Biomaterials for MEMS

174 K.Yu,G.GaoandJ.N.Kizhakkedathu

on the surface (linear vs. branched), chemistry of the polymers and molecular

weight of the grafted chains.

This chapter is organized based on the application of different polymers and

approaches used for the development of anti-fouling coatings.

8.2 NON-FOULING SURFACES BASED ON POLY(ETHYLENE

GLYCOL)

Poly(ethylene glycol) (PEG) or polyethylene oxide (PEO) has been widely used

for the development of non-fouling surfaces because of its capacity to resist the

attachment of cells and proteins.

36

It is also nontoxic and nonimmunogenic.

36

PEG is composed of -CH

2

-CH

2

-O- repeating units with a hydroxyl group at each

end of the polymer chain. The mechanisms of the antifouling ability of PEG are

not fully understood. It is believed that the antifouling ability of PEG is due to

the combined effects of steric repulsion, large excluded volume, configurational

entropy, hydrated chain mobility, molecular weight and surface coverage.

4,19,37−39

Several surface modification approaches have been reported for the devel-

opment of PEG surfaces. We can classify these methods in terms of the at-

tachment strategies; physical adsorption vs. chemisorption, self assembly vs.

covalent attachment etc. Each method has its own advantages or disadvantages

depending on the ease of the synthesis or its performance. The physical adsorp-

tion of PEG-containing copolymers,

40−48

oligo(ethylene glycol)-terminated self-

assembled monolayers (SAMs),

49−65

grafted polymers based on PEG,

66−81

and

surface initiated polymerization of a PEG-containing monomer

82−90

are the most

commonly used approaches for the development of PEG surfaces. In the following

section we will discuss different strategies adopted for the development of PEG

grafted surfaces.

8.2.1 Physical Adsorption of PEG-containing Copolymers

8.2.1.1 Hydrophobic Adsorption

This method allows the attachment of PEG chains to a variety of surfaces solely

based on the hydrophobicity of the material. One example is the use of triblock co-

polymer, polyethylene glycol-b-polypropylene oxide-b-polyethylene glycol (PEG-

b-PPO-b-PEG)

40

that assemble spontaneously on hydrophobic surfaces through

hydrophobic-hydrophobic interactions. This class of polymer is also known as

poloxamers or pluronics and has been extensively studied

41−45

Liu and Bhatia

reported an application of a commercially available, PEG-terminated triblock poly-

mer (Pluronic™F108) to create nonadhesive domains on a variety of biomaterials

that prevented cell adhesion for up to four weeks in culture medium.

45

They also

demonstrated the ability to micropattern the growth of murine fibroblasts in 5%

serum and retained cell-free domains for up to four weeks on polystyrene. The

pluronics was also shown to adsorb to a variety of surfaces including tissue culture

plates, methylated glass, silicone and polylactic-co-glycolic acid.

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