Stephan K. W. Dertinger

Neutrophil chemotaxis in linear and complex gradients of interleukin-8 formed in a microfabricated device.

Although a wealth of knowledge about chemotaxis has accumulated in the past 40 years, these studies have been hampered by the inability of researchers to generate simple linear gradients instantaneously and to maintain them at steady state. Here we describe a device microfabricated by soft lithography and consisting of a network of microfluidic channels that can generate spatially and temporally controlled gradients of chemotactic factors. When human neutrophils are positioned within a microchannel, their migration in simple and complex interleukin-8 (IL-8) gradients can be tested. The cells exhibit strong directional migration toward increasing concentrations of IL-8 in linear gradients. Neutrophil migration halts abruptly when cells encounter a sudden drop in the chemoattractant concentration to zero (“cliff” gradient). When neutrophils are challenged with a gradual increase and decrease in chemoattractant (“hill” gradient), however, the cells traverse the crest of maximum concentration and migrate further before reversing direction. The technique described in this paper provides a robust method to investigate migratory cells under a variety of conditions not accessible to study by earlier techniques.

Gradients of substrate-bound laminin orient axonal specification of neurons

Little is known about the influence of substrate-bound gradients on neuronal development, since it has been difficult to fabricate gradients over the distances typically required for biological studies (a few hundred micrometers). This article demonstrates a generally applicable technique for the fabrication of substrate-bound gradients of proteins with complex shapes, using laminar flows in microchannels. Gradients that range from pure laminin to pure BSA were formed in solution by using a network of microchannels, and these proteins were allowed to adsorb onto a homogeneous layer of poly-l-lysine. Rat hippocampal neurons were cultivated on these substrate-bound gradients. Analysis of optical images of these neurons showed that axon specification is oriented in the direction of increasing surface density of laminin. Linear gradients in laminin adsorbed from a gradient in solution having a slope of ∇[laminin] > about 0.06 μg (ml⋅μm)−1 (defined by dividing the change of concentration of laminin in solution over the distance of the gradient) orient axon specification, whereas those with ∇[laminin] < about 0.06 μg (ml⋅μm)−1 have no effect.

Patterning Flows Using Grooved Surfaces: Application to Microfluidics

Pressure-driven flows over grooved surfaces are shown to develop transverse components. This induces helical recirculation in channels or capillaries with grooved walls, and more generally permits the design of 3D flows with simple patterns of grooved regions. This strategy is easy to implement with standard methods of microfabrication, and permits for example the realization of a low Reynolds number chaotic mixer.