Biomedical Engineering Reference
In-Depth Information
Days to years: implant site.
Distinction should be made here between surfaces
with high bone-compatibility and low bone-compatibility; in-between exists a grey
zone showing a mixed response. In the scenario of low bone-compatibility, the
unwelcome guest is finally sequestered by fibrous capsulation. The latter consists
of a layer of an extracellular matrix of collagen fibers, more or less dense, roughly
parallel to implant's surface, poorly seeded with cells (Fig.
4.4
).
Tissue near the interface is populated with multinuclear foreign-body giant cells
(Fig.
4.5
).
This reaction is common for polymer implants and for metals with inappropriate
surface treatment. Inappropriate stress conditions, as is the case in stress shield-
ing, may lead to necrosis by strong phagocytic activity. For soft-tissue implants,
the encapsulation is generally not hindering their function. For orthopedic implants,
however, fibrosis severely affects the stability of the implant, leads to loosening and
makes revision surgery necessary.
collagen
fibers
cells
Fig. 4.4
Fibrous tissue:
collagen fibers sparsely
seeded with fibroblasts. Photo
by S.Jaecques
Fig. 4.5
Foreign body giant
cells (
arrows
). Photo by
S.Jaecques
