(161l) Design and Operation of a Low-Cost, Open-Source Syringe Pump for Electrospinning Applications

The design and publication of open-source and reproducible laboratory equipment is central to the democratization of chemical engineering sciences and the development of novel technologies by laboratories and individuals without access to the same degree of funding as more well-established groups. Many chemical and biological processes require syringe pumps, which offer precise control of volume or flow rate. Syringe pumps consist of a syringe attached to a linear actuator, driven by an external motor driver and microcontroller. With the recent development of low-cost stepper motor drivers and microcontrollers, as well as the standardization of stepper motors, syringe pumps are far more amenable to use by the open-source movement due to the availability of their components and the ease of their construction. In this work, a novel syringe pump design and control system is demonstrated, with emphasis on its integration and operation on an in-house electrospinning apparatus.

Most open-sourced syringe pump designs rely on 3D printed parts for the syringe housing and motor mount. The recent proliferation of 3D printing makerspaces allows for such designs to be rapidly fabricated with few parts, but 3D printed parts come with some inherent drawbacks in both dominant consumer technologies, Fused Deposition Modeling and Stereolithography. There is a tradeoff between print time, structural integrity, and dimensional tolerance for FDM, where higher infill and thinner layers will produce a stronger and smoother part, but at the cost of extremely long print times. Low infill and thicker layers allows for faster print time, but at the cost of a more brittle part with poor bonding and fatigue tolerance.[1] SLA produces much stronger and precise parts, but the required resin is far more expensive and the print times are longer. For these reasons, this syringe pump was fabricated from a single acrylic panel using a laser cutter, which offers lower material cost, faster fabrication time, and better material properties, specifically fatigue resistance.

For mechanical stability, the syringe is typically mounted along guide rails and driven by a lead screw separate from the driving motor, which necessitates additional parts to mount the motor to the rails and a shaft coupler between the stepper motor and the lead screw. This increases the footprint of the syringe pump, with the minimum length being the total length of the extended syringe, the coupler, and the motor. Growth in consumer 3D printing has introduced stepper motors with integrated lead screws onto the market, allowing for large simplifications to be made to the syringe pump design by utilizing the mechanical stability offered by the fixed lead screw. A NEMA 17 stepper motor was chosen despite smaller stepper motors being available for cost, mechanical, thermal reasons; the NEMA form factor is large enough to easily mount the syringe to, allowing the body of the syringe itself to be used to guide the plunger, and NEMA motors have better thermal dissipation due to their larger surface area (Figure 1, 2).

The control system for the syringe pump is nearly as important as the mechanical apparatus itself, and significant effort has been made to differentiate this design. Most current open source syringe pump designs use the Raspberry Pi single board computer due to its low cost and ease of development, as it allows control software to be written and executed in a Python interpreter within a full operating system.[2, 3] However, our design aims to achieve precise control over flowrate, and the ability to control and coordinate multiple syringe pumps from a single controller for copolymer electrospinning. As such, a low-cost Lavin Nano (Arduino Nano clone) with a 16 MHz ATmega328 processor is used as the controller, and the firmware is written to be event-based, allowing for concurrent control of multiple outputs without thread locking or delays due to CPU scheduling as in Raspberry Pi based systems (Figure 3).

Testing and calibration of volumetric accuracy of fluid delivery was performed using an experimental setup at the Peron Lab at the Center for Neural Science at New York University, with promising results (Figure 4). Plans are in place for this syringe pump design to be evaluated as a drop-in replacement for a pressure-fed water delivery system on animal training rigs at the Peron Lab, and functional trials of the syringe pumps on the training rigs have been performed. Due to external factors beyond our control, testing of the syringe pump in an electrospinning apparatus has been postponed and is planned for the future.

References

[1] D. Popescu, A. Zapciu, C. Amza, F. Baciu, R. Marinescu, FDM process parameters influence over the mechanical properties of polymer specimens: A review, Polymer Testing 69 (2018) 157-166.

[2] B. Wijnen, E.J. Hunt, G.C. Anzalone, J.M. Pearce, Open-source syringe pump library, PLoS One 9 (2014) e107216-e107216.

[3] K. Akash, M.P. Kumar, N. Venkatesan, M. Venkatesan, A single acting syringe pump based on Raspberry Pi - SOC, 2015 IEEE International Conference on Computational Intelligence and Computing Research (ICCIC), 2015, pp. 1-3.