Biomedical Engineering Reference
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Fig. 7 AFM images of collagen and collagen-glycosaminoglycan fibrils attached to thin
films of poly(octadecen- alt -maleic anhydride). Image size is given in brackets
shape and dimensions of the surface-bound fibrils significantly differed from
those of pure collagen. Wide and straight fibrils were formed in the presence
of heparin whereas hyaluronic acid caused the generation of more twisted col-
lagen assemblies. In both cases no dense fibrillar network was formed, only
separate fibrils were attached to the polymer surface and many small fibrils
filled the spacings between the larger filaments. Additionally, the deposited
layers appeared more smooth and thinner in comparison to pure collagen
meshworks. All fibrillar variants revealed their characteristic banding pattern
indicating that the native structure was retained after deposition. These ob-
servations endorsed the ellipsometric measurements as well as the results of
quantified surface-bound collagen.
It should be noticed that the surface pattern of the immobilized collagen-
glycosaminoglycan assemblies does not reflect the volume phase composition
of collagen gels reconstituted in the presence of heparin or hyaluronic acid.
When desiccating such gels on top of planar surfaces quite different surface
structures regarding fibril size and density were observed. Larger and more
elongated fibrils forming a tight fibrillar meshwork were detected in that case.
Thus, fibrils attached to the polymer-coated surfaces did not represent the
meshwork features of the gel bulk phase. The differences between surface-
bound fibrillar collagen and collagen fibrils which were deposited in the pres-
ence of glycosaminoglycans were attributed to strong interactions of collagen
with heparin or hyaluronic acid, respectively. Obviously, the attachment of
the highly negatively charged glycosaminoglycans to the protein collagen—
caused by ionic interactions as described for chondroitin-6-sulfate [2] or
heparin [7] and via specific binding sites as specified for heparin [109]—may
partially occupy the positively charged lysine side chains resulting in a re-
duced attachment of collagen to the poly(octadecen- alt -maleic anhydride)
films.Furthermore,glycosaminoglycansmostprobablyaffectthecohesionof
the fibrillar meshworks and therefore less fibrils remained on the polymer-
coated surface after displacement of the gel volume phase.
 
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