Biomedical Engineering Reference
In-Depth Information
The Vroman-effect describes the changes in protein adsorption and release which
is determined by the mobility of the protein and the affinity to the implant surface.
At the moment of insertion, the proteins with the highest mobility will arrive at the
implant site first and adsorb at the surfaces. Later, they will be replaced by slower
proteins with a higher affinity to the implant material. The blood-material-inter-
actions are described by the hematocompatibility of the biomaterial. Several
surface modifications may improve the hematocompatibility and the biocompati-
bility of the biomaterial. Due to the adsorption of proteins at the implant surface
directly after implantation, PMNs, monocytes and macrophages are attracted and
will bind to that layer by specific protein receptors. A modulation of the surface
protein deposition layer would restrict the binding of proteins and select required
types of proteins.
Other types of modification are the alteration of the surface roughness and
topography or the mimicking of the extracellular matrix. Also the loading with
anti-inflammatory mediators could improve the acceptance of the biomaterial and
down-regulate the foreign body reaction.
However, when these materials are used as scaffolds, matrices or substrates
for anchoring of living cells or layers of biological active molecules, the host
response to the
bioactive
composite of the biohybrid has
to be
taken
into
account.
3 Compatibility of the Bioactive Compound
A critical issue in the therapeutic use of any bioactive implant is its biosafety. The
biological compound must be well tolerated by the host immune system, and it
needs to prove therapeutic effect over a longer period of time. Especially when
using differentiated or redifferentiated cells, absolutely no remaining proliferating
cells causing any types of tumors or teratomas are tolerated and the biological
compound has to integrate site-specifically.
The failure or lacking of one of these issues excludes the bioactive com-
pound from any use in humans. Therefore, extended in vitro and in vivo testing
has to be performed and the data have to be analyzed very carefully to avoid
any health risk.
An always existing risk associated with cell or tissue transplantation is the
graft-versus-host-reaction (GvHR). The GvHR is an immunological reaction
between an organism (host) and inserted cells or tissues (graft). In the majority
of cases, the origin of the transplanted cells or tissues is allogeneic, that means
that the donor and the recipient are different individuals of the same species.
In this case the specific major histocompatibility complex (MHC) of the donor
maybe different from that one of the host which leads to the rejection of the
transplant. Current therapy of that rejection is the suppression of the recipient's
immune system to inhibit the defence of the grafted implant by administrating
steroids.
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