Biomedical Engineering Reference
In-Depth Information
also diminished on nanophase materials [25]. Decreased bacterial
colonization on nanostructured TiO
2
and ZnO is observed even though
these surfaces promote osteoblast adhesion and differentiation.
For osteoblast, several investigators have shown nanoscale
topography enhances osteoblast differentiation [133]. Webster
revealed that alkaline phosphatase synthesis and calcium mineral
content increased in cell layers formed on nano-sized materials after
21 and 28 days.
The chemical and topographical properties of the implant surface
strongly inluence the properties of the layer. Since proteins and cells
range in size from nano- to micrometer, these are relevant length
scales for the problem. Of equal importance are the properties of
the cells, e.g. their ability to communicate through the extracellular
matrix by signal molecules. During tissue healing, numerous
bioactive signal molecules control the formation and some proteins
have shown capability of stimulating healing near the implant.
The implant surface plays an important role in biological
interactions [119, 145]. Various properties of the implant
surface such as surface chemistry, energy, topography, and
surface roughness are relevant factors for implant integration in
bone tissue and, consequently, for osseointegration [1, 6, 7, 152].
The quality of titanium surfaces can be described in terms of
surface chemistry, which refers to the critical surface tension (CST) or
surface energy [66]. The CST is related to the contact angle of a liquid
drop on the surface and, thus, provides an indicator of the potential
of cell adhesion or surface wettability [33]. Complete moistening
and distribution of a liquid on a surface indicates high surface
energy, biocompatibility, and hydrophilicity of a material. It has
been observed that chemically activated and hydrophilic sandblasted
and acid-etched (SLA) surfaces resulted in a greater percentage of
bone-implant contact in the irst weeks of osseointegration [22].
The surface properties of the implants can be change by different
methods of cleaning, sterilization, and storage [45, 61, 82]. For
example, it has been observed that discs with an active SLA surface
sterilized by gamma irradiation and continuously submersed in
isotonic NaCl presented less contamination with hydrocarbons and
carbonates from the atmosphere, producing a chemically clean and
reactive surface [155].
Another aspect of surface chemistry determined by the oxide
layer refers to the atomic and molecular structure of the biomaterial
[59, 103]. Titanium forms various stable oxides such as TiO, TiO
2
,
