Biomedical Engineering Reference
In-Depth Information
applications towards miniaturized and integrated on-chip formats, with high speed,
high sensitivity, high resolution, and minute sample consumption [
62
]. Recently,
microfluidic chips have been applied to manipulate and analyze cells and to
interrogate molecules inside the cell [
63
-
65
]. These cell-based microfluidic chips
contribute to and advance genomic, proteomic, and cellomic research at the micro-
and nanoscale levels [
66
,
67
]. As the development of cell encapsulation and tissue
engineering technologies progresses, hydrogels have been utilized to encapsulate
cells in microfluidic chips.
8.2 Fabrication and Operation of Cell-Based Biochips
Integration of the PMBV/PVA hydrogel system and microfluidics for the encapsu-
lation and preservation of cells on-chip has been investigated [
68
,
69
]. The PMBV/
PVA hydrogel spontaneously encapsulated cells on-chip without inflicting any
adverse physical effects (such as seen with thermal- and phototreatments), and
the cells encapsulated in the hydrogel in the chip exhibited high viability and low
proliferation over a period of days and weeks under cell-based assay conditions.
Hence, the research not only presents a promising hydrogel material for long-term
cell preservation without perfusion culture on-chip, which has not been realized
before, but also expands the application of the PMBV/PVA hydrogel system for
cell-based assays from bulk scale to microscale.
The microfluidic chip system for preparing a miniaturized PMBV/PVA hydrogel
consists of a two-chamber chip, an aluminum custom-made chip holder, Teflon
capillaries, microtubes, and syringes equipped with a microsyringe pump (Fig.
15
).
The two-chamber chip was fabricated by a photolithographic wet etching tech-
nique. Whereas both channels and chambers (200
m
m in depth) were fabricated on
the top plate, only chambers (200
m
m in depth) were fabricated on the bottom plate.
To encapsulate cells in the chip, first, 5
m
L of 2.5 wt% PVA solution was delivered
into the cell-container chamber through the introducing microchannel using a
microsyringe pump with a withdraw mode. Then, 15
m
Lofcellsuspensionina
culture medium containing PMBV (5.0 wt%) was introduced. After that, PMBV/
PVA hydrogel spontaneously formed and encapsulated the cells in the cell-container
chamber. The viability of the cells encapsulated in the miniaturized hydrogel in the
chip was investigated using fluorescence-based LIVE/DEAD assays.
8.3 Long-Term Viability of Cells in the Cell-Based Chip
Two mammalian cell lines, mouse fibroblasts (L929 cells) and human arterials
endothelial cells (HAECs) were used in the investigation of cell encapsulation.
Fibroblast cells and endothelial cells are model cells widely used in many
cell biology applications such as cytotoxicity assays and tissue engineering.
Cell-encapsulating PMBV/PVA hydrogels with L929 cells and HAECs were
