Biomedical Engineering Reference
In-Depth Information
5.4.2 The Wound Healing Response after Biomaterial Implantation
The implantation of a biomaterial creates a disruption of the anatomic continuity of
tissue and, as such, creates a wound. The body has a highly developed wound-healing
response that is immediately triggered by the wounding during biomaterial implantation.
Much is known about the normal cellular events that transpire after the initiation of a
wound (see Chapter 7), and this knowledge provides a foundation to understand and antic-
ipate tissue-biomaterial interactions. From the perspective of tissue-biomaterial interac-
tions, four overlapping phases will always occur (Figure 5.9):
Platelet cells control bleeding through coagulation by adhering to the proteins
attached to the biomaterial surface and by releasing clot-forming proteins. The clot that
is formed acts as a provisional matrix for the initiation of repair tissue and fills the gaps
around the implanted biomaterial.
1.
Hemostasis:
2.
Inflammation:
Clot formation induces the production of cell-signaling molecules (cytokines)
that induce the recruitment of inflammatory cells from a nearby bloodstream. These cells
(neutrophils, monocytes, lymphocytes, and macrophages) arrive and attempt to digest
tissue debris and the biomaterial by a process known as phagocytosis. The growth factors
released at the wound site by the inflammatory cells initiate mitosis (cell replication) of
sedentary connective tissue cells at the wound margin.
3.
Proliferation/initial repair:
As a result of all the growth factor signaling by the inflammatory
cells, there is a proliferation and population of the biomaterial with cells that can recreate
the lost or damaged tissue. A nondegrading biomaterial located in the center of the
wound typically becomes encapsulated with tight fibrous tissue. The fibrous capsule
isolates the material from the biological environment and protects the host. The extent
of the inflammatory foreign body response governs the thickness of the fibrous capsule.
The chemical characteristics, the shape and physical properties of the biomaterial implant,
and the rate of release, accumulation, and bioactivity of released chemicals and corrosion
products from implanted materials all also affect the thickness of the fibrous capsule. If the
implant is permanent and does not biodegrade, then a small capsule remains throughout
FIGURE 5.9 Normal tissue-biomaterial
interactions involve the four overlapping
and interdependent phases of wound heal-
ing: hemostasis, inflammation, proliferation/
repair, and tissue remodeling. (a) Protein
attachment to the biomaterial surface guides
cellular interactions. (b) Hemostasis is accom-
plished by clot formation. (c) Cells found in
blood and other inflammatory cells attempt
to process the foreign biomaterial and repair
adjacent material. (d) The host protects itself
from the foreign biomaterial through encap-
sulation with fibrous tissue.
Cells migrate to the
wounded tissue and
biomaterial
C
macrophage
T-cell
monocyte
eosinophil
bFGF
TGF- β
Blood
clot
B
Ions or fragments
of the biomaterial
diffuse away
platelets
biomaterial
Proteins attach to
the foreign biomaterial
surface
A
Fibrous tissue
encapsulation
D
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