A tunable micro filter modulated by pneumatic pressure for cell separation

This study reports a new microfluidic-based filter for size-tunable separation of microbeads or cells. The filtration separation mechanism is based on the pneumatically tunable deformation of poly-dimethylsiloxane (PDMS) membranes, which block the fluid channel with a varied degree. This defines the dimensions of the open area of the fluid channel and thus determines the maximum diameter the microbeads or cells which can pass through. The proposed device incorporates pneumatic micropumps for automatic liquid handling. Another unique feature of this filter is an unclogging mechanism using a back-flush operating mode, by which a reverse-directional flow is utilized to flush the clogged filter zone. The separation performance of the proposed device has been experimentally evaluated. Results show that this developed device is able to provide precise size-dependent filtration, with a high passage efficiency (82–89%) for microbeads with sizes smaller than the defined void space in the filter zone. Also, the proposed separation mechanism is also capable of providing a reasonable filtration rate (14.9–3.3 μl/min). Furthermore, the separation of chondrocytes from a 30 μl suspension of enzymatically digested tissue is successfully demonstrated, showing an excellent cell passage efficiency of 93% and a cell viability of 96%. The proposed device is therefore capable of performing cell separation in situations where either the harvested specimen is limited or the sample cell content is sparse. It also paves a new route to delicately separate or to isolate cells in a simple and controllable manner.