Biomaterials 25 (2004) 2867–2875
Improved biological performance of Ti implants due to surface
modification by micro-arc oxidation
Long-Hao Li
a
, Young-Min Kong
a
, Hae-Won Kim
a
, Young-Woon Kim
a
,
Hyoun-Ee Kim
a,
*, Seong-Joo Heo
b
, Jai-Young Koak
b
a
School of Materials Science and Engineering, Seoul National University, Seoul, 151-742, South Korea
b
Department of Prosthodontics, College of Dentistry, Seoul National University, Seoul, South Korea
Received 11 May 2003; accepted 4 September 2003
Abstract
The surface of a titanium (Ti) implant was modified by micro-arc oxidation (MAO) treatment. A porous layer was formed on the
Ti surface after the oxidation treatment. The phase and morphology of the oxide layer were dependent on the voltage applied during
the oxidation treatment. With increasing voltage, the roughness and thickness of the film increased and the TiO
2
phase changed
from anatase to rutile. During the MAO treatment, Ca and P ions were incorporated into the oxide layer. The in vitro cell responses
of the specimen were also dependant on the oxidation conditions. With increasing voltage, the ALP activity increased, while the cell
proliferation rate decreased. Preliminary in vivo tests of the MAO-treated specimens on rabbits showed a considerable improvement
in their osseointegration capability as compared to the pure titanium implant.
r 2003 Elsevier Ltd. All rights reserved.
Keywords: Titanium; Oxidation; Biocompatibility; In vitro; Osseointegration; In vivo
1. Introduction
Pure titanium (Ti) and titanium alloys are frequently
used as dental and orthopedic implant materials because
of their excellent mechanical strength, chemical stability,
and biocompatibility [1]. The biocompatibility of
titanium is closely related to the properties of the
surface oxide layer, in terms of its structure, morphology
and composition. Various physical and chemical treat-
ments of the Ti surface have been proposed with a view
to obtaining the most biocompatible implant surface.
Among the techniques, which have been found to be
beneficial to the biological performance of the implants,
are increasing the surface roughness, the oxidation of Ti
to form a TiO
2
layer on the surface. The incorporation
of Ca or P ions into the surface layer, and the validity of
these results has been confirmed by several different
researchers [2–5]. The most widely used commercial
techniques are sandblasting, acid-etching, and the
plasma spraying of hydroxyapatite [6,7].
Recently, an electrochemical procedure for modifying
the Ti surface was proposed, which has since attracted
much attention. By applying a positive voltage to a Ti
specimen immersed in an electrolyte, anodic oxidation
(or anodizing) of Ti occurs to form a TiO
2
layer on the
surface. When the applied voltage is increased to a
certain point, a micro-arc occurs as a result of the
dielectric breakdown of the TiO
2
layer. At the moment
that the dielectric breakdown occurs, Ti ions in the
implant and OH ions in the electrolyte move in opposite
directions very quickly to form TiO
2
again. This process
is generally referred to as micro-arc oxidation (MAO) or
plasma electrolysis [8]. The newly formed TiO
2
layer is
both porous and firmly adhered to the substrate, which
is beneficial for the biological performance of the
implants. Another advantage of this MAO process is
the possibility of incorporating Ca and P ions into the
surface layer, by controlling the composition and
concentration of the electrolyte [9,10]. The incorporated
Ca and P ions were even crystallized into hydroxyapatite
or other calcium phosphates by a hydrothermal treat-
ment [10,11]. Recent studies on the biological response
of Ti implants demonstrated that the MAO process
constitutes one of the best methods of modifying the
ARTICLE IN PRESS
*Corresponding author. Tel.: +82-2-880-7161; fax: +82-02-884-
1413.
E-mail address: kimhe@snu.ac.kr (H.-E. Kim).
0142-9612/$ - see front matter r 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biomaterials.2003.09.048