Biomedical Engineering Reference
In-Depth Information
The behavior of these circulating cells and biomolecules can be modulated
by varying the interfacial physical and chemical properties (Figure 7.1 panels
II and III).
When implanted into the body, biomaterials can be recognized by an
intricate recognition system. This includes scavenger (SR), toll-like (TLR) and
integrin (IR) receptors and other surface proteins of host cells, e.g., immune
and endothelial cells. Hydrophilic materials such as hydrogels tend to be
recognized by SR and TLR of both macrophages and endothelial cells.
Hydrophobic materials, however, tend to be recognized by IR of neutrophils,
monocytes and macrophages. The magnitude and type of the body response
varies from one material to another.
The hydrophobicity/hydrophilicity of the interface can affect the behavior
of anchorage-dependent cells, e.g., osteoblasts. With hydrophobic interfaces,
osteoblasts may be unable to generate sucient adhesion signals necessary
for their adhesion which is a prerequisite for other cellular activities.
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The
interface could also affect
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the recruitment of
leukocytes and the in-
flammatory response.
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This is particularly important
for implantable
Figure 7.1
(I) Diagrammatic representation of the interface between a filler particle
and a polymer matrix in a composite; the interface composed of
adsorbed polymer chain that has point contact (anchor or trains) with
the filler particle, unadsorbed polymer segment (e.g., loops and tails)
that are entangled with other chains adsorbed on filler surface. Modified
from Ciprari et al.
51
(II) Diagrammatic representation of cell-biomaterial
surface interaction: once the biomaterial is implanted into the body,
blood contact occurs; water molecules and proteins from the blood
become adsorbed onto the surface of the biomaterial (a), then a specific
and complex protein layer forms over the surface providing binding sites
for cell surface integrins (b), immune cells e.g., macrophages and
neutrophils reach the implanted site to phagocytose the implanted
material otherwise they fuse together forming foreign-body giant cells
that release cytokines to recruit fibroblasts (c); fibroblasts infiltrate the
surface and secrete collagen and other proteins of the extracellular
matrix (ECM) (d) that subsequently form a fibrous capsules around the
implanted biomaterial (e). Modified from Harvey et al.
73
(III) Scanning
electron microscopy images showing the behavior of human mesench-
ymal stem cells (HMSCs) attached to composite (calcium phosphate
filled polylactic-co-glycolic acid dimethacrylate) surface: HMSCs extend
filopodia to sense the surface, when they encounter an optimal surface
condition (a protein layer, which is vital to specific-cell interaction,
adsorbed on the surface in such case), they showed extended like-
morphology (a) but rounded morphology when the surface is not an
optimal (lack of adsorbed protein in such case) (b). (IV) Diagrammatic
representation of self-healing composites: once the crack, initiated
within the composite, reaches the healing microcapsules (a), the healing
agent incorporated into microcapsules will be released to fill the micro-
crack (b), the polymerization of the released healing agent will then
occur upon its contact with the catalyst incorporated into the polymeric
matrix resulting in complete crack closure (c).
Adopted from White et al.
97
.
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