Master's student at the University of Kufa Bio tribo corrosion characterization of Ti-bio materials hydroxyapatite coating BY Ali Hameed Kamel Master's student at the University of Kufa Faculty of Engineering _ Department of Materials Supervisor : Asst. Prof. Dr. Ali Sabea Hammood

INTRODUCTION

Metals in Biomedical Applications

Titanium and its alloys .

Types of corrosion in implants

PHYSICAL PROPERTIES OF HYDROXYAPATITE MATERIALS The hydroxyapatite is known to be very brittle ,like most ceramics. The color of apatite depends on the type of apatite,but is usually green,gray,red,brown,blue,violet or colorless. The mineral may be transparent or opaque. Most apatite is fluorescent in UV RAY. Compressive strength is dependent on density and porosity. HA is reported to be similar that of the human tooth enamel. Degrades in pH 2.0 solution.

Limitations of Metallic Implants Solution Advantages Bio-inert : Do not promote the formation of apatite layer on its surface Release metallic ions : May combine with biomolecules and cause adverse biological reaction Solution Surface modification: Coating with bioactive material Advantages Accelerate bone healing and bonding of the coatings with bone Enhance the corrosion resistance of metallic implant where coating layer will reduce the release of metallic ions by acting a barrier Combine the mechanical benefits of metal alloys with bioactivity of bioactive materials

Hydroxyapatite coating on Ti-alloys

Dip-Coating Technique

Bio-Tribo corrosion *Tribology is concerned with the study of friction, lubrication and wear and corrosion is concerned with the chemical and electrochemical interactions between a material. *Tribo corrosion is a material degradation process due to the combined effect of corrosion and wear. * Bio-tribo corrosion covers the science of surface transformations resulting from the interactions of mechanical loading and chemical/electrochemical reactions that occur between elements of a tri-bological system exposed to biological environments

Corrosion behavior of Hydroxyapatite Coatings on Ti6Al4V Fabricated by Electrophoretic Deposition Experimental details 1-Electrophoretic deposition Three commercial submicron HA powders with different sizes and morphologies (spherical, flake-shaped and needle-shaped) were used as the coating materials. As-received titanium alloy Ti6Al4V (designated as AR-Ti) in the form of circular bar with a diameter of 13 mm was cut into discs with thickness of 5 mm as the substrate. The discs were mechanically ground with 800-grit silicon carbide paper, washed thoroughly with water, degreased with ethanol in an ultrasonic bath, and then allowed to dry in air for the EPD process. Each type of HA powders (2.5 wt%) was added to ethanol and mixed by a magnetic stirrer for 10 minutes. The powder was dispersed ultrasonically by a sonicator (Sonics, VCX 750) at 20 kHz for 30 minutes to obtain a homogeneous colloidal suspension.

Electrophoretic deposition

2-Electrochemical measurements Plots of OCP versus time and the cyclic potentio-dynamic polarization curves for various specimens in Hanks’ solution are shown in Fig. 1. The corrosion parameters extracted from these curves are shown in Table 1. Fig. 1(a) Plot of OCP vs time and (b) potentiodynamic polarization curves of HA coated Ti6Al4V in Hank’s solution at 37 oC.

Table 1. Corrosion parameters, average hardness, and average adhesion strength of various specimens.

Table 2. Designations, average particle and crystallite sizes for various HA powder sand HA coatings on Ti6Al4V substrate.

Corrosion is associated with the penetration of chloride ion and water into the coating, transport of ions through the coating, and the subsequent electrochemical reactions at the interface of HA and Ti6Al4V as shown in Fig. 2. Fig.2. Morphology of failed surface of (a) sHA-Ti and (b) fHA-Ti showing the coatings peeled off from the substrate after adhesion test.

Wear behaviors of HAp coating promoted by propagations of delamination Figures 3 show generations behaviors of wear powders during fretting fatigue. Figure 4 shows SEM pictures on the interface of HAp coating after fretting fatigue. At interfaces between HAp coating with substrates of titanium alloys, many wear particles were ejected from the interfaces as delamination grew to longer. Fig. 3 Observations on generation behaviors of wear paowders by delamination propagation of HAp coating during fretting fatigue. Testing condition swere ;max= 250 MPa, Pc= 30 MPa, R=0.1 and f= 5 Hz,

Fig. 4 SEM pictures for wear behaviors of HAp coating Fig. 4 SEM pictures for wear behaviors of HAp coating. Testing conditions were ;max= 250 MPa, Pc= 30 MPa, R=0.1 and f= 5 Hz, respectively .

Conclusions The HA coated Ti6Al4V possessed higher corrosion resistance compared to the uncoated Ti6Al4V substrate. This improvement was supported by a noble shift of open-circuit potential and a lower corrosion current density. In-situ observations on delamination / wear behavior of HAp coating with porous polypropylene artificial bone by fretting fatigue were conducted to reveal the effects of delamination on fretting wear behaviors of HAp coating. Summary of the results are the follows; * Both interfaces at HAp coting with porous PP resin / HAp coating with substrates of titanium alloy could generate wear particles by fretting fatigue. *Delamination of HAp coating promoted wear behaviors of HAp coating by increasing relative slip amplitudes. Adhering contact pad with HAp coating could initially suppress delamination.

References 1-Leyens, C., Peters, M., Titanium and titanium alloys: fundamentals and applications, 2003, WILEY-VCH, Germany, ISBN 3-527-30534-3. 2.L. Guo, H. Li, Fabrication and characterization of thin nano-hydroxyapatite coatings on titanium, Surface and Coatings Technology, Volume 185,April 2004, pages 268-274. 3.Y. O., D. K., Y. M., Prediction of cyclic delamination lives of plasma-sprayed hydroxyapatite coating on Ti–6Al-7V substrates with considering wear and dissolutions, Journal of the Mechanical Behavior of Biomedical Materials , Volume 64, December 2016 , Pages113-124. 4.C.T. Kwok, P.K. Wong, F.T. Cheng, H.C. Man, Characterization and corrosion behavior of hydroxyapatite coatings on Ti-6Al-4V fabricated by electrophoretic deposition, Applied Surface Science, Volume 255 , Issues 13-14,15 April 2009, Pages 6736-6744.