Three-dimensional Printing of Thermoplastic Materials to Create Automated Syringe Pumps with Feedback Control for Microfluidic Applications

This method can help enable research in any field requiring precision liquid handling including molecular, cell, and systems biology, chemical engineering and microfabrication. The main advantage of this approach is that we are able to fabricate low-cost pressure-regulated syringe pumps. This technique should save money across a wide range of disciplines.

This technique showcases how we can couple additive manufacturing with open-source electronics to make a useful piece of laboratory instrumentation. To begin, download the STL design files from the supplemental files of this publication. Prepare these files for printing by opening them in a software package dedicated to the conversion of STL model files to executable instruction sets for the 3D printer being used.

Ensure that the proper software is being used as some printers will require proprietary software whereas others may be able to print directly from the STL file. Now print the plastic components using acrylonitrile butadiene styrene with a high-quality 3D printer setting. If other common 3D printing materials are being used such as polylactic acid or other thermoplastic elastomers, make sure that the finished mechanical properties are comparable.

Once complete, detach the printed parts from the printing platform of the 3D printer. Remove the printed supporting structure from the finished parts. Smooth the printed components by sanding any rough edges using sandpaper.

For best results, use sandpaper with a grit size below 220. Make sure all components are smooth before assembling and ensure that all seven parts have been printed. Fasten the stepper motor to a threaded rod using a motor shaft z-axis flexible coupler with set screws.

Before continuing, make sure that rotating the stepper motor shaft drives the threaded rod without slippage. Connect the syringe platform to the motor connector by firmly pressing the syringe platform's connection pegs into the mating holes on top of the motor connector. Attach the two parts by fastening four 16 millimeter screws through the motor connector.

Now insert two linear ball bearings and a 0.8 millimeter hex nut into the openings located on the bottom of the traveler push. Align the threaded rod on the motor connector through the 0.8 millimeter hex nut in the traveler push. Then insert the two linear shafts through the traveler push in the motor connector.

Now place two hex nuts in the hexagonal spaces of the motor connector piece and then use two 16 millimeter screws to tighten the connections securing the linear shafts from moving. Insert the ball bearing into the middle opening of the end stop. Connect the end stop with the assembled components.

Place two hex nuts in the hexagonal spaces of the end stop piece and then use two 16 millimeter screws to tighten the connections to affix the end stop to the assembly. Next, attach the syringe plunger female connector piece to the traveler push piece using two steel locknuts and two 16 millimeter screws. Place a 10 milliliter syringe on the top of the pump.

Ensure the head of the plunger is aligned into the notch of the syringe plunger female connector piece and that the top of the syringe barrel is fixed into the slot of the motor connector. Now insert the syringe plunger male connector piece into the syringe plunger female connector. Connect the syringe clamp to the syringe platform using two hex nuts and two 35 millimeter screws ensuring the syringe barrel is fixed into the slot of the syringe clamp.

Ensure that there is a tight fit between the male and female components securing the plunger in place. Proceed to microfluidic device preparation as detailed in the text protocol. To begin the syringe pump system assembly, remove 80%of the length of the wire insulation and shielding from the pressure sensor's electrical cable using a razor.

Be gentle when cutting to ensure the wires are not compromised above the desired length. Once the insulation and shielding are removed, connect the wires to male rectangular connectors. Using a similar approach, remove one to two centimeters of the wire insulation from a stepper motor's leads and connect the wires to male rectangular connectors.

Now affix the syringe onto the inlet side of the pressure sensor. Connect the 22 gauge dispensing needle onto the outlet side of the pressure sensor. Slide one end of 0.51 centimeter diameter tubing over the 22 gauge dispensing needle attached to the pressure sensor.

Slide the other end of the tubing over a 22 gauge dispensing needle that can be connected to the microfluidic device. Then connect the needle to the inlet port of the microfluidic device. Connect the outlet port of the microfluidic device to a waste disposal reservoir using a 22 gauge needle and 0.51 centimeter diameter tubing similar to the inlet port's connection.

Next, assemble the electronic circuit on a prototyping breadboard according to the diagram in the text protocol. Connect the wires from the stepper motor with the stepper motor driver. Then connect the wires from the pressure sensor and the stepper motor driver to the breadboard.

Now connect the output signal from the breadboard with the analog input pin on the microcontroller. Connect the logic input pins from the stepper motor driver with the digital pins on the microcontroller. The step input on the stepper motor driver is connected with a pulse width modulated port of digital pins on the microcontroller denoted by a tilde sign.

Connect the power supply to the breadboard as shown in the text. Then set the power supply to 10 volts for the breadboard and the stepper motor driver. To control the syringe pressure pumps, first open the Integrated Development Environment or IDE for the open-source microcontroller.

Download the Timer. h and ExcelStepper. h libraries to the microcontroller's IDE library directory.

Download the controller code titled Dual Pump PID Control.INO. This code is used to control the feedback-controlled syringe pump system with two pumps. Program the controller code so that it fits the experiment being conducted.

Modify the control parameters for the timing parameters to fit the desired response and duration of the experiment. Compile and upload the code to the microcontroller before running the experiment. Turn on the power supply for the syringe pump system.

Finally, set the voltage to 10 volts for the stepper motor power supply. Shown here are representative results showing how control parameters may be tuned. Modifying the proportional coefficients as shown here lead to different response profiles for the pressure signals.

Modifying the integral and differential coefficients also lead to changes in the response profiles. Parameters may be optimized for different experimental designs. Shown here are representative results showing the control and modulation of a laminar flow profile in a microfluidic device.

By controlling the inlet pressure at two inlet ports of a Y-shaped microfluidic device, the interface position may be precisely controlled downstream. Following this procedure, other techniques such as cell culturing and microscopy can be performed in order to answer questions related to synthetic gene network regulatory dynamics, cell physiology and biological regulatory networks. These syringe pump systems have enabled more rapid development of microfluidic procedures within our lab group.

These devices are an inexpensive and time-efficient way for groups to control flow through many different microfluidic devices. We hope that researchers across a wide range of disciplines will be able to use and extend these pressure-regulated syringe pumps for their microfluidic needs.