes. The microstructure, surface morphology, phase composition and corrosion resistance of MAO films were analyzed by XRD, SEM and potentiodynamic polarization test unit. The results showed that the voltage mode is significantly influenced the microstructure and morphology. In addition, it was observed that the voltage modes effected the corrosion resistance of the oxide coatings.

Key Words: Ti alloys, MAO process, Corrosion resistance

The surface characteristics of the implant materials determine the biocompatibility. This study was to investigate the application of electrochemical anodization surface treatment to improve the corrosion resistance and biocompatibility of Ti-6Al-7Nb for implant application. An oxide layer with nanoscaled porosity was produced on the Ti-6Al-7Nb alloy surface through an electrochemical anodization treatment. Surface characterizations, including the topography, microstructure, chemistry, wettability and protein adsorption, of the test specimens were evaluated using various surface analysis techniques. The corrosion resistance of the test specimens was investigated using potentiodynamic polarization curve measurement in the simulated body fluid (SBF). The responses of human bone marrow mesenchymal stem cells on the test specimens were evaluated using various biological analysis techniques. Results showed that comparing to the untreated Ti-6Al-7Nb alloy, the presence of the nanoporous oxide layer on the anodized Ti-6Al-7Nb alloy increased the corrosion resistance (i.e. decreased the corrosion rate and passive current) in SBF. This nanotopography also improved the wettability, protein adsorption, cell adhesion, cell migration and cell proliferation on Ti-6Al-7Nb alloy. We would conclude that a fast and simple electrochemical anodization treatment can be used for the improvement of the corrosion resistance and biocompatibility of Ti-6Al-7Nb alloy surface for implant application.

Delamination has been the key issue barring widespread use of diamond-like carbon layers on joint implants. Silicon-based interlayers, such as grown from PACVD of silanes or silazanes, have been successfully used as interlayers for DLC in industry, but reports of failures in-vivo are published.

In the last years many surface modification processes have been developed in order to induce the osseointegration on titanium surface and thus to improve the implants’biocompatibility. So in this work, Ti surface has been modified by shot blasting and anodic oxidation processes in order to associate the good surface characteristics of both processes to obtain a roughouss and porous surface able to increase the titanium bioactivity. Otherwise the behavior and success of the implants can be evaluated by electrochemical measurements for a variety of reasons. Corrosion processes that occur at implant surfaces, the role of oxide films in the corrosion process, alloy biocompatibility and the electrochemical response of these biomaterials to mechanical and electrical transients.

Commercially pure titanium (grade 2) plates were ultrasonically cleaned with acetone, ethanol and water. The shot blasting was performed using Al₂O₃ particles with 280µm average diameter and air pressure of 20 bars during 6s. The anodic oxidation (AO) was carried out using NaOH electrolyte 0.1 mol/L and constant current density of 150 mA/cm² for a minute. After AO the specimens were dried at 40^oC for 24h. The morphology of the films was analyzed using a scanning electronic microscopy (SEM) Jeol JSM-6360LV. Structural changes were studied by X-ray diffraction (XRD Shimadzu XRD-7000) using Cu radiation at 40 kV and 20 mA to verify the phases present on the anodic film after heat treatment (HT) at 600^oC. The open-circuit potentials (OCP) were obtained using a conventional cell with SCE as reference electrode and Voltalab 40 (PGZ300) equipment. The electrolyte was a PBS (phosphate buffer solution) solution.

It can observed an increase on the rugosity of the blasted surface and a roughous and porous surface after AO process. The anodic film produced is thin and followed the blasted surface topography. It can be observed small pores size with regular shape covering all the surface. X-ray diffraction results showed that after HT at 600^oC/1h the presence of the anatase and rutile phases on the blasted and anodized surface.

Concerning to electrochemical measurements when the different samples were submitted to open-circuit conditions, the protective effect increases with the oxidation process, because the oxide layer. This protective effect could be evidenced by the open circuit potential (OCP) values: Shot blasted Ti surface: -0.728V , Polished Ti: -0.653 V and Blasted and oxidized Ti surface: -0.492 V. When the surface was blasted the OCP was more cathodic when compared with the Ti surface without surface treatments.

Titanium (Ti) and Ti alloys are used for the manufacture of dental and orthopedic prostheses. These materials must have appropriate properties, such as zero toxicity, good mechanical properties and resistance to corrosion. In addition, a short time of osseointegration is also desired to promote the rapid recovery of the patient . The film deposition or surface modification can be employed to obtain or improve these characteristics in a biomaterial. So in this work titanium oxide films produced on Ti commercially pure by anodic oxidation technique using a mixture of sulphuric and phosphoric acid as electrolyte in differerent proportion were analysed. Anodic oxidation was carried out at room temperature using a platinum counter electrode, 1.M H₂SO₄ plus 1M H₃PO₄ as electrolyte (proportion of (a) 1 H₂SO₄ : 0,5 H₃PO_4, (b) 1 H₂SO₄ : 1 H₃PO_4, and (c) 1 H₂SO₄ :1,5 H₃PO₄, at 180V/60s. The morphology of the films were analysed with scanning electron microscopy and hardness and elastic modulus profiles were obtained by instrumented indentation following the Oliver and Pharr method. The maximum applied load was 400mN in eight successive loading/unloading cycles at increasing loads using a Berkovich diamond indenter. It was observed that porous titanium layers were formed irrespective of the electrolyte mixture. Initially the film is relatively uniform with small and round pores and with the increase of the content of the phosphoric acid the porosity and the pore size increased. The anodic film obtained with same proportion of H₂SO₄ plus H₃PO₄ (case b 1:1) shows an appearance of pores and craters formed on the relatively flat ground oxide surface. The larger porous size (craters) observed in this case is probably due to interconnection of some pores. The nanoindentaion results showed that the anodic films obtained in different conditions present similar hardness values (3,3 GPa) and elastic modulus values (70,5 GPa) indicating that the H of anodic films increased compared with Ti substrate (2,2GPa) while elastic modulus decreased (110GPa).

Micro arc oxidation (MAO) is an effective technique to improve the surface properties of light materials by forming ceramic films on the surface. A number of studies have been carried out for depositing on Mg and Mg alloys. However, only a few have focused on wear, corrosion or tribocorrosion properties. In this study, MAO process was carried out on AZ91 Mg alloy in two different electrolyte solution namely phosphate-silicate and potassium stannate. The microstructures, morphology and crystallographic structure were analyzed by SEM and XRD. The wear, corrosion and tribocorrosion properties of the coatings were investigated by pin-on-disc wear test, potentiodynamic polarization test and combining tribocorrosion test unit, respectively. The results showed that solution has an important role on the wear, corrosion and tribocorrosion resistance of MAO coating.

Key Words: Mg alloys, MAO process, wear resistance, corrosion resistance and tribocorrosion resistance.