Biomaterials for MEMS

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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