Biomedical Engineering Reference
In-Depth Information
teins adsorbed onto the biomaterial support. In addition, protein adsorption
considerations are critical to various classes of biosensors, where nonspecific
adsorption (fouling) typically limits sensor performance. Hence, adsorbed
proteins function as signal transduction elements at the interface of the ma-
terial and the biological system.
Protein adsorption is a complex, dynamic, energy-driven process involv-
ing noncovalent interactions, including hydrophobic interactions, electro-
static interactions, hydrogen bonding, and van der Waals forces [32, 33]. Pro-
tein parameters such as primary structure, size, and structural stability and
surface properties including surface energy, roughness, and chemistry have
been identified as key factors influencing the adsorption process. Further-
more, multicomponent systems, such as plasma and serum, exhibit dynamic
adsorption profiles. In this phenomenon, known as the Vroman effect, the
protein film at the interface changes over time as proteins in high concentra-
tion adsorb first but are subsequently displaced by proteins that have higher
affinitiy for the surface [32]. Therefore, adsorption from protein mixtures
is selective and leads to enrichment of the surface phase in particular pro-
teins. In addition to differences in adsorbed density, many proteins undergo
changes in structure upon adsorption, and these structural changes alter their
biological activity. Thus, analyses of protein adsorption must consider ad-
sorbed protein species (for multicomponent systems), density, and biological
activity. Finally, while most detailed studies of protein adsorption continue
to be experimental in nature, new computational approaches are expected to
provide insights into mechanisms controlling protein adsorption at the mo-
lecular level [34-36].
2.2
Surfaces That Resist Protein Adsorption
The generation of nonfouling surfaces that resist the nonspecific adsorp-
tion of biomolecules is critical to the biological performance of numerous
biomedical devices, including blood-contacting devices, catheters, and sens-
ing/stimulating leads [33]. In addition, nonfouling surfaces are important to
in vitro applications such as oligonucleotide, protein, and cell arrays. The mo-
tivation for the development of these nonfouling surfaces is that prevention of
protein adsorption will minimize cell adhesion and inflammatory responses
and result in improved device performance. Despite considerable research ef-
forts over the last three decades, robust surface treatments that
completely
eliminate protein adsorption over the lifetime of a device have not been ob-
tained. Nevertheless, significant progress has been attained in understanding
the mechanisms driving protein adsorption, and several chemical groups that
resist protein adsorption have been identified. A key element in resistance to
protein adsorption is the energetics of interfacial solvent water molecules, i.e.,
hydration layers associated with the proteins and the surface. For example, it
