8. Pump the solution into the spiral microfluidic chip and collect

the separated cells/microcarriers from the respective outlets in

50-mL tubes (Fig. 3b, c). The operation flow rate is 3 mL/

min and 30 mL/min for the direct-printed and PDMS chip,

respectively (see Note 14).

9. Extra rounds of separation can be performed to increase the

desired yield. Inner outlet solution can be reintroduced into

the device to harvest more cells. The yield of cells depends on

the inlet-outlet ratio. In this work, the cell recovery rate in one

round can be as high as 77% and reach ~95% in two rounds of

separation with the cell properties preserved (Fig. 3).

4

Notes

1. The printing resolution of the printer affects the geometry and

surface roughness of the mold and channel, thus altering the

inertial focusing attribute.

2. Washing the device/mold by 100% ethanol if the remaining

resin is hard to clean. The printed part can also be cleaned by

sonicating the part in a flask of IPA/ethanol for 5 min.

3. PMMA sheet is a transparent and rigid plastic sheet used as a

base for binding. It can be replaced with any flat surface mate-

rial. Depending on the printer, protocol and settings, some

Fig. 2 Running the spiral microfluidic chips with different pumping systems. (a) The schematic illustration of

the simple system setup. (b) The direct printed resin chip with a Syringe pump and (c) the PDMS chip with

peristaltic pump. Direct-printed chip and PDMS chip can be operated with both pumps’ settings. The scale-

bars in (b) and (c) are 250 μm and 1 mm, respectively. (Reproduced from [12] with permission from Nature)

Bioreactor-Based Adherent Cells Harvesting from Microcarriers with 3D. . .

263