Biomedical Engineering Reference
In-Depth Information
kidney and chondroitin sulfate from bovine trachea) can be
purified using papain digestion, alkaline borohydride treatment,
diethylaminoethyl cellulose (DEAE) ion-exchange chromatography,
and glycosidase digestion.
31
Isolated glycosaminoglycans are char-
acterized by agarose gel electrophoresis
32
and quantified using a
modifiedFarndaleassay.
33
Growthfactorsareproducedinmilligram
quantities using recombinant DNA technology and purified using
immobilizedheparina
nitychromatography,forexample,vascular
endothelial growth factor (VEGF)
34
and fibroblast growth factor 2
(FGF2).
35
20.3.2
Cross-Linking and Covalent Attachment of
Glycosaminoglycans
Cross-linkingofscaffoldswillmakethemmoreresistanttodegrada-
tion and will add to their mechanical stability. We generally use the
nontoxic1-ethyl-3-(3-dimethylaminopropyl)carbodiimide(EDC)in
combination with
N
-hydroxysuccinimide (NHS) because it yields
zero-length cross-links, introducing an amide bond. The strength
of the scaffold and the rate of biodegradation can be varied by the
cross-linkingconditions.
2
Glycosaminoglycans can be bound to lyophilized scaffolds in
the cross-linking step, thereby covalently attaching them to the
scaffold.
31
In the human body, glycosaminoglycans are present in
the ECM, where these linear polysaccharide chains are important
for hydration of the tissue and binding and modulation of growth
factors and cytokines.
36
When binding glycosaminoglycans, such as
chondroitinsulfate,tocollagenscaffolds,thewater-bindingcapacity
increases over 50%.
11
20.3.3
Binding of Growth Factors
Bindingofgrowthfactorsisoftenmodulatedbyglycosaminoglycans,
and we therefore use the intrinsic properties of glycosaminoglycans
to bind, for example, heparin-binding growth factors to scaffolds.
A wide variety of heparin-binding growth factors is known, includ-
ing FGFs, VEGF, heparin-binding epidermal growth factor (hbEGF),
placental growth factor (PlGF), hepatocyte growth factor (HGF),
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