Cell handling using microstructured membranes

Abstract

Gentle and precise handling of cell suspensions is essential for scientific research and clinical diagnostic applications. Although different techniques for cell analysis at the micro-scale have been proposed, many still require that preliminary sample preparation steps be performed off the chip. Here we present a microstructured membrane as a new microfluidic design concept, enabling the implementation of common sample preparation procedures for suspensions of eukaryotic cells in lab-on-a-chip devices. We demonstrate the novel capabilities for sample preparation procedures by the implementation of metered sampling of nanoliter volumes of whole blood, concentration increase up to three orders of magnitude of sparse cell suspension, and circumferentially uniform, sequential exposure of cells to reagents. We implemented these functions by using microstructured membranes that are pneumatically actuated and allowed to reversibly decouple the flow of fluids and the displacement of eukaryotic cells in suspensions. Furthermore, by integrating multiple structures on the same membrane, complex sequential procedures are possible using a limited number of control steps.

Microvalves and Micropumps for BioMEMS

“…Application of vacuum to the control line deflects the membrane downwards, allowing mass transport by convection, diffusion, or both. The doormat design does not have the aforementioned shortcomings of the Quake valve, and issues of bonding the membrane to the valve seat can be mitigated [7,12,44,45]. Since the valve is actuated from the channel floor, it can actuate both deep and shallow channels.…”

“…One may choose to selectively prevent the membrane from bonding to the valve seat by using a non-PDMS valve seat (e.g., metal [12]) or a sacrificial barrier on the membrane during the bonding process [12]. These bonding prevention strategies present a unique challenge to the fabrication process that adds to its complexity.…”

“…Finally, since the valves are closed at rest, the devices can be unplugged and transported to a different location with all the fluids stored safely in microchambers. The "curtain" style microvalve developed by Irimia and Toner [12] is another normally-closed valve design ( Figure 9). As opposed to the doormat design described previously, the channel barrier on the curtain valve is a microstructure integrated with the membrane layer instead of the channel layer.…”

“…At zero pressure, the membrane sits flush with the valve seat and blocks the flow channel. In the two-layered membrane design, the leaky barrier serves as a cell trap that may be used for cell enrichment and separation [12]; positive pressure can be applied to the control layer to shut the leaky channels as well. By drawing vacuum on the control layer, the membrane and barrier(s) are lifted upward and open the fluidic passage.…”

“…The valves can be actuated mechanically [1][2][3][4], pneumatically [5][6][7][8][9][10][11][12][13], electrokinetically [14][15][16][17], by phase changes [10,11,[18][19][20][21][22], or by introduction of external force [23,24]. Using the method of actuation as the differentiating parameter, five major classes of active microvalves can be identified in the literature: electrokinetic, pneumatic, pinch, phase change, and burst.…”