these cells could cause extra loss on the overall cell survival rate,
though not significant.
2. Focusing local electric pulses. Micropillars in MAE also help
focus the electric field with their microscale far end that protrudes towards the cell membrane, similar to what occurs in
some other electrode configurations with microfeatures
[5–7]. According to the continuity of the electric field, the
focusing level depends on the surface area (or size) of micropillars. As the focused electric pulses affect mainly a tiny portion
of the cell membrane each micropillar faces, these locations
more incline to form temporary openings than elsewhere during electroporation. This gives additional localized electroporation benefit on the subjected cell. But unlike many micro/
nanofluidic electroporation systems, MAE does not require
fluidic components to trap cells to accomplish these benefits.
Its operation is therefore more compatible and similar to the
commercial electroporation systems.
3. The dimensions of individual micropillar and their pitch size in
the micropillar array electrode do affect the enhancement of
cell transfection in MAE as they determine the number of
micropillars each cell faces during electroporation. To demonstrate such effect, we fabricated micropillars of two different
sizes (6 μm and 2 μm in diameter with the same gap size of
2 μm). With the same gap size, the 2-μm micropillar electrode
has more micropillars cover each cell and less incomplete coverage than that in the 6-μm micropillar array electrode despite
the random location of cells (Fig. 1a). Therefore, the number
of 2-μm micropillars varies more accurately with the actual size
of individual cells. As the consequence, the number of locally
porated openings and the total effective permeable area on the
cell membrane should become more size specific and the DNA
delivery dosage to cells of various size populations get
improved. As demonstrated in Fig. 5a, the transfection efficiency of 2-μm micropillar MAE is ~65%, ~70%, and 71% for
3T3 cells, K562, and A549 cells, respectively, while only ~55%,
~59%, and ~61% for those using 6-μm micropillar MAE electrodes. This additional gain on the transfection efficiency is
believed the result of more accurate and uniform allocation of
pulse on cells based on their size in 2-μm micropillar MAE. Its
electroporation works more effectively to cells of different sizes
than the 6-μm ones and accomplishes better transfection
performance.
4. When cotransfection of plasmids and siRNA is used, the delivery enhancement on the targeting reporter gene and its
corresponding siRNA occur simultaneously in MAE. It must
shut off more protein expression than the BTX system to reach
the similar protein level (Fig. 5b).
Cell Size-Specific Transfection by Micropillar Array Electroporation
11
though not significant.
2. Focusing local electric pulses. Micropillars in MAE also help
focus the electric field with their microscale far end that protrudes towards the cell membrane, similar to what occurs in
some other electrode configurations with microfeatures
[5–7]. According to the continuity of the electric field, the
focusing level depends on the surface area (or size) of micropillars. As the focused electric pulses affect mainly a tiny portion
of the cell membrane each micropillar faces, these locations
more incline to form temporary openings than elsewhere during electroporation. This gives additional localized electroporation benefit on the subjected cell. But unlike many micro/
nanofluidic electroporation systems, MAE does not require
fluidic components to trap cells to accomplish these benefits.
Its operation is therefore more compatible and similar to the
commercial electroporation systems.
3. The dimensions of individual micropillar and their pitch size in
the micropillar array electrode do affect the enhancement of
cell transfection in MAE as they determine the number of
micropillars each cell faces during electroporation. To demonstrate such effect, we fabricated micropillars of two different
sizes (6 μm and 2 μm in diameter with the same gap size of
2 μm). With the same gap size, the 2-μm micropillar electrode
has more micropillars cover each cell and less incomplete coverage than that in the 6-μm micropillar array electrode despite
the random location of cells (Fig. 1a). Therefore, the number
of 2-μm micropillars varies more accurately with the actual size
of individual cells. As the consequence, the number of locally
porated openings and the total effective permeable area on the
cell membrane should become more size specific and the DNA
delivery dosage to cells of various size populations get
improved. As demonstrated in Fig. 5a, the transfection efficiency of 2-μm micropillar MAE is ~65%, ~70%, and 71% for
3T3 cells, K562, and A549 cells, respectively, while only ~55%,
~59%, and ~61% for those using 6-μm micropillar MAE electrodes. This additional gain on the transfection efficiency is
believed the result of more accurate and uniform allocation of
pulse on cells based on their size in 2-μm micropillar MAE. Its
electroporation works more effectively to cells of different sizes
than the 6-μm ones and accomplishes better transfection
performance.
4. When cotransfection of plasmids and siRNA is used, the delivery enhancement on the targeting reporter gene and its
corresponding siRNA occur simultaneously in MAE. It must
shut off more protein expression than the BTX system to reach
the similar protein level (Fig. 5b).
Cell Size-Specific Transfection by Micropillar Array Electroporation
11