P. Schneider, B. Bosinski, D. Koh, A. Wang, A. Trimper, K. Oh
University at Buffalo's Sensors & MicroActuators Learning Lab (SMALL),
Keywords: microfluidics, serial dilution, wax base microfluidics
Summary:Phase 1. Traditional Microfluidics using Soft Lithography: SMALL (Sensors and MicroActuators Learning Lab) has created a generalized serial dilution module. Serial dilution is the stepwise dilution of a substance in a solution. By controlling the lengths of the channels, we can adjust the flow rate which is proportional to the fluidic resistance in the channels. Our new method of implementation is a wax-based microfluidics approach that surpasses the traditional resolution limitations. Figure. 1 is our serial dilutor created by the photolithography method . Phase 2. Proof of Concept of Innovative Wax Based Technique: Traditional wax microfluidics are done on paper whereas the pattern is mechanically printed on the paper by an ink jet printer. Compared to paper based wax microfluidics, wax spreads on the paper due to the porosity of the paper . This is usually done using expensive wax printers or wax paper. Figure 2 is a review of the various wax printing techniques seen in research. We have devised a way to print on a glass substrate using a wax stylus. The first step is to simply draw the desired design onto a glass slide. After the wax hardens, PDMS is poured on the wax and an imprint of the design is created. Once the PDMS dries, it is torn off and implemented on a new glass slide. Figure 3 is an illustration of our fabrication method. As shown imaged under a microscope in figure 3 we were able to achieve a diameter of 30μm as shown in figure 4. Using different extruder tip sizes, we were able to change the diameter of these channels. As shown in figure 5, we created channels 200μm in diameter and pumped fluid through proving that these crude prototypes were successful in producing functional microscale channels. Phase 3. Mechanical Actuation of Stylus: The next step is to refine the process through implementation of a mechanical actuator to draw more accurate and smoother designs. The machine currently being used to do this allows for the stylus to be move in the x,y,z axis with a high resolution step motor. This allows for a refined and smoothed designed in a compact setting both of which could not be achieved by human hand. Now one can upload the CAD design file of the serial dilutor from Phase 1 into the microcontroller allowing for the design to be drawn on the glass substrate by the extender head. Comparison and Innovation: The two microfluidic devices will be compared taking into account time, cost, quality, resolution, and device performance. The traditional dilution device has been characterized. In terms of cost analysis the soft lithography technique is estimated to be in the $200-$300 range while our proposed wax technique could potential create devices for under $10. We have found this method can also be used for teaching purposes. Using the wax stylus we have had multiple undergraduate students learn about how microfluidics works, creating their own microfluidic designs and fabricating them all within a few hours’ time.