Polymer-Based Biocompatible Surface Coatings 185
Messersmith et al. presented a comparative study on the antifouling prop-
erties of poly(ethylene glycol) (PEG)-based polymer coatings prepared by the
attachment of preformed polymers and those prepared by surface-initiated
polymerization.
84
OEGMA monomers containing side chains of 4, 9, and 23 EG
units were used in surface-initiated ATRP to form polymer brushes. Greatly im-
proved short-term antifouling properties for all three POEGMA modified samples
were demonstrated by substantially reduced cell attachment for a period of three
weeks as compared to bare Ti. The dependence of antifouling performance on
EG side chain length was systemically tested and compared by 3T3 fibroblast cell
adhesion assays. It was found that excellent cell fouling resistance continued with
little dependence on EG side chain length up to three weeks but a complete cell
coverage was reached at 7, 10 and 11 weeks respectively for POEGMA with side
chainlength4,9,and23EGunits.
Kang et al. prepared heparin-coupled POEGMA-Si(111) hybrids via surface-
initiated ATRP of oligo(ethylene glycol) monomethacrylate and subsequent im-
mobilization of heparin(14 μg/cm
2
) onto the POEGMA brushes.
85
The protein
adsorption and platelet adhesion were significantly suppressed for heparinized
POEGMA-Si hybrid surfaces. The resulting silicon surface exhibited significantly
improved antithrombotic effects with a plasma recalcification time about 150 min.
The persistence of high bioactivity of the immobilized heparin was attributed
to the biocompatibility of the PEGMA units as well as their role as spacers in
providing higher degree of conformational freedom for immobilized heparin in
a hydrophilic environment.
Andruzzi and Ober prepared OEG
n
-containing styrene-based homopolymer
and block copolymer brushes with controlled architecture and high surface cover-
age using surface initiated nitroxide-mediated polymerization on a SiO
X
surface
(Fig. 8.13).
86
The preference for nitroxide mediated polymerization over ATRP was
dictated by the fact that the former process does not utilize metal-based catalysts.
Metal impurities are not always easy to eliminate from the polymerization product
and are undesired in many biological applications. The biocompatibility of these
polymer brushes was studied and compared with deposited assemblies of surface-
bound OEGn-terminated silanes with selected chain lengths. Polymer brushes
possessed superior abilities to inhibit protein and cell adhesion when compared
to surface assemblies with the same OEG length. This was attributed to the greater
thickness and surface coverage of polymer brushes compared to monolayers.
8.3 NON-FOULING SURFACES BASED ON ZWITTERIONIC GROUPS
Another important class of non-fouling surface treatments is based on phospho-
rylcholine (PC) functionalized materials.
93108
This modification was based on the
fact that zwitterionic phospholipids, which are major components of the outer
cell membranes, have excellent non-thrombogenic property and biocomptability.
The hydration of PC-based materials was thought to be the primary mechanism
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