Team:Madrid-OLM/HardawareMicrofluidics

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Microfluidics

When the need of moving microvolumes arise as a mandatory requirement of design, microfluidics pops up as the one and only solution. Although there is at hand a wide range of microfluidic commercial solutions, many of them are too expensive to start experimenting with.

That is why our method comes to give an alternative solution. The PDMS manufacturing reveals itself as a tough rival with respect to other alternatives. PDMS was our initial choice, due to its reasonable price and ease of use. As DIY and digital manufacturing constitute the basis of our hardware, we built a workflow around the PDMS chip

The lab workflow for PDMS chips:

Foto diagrama workflow

1-Molding of the upper half

1. Negative: a laser cuts the tape that is adhered to an acetate. The remaining tape is removed carefully. The channels and the chambers, as well as the input and the output have been cutted and the negative has been created. More info about the protocols involved here.

2. Molding box: (Find the polymerization chamber in our github). Once the negative has been created, it is time to align the acetate with the marks in the polymerization chamber. Depending on the chosen configuration, it might be worth to place the perforated base on the bottom of the acetate.

3. PDMS casting: PDMS casting was made inside an lab oven most of times. Curing time depended on the drying method selected. More info about the protocols involved here.

2-Molding of the lower half

The process is repeated without the negative.

3-Fixing the two halves

The selected method for fixing both halves was plasma bonding.More info about the protocols involved here.

4-Creating the input and the outputs

We usually used to hole punch the PDMS inlet/outlet with a needle. But we cured the PDMS with a needle inside as another negative volume for molding.More info about the protocols involved here.

5-Injecting fluids into the chip

Automatic controlled microvolume pressure pumps have been developed specifically for our microfluidic chips. Specific plans of the pumps design can be found in our github.

The hardware is mainly composed of different modules, interconnected for two main purposes: distributing the powers rails through all the modules and communicating each module with the main controller.

Figure 1: Diagram of the different platforms that run the system.

Broadly the system is composed of four main sections:

1. A pump system on a microlitre scale. Composed of eight stepper motors, controlling the syringe’s pumps. It is in charge of injecting and removing the fluid from the chips. This system is directly connected to a 12V power supply and controlled through the digital pins from the main controller, Arduino Mega.

2. A potentiostatic measurement system, the Rodeostat, directly connected to the microfluidic chip. It connects directly to the Arduino (Which governs the device) through Serial communication. For that purpose, the pins 26 and 31 of the P14 connector in the RodeoStat have been connected to the RX2 and TX2 pins on the Arduino Mega. The system is supplied by the 5V pin of the Arduino Mega power converter. For a more detailed description of the system, connection checks this threat where we have explained to the RodeoStat community our set up.

3. A WiFi module, designed and developed by ourselves. The system is based on the board ESP8266, broadly extended in IoT applications. It communicates to Arduino through Serial protocol through its RX3 and TX3 pins. The purpose of this module is to uploads the data sent by Arduino to an external cloud server on FireBase. You could go over all the schematic and board designs on our GitHub.

The main controller which operates the rest of the components, Arduino Mega 2560.

CAUTION: The controllers has several modifications that allow it to work in the device. Trying to replicate it without the modifications is dangerous and can imply the universe destruction:

1. Arduino’s M7 diode, which job is to avoid an eventual situation of reverse current, has been removed. This is because of his inability to stand the 4 amperes that go through the system when the 8 motors are at their full capacity. In its position, we have solder a IRLZ44N transistor, able to stand up to 50 A. To do it, the pins of the source and drain were connected in a similar way as the pins of the diode and the gate pin was connected to the 12V power supply. A heat sink was also put in the upper side.

2. An Arduino Shield was mounted to increase the total of pins to 8 Vin an 8 GND, to connects the power of the motor drivers.

Foto Arduino

Software

As we have introduced in the previous section, our system is like a patchwork, with several different platforms including actuators, sensors and control elements.

Although is essential to correctly choose the programming language for the different platforms, it is mandatory to keep an eye choosing the communication protocols between all of the device’s platforms.

Figure 3: The platform’s programming languages employed and the communication protocols between all of them.

In our circuit there are five platforms liable to be programmed:

1. The ESP8266, module in charge of all the wifi communications. We have kept the original firmware because we didn’t have time to reprogramme it during this call.

2. In the Rodeostat, potentiostat responsible of the electrochemical measurements of the sensor, we modify the original firmware so it could be controlled through the Arduino Mega, instead of a computer.

3. The Arduino Mega controls all the device, handling the motors, receiving the Rodeostat measurements and sending them to the cloud through the WiFi module or the serial communication with the PC.

4. Outside the device, the data go to Firebase server. The server, on one hand, gets all the data and send them to an iOS design app, where the final user can watch the development of the data in real time.

5. Finally, a PC program, written in python with Qt creator, is able to communicate through the serial protocol with the device. The application let you configure 8 different motors, run protocols sequentially or inject liquid in the microfluidic chips.

You can find the code for the PC app, the Arduino control and the Rodeostat’s modified firmware in our GitHub. Both the iOS app and the firebase server was set up thanks to the help of Marcos Hernández Cifuentes.