Design of Mobile Supramolecular Biointerfaces for Regulation of Biological Responses - Biointerfaces: Where Material Meets Biology - page 344

of the biological reactions on the biomaterials. After initial contact of the
surface with proteins they adsorbed, and continuously migrating on the
surfaces until they determine thermodynamic standpoint for the final con-
formation on the materials surfaces. 3 Because the conformational states on
the materials surfaces is different from those in the body fluidics, hindered
bioactive domain of protein molecules is easily exposed to the biological
environments via strong interaction with the materials surfaces. 4 At this
stage, the artificial materials are eventually recognized by a biological sys-
tem, and various biological responses are triggered on their surfaces by the
exposed bioactive domain. Therefore, the total amount of protein adsorption
and the following degree of conformational change, i.e., adsorption state
of the surface proteins, has been considered as a criterion to estimate the
degree of biological responses on the materials surfaces.
The critical factors affecting the amount of protein adsorption on the
biomaterials are relatively well known. For example, it is well established
that electrically neutral and chemical groups of non-hydrogen binding donor
but acceptor are more favorable to reduce the amount of protein adsorption
on the biomaterials surfaces. 5 Surface free energy, one of the traditional
physicochemical factors explaining the polarity of the surfaces, is also
known as a useful factors impacting on the amount of protein interactions
on the biomaterials. 6 Biomaterials surface with high value of surface free
energy, i.e., polar surface, are known to reduce protein adsorption induced
by hydrophobic interaction between protein and materials surfaces. There-
fore, much effort has been made to provide a hydrophilic nature on the
materials surfaces to reduce total amount of protein adsorption for the de-
velopment of 'bio-inert' surfaces. 7-10
The physicochemical factors affecting the adsorption state of the surface
proteins is, however, relatively not yet clearly understood. Three dimensional
conformations of protein molecules are normally stabilized by the hydro-
phobic collapse between hydrophobic cores in protein molecules. 11 This
intermolecular hydrophobic interaction is greatly diminished when the
protein molecules get a chance to develop hydrophobic interaction with
extra molecules such as hydrophobic material surfaces. Therefore, it is be-
lieved that the protein molecules adsorbed onto more hydrophobic surface
show higher degree of conformational changes. 12 Ishihara et al. reported the
importance of hydrated states near polymer surfaces in discussion of the
conformational change of the surface proteins. 13 A hydrated layer containing
higher fraction of free water layer could induce reverse contact of the protein
molecules with the hydrated polymer surfaces, thus it could preserve the
three dimensional conformation of proteins on the surfaces. This result
suggests that the hydrated states of the polymer surfaces is one of the
considerable factors dominating the adsorption state of proteins. Recently, it
was suggested that the surface elasticity could also make an effect on the
adsorption state of protein molecules. The surface elasticity of elastomer
surfaces has been known to affect the adhesion behavior of cells, such as
adhering morphologies, proliferation rate, or stem cell

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lineages. 14,15