Biomedical Engineering Reference
In-Depth Information
adhesion, proliferation, and differentiation of cells as well as the osseointegration of implants. Future
implant surfaces may improve the tissue-integrative properties and long-term clinical success for the
benefits of patients.
5.2
NANOSCALE SURFACE MODIFICATIONS
Surface properties play a determinant role in biological interactions. In particular, the nanometer-
sized roughness and the chemistry have a key role in the interactions of surfaces with proteins and
cells. These early interactions will in turn condition the late tissue integration. In this prospect, differ-
ent methods have been reported for enhancing bone healing around metal implant
[2,7]
.
Modifying surface roughness has been shown to enhance the bone to implant contact and improve
their clinical performance
[2,8]
.
Grid-blasting, anodization, acid-etching, chemical grafting, and
ionic implantation were the most commonly used methods for modifying surface roughness of metal
implants. Combinations of these techniques could be used such as acid-etching after grit-blasting in
order to eliminate the contamination by blasting residues on implant surfaces. This grit-blasting resi-
due may interfere with the osseointegration of the titanium dental implants
[9-11]
. It has been shown
that grit-blasting with biphasic calcium phosphate (BCP) ceramic particles gave a high average surface
roughness and particle-free surfaces after acid-etching of titanium implants. Studies conducted both
in vitro
and
in vivo
have shown that BCP grit-blasted surfaces promoted an early osteoblast differen-
tiation and bone apposition as compared to mirror-polished or alumina grit-blasted titanium
[12,13]
.
Anodization is a method commonly used to obtain nanoscale oxides on metals including titanium
[14,15]
. By adjusting the anodization condition such as voltage, time, and electrolyte, nanoscale prop-
erties could be controlled. Shankar et al.
[16]
have reported that the diameters of the nanotubes could
be modified to a range from 20 to 150 nm in modifying voltage conditions. On the other hand, Kang
et al.
[17]
found that TiO
2
nanotube arrays were more uniform on electro-polished than machined tita-
nium. Moreover, TiO
2
nanotubes on Ti improved the production of alkaline phosphatase (ALP) activity
by osteoblastic cells. In particular, nanotubes with a diameter of 100 nm upregulated level of ALP activ-
ity as compared to 30-70 nm diameter nanotube surfaces
[18]
. Since ALP is a marker of osteogenic dif-
ferentiation, these surfaces may demonstrate enhanced bone tissue integrative properties.
Another approach for improving osseointegration of dental implants is to apply a CaP coating hav-
ing osteoconductive properties
[19-21]
. Different methods have been developed to coat metal implants
with CaP layers such as plasma spraying, biomimetic, and electrophoretic deposition. Nevertheless,
plasma-sprayed HA-coated dental implants have been related to clinical failures due to coating delimi-
tation and heterogeneous dissolution rate of deposited phases
.
An electrochemical process which con-
sists of depositing CaP crystals from supersaturated solutions has been proposed for coating titanium
implants with CaP layers
[22,23]
. Upon implantation, these CaP coatings dissolve and release Ca
2
and HPO
4
2
2
increasing saturation of blood in the peri-implant region. This dissolution led to the pre-
cipitation of biological apatite nanocrystals with the incorporation of various proteins. This biological
apatite layer will promote cell adhesion, differentiation into osteoblast and the synthesis of mineral-
ized collagen, the extracellular matrix of bone tissue. In addition to dissolution, osteoclast cells are
also able to resorb the CaP coatings and activate osteoblast cells to produce bone tissue. As the result,
these CaP coatings promote a direct bone-implant contact without an intervening connective tissue
layer leading to a proper biomechanical fixation of dental implants.
