Biomedical Engineering Reference
In-Depth Information
probes. The manner of protein binding and patterning on biomaterial sur-
faces directly impacts their biocompatibility and bio-functionality [21-24].
Interactions between soluble proteins and material surfaces are dominated by
thermodynamic criterion, namely, the principle of lowest surface (interface)
energy and maximal surface entropy. Compared with most types of polymers,
water-soluble proteins are usually more hydrophilic and always have some
amphiphilic characteristics. When protein-containing fluid contacts polymer
surfaces, proteins will spontaneously attach to the foreign interface bridging
and isolating the material from the water phase, by which the surface energy
is minimized. Simultaneously, the original uniformly arranged intermole-
cular H-bonds in the superficial layer (interface) of the water phase (because
of a lack of interference by the relatively hydrophobic polymer interface) is
disturbed by the inserting amide groups of the proteins, which are efficient
H-bond “vectors”. Consequently, the randomization of H-bond arrangement
leads to an increase of interface entropy. Therefore, in general, the more
hydrophobic material surface usually induces a stronger tendency for solu-
ble protein adsorption. Besides thermodynamic factors, a material surface's
electrical properties also influences protein-adsorbing behavior. Since pro-
tein backbones mostly bear negative changes, despite some positively charged
peptide side-chains, protein adsorption is always more prone to occur on pos-
itively charged material surfaces.
All soluble proteins have their specific 3D conformations in the water
phase, which is engendered by the protein-chain intra-molecular polarity
and dispersion, plus intermolecular disulfide bridging, and also relates to the
interaction with solvents. Usually spontaneous protein adsoption reduces sur-
face energy, while also inevitably accompanies with conformational variation
of the committed proteins. If the change is irreversible, variable extents of
protein denaturation will occur [25, 26]. How to avoid denaturation of the
binding proteins remains a significant topic. Investigations indicate that, for
the binding proteins, reversible adsorption frequently hints at reversible con-
formation changes, which suggests a strategy of dynamically balancing the
counteractions of protein adsorption-desorption. Another important finding
for multi-species protein adsorption is the predominance of preoccupation.
When blood contacts a material's surface, the largest family of serum pro-
teins, albumin, will always reach the interface first and consequently domi-
nate the following manner of serum protein adsorption.
1.2.2
Biological Recognition of Cell Adhesion
No matter whether at the interface of foreign materials or under in vivo
conditions, cell adhesion is always accomplished via interactions between ex-
tracellular ligands and receptors on the cell surface. Typical species of cell
adhesion receptors are integrins, proteoglycans, and selectins. Accordingly,
