Art-on-a-Chip: Preserving Microfluidic Chips for Visualization and Permanent Display.

"After a certain high level of technical skill is achieved, science and art tend to coalesce in aesthetics, plasticity, and form. The greatest scientists are always artists as well." said Albert Einstein. Currently, photographic images bridge the gap between microfluidic/lab-on-a-chip devices and art. However, the microfluidic chip itself should be a form of art. Here, novel vibrant epoxy dyes are presented in combination with a simple process to fill and preserve microfluidic chips, to produce microfluidic art or art-on-a-chip. In addition, this process can be used to produce epoxy dye patterned substrates that preserve the geometry of the microfluidic channels-height within 10% of the mold master. This simple approach for preserving microfluidic chips with vibrant, colorful, and long-lasting epoxy dyes creates microfluidic chips that can easily be visualized and photographed repeatedly, for at least 11 years, and hence enabling researchers to showcase their microfluidic chips to potential graduate students, investors, and collaborators.

Well plate microfluidic system for investigation of dynamic platelet behavior under variable shear loads.

The study of platelet behavior in real-time under controlled shear stress offers insights into the underlying mechanisms of many vascular diseases and enables evaluation of platelet-focused therapeutics. The two most common methods used to study platelet behavior at the vessel wall under uniform shear flow are parallel plate flow chambers and cone-plate viscometers. Typically, these methods are difficult to use, lack experimental flexibility, provide low data content, are low in throughput, and require large reagent volumes. Here, we report a well plate microfluidic (WPM)-based system that offers high throughput, low reagent consumption, and high experimental flexibility in an easy to use well plate format. The system consists of well plates with an integrated array of microfluidic channels, a pneumatic interface, an automated microscope, and software. This WPM system was used to investigate dynamic platelet behavior under shear stress. Multiple channel designs are presented and tested for shear loads with whole blood to determine their applicability to study thrombus formation. Normal physiological shear (0.1-20 dyn/cm(2) ) and pathological shear (20-200 dyn/cm(2) ) devices were used to study platelet behavior in vitro under various shear, matrix coating, and monolayer conditions. The high physiological relevance, low blood consumption, and increased throughput create a valuable technique available to vascular biology researchers. The approach also has extensibility to other research areas including inflammation, cancer biology, and developmental/stem cell research.

Using well-plate microfluidic devices to conduct shear-based thrombosis assays.

Shear stress plays a critical role in regulating platelet adhesion and thrombus formation at the site of vascular injury. As such, platelets are often examined in vitro under controlled shear flow conditions for their hemostatic and thrombotic functions. Common shear-based platelet analyses include the evaluation of genetic mutants, inhibitory or experimental compounds, matrix substrates, and the effects of different physiological and pathological shear forces. There are several laboratory instruments widely used for studying shear flow, including cone and plate viscometers and parallel plate perfusion chambers. These technologies vary widely in the types of samples, substrates, blood volumes, and throughput that are involved. Here, we describe a microfluidic system for platelet analysis under shear flow. We used the devices to study thrombus formation on collagen I and von Willebrand factor. The system was also used to investigate dose response to the antiplatelet compound, Abciximab, under shear flow conditions with an emphasis on maximizing the number of data points per single patient sample. The presented method confers multiple advantages over conventional approaches. These include the ability to assess up to 24 conditions simultaneously in real time, maintain identical physical conditions across experiments, and use extremely low donor volumes.

Continuous differential impedance spectroscopy of single cells.

A device for continuous differential impedance analysis of single cells held by a hydrodynamic cell trapping is presented. Measurements are accomplished by recording the current from two closely-situated electrode pairs, one empty (reference) and one containing a cell. We demonstrate time-dependent measurement of single cell impedance produced in response to dynamic chemical perturbations. First, the system is used to assay the response of HeLa cells to the effects of the surfactant Tween, which reduces the impedance of the trapped cells in a concentration dependent way and is interpreted as gradual lysis of the cell membrane. Second, the effects of the bacterial pore-forming toxin, Streptolysin-O are measured: a transient exponential decay in the impedance is recorded as the cell membrane becomes increasingly permeable. The decay time constant is inversely proportional to toxin concentration (482, 150, and 30 s for 0.1, 1, and 10 kU/ml, respectively). ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s10404-009-0534-2) contains supplementary material, which is available to authorized users.

Expansion channels for low-pass filtering of axial concentration gradients in microfluidic systems.

Chemical gradients that run axially in a microfluidic channel often contain undesirable high-frequency concentration variations, or noise, that results from mechanical and thermal fluctuations in the system. In this paper, we describe a passive microfluidic component called an 'expansion channel' (EC), that removes high frequency noise through axial dispersion. We show that the behavior of the filter can be modeled analytically, using an expression for the transfer function of the microfluidic channel, derived by Xie et al. (Y. W. Xie, L. Chen and C. H. Mastrangelo, Lab Chip, 2008, 8, 907-912). The use of ECs to remove noise from gradients formed in enyzmatic assays in a microfluidic channel is demonstrated. The resulting data quality is improved which enables better fits to chemical models and more accurate analysis. ECs should be very effective in removing noise from axial concentration gradients found in many microfluidic applications, e.g. liquid chromatography, biochemistry, and chemotaxis studies.

A low-cost, manufacturable method for fabricating capillary and optical fiber interconnects for microfluidic devices.

Microfluidic chips require connections to larger macroscopic components, such as light sources, light detectors, and reagent reservoirs. In this article, we present novel methods for integrating capillaries, optical fibers, and wires with the channels of microfluidic chips. The method consists of forming planar interconnect channels in microfluidic chips and inserting capillaries, optical fibers, or wires into these channels. UV light is manually directed onto the ends of the interconnects using a microscope. UV-curable glue is then allowed to wick to the end of the capillaries, fibers, or wires, where it is cured to form rigid, liquid-tight connections. In a variant of this technique, used with light-guiding capillaries and optical fibers, the UV light is directed into the capillaries or fibers, and the UV-glue is cured by the cone of light emerging from the end of each capillary or fiber. This technique is fully self-aligned, greatly improves both the quality and the manufacturability of the interconnects, and has the potential to enable the fabrication of interconnects in a fully automated fashion. Using these methods, including a semi-automated implementation of the second technique, over 10,000 interconnects have been formed in almost 2000 microfluidic chips made of a variety of rigid materials. The resulting interconnects withstand pressures up to at least 800psi, have unswept volumes estimated to be less than 10 femtoliters, and have dead volumes defined only by the length of the capillary.

Integrated microfluidic cell culture and lysis on a chip.

We present an integrated microfluidic cell culture and lysis platform for automated cell analysis that improves on systems which require multiple reagents and manual procedures. Through the combination of previous technologies developed in our lab (namely, on-chip cell culture and electrochemical cell lysis) we have designed, fabricated, and characterized an integrated microfluidic platform capable of culturing HeLa, MCF-7, Jurkat, and CHO-K1 cells for up to five days and subsequently lysing the cells without the need to add lysing reagents. On-demand lysis was accomplished by local hydroxide ion generation within microfluidic chambers, releasing both proteinacious (GFP) and genetic (Hoescht-stained DNA) material. Sample proteins exposed to the electrochemical lysis conditions were immunodetectable (p53) and their enzymatic activity (HRP) was investigated.