Development of microfluidic gradient generator for bio-applications

Abstract

Microfluidic gradient generators are being developed for combinatorial and concentration-dependent studies. It is advantageous for biological applications because it eliminates the use of large amount of expensive reagents and gives higher throughput.

This study successfully developed a new microfluidic gradient generator device that is able to create shear-free, stable, movable and tunable concentration gradients for cell-based applications. It is a PDMS chip patterned with four diffusion channels connected to a square diffusion chamber and bonded to a glass for optical visibility. The four injected streams acted as constantly replenished source and sink, subsequently, a gradient was formed across the shear-free stagnation point. It was found that gradient was formed rapidly, can be tuned by changing the driving pressures, and can be moved hydrodynamically in two-dimensional plane. Moreover, the device could be operated using only positive pressure supply, simplifying the system setup.

For evaluation of the device, fluorescence sodium was used to create concentration gradients and its intensity was measured across a diffusion path to get the gradient profile. Experimental results showed that single-component concentration gradients were successfully formed at the stagnation point that experienced no flow and thus no shear stress. It is an improvement of the existing similar devices, which impose high shear stress on cells. Multi-component concentration gradient profiles were also obtained by superimposing multiple individual concentration gradient profiles, showing that diffusion between multiple components can occur independently.

Having the capability to generate shear-free and tunable gradients, combined with high-resolution video microscopy, the microfluidic gradient generator device should be able to provide an ideal experimental platform for high throughput long-term cell- based assays.