Coatings for Bio-corrosion, Tribo-corrosion, and Bio-tribology

Tuesday, April 29, 2014 2:10 PM in Room Sunrise

Start Invited? Item
2:10 PM D2-2-3 Discovering Nanotechnology and Picotechnology for Medical Applications
Thomas Webster (Northeastern University, US)

Inspired from biological systems, nanotechnology (and more recently, picotechnology) is beginning to revolutionize medicine including improving the prevention, diagnosis, and treatment of numerous diseases. This talk will summarize efforts over the past decade that have synthesized novel nanoparticles, nanotubes, and other nanomaterials to improve medicine. Efforts focused on the use of nanomaterials to minimize immune cell interactions, inhibit infection, and increase tissue growth will be especially emphasized. Tissue systems covered will include the nervous system, orthopedics, bladder, cardiovascular, vascular, and the bladder. Materials to be covered will include ceramics, metals, polymers, and composites thereof. Self-assembled nano-chemistries will also be emphasized.

Thus, this talk will:

· Summarize recent advances in novel coatings for medical devices

· Emphasize novel properties of nano and pico-technology derived materials, and

· Identify how such materials can be used to decrease inflammation, infection and improve tissue growth.

2:50 PM D2-2-5 Improved Corrosion Resistance of Mg-Y-RE Alloy Coated with Niobium Nitride
Weihong Jin, Guosong Wu, Penghui Li, Paul Chu (City University of Hong Kong, Hong Kong Special Administrative Region of China)
Magnesium-based materials have attracted much attention in recent years due to their potential applications on cardiovascular stents and bone implants. However, their inadequate corrosion resistance in a physiological environment is the major obstacle limiting wider applications. In this work, a niobium nitride (NbN) film is deposited on Mg-Y-RE alloy (WE43) by reactive magnetron sputtering to improve the corrosion resistance. The structure of the nitride film is determined by X-ray photoelectron spectroscopy. The corrosion behavior of the untreated and NbN-coated WE43 is evaluated in simulated body fluids by electrochemical impedance spectroscopy, polarization tests, and immersion tests. The surface morphology of the samples before and after the immersion tests was examined by scanning electron microscopy to assess the extent of corrosion. Our results indicate that the corrosion resistance of the WE43 substrate is enhanced due to the formation of an anticorrosion nitride film and the NbN-coated WE43 may be promising in biomedical applications.
3:10 PM D2-2-6 Achieving Controlled Degradation and Better Biocompatibility of Magnesium by a Combination of Microarc Oxidation and Highly Textural Lamellar Mesostructured Mg(OH)2 Coatings
SankaraNarayanan Nellaiappan, IlSong Park, MinHo Lee (Chonbuk National University, Jeonju, Republic of Korea)
The development of magnesium based biodegradable implants is indeed a fascinating area of research. The rapid corrosion rate, generation of a large volume of hydrogen gas, accumulation of the hydrogen bubbles in gas pockets adjacent to the implant, increase in local pH of body fluid, are the most critical limitations in using Mg and its alloys as implant materials. Surface modification is a viable approach to overcome these limitations and among them microarc oxidation (MAO) has received considerable attention. The architecture of MAO coatings on Mg and its alloys has a three-layered structure; a porous outer layer with several large-sized, deep pores/cavities, a middle layer with less porosity and a thin barrier layer. The presence of pores and cracks in the MAO coatings on Mg and its alloys has both beneficial and detrimental effects. The micropores and cracks generated during the microarc discharges helps to release residual stress of the coating. The presence of a porous outer layer would significantly improve the mechanical interlocking effect, the bonding area and stress distribution across the adhesive-substrate interface of the joints, resulting in higher bond strength. However, the presence of a higher pore density on the surface of the MAO coatings increases the effective surface area and thus the tendency of the corrosive medium to adsorb and concentrate into these pores. This would facilitate quicker infiltration of the corrosive medium into the inner regions of the coating and subsequently down to the substrate, thus deteriorating the corrosion resistance of the coating by changing its local pH. The porous nature of MAO coating deposited on Mg and its alloys promotes inhomogeneous degradation due to severe localized corrosion attack and an ever-increasing surface area to volume ratio. The pores could be sealed using sol-gel and polymer coatings. However, this could impair the bioactive property of the coating, limiting the growth of calcium phosphates. The approach made in the present study aims to improve the corrosion resistance and biocompatibility of Mg by a duplex treatment - microarc oxidation (MAO) as the first stage treatment followed by deposition of a highly textural lamellar mesostructured Mg(OH)2 coating by a chemical treatment. The MAO coating deposited on Mg offers an improvement in corrosion resistance. The lamellar mesostructured Mg(OH)2 coating deposited on MAO coated Mg provides a unique morphological features and a higher surface area to promote deposition of calcium phosphate. The beneficial role of this duplex treatment in achieving a controlled degradation and better biocompatibility of Mg is addressed in this paper. (This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (2011-0028709 & 2013R1A1A2012322)).
3:30 PM D2-2-7 Improvement of Titanium Wear and Corrosion Resistance by Plasma Electrolytic Oxidation: Effects of Applied Voltage and Annealing Treatment
Carlos Laurindo, RicardoDiego Torres, Paulo Soares (Pontificia Universidade Católica do Paraná, Brazil); Jeremy Gilbert, Sachin Mali (Syracuse University, NY, US)

Despite the excellent properties of titanium such as, low density, corrosion resistance and biocompatibility, it usually presents poor tribological behavior. The Plasma Electrolytic Oxidation (PEO) promotes the transformation of the titanium substrate into a high hardness ceramic layer by the interaction of anodic oxide growth and plasma channel shock caused by the dielectric break down at high voltages, taking place in an aqueous electrolyte. The characteristics of the oxide layer, as well as its crystallinity can be tailored by changing the applied voltage during the PEO process or by a posterior annealing treatment at 600 – 800 oC. The aim of this work was to evaluate the influence of the PEO voltage and annealing treatment on the surface, wear and corrosion properties. Samples of cp-titanium were submitted to potentiostatic PEO treatment at 250 – 400V for 60 s in an electrolyte containing Ca and P. The surface morphology, cristallinity and roughness were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and profilometer. The corrosion properties were evaluated by open circuit potential, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The wear resistance was evaluated using a reciprocating linear ball on flat test machine. The results show that the annealing treatment increases the amount of rutile phase in the samples anodized with 250 and 300 V, but do not affect the crystallinity of the 350 and 400 V samples. The annealing also originated several cracks on the oxide layer for all annealed samples. There is an increase of wear resistance for the 250 and 300 V anodized samples after the annealing treatment. Rutile phase originated by annealing treatment or higher applied voltage is responsible for the wear resistance enhancement. However, the corrosion resistance is compromised due to the appearance of cracks on the oxide layer.



3:50 PM D2-2-8 Microstructure And Physical Properties Of Thermal Spraying AZO Coatings
Ming-Sheng Leu (Material and Chemical Research Laboratories, Industrial Technology Research Institute, Taiwan)
Zinc-oxide (ZnO) is a good photocatalyst in environmental purification owing to its simplicity, mild reaction conditions, and low cost. The novel Al-doped ZnO (AZO) powders with 3wt.% Al2O3 have been prepared as a photocatalytic coating ( > 1 0 μ m ) by using the air plasma spraying system. During thermal spray process, the AZO photocatalysts could be made as nano-particles composite coating structures. In this study, t he obtained AZO coatings were characterized by an optical microscop ( OM ), X-ray diffraction (XRD), scanning electron microscop (SEM) combined with EDX and UV-vis spectroscopy . According to the experimental results, the XRD patterns of both AZO powders and coatings were assigned to wurtzite structure of ZnO. The photocatalytic activities of the specimens were evaluated by phoyocatalytic degradation of methyl blue under UV-light, and sunlight irradiation. There are three different microstructures observed in the coating by using OM and SEM examination, including nano-particles, slate layers and holes. The high proportion of the nanoparticles ( > 20%) and porosities ( > 15%) distributed in the coating are helpful to improve the photocatalytic effect and its life time. The adhesion between the AZO coating and stainless substrate can be attended to about 52 MPa. By compare with TiO2 potocatalyst, it has 20% increasing on the phoyocatalytic degradation for this AZO coating.
4:10 PM D2-2-9 Significance of Corrosion and Tribocorrosion in Dentistry
Valentim Barão (University of Campinas (UNICAMP), Piracicaba Dental School, Brazil); Mathew Mathew (Rush University Medical Center, US); Leonardo Faverani, Wirley Assunção (Sao Paulo State University (UNESP), Brazil); Judy Yuan (University of Illinois at Chicago, US); Marcelo Mesquita (University of Campinas (UNICAMP), Piracicaba Dental School, Brazil); Cortino Sukotjo (University of Illinois at Chicago, US)

The use of dental implant for tooth rehabilitation has increased significantly in the past several years.In oral cavity, dental implant is exposed to many challenging environment such as saliva, different pHs, food, mouthwashes, infection and mastication load.Titanium and its alloy have been used for dental implant due to their good strength, corrosion resistance, and biocompatibility. However, titanium reacts chemically in electrolytic solution, and degrades mechanically during mastication. This corrosion/wear process causes the release of metal ions and wear particles into the surrounding tissue. Titanium ions and particles induce cytotoxicity and inflammation at the implant-bone interface and surrounding soft tissue, contributing to bone loss, and possibly implant failure. Other factors such as smoking and diabetes have long been indicated as risk factors for dental implants survival. In this presentation, we will discuss the basic corrosion kinetics and tribocorrosion behavior of titanium into simulated oral environment (saliva pH, temperature, mastication load). The roles of infection (simulated by the presence of lipopolysaccharide), smoking products (e.g. nicotine and cotinine), caffeine and mouthwashes (e.g. chlorhexidine gluconate, cetylpyridinium chloride and hydrogen peroxide) on the electrochemical activity of titanium will be presented. The influence of hyperglycemic condition observed in patients with diabetes will also be discussed. The possible implications of corrosion on the lipopolysaccharide affinity and periodontopathogenic bacteria attachment will be assessed.

This work was funded by the State of Sao Paulo Research Foundation (FAPESP), Brazil (#2011/20017-0 ; #2011/20021-7 ; #2012/14282-5 and #2013/08451-1 ).