Biomedical Engineering Reference
In-Depth Information
4.1
Fibronectin Anchorage to Polymer Films Directs Fibrillogenesis
by and Angiogenesis of Endothelial Cells
This subsection is intended to illustrate the impact of a variation of the
anchorage strength of fibronectin to polymer substrates on the formation
of fibronectin fibrils and its relation to the morphogenesis of vascular-like
structures of endothelial cells. The physicochemical surface characteristics of
the substrates is modulated by a polymeric model system consisting of thin
films of maleic anhydride copolymers. The used copolymers can be cova-
lently attached onto a variety of substrates bearing amine moieties due to the
high reactivity of the anhydride functionality towards primary amines. The
versatility and broad applicability of this platform technology was recently
described in more detail in [94] for example to modify silanized glass surfaces
and silicon wafers, and low pressure plasma functionalized polymers. One in-
teresting feature of this model system is the possible combinatorial approach
to protein attachment. The different chemical attachment schemes of covalent
binding of proteins to anhydride bearing surfaces or physisorptive anchor-
age to hydrolyzed surfaces bearing carboxylic acid groups are combined with
avariabilityofthekindofthecomonomerleadingtoabroadvariationin
the anchorage strength of the protein to the substrates. Although the sur-
face chemistry remains almost constant—despite the variation of the surface
density of carboxylic acid groups—the protein-substrate interaction can be
varied between covalent and non-covalent binding as well as different degrees
of polar and hydrophobic interactions.
The impact of different maleic anhydride copolymer surfaces on the ad-
sorption behavior of fibronectin was investigated in detail by protein ad-
sorption, and exchange experiments in [95, 96] and revealed dominant dif-
ferences in the fibronectin anchorage strength besides slight conformational
changesinthetertiaryproteinstructure.Thevariationoffibronectinan-
chorage strength was measured in terms of the displacement kinetics by
human serum albumin, and characterized by a double exponential de-
cay in fibronectin surface coverage. Figure 1 shows the dependence of the
fast displaced species on three different maleic anhydride copolymers, i.e.
poly(octadecene-
alt
-maleic anhydride), poly(propene-
alt
-maleic anhydride),
poly(ethylene-
alt
-maleic anhydride).
On the basis of these data the impact of a varied protein anchorage
strength on fibronectin fibrillogenesis by endothelial cell was investigated by
fluorescence and scanning force microscopy. Initial investigations [97] re-
vealed a clear dependence of focal adhesion and fibronectin fibril formation.
While covalent fibronectin attachment resulted in an impaired development
of focal adhesions and fibronectin fibrils, an enhanced fibrillogenesis was ob-
served on more hydrophilic substrates with physisorptive protein anchorage.
More refined experiments [98] allowed for a quantification of the fibronectin
