Electrochemical characterization of surface reactions on biomedical titanium alloys [Elektronische Ressource] = Elektrochemische Charakterisierung von Oberflächenreaktionen auf biomedizinischen Titanlegierungen / vorgelegt von Emad Hashim Alkhateeb

Emad Alkhateeb

Sujets

• Biologie
• Gesundheit

Informations

• Publié par: friedrich-alexander-universitat_erlangen-nurnberg
• Publié le: 01 janvier 2008
• Nombre de lectures: 10
• Langue: English
• Poids de l'ouvrage: 10 Mo

Extrait

Electrochemical Characterization of Surface
Reactions on Biomedical Titanium alloys


Elektrochemische Charakterisierung von
Oberflächenreaktionen auf biomedizinischen
Titanlegierungen



Der Technischen Fakultät der
Universität Erlangen-Nürnberg



zur Erlangung des Grades

DOKTOR-INGENIEUR



vorgelegt von

Emad Hashim Alkhateeb

Erlangen 2008





























Als Dissertation genehmigt von
der Technischen Fakultät
der Universität Erlangen-Nürnberg




Tag der Einreichung: 30.06.2008
Tag der Promotion: 30.10.2008
Dekan: Prof. Dr.-Ing. habil. Johannes Huber
Berichterstatter: Prof. Dr. Sannakaisa Virtanen
PD Dr.-Ing. Carolin Körner





















This work is dedicated to

Father and Mother
In spite of the long distance, you have been my guiding light and spiritual supports

Wife and Children
Your love, patients and support made the work possible

Brothers and Sister
Your encouragement constantly inspires me to excel in all my endeavors












Acknowledgements
At the top of my list of acknowledgments, I would like to thank my
supervisor Prof. Sannakaisa for her guidance, support and encourage
talks in all the topics of my Ph.D.
I am indebt to Prof. Schmuki for giving me the possibility to carry out
my thesis at LKO.
I am also appreciative to Prof. Körner, Prof. Popovska and Prof. Roosen
for their valuable discussions and useful suggestions.
I appreciate all my colleagues and friends who have helped me with
surface analysis and technical stuff, especially Helga, Anja and Ulrik
for the XPS, SEM, EDS and XRD analysis.
Also I appreciated the help received from the mechanical and electrical
workshops Mr. Rollig for building up new electrochemical cells with
temperature control.
I would also thanks Eng. Helmut and Mr. Stefan for helping me in the
translation of abstract into German.
Many and many thanks to my brothers and sister who have always
supported and encouraged me.
I would also like to take this occasion to express my love to those close to
me, my wife Hanadi and my adore children, Hashim and Luai for their
love and patient during the years I spent in my Ph.D thesis.
Finally, special thanks to my mother and father whom indoctrination
in me the value of education and encourage me for bright future and
science.
Many thanks to those not mentioned, but helped me in my thesis. ii
Abstract

Titanium and its alloys are successfully used as implant materials for dental,
orthopedic and osteosynthesis applications. The processes that take place at the
implant tissue interface are important for the acceptance and integration of the
implant.
This thesis is divided into two parts: the first part deals with surface modification of
titanium to improve the osseointegration, and the second part studies metastable
pitting of titanium and its alloys.
The weakly attached layer of a bone-like structure to the titanium surface compels
us to find new methods to improve the osseointegration. This work studies
different chemical surface modifications methods, to enhance and accelerate the
formation of calcium phosphate deposit layers on the surface of titanium during
exposure to a simulated biological environment – such a Ca-P deposition is
supposed to be a pre-requisite for osseointegration.
X-ray photoelectron spectroscopy (XPS) was used to study the chemical
composition on the Ti surface after pre-treatments in different solutions.
Electrochemical Impedance Spectroscopy (EIS) was used in situ to monitor the
growth and coverage by the calcium phosphate with time. Monitoring the
capacitance and resistance change over time allowed elucidating the interaction
between the calcium phosphate layer and the sample passive film.
Three different electrolyte solutions were studied for the titanium surface pre-
treatment: Electrolyte System for Osseointegrative Coating (ESOC) , sodium
hydroxide, and phosphoric acid. The Ti surface was either simply soaked in these
solutions at the open-circuit potential, or alternatively anodized at 1.5 V. After the
pre-treatment, the samples were exposed to Ringer’s solution for 2 days.
Scanning electron microscopy images of the titanium samples after two days of
soaking in Ringer’s solution, show strong differences in the coverage of the Ca-P-
containing surface layer depending on the previous pre-treatment. The best
surface coverage was obtained by pre-treating the Ti surface in H PO . soaked or 3 4
anodized. X-ray photoelectron spectroscopy (XPS) study of the pre-treated
surfaces (prior to exposure to Ringer’s solution) indicates that the formation of the
Ca-P deposit layer depends on the amount of phosphorus on the surface after the

 Frauchiger VM. Anodic plasma-chemical treatment of titanium implant surfaces. Dissertation ETH-Zürich; 2002. iii
pre-treatment. Treatment of titanium by soaking in ESOC led to formation of
scattered clusters of the adsorbate calcium phosphate layer in the subsequent
exposure to Ringer’s solution, while by anodizing in ESOC, the Ca-P formation led
to good coverage of most of the surface. Treatment with NaOH solution led to
weak attachment and minute coverage of the Ca-P layer.
The morphology and chemical composition of the titanium surfaces before and
after immersion in Ringer’s solution were studied by SEM and EDS. In general,
observation of scattered clusters of precipitates on the pretreated titanium surface
after immersion in Ringer’s solution suggests that the adsorption of the calcium
phosphate layer preferentially takes place at specific active sites on the surface.
The relative concentration of phosphorous and calcium formed on pretreated
titanium increased with the immersion time, indicating that the uptakes of these
elements caused growth of the surface film on titanium. Special interest was given
to titanium pre-treatment with phosphoric acid.
Corrosion in the form of metastable pitting (i.e., initiation and repassivation of small
pits) and passive dissolution are two mechanisms responsible for introducing
metal ions into the body from the implants. With the help of special
microelectrochemical cell, we were able to study small current transients
corresponding to early stages of metastable pitting on titanium and its alloys. This
technique is based on using microcapillaries with diameters in the range of few
micrometers and high current resolution (in the fA-range). The study demonstrates
that metastable pitting corrosion takes place on Ti and its alloys within a wide
range of the passive area. Effects of titanium alloying, pH and solution composition
were studied with regard to their influence on the metastable pitting activity.
The calculated total mass loss of Ti6Al4V in sodium chloride solution was the
highest compared to titanium and Ti6Al7Nb. On one hand, presence of aluminum
in the Ti6Al4V and Ti6Al7Nb alloys results in an increase of the metastable pitting
activity. On the other hand, Niobium was found to decrease the total mass loss.
In Ringer’s solution the passive current shows much more current fluctuations than
in the simple saline solution. This may be related to pH changes on the surface
leading to unsteady precipitation/dissolution equilibrium of the calcium phosphate
layer.
The electrochemical behavior of Ti was compared in a simple NaCl and in Ringer’s
physiological solution. Potentiodynamic polarization curves show significantly iv
higher passive current densities in Ringer’s solution as compared with the simple
saline solution. Furthermore, impedance spectra measured at the open-circuit
potential as a function of time indicate that in saline solution a long-term exposure
over some days leads to a strong increase of the protectiveness of the passive
film. This improvement of the passive behavior cannot be observed