Biomedical Engineering Reference
In-Depth Information
hydrophobic dehydration and electrostatic forces certainly provide the most
important contributions to protein adsorption as well as to the formation of
supramolecular structures in aqueous environments the related surface char-
acteristics of the solids were considered most carefully. Emphasis was put on
the comparison of hydrophobic and hydrophilic surfaces used as substrates
for the precipitation of protein assemblies and various studies used atomic
force microscopy (AFM) to unravel differences in the interfacial protein
structures. For example, it was reported that on hydrophilic mica
peptides formed particulate, pseudomicellar aggregates, but on hydrophobic
graphite the same protein organized into uniform, elongated sheets [86]. In
another study, recombinant human elastin peptides were shown to adsorb as
discrete, rounded aggregates on hydrophilic surfaces but on a hydrophobic
surface the peptides self-assembled into an energetically favorable hexago-
nally closed packed fibril arrangement [87]. Also, for the binding of integrins
to surface-bound fibronectin substrate-specific conformational changes have
been inferred on hydrophobic and hydrophilic surfaces [88] and correlated
with solid-phase cell binding assays [89]. Providing another instructive ex-
ample Sherratt et al. [90] demonstrated that fibrillin and type VI collagen mi-
crofibrils exhibit substrate dependent morphologies. Recent work of Muller
and coworkers [91] demonstrated how well-defined artificial assemblies can
be obtained using the atomic force microscope as a biomolecular manipu-
lation machine. Native collagen I molecules were mechanically directed on
mica surfaces into well-defined, two-dimensional templates exhibiting pat-
terns with feature sizes ranging from a few nanometers to several hundreds
of micrometers.
As seen from these examples, insights on protein adsorption gained in col-
loid and interface science throughout the previous years [92, 93] are highly
relevant for the understanding of ECM brought into contact with artificial
materials. The formation as well as the functionality of the resulting matrix
structures is strongly influenced by environmental constraints. This can be
utilized not only to more efficiently mimic natural ECM templates, i.e. tissue-
specific matrices, by artificially reconstituted matrix structures but also to
design matrices which deviate in structure and function from any natural
ECM to (re)activate pathways of tissue regeneration absent or insufficient in
the adult organism. Expanding this idea the novel discipline of “matrix en-
gineering” can be expected to play a key role in the future perspective of
regenerative medicine.
As polymer materials permit a most versatile variety of surface character-
istics efficient control over processes of ECM reconstitution can be achieved
by the interaction of polymeric materials with the biopolymers of the ECM.
With the following subsections the modulation of ECM biopolymer assembly
at polymer interfaces is illustrated for two selected examples of own research
in more depth and the relevance of the resulting differences is discussed for
cellular systems.
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