Abstract
Microfluidic chemical gradient generators enable precise spatiotemporal control of chemotactic signals to study cellular behavior with high resolution and reliability. However, time and cost consuming preparation steps for cell adhesion in microchannels as well as requirement of pumping facilities usually complicate the application of the microfluidic assays. Here, we introduce a simple strategy for preparation of a reusable and stand-alone microfluidic gradient generator to study cellular behavior. Polydimethylsiloxane (PDMS) is directly mounted on the commercial polystyrene-based cell culture surfaces by manipulating the PDMS curing time to optimize bonding strength. The stand-alone strategy not only offers pumpless application of this microfluidic device but also ensures minimal fluidic pressure and consequently a leakage-free system. Elimination of any surface treatment or coating significantly facilitates the preparation of the microfluidic assay and offers a detachable PDMS microchip which can be reused following to a simple cleaning and sterilization step. The chemotactic signal in our microchip is further characterized using numerical and experimental evaluations and it is demonstrated that the device can generate both linear and polynomial signals. Finally, the feasibility of the strategy in deciphering cellular behavior is demonstrated by exploring cancer cell migration and invasion in response to chemical stimuli. The introduced strategy can significantly decrease the complexity of the microfluidic chemotaxis assays and increase their throughput for various cellular and molecular studies.
Highlights
Microfluidic chemical gradient generators enable precise spatiotemporal control of chemotactic signals to study cellular behavior with high resolution and reliability
Cell culture reagents including Dulbecco’s phosphate buffer saline (DPBS), Dulbecco’s modified eagle medium (DMEM), fetal bovine serum (FBS), trypsin-Ethylenediaminetetraacetic acid (EDTA), penicillin/streptomycin, and Geltrex® were purchased from Gibco (Thermofisher Scientific, USA) while CellTrackers were obtained from Invitrogen (Thermofisher Scientific, USA)
To resolve the challenges associated with complicated preparation process of microfluidic gradient generators, here we introduced a simple but robust strategy by application of a stand-alone detachable microfluidic device (Fig. 1)
Summary
Microfluidic chemical gradient generators enable precise spatiotemporal control of chemotactic signals to study cellular behavior with high resolution and reliability. The traditional “Boyden chamber” is the most widely used chemotaxis device, which generates concentration gradients between two centimeter-scale wells separated by a permeable m embrane[4] Simple, this approach (and similar traditional a pproaches2) suffer from (i) inability for monitoring cellular morphology and migration path, (ii) inaccurate control on the generation of micrometer-scale chemical signals crucial for mimicking in vivo microenvironment, (iii) consumption of a large amount of expensive bioactive factors, (iv) inability for generation of realistic 2D or 3D signals or application of more than one chemotactic factor, and (v) instability in generating long-lasting concentration gradients for long time e xperiments[5]. Microfluidic devices provide highly biocompatible microenvironment which can be used for real-time monitoring of cellular b ehavior[6,7,8] These systems can generate small characteristic scale chemical signals with accurate spatiotemporal control to study cellular response down to single-cell level[9,10,11]. Porous materials such as hydrogels along with large reservoirs have been integrated into such devices to optimize the diffusion of chemotactic factors inside the microfluidic network, increase the stability of the gradient during the assay, and prolong the life of the generated gradient[19,20]
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