188 K.Yu,G.GaoandJ.N.Kizhakkedathu
(N/P) ratio was close to 1 and the charges were balanced. The molecular
simulation results showed that PC head groups had packing densities similar
to membrane lipids and preferred to have an anti-parallel orientation for the
minimization of net dipole.
8.3.2 Surface Initiated Polymerization of Zwitterionic Group
Containing Monomers
In this case surface initiated polymerization of zwitterion containing monomers
were used for the surface functionalization. Feng and Zhu prepared biomimetic
poly(2-methacryloyloxyethyl phosphorylcholine) (poly(MPC)) grafted surfaces
with graft density 0.06–0.39 chains/nm
2
and chain length 5–200 monomer units on
a silicon wafer surface.
102
They investigated the relationship between graft density
and chain length on the non-fouling properties of grafted Poly(MPC) brushes. The
fibrinogen adsorption from tris-buffered saline at pH 7.4 decreased significantly
with increasing graft density and/or chain length of poly(MPC) and reached a
level of <10 ng/cm
2
at graft density 0.29 chains/nm
2
and chain length 100
units, compared to ca. 570 ng/cm
2
for the unmodified surfaces (Fig. 8.17). The
graft density appears to be more important than the chain length in determining
the non-fouling properties of the surface.
Chio et al. described the formation of highly efficient non-biofouling polymeric
thin films of poly((3-(methacryloylamino)propyl)-dimethyl(3-sulfopropyl)ammo-
nium hydroxide), (poly(MPDSAH)).
103
The amount of proteins nonspecifically
adsorbed onto the poly(MPDSAH) films was evaluated by surface plasmon res-
onance spectroscopy. The adsorption of proteins was <0.6 ng/cm
2
on the surfaces
for all of the model proteins studied. In another report, Zhang and Jiang et
al described the non-fouling properties of glass slides grafted with zwitterionic
polymers (poly(sulfobetaine methacrylate) (polySBMA) and poly(carboxybetaine
methacrylate) (polyCBMA) to resist the protein adsorption and the adhesion
of mammalian cells (Fig. 8.18).
104
The grafted surfaces were synthesized from
respective monomers using surface-initiated ATRP method. The surfaces with
polySBMA or polyCBMA layers were shown to reduce fibrinogen adsorption to
a level comparable with that of adsorption on PEG-like films (Fig. 8.19). The
polySBMA or polyCBMA grafted glass surface were also highly resistant to the
adhesion of bovine aortic endothelial cells.
In another study Chang and Chen et al. demonstrated the performance
and stability of an antifouling surface with grafted zwitterionic sulfobetaine
methacrylate.
106
The SBMA was grafted from a bromide-functionalized gold sur-
face via surface-initiated ATRP to form well-defined polymer brushes. PolySBMA
brushes showed excellent non-biofouling property and stability during the re-
peated protein adsorption tests and under a wide range of ionic strengths from
0.1 to 1.0 M, pH values from 7.4 to 11, and temperature cycling from 22 to 37
C
in PBS buffer. The polySBMA grafted surface effectively reduced the plasma
protein adsorption from platelet-poor plasma and was superior to that of surfaces
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Polymer-Based Biocompatible Surface Coatings 189
Figure 8.17. Profile of fibrinogen adsorption on poly(MPC)-grafted silicon surfaces with
varying graft density and chain length in TBS buffer for 2 h at room temperature. Fibrinogen
concentration: (a) 0.05 mg/ml; (b)1.0 mg/ml. Data precision: 5–25%. Images adapted from
Ref. 102.
terminated with tetra(ethylene glycol). The adhesion and activation of platelets
were not observed on the polySBMA grafted surface. Their results suggested
that zwitterionic polySBMA is an effective and stable nonbiofouling material to
provide a surface for uses in human blood and biomedical implants.
Bernards and Jiang et al described the development of a non-fouling
polymer brushes formed from a surface-initiated, two-component ATRP.
108
The polymer brushes were composed of varying mixtures of positively
(2-(methacryloyloxy)ethyl]trimethylammonium chloride) and negatively charged
(3-sulfopropyl methacrylate potassium salt) monomers depending on the poly-
merization conditions. The non-specific adsorption of fibrinogen, lysozyme, and
bovine serum albumin were measured using a surface plasmon resonance biosen-
sor. It was found that the statistical copolymer surfaces made up of two charged
components was protein resistant. The best nonfouling surface coating was found
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