Biomedical Engineering Reference
In-Depth Information
2 h
48 h
5 days
PB/BSA
100 µm
FIGURE 2.2
Degradation.of.cell.attachment.selectivity.at.a.BSA/ibronectin.interface.on.a.polystyrene.
(PS).surface..(From.A..Tourovskaia,.T..Barber,.B..Wickes,.D..Hirdes,.B..Grin,.D. G..Castner,.K. E..Healy,.
and.A..Folch,.“Micropatterns.of.chemisorbed.cell.adhesion-repellent.ilms.using.oxygen.plasma.etching.
and.elastomeric.masks,”.
Langmuir
.19,.4754,.2002..Figure.contributed.by.Anna.Tourovskaia.)
play intertwined roles in the attraction between a surface and the polar as well as apolar amino
acid side chains on a protein. Exposing the surface to a surfactant (a compound that lowers the
surface tension of a liquid) during protein adsorption can substantially decrease physisorption
on hydrophobic surfaces.
Colossal research eforts have focused on the development of materials that do not support
platelet or microbial adhesion for implantation and surgery. Examples of nonadhesive surfaces
oten encountered in the BioMEMS literature are cellulose acetate, agarose,
poly(ethylene gly-
col) (PEG)
, luorocarbon polymers, and poly(vinyl alcohol). Surfaces may also be engineered to
present functionalities that repel protein and cell adhesion; following are a few notable examples:
When a glass surface derivatized with (3-mercaptopropyl)trimethoxysilane (i.e., a
silane molecule terminated in a thiol group) is exposed to UV light in air, the thiol
terminal oxidizes to sulfonate (presumably via reaction with UV-generated ozone
from air), which can resist protein adsorption by as much as 75% to 90%, depending
on the protein.
By functionalizing PEG with SiCl
3
, PEG can be reacted with hydroxyl groups on
glass or silicon surfaces as well as on PEG itself, thus forming a multilayer of PEG
ilm the thickness of which is controlled by the duration of the reaction (
Figure 2.3
).
Functionalized PEGs have not always been commercially available. (For example, a
company called Shearwater Polymers sold them for many years but went out of busi-
ness and it was not until recently that another one, LaySan Bio from Alabama, took
their place in the market.) PEGs with other biofunctionalities such as biotin and cross-
linkers are also available.
OCH
2
CH
3
OCH
2
CH
3
CH
3
CH
2
O Si
H
C
H
PEG
H
C
O
H
n = 70
n
CH
3
CH
2
O Si
OCH
2
CH
3
O
Si
Glass
FIGURE 2.3
Direct.immobilization.of.PEG.on.silicon.or.glass..(From.D..Irimia.and.J..O..M..Karlsson,.
“Development. of. a. cell. patterning. technique. using. poly(ethlylene. glycol)disilane,”.
Biomed.
Microdevices
.5,.185,.2003..Figure.contributed.by.Daniel.Irimia.)
