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.

Manufacturing the PMMA chips

Although we are proud of having implemented an affordable workflow for developing functional PDMS chips, we manufactured PMMA chips with micromachining techniques. Our University has a Mechanical workshop that usually machines vacuum chambers, or metallic parts of machines, bending aluminum sheets, etc.

We visited the workshop and asked the workers how to micromachine a PMMA chip with almost 0.2 mm height and 0.8 channel width. We purchased a 0.4 mm tip diameter and adapted the manufacturing to other available tools.

The input and output needed to be modified, and we used 21G needles (0.8 mm) as inlet and outlet. The fitting was made with High Performance Liquid Chromatography (HPLC) 0.8 mm tubes. They fitted tight enough to avoid leaks.

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.