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Supplementary Information
Detailed description of fabrication steps of the cell-migration chip
The fabrication steps for the multi-region cell migration chip are presented in Fig. S1.
Fig. S1 Schematic of fabrication steps for cell-migration chip. The dry nanoparticle embedding technique is
demonstrated.
First, standard photolithography was used to create a SU8 master of the micropillar array.
To do this, SU8 3050 (Microchem) was spin-coated on a silicon wafer to a height of 80
µm and soft-baked for 2 minutes at 65ºC and 26 minutes at 95ºC. A Canon PLA-501F
mask aligner was then used to contact-align a transparency mask containing the chip
design with the wafer, and the SU8 was exposed to 1000 mj/cm2 of UV light. Postexposure bake was conducted for 2 minutes at 65ºC and 6 minutes at 95ºC. The exposed
SU8 layer was then developed in a solution of SU8 developer (Microchem) for 6 minutes
and hard-baked at 150ºC for 24 hours to obtain the final SU8 micropillar master.
A replica-molding technique was employed to obtain a reusable polyurethane (PU)
negative from the SU8 master. To do this, a polydimethylsiloxane (PDMS) polymer
solution (Sylgard 184, Dow Corning) was prepared by mixing the polymer base and
cross-linker at a 10:1 ratio. The PDMS solution was then cast on the SU8 master, cured at
70ºC for 6 hours and de-molded to obtain a PDMS negative of the SU8 master. The
PDMS negative was then silanized by exposure to oxygen plasma at 700 mTorr for 2
minutes followed by incubation with a hexamethyldisilazane solution (HMDS, Sigma
Aldrich) overnight. The silanization step allows the casting of a second PDMS solution
on the PDMS negative. A second PDMS solution was then cast on the PDMS negative,
cured at room temperature for 24 hours and demolded to obtain a PDMS replica of the
SU8 master. Finally, a PU solution (Smoothcast 310, Smooth-on inc.) was prepared at 1:1
ratio, cast on the PDMS master, cured at room temperature for 6 hours and de-molded to
obtain the reusable PU negative.
Finally, to fabricate PDMS migration chips using the dry nanoparticle embedding
technique, masking tape was used to cover parts of the PU mold (PU negative)
corresponding to non-magnetic pillar regions on the migration chip (regions 1, 2, 8 and 9)
to prevent embedding of magnetic particles in the cavities of those regions. Carbonyl Iron
magnetic particles (FeC Powder, Chemical Store inc.) were then applied to the surface of
the mold, and a permanent magnet was used to pull the particles into the cavities of the
unmasked regions (regions 3, 4, 6 and 7). Excess particles were then removed by wiping
off with a cotton applicator. Next, the masking tapes were removed and a PDMS polymer
solution was cast on the PU mold and allowed to cure at room temperature. Once cured,
the PDMS was de-molded from the PU mold to obtain the final cell-migration chip which
has 4 regions with magnetic PDMS pillars, 4 regions with non-magnetic PDMS pillars
and a region with flat PDMS.
Magnetic actuators used for cell migration experiments
a) Permanent magnet actuator
Fig. S2 shows images permanent magnet actuator setup that we designed and built for the
purpose of micropillar actuation in cell-migration experiments. In this design the flywheel
and link convert rotational movement of the motor shaft into a sinusoidal back and forth
movement of the magnet holders on the rail guides. Permanent magnets inserted into the
magnet holders apply a magnetic field to the migration chips sitting at the bottom of the
petri-dishes. Movement of the magnets to and away from the petri-dishes causes the
cyclic actuation of the magnetic micropillars on the migration chip at 1 Hz.
Fig. S2 Permanent magnet actuator setup used for cell migration experiments.
When designing the magnetic actuator setup we took careful consideration to minimize
the vibrations induced to the platform from the moving motor and magnets. The design
demonstrated in Fig. S2 was chosen for this very purpose. The inertia of the heavy and
fully balanced rotating flywheel and the sinusoidal back and forth movement of the
carriages, which slow down before changing their direction of travel, minimizes
unwanted vibrations and the self-lubricating guide rails minimize friction which
eliminates frictional sources of vibration. Furthermore, all moving parts are connected to
mounting brackets which are themselves connected to the main base with foam paddings.
These foam paddings which act as vibration dampers further impede transferring of any
induced vibrations to the culture dishes which house the migration chips. Due to these
considerations, in our experiments any influence of platform vibration on cell migration is
very minimal if not non-existent. This conclusion was verified by an experiment
comparing cell migration rates on migration chips placed on the platform with those of a
control chip, i.e., a migration chip placed off the platform but in the same incubator. We
observed no significant differences in cell migration rates between the chips
b) Electromagnet actuator
Fig. S3 shows the custom-made electromagnet actuator, the custom designed and 3Dprinted microchip housing, and the incubated microscope setup used for cell-migration
experiments with live imaging.
Fig. S3 Electromagnet actuator setup used for cell migration experiments.
The 3D printed microchip housing has a glass base which allows for the live imaging of the cells
on the migration chip using the inverted microscope. The electromagnet, run by a signal
generator and current amplifier, applies a 1 Hz cyclic magnetic field of approximately 200 mT to
the migration chip.