Computer-controlled microfluidics would advance many types of cellular assays and microscale tissue engineering studies wherever spatiotemporal changes in fluidics need to be defined. However, this goal has been elusive because of the limited availability of integrated, programmable pumps and valves. This paper demonstrates how a refreshable Braille display, with its grid of 320 vertically moving pins, can power integrated pumps and valves through localized deformations of channel networks within elastic silicone rubber. The resulting computerized fluidic control is able to switch among: ( i ) rapid and efficient mixing between streams, ( ii ) multiple laminar flows with minimal mixing between streams, and ( iii ) segmented plug-flow of immiscible fluids within the same channel architecture. The same control method is used to precisely seed cells, compartmentalize them into distinct subpopulations through channel reconfiguration, and culture each cell subpopulation for up to 3 weeks under perfusion. These reliable microscale cell cultures showed gradients of cellular behavior from C2C12 myoblasts along channel lengths, as well as differences in cell density of undifferentiated myoblasts and differentiation patterns, both programmable through different flow rates of serum-containing media. This technology will allow future microscale tissue or cell studies to be more accessible, especially for high-throughput, complex, and long-term experiments. The microfluidic actuation method described is versatile and computer programmable, yet simple, well packaged, and portable enough for personal use.

The lodging mechanisms and dynamics of cardiovascular gas bubbles are investigated in microfluidic model bifurcations made of poly(dimethylsiloxane). This work is motivated by gas embolotherapy for the potential treatment of cancer by tumor infarction. The results show that the critical driving pressure below which a bubble will lodge in a bifurcation is significantly less than the driving pressure required to dislodge it. From the results the authors estimate that gas bubbles from embolotherapy can lodge in vessels 20μm or smaller in diameter, and conclude that bubbles may potentially be used to reduce blood flow to tumor microcirculation.

We developed a simple system that regulates CO₂ and O₂ levels within a microfluidic chip. This system enables long-term cell culture under hypoxic conditions without the need of a CO₂ incubator or a multi-gas incubator. Hypoxic conditions were generated using a miniature water jacket containing dissolved ascorbate as an oxygen scavenger. Formulations of the water jacket were determined that enables both 5% pCO₂ and desired pO₂ levels ranging from 5 to 15%. We also cultured PC-12 cells and primary neuronal cells from chick embryos under hypoxia and observed hypoxia-induced cell death and inhibition of neurite outgrowth.

We have developed a cast microfluidic chip for concentration gradient generation that contains a thin (~5 µm² cross-sectional area) microchannel. The diffusion of diffused 185 nm ultraviolet (UV) light from an inexpensive low-pressure mercury lamp exposed a layer of the SU-8 photoresist from the backside and successfully patterned durable 2 µm-high microchannel mold features with smooth bell-shaped sidewalls. The thin channel had appropriate flow resistance and simultaneously satisfied both the rapid introduction of test substance and long-term maintenance of gradients. The average height and width at the half height of the channel, defined by a 2 µm-wide line mask pattern, were 2.00 ± 0.19 µm, and 2.14 ± 0.89 µm, respectively. We were able to maintain the concentration gradient of Alexa Fluor 488 fluorescent dye inside or at the exit of the thin microchannel in an H-shaped microfluidic configuration for at least 48 h. We also demonstrated the cultivation of chick embryo dorsal root ganglion neuronal cells for 96 h, and the directional elongation of axons under a nerve growth factor concentration gradient.