Chemistry Reference
In-Depth Information
several types of silsesquioxane cages.
131
The peptide units that bonded
most readily were proline, histidine, and threonine. Another example of
favorable interactions involves polysiloxanes in both the liquid and elasto-
meric forms in the presence of nonionic surfactants. These environments
increase
the activity of a number of enzymes, including α-chymotrypsin
and a lipase. Studies have also been carried out on carbohydrate-modified
siloxane surfactants.
132
In many applications it is important to have surfaces that repel proteins.
Hydrophilic poly(ethylene oxide) segments are effective in this regard.
Such segments make polyoxide surfaces protein-repellant when either in-
corporated in the bulk material
133
or covalently bonded to its surface.
134,
135
6.8.4 Cells and Antigen Molecules
The attachment and growth of several types of mammalian cells on fibro-
nectin-coated PDMS have been reported.
136
All cells grew at the same rate
on the PDMS irrespective of its degree of cross linking, but the compati-
bility of the cells on the surfaces did depend on the cell type. Similar re-
sults were obtained when micropatterns of hydrophilic regions were
placed on PDMS by means of a gas plasma.
137
These modifications of the
PDMS surfaces were found to increase the adhesion of fibroblast cells. On
the other hand, grafting sulfobetaine onto PDMS surfaces decreases the
adsorption of blood platelets.
138
Geometric aspects can also be important, as illustrated by control of
the spreading of mammalian cells on wavy PDMS surfaces.
139
Wav y sur-
faces were generated by stretching a sheet of the elastomer, exposing it to
a oxygen plasma, and the allowing it to relax.
Another study focused on PDMS surfaces made hydrophilic by modifi-
cation with hydrophobins (small, cysteine-rich and amphiphilic fungal
proteins).
75
This approach was used to pattern antigen molecules, followed
by immunoassays. For example, chicken immunoglobulin G was found to
be compatible with the hydrophhobin-modified PDMS.
Some related work involved cellular interactions of collagen-immobi-
lized PDMS surfaces,
140
and the immobilization of antibody fragments on
polymer brushes supported by silicone nanofilaments.141
141
6.8.5 Biofouling
PDMS surfaces modified with poly(ethylene glycol) have a near-perfect
resistance to nonspecific protein adsorption, making them effective for
