Biomedical Engineering Reference
In-Depth Information
This chapter reviews the different steps of the interactions between biological fluids, cells, tis-
sues, and surfaces of implants. Recent nanoscale surface modifications and CaP coating technolo-
gies of dental implants are discussed. The sequence of biological events in relation to surface
properties is related. Mechanisms of interaction with blood, platelets, and hematopoietic and mes-
enchymal stem cells (MSCs) on the surface of implants are described. These early events have
shown to condition the adhesion, proliferation, and differentiation of cells as well as the osseointe-
gration of implants. Future implant surfaces may improve the tissue-integrative properties and
long-term clinical success for the benefits of patients.
16.2
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, dif-
ferent methods have been reported for enhancing bone healing around metal implants
[2,7]
.
Modifying surface roughness has been shown to enhance the bone to implant contact and improve
their clinical performance
[8,2]
. Grit 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 residue 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 differentiation 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 shaking, nanoscale properties 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 titanium. Moreover, TiO
2
nanotubes on Ti improved the produc-
tion of alkaline phosphatase (ALP) activity by osteoblastic cells. In particular, nanotubes with a
diameter of 100 nm upregulated the level of ALP activity as compared to nanotube surfaces with a
diameter of 30
70 nm
[18]
. Since ALP is a marker of osteogenic differentiation, these surfaces
may demonstrate enhanced bone tissue-integrative properties.
Another approach for improving osseointegration of dental implants is to apply a CaP coating
having osteoconductive properties
[19
21]
. Different methods such as plasma spraying, biomimetic,
and electrophoretic deposition have been developed to coat metal implants with CaP layers.
Nevertheless, plasma-sprayed HA-coated dental implants have been related to clinical failures due to
coating delimitation and heterogeneous dissolution rate of deposited phases. An electrochemical
process which consists 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
1
and HPO
2
4
increasing saturation of blood in the periimplant region. This
dissolution led to the precipitation of biological apatite nanocrystals with the incorporation of various
