J. Patrick Shelby

A microfluidic model for single-cell capillary obstruction by Plasmodium falciparum-infected erythrocytes

Severe malaria by Plasmodium falciparum is a potentially fatal disease, frequently unresponsive to even the most aggressive treatments. Host organ failure is associated with acquired rigidity of infected red blood cells and capillary blockage. In vitro techniques have played an important role in modeling cell deformability. Although, historically they have either been applied to bulk cell populations or to measure single physical parameters of individual cells. In this article, we demonstrate the unique abilities and benefits of elastomeric microchannels to characterize complex behaviors of single cells, under flow, in multicellular capillary blockages. Channels of 8-, 6-, 4-, and 2-μm widths were readily traversed by the 8 μm-wide, highly elastic, uninfected red blood cells, as well as by infected cells in the early ring stages. Trophozoite stages failed to freely traverse 2- to 4-μm channels; some that passed through the 4-μm channels emerged from constricted space with deformations whose shape-recovery could be observed in real time. In 2-μm channels, trophozoites mimicked “pitting,” a normal process in the body where spleen beds remove parasites without destroying the red cell. Schizont forms failed to traverse even 6-μm channels and rapidly formed a capillary blockage. Interestingly, individual uninfected red blood cells readily squeezed through the blockages formed by immobile schizonts in a 6-μm capillary. The last observation can explain the high parasitemia in a growing capillary blockage and the well known benefits of early blood transfusion in severe malaria.

Dynamic formation of ring-shaped patterns of colloidal particles in microfluidic systems

This letter reports the formation of patterns of micrometer-sized beads within the steady-state recirculation flow of a microvortex generated in a microfluidic system. The mechanism by which these patterns form relies on a delicate balance between the centrifugal and displacement forces experienced by the recirculating particles with a lift force exerted on the particles near the solid boundary of the microcavity. Our observation was made possible by the small dimensions of the microchannels we used and by the presence of steep velocity gradients unique to microfluidic devices.

Monitoring cell survival after extraction of a single subcellular organelle using optical trapping and pulsed-nitrogen laser ablation.

Abstract This paper characterizes cell viability in three different cell lines—Chinese hamster ovary cells (CHO), neuroblastoma cells fused with glialoma cells (NG108-15) and murine embryonic stem cells (ES-D3)—after N2 laser disruption of the cell membrane and removal, via optical trapping, of a single subcellular organelle. Morphological changes and viability (as determined by live/dead fluorescent stains) of the cell were monitored every half hour over a 4-h period postsurgery. The ability of the cell to survive organelle extraction was found to depend both on the conditions under which surgery was performed and on the cell type. The average viability after surgery for CHO cells was approximately 80%, for NG 108 cells it was approximately 30% and for ES-D3 cells postsurgery viability was approximately 10%. From over 600 surgeries we found the survival of the cell is determined almost exclusively within the first hour postsurgery regardless of cell line. The optimal pulse energy for N2 laser ablation was approximately 0.7 μJ. The N2 pulse produced an approximately 1–3 μm hole in the cell membrane and proved to be the primary source of cell death in those cells that did not survive the procedure.

Controlled rotation of biological micro- and nano-particles in microvorticesElectronic supplementary information (ESI) available: Video clips of controlled rotation of micro- and nano-particles and rotation of single cells in microvortex. See http://www.rsc.org/suppdata/lc/b4/b402479f/

Micrometer-sized re-circulating flows generated in a microfluidic system are used to drive the controlled rotation of biological particles of both micro- and nano-meter scale dimensions. This technique is independent of the intrinsic nature of the particle, and possesses the potential to rotate particles at high rates. We demonstrate in such microvortices the orientation control of single DNA molecules, and the axial rotation of biological cells in which the cellular contents were visibly affected by rotation.

The Generation, Characterization and Application of Microvortices in Microfluidic Systems (Keynote Paper)

This review describes the formation of microvortices in microfluidic systems, and discusses our experimental measurements that illustrate the velocity profiles inside such microvortices. Because of the micrometer dimensions of these vortices and the presence of high rotational velocities, we have observed a number of unique phenomena. One example is the dynamic formation of ring patterns of particles within the microvortex. The mechanism by which these patterns form relies on a balance between the centrifugal and displacement forces experienced by the re-circulating particles with a lift force exerted on the particles near the solid boundary of the microcavity. We also demonstrate the ability to orient and rotate precisely micro and nanometer -sized particles, individual DNA molecules, and single cells. Because of the high linear velocity (m/s) of fluid flow in constricted microchannels and to the small radii (< 10μm) of the microvortices, we have measured the presence of ultrahigh radial accelerations (v2 /r) in such microvortices, which can reach 107 m/s2 or 106 times the gravitational acceleration (g).Copyright