Biomedical Engineering Reference
In-Depth Information
biomineralization. The biomimetic deposition of calcium phosphate onto
surfaces of implant materials is the most successful example of biological
mimicry, or biomimetics, in fields of osseointegration. This technique tried
to mimic some of the properties of bone by adjusting the composition, intro-
ducing interconnecting porosity, and incorporating osteoinductive factors or
biologically active molecules. This technique was originally developed by
Kokubo et al. (1990). This method allows HAp and other calcium phosphate
surfaces to be deposited on substrates in a SBF under physiological condi-
tions of temperature and pH (Kuroda et al. 2004), on complex geometrical
shapes, primarily to improve their biocompatibility and biodegradability.
5.4.2 Biological Performance of Biomimetic and
Biomineralized Bioceramics
Regardless of the nature of the biomaterials,
multiple events occur immediately
after
osteotomy and implant installation. The peri-implant wound healing
process starts with extravasation (bleeding), so that blood is the first tissue
that comes in contact with the implant surface after implantation. This con-
tact results in a series of immediate and early processes including adsorp-
tion of proteins and other molecules from the biological microenvironment
onto its surface (Shard and Tomlins 2006; Thevenot et al. 2008). The next
stage involves the interaction of cells with the “surface” of the implant via
the adsorbed protein layer. The cell-protein bound surface interface, occur-
ring from as short as minutes after and up to days following implant place-
ment, initiates cellular adhesion, migration, and differentiation, which
occurs from a few hours to several days after implantation (Wilson et al.
2005). Erythrocytes, thrombocytes (platelets), and leukocytes are the first cel-
lular participants at the interface and, consequently, a dense fibrin network is
formed, resulting in provisional matrix formation. This stage is tightly regu-
lated by numerous biological factors, including extracellular matrix proteins,
cell surface-bound and cytoskeletal proteins, by chemical characteristics and
topographies at the implant surface, and by the released ions and products
from the material (Ratner and Bryant 2004). Further, inflammatory cells such
as monocytes or macrophages can be seen at a very early stage at the bone
interface with HAp surfaces (Muller-Mai et al. 1990) and they have been
regarded as a pivotal cell lineage both during successful osseointegration
and in the pathogenesis of implant failure (Aubin 1998). Thereafter, at the
end of the first week of implantation, callus and mesenchymal tissues will
have entirely replaced blood while host bone resorption has started. Finally,
between the second and fourth weeks of implant installation, callus, mesen-
chymal tissues, and host bone will have gradually disappeared in favor of
newly formed bone while bone remodeling takes place.
The biomaterials features can affect the molecular and cellular interac-
tions at their surface and consequently can affect the process of bone forma-
tion. Calcium phosphate bioceramics are integrated within bone by a unique
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