López-Martínez, Manuel A.

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    Characterization of a microfluidic device for autonomous biological cell entrapment and electrical interrogation
    (2011) López-Martínez, Manuel A.; Díaz-Rivera, Rubén E.; College of Engineering; Quintero, Pedro; Jia, Yi; Department of Mechanical Engineering; Couvertier, Isidoro
    Microfluidic devices have become a great tool to target biological cells individually. They are easy to manufacture, involve short time assays, use small sample and reagent volumes, and usually have low Reynolds number (Re), which is adequate for the handling of biological cells. However, these devices usually require complicated pumping mechanisms that work with external connections, tethers or tubing to transport and study cell samples. A microfluidic device to capture single biological cells with hydrodynamic traps for subsequent electrical treatment in parallel is proposed in this thesis by the use of a new autonomous pumping mechanism. The device presented in this research project was manufactured by photolithography and Polydimethylsiloxane (PDMS) soft lithography. The system is designed to capture individual cells in hydrodynamic traps autonomously by the use of two main microchannels: one for loading the cell sample and another to drain the channel. The two main channels share a fluidic connection through the trap area where particles are trapped individually following the streamline at the vicinity of each trap. The fluid was introduced into the main channels by filling up polystyrene fittings with a micropipette. The volume and thus the fluid level at each fitting could be controlled individually to achieve a pressure driven flow. Each fitting was also integrated with a silver/silver-chloride electrode for subsequent electrical treatment. To inhibit biological cell adhesion to the PDMS walls or glass substrate, the channels were functionalized with Bovine Serum Albumin (BSA). The fluidic behavior of the passive pumping mechanism was characterized using micron sized polystyrene beads (15µm diameter) to determine the optimal flow for cell handling (trapping/release). Experimental results show that the efficiency of the trapping and/or release of microbeads are a function of the fluid volume ratio among fluidic inlet/outlet ports. Results with HeLa cells (cervical cancer cells) show the same behavior observed with polystyrene beads. However, the range of operation is narrower since the biological cells tend to deform and pass through the traps when the local fluid flow is above a critical value. The observed deformation of the biological cells at the traps is attributed to their viscoelastic nature. Electrical interrogation experiments suggest that the dimensions at the trap zone should be smaller in order to achieve effective electroporation of cells with real-time ionic current feedback. In this work we have demonstrated that the passive pumping mechanism is effective in transporting and immobilizing single cells when the geometrical design of the fluidic channel is appropriate. In addition, we have demonstrated that it is possible to monitor the device’s trapping efficiency by electrical means, removing the need to use a complex microscopic setup to operate the system. This device represents a step towards developing high-throughput cell-based assay for drug screening, cellular electroporation, and other applications in the field of bioengineering.