Biomedical Engineering Reference
In-Depth Information
a
b
e
9.28 M
Ω
Suction
1
Intracellular
side
Buried
capillary
Bath
outlet
2
3
Bath
inlet
Bath side
857 µm
60 µm
c
d
f
8.42 G
Ω
1.52
µ
m
Capillary
opening
Capillary
opening
23.1 µm
20 µm
FIGURE 5.56
Microfabricated. glass. capillaries. for. patch. clamp. on. a. chip.. (From. Wee-Liat. Ong,.
Kum-Cheong. Tang,. Ajay. Agarwal,. Ranganathan. Nagarajan,. Lian-Wee. Luo. and. Levent. Yobas,.
“Microluidic.integration.of.substantially.round.glass.capillaries.for.lateral.patch.clamping.on.chip,”.
Lab Chip
.7,.1357-1366,.2007..Reproduced.with.permission.from.The.Royal.Society.of.Chemistry.)
As a variation on the patch clamp theme, several other groups have seized the opportunity to
develop devices that are able to introduce compounds (i.e., DNA, proteins) into the cells, either
using the patch clamp aperture or using very sharp needles that perforate the cell membrane.
he needles, which can be deposited serially, surface-micromachined, or grown at random by a
chemical process, are typically coated with the delivery agent or can be made of a biodegradable
polymer mixed with it. As the cells are much bigger than the needles, the cell membrane self-
heals rapidly around the perforation made by the needle, which releases the agent once inside
the cell.
5.9 Cryopreservation
Cryopreservation is the process used to stop all biological activity by cooling the cells to low
subzero temperatures. A recurrent problem in cryopreservation has been to ind the right con-
ditions to freeze biological tissue because ice crystals can form inside a cell and burst the cell
membrane if cryoprotectants are not introduced into the cell. To ind the optimal cryopreserva-
tion conditions of cells, it is necessary to better understand the properties of membrane trans-
port and cell osmotic behavior. Dayong Gao and colleagues at the University of Washington
have developed a microluidic system for trapping isolated RBL cells (which, conveniently, live
in suspension) in weir microstructures that let the luid through but not the cells (
Figure 5.57
).
his simple system allows for monitoring kinetic changes of cell volume under various extracel-
lular conditions, either hypertonic solutions of nonpermeating solutes (e.g., NaCl) or solutions
containing permeating cryoprotective agents (e.g., dimethlysulfoxide), from which it is possible
to obtain the cell's osmotically inactive volume and the permeability coeicient of water and of
dimethlysulfoxide for RBL cells.
