Biomedical Engineering Reference
In-Depth Information
In 1998, Mehmet Toner's group at Harvard Medical School pioneered the use of microluidics
to create ECM protein templates for selective cell attachment; the templates were physisorbed on a
variety of biocompatible materials, such as polystyrene, PDMS itself, polycarbonate, and PMMA
(or heterogeneous surfaces containing metal circuits or more than one protein), to produce pat-
terns of hepatocytes and keratinocytes on collagen or ibronectin. Ater the channels were lushed
and the elastomer was removed, cells attached only on the protein template (
Figure 2.38
).
Scientists have fancied for a long time the use of readily available devices that deliver tiny
amounts of solutions of proteins and cells to selected locations of a substrate—it is a simple
dream: apply the device, and the cells selectively attach to the desired locations. hat is what
microluidic devices are about, but the technology is not readily available to everyone. As it turns
out, there is a microluidic device that is commercially available: the inkjet printer! Because of its
convenience, several groups have explored the use of printers to deposit scafolds for cell culture
for a long time. Among them, Sawyer Fuller, then at MIT, constructed a custom-built inkjet
printer capable of depositing protein droplets (gap resolution, 8 ± 2 μm; smallest islands, 65 ±
5 μm). Dissociated rat hippocampal neurons recognized patterns of collagen/PDL mixture on
a PEG background up to 10 days in culture and were electrophysiologically and immunocyto-
chemically normal compared with control cultures (
Figure 2.39
).
he device developed by Fuller's group is simple but requires the protein to be deposited from
the soluble phase onto a dry surface. Can this concept be generalized to work under luids, to
keep the protein in its natural (nondenatured) state? Emmanuel Delamarche's group at IBM
Zurich has precisely developed a microluidic probe that can be used as a noncontact “fountain
pen” to write or deposit materials on surfaces—including onto live cells (see Section 3.9.4).
2.6.2.6 Selective Microluidic Delivery of Cell Suspensions
he concept of microluidic protein patterning pioneered by Friedrich Bonhoefer and Hans
Biebuyck (Section 2.4.3) can be generalized to cell suspensions (
Figure 2.40
). In this case, the
microchannels must feature deep (~100 μm) channel dimensions to enable the direct injection of a
cell suspension. With shallower (<50 μm) microchannels, cell accumulation occurs at the channel
entrance, which efectively reduces the cell suspension density in the channel. Ater cell attach-
ment (~1 hour) under non-low conditions, the microchannels are removed and a cellular micropat-
tern remains. he technique can be used straightforwardly to micropattern several other cell types
simultaneously; because cell attachment is a highly metabolic, oxygen-dependent process, cell types
such as hepatocytes or neurons that have high oxygen uptake rates might require a specialized oxy-
genation scheme. he method uniquely allows for micropatterning homogeneous surfaces at very
low cost. Importantly, it can be used in combination with cell types such as ibroblasts that secrete
large amounts of ECM and thus do not attach selectively to templates of ECM protein.
Cells
FIGURE 2.40
Selective.microluidic.delivery.of.cells..Scale.bar.is.100.μm..(From.A..Folch,.A..Ayon,.
O..Hurtado,.M..A..Schmidt,.and.M..Toner,.“Molding.of.deep.polydimethylsiloxane.microstructures.
for.microluidics.and.biological.applications,”.
J. Biomech. Eng.
.121,.28,.1999..Figure.contributed.
by.the.author.)
