Biomedical Engineering Reference
In-Depth Information
Fluorescent-labeled collagen, heparin, and hyaluronic acid were used for
the visualization of interactions between collagen and glycosaminoglycans
attached to polymer films by confocal laser scanning microscopy (Fig. 8).
Compared to the fluorescent-labeled layer of pure collagen, heparin induced
the formation of straight fibrillar structures whereas hyaluronic acid contain-
ing assemblies provided less sharp structures. The detection of fluorescence
in close proximity to collagen fibrils demonstrated the strong interactions be-
tween collagen fibrils and glycosaminoglycans. Thus, the results permit us
to conclude on the incorporation of heparin or hyaluronic acid into fibrillar
collagen structures.
To obtain a first measure for the interaction of cells with fibrillar and
non-fibrillar matrix coatings in vitro the migration of human hematopoi-
etic stem cells on various collagen substrates was analyzed [110]. There-
fore, hematopoietic stem cells were isolated from umbilical cord blood using
immunomagnetic selection and subsequently cultivated on collagen and
collagen-glycosaminoglycan-modified cell culture carriers for 4 days. After
removal of non-adherent cells migration of the remaining cell fraction was
followed using time-lapse microscopy (Fig. 9).
In comparison to pure non-fibrillar tropocollagen minor migration rates
were measured on fibrillar collagen indicating a stronger interaction of
the cells with the fibrillar structures. Interestingly, the migration rates on
collagen-glycosaminoglycan assemblies were again slower compared with fib-
rillar collagen. One possible explanation for the reduced motility of the cells
on substrates containing heparin could be the binding of heparin/heparan
sulfate receptors of hematopoietic stem cells to the collagen-bound heparin
which was similarly described for endothelial cell surface heparin sulfates
which participate in the adhesion cascade between hematopoietic progeni-
tor cells and bone marrow endothelial cells and thus support the homing of
hematopoietic progenitor cells [111]. The low cell migration on substrates
containing hyaluronic acid could be ascribed to the high expression of CD44,
the receptor for hyaluronic acid, which also plays an important role in homing
and mobilization of hematopoietic stem cells [112].
Fig. 8 Confocal laser scanning microscopy of collagen fibrils visualized by the addition of
collagen-FITC ( a ), hyaluronic acid-FITC ( b ) and heparin-FITC ( c ). Image size is 125
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