Biomedical Engineering Reference
In-Depth Information
substrate, intermixing the components of the substrate
and the surface film at an interfacial zone (for example, an
interpenetrating network (IPN)), applying a compatibi-
lizing (''primer'') layer at the interface, or incorporating
appropriate functional groups for strong intermolecular
adhesion between a substrate and an overlayer (Wu, 1982).
Table 3.2.14-1 Some physicochemically surface-modified
biomaterials
To modify blood compatibility
Octadecyl group attachment to surfaces (albumin affinity)
Silicone-containing block copolymer additive
Plasma fluoropolymer deposition
Surface rearrangement
Plasma siloxane polymer deposition
Surface rearrangement can readily occur. It is driven by
a thermodynamic minimization of interfacial energy and
enhanced by molecular mobility. Surface chemistries and
structures can ''switch'' because of diffusion or trans-
lation of surface atoms or molecules in response to the
external environment (see Section 3.1.4 and Fig. 3.1.4-2
in that section). A newly formed surface chemistry can
migrate from the surface into the bulk, or molecules
from the bulk can diffuse to cover the surface. Such re-
versals occur in metallic and other inorganic systems, as
well as in polymeric systems. Terms such as ''re-
construction,'' ''relaxation,'' and ''surface segregation'' are
often used to describe mobility-related alterations in
surface structure and chemistry (Ratner and Yoon, 1988;
Garbassi et al., 1989; Somorjai, 1990, 1991). The driving
force for these surface changes is a minimization of the
interfacial energy. However, sufficient atomic or molecular
mobility must exist for the surface changes to occur in
reasonable periods of time. For a modified surface to
remain as it was designed, surface reversal must be
prevented or inhibited. This can be done by cross-linking,
sterically blocking the ability of surface structures to
move, or by incorporating a rigid, impermeable layer be-
tween the substrate material and the surface modification.
Radiation grafted hydrogel
Chemically modified polystyrene for heparin-like activity
To influence cell adhesion and growth
Oxidized polystyrene surface
Ammonia plasma-treated surface
Plasma-deposited acetone or methanol film
Plasma fluoropolymer deposition (reduce endothelial adhesion
to IOLs)
To control protein adsorption
Surface with immobilized poly(ethylene glycol) (reduce adsorption)
Treated ELISA dish surface (increase adsorption)
Affinity chromatography column
Surface cross-linked contact lens (reduce adsorption)
To improve lubricity
Plasma treatment
Radiation grafting (hydrogels)
Interpenetrating polymeric networks
Surface analysis
To improve wear resistance and corrosion resistance
Ion implantation
Surface modification and surface analysis are comple-
mentary and sequential technologies. The surface-
modified region is usually thin and consists of only
minute amounts of material. Undesirable contamination
can readily be introduced during modification reactions.
The potential for surface reversal to occur during sur-
face modification is also high. The surface reaction
should be monitored to ensure that the intended surface
is indeed being formed. Since conventional analytical
methods are often insufficiently sensitive to detect
surface modifications, special surface analytical tools are
called for (Section 3.1.4).
Diamond deposition
Anodization
To alter transport properties
Polyelectrolyte grafting
To modify electrical characteristics
Polyelectrolyte grafting
Magnetron sputtering of titanium
Delamination resistance
Commercializability
The surface-modified layer should be resistant to de-
lamination and cracking. Resistance to delamination is
achieved by covalently bonding the modified region to the
The end products of biomaterials research are devices
and
materials
that
are
manufactured
to
exacting
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