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Design and Engineering of Open Source Hardware for Pressure Regulation in the Study of Vascular Processes

Alexander Novokhodko1, Christian Mandrycky1, and Ying Zheng1,2,3

1Department of Bioengineering, 2Center for Cardiovascular Biology, 3Institute of Stem Cell and Regenerative Medicine, University of Washington, Seattle, WA ZHENGLAB

Goal: Controlling Pressure to study endothelial cell response in vitroApproach:

o Syringe Pump based Control Systemo Ensuring Steady Flowo In vitro microvessels in flow chamber

3

Existing Problems:Oscillation at set point:• Current Percent Error: 2.95%, 2.97%, 4.547%.Imperfect Adaptation: Steady state deviation from set point• .0935%, 1%, 2.835% Target: Maximum Percent Error + Adaptation must not exceed 2% to match [6]• Currently, worst case error is 7.382%. Too high!Solution: PID Control (Proportional, Integral, Differential)• Problem: Motor step size is too large to implement a

PID Duty Cycle• Solution: Gearing down the motor (see Figure 6)Unsteady flow: Flow is currently pulsatile/disrupted• Adjust when the valve (figure 5) is open or closed

Figure 1: Forces on Endothelial Cells. [1]

Results

The Biological Need: Cells Under Pressure

Problem: High cost of commercially available hardware• $4,767 for Constant Pressure

Syringe Pump from Harvard Apparatuses [6]

Solution: Open Source HardwareExchange of CAD files• OpenSCAD• My work is based on “Open-

Source Syringe Pump Library” [7] published in PLOS ONE

• Creative Commons Attribution License

3D Printing• Low cost (see Table 1)Rapid Prototyping• See Figures 5 and 6CustomizabilityArduino Microcontroller• Arduino code and explanation of

algorithm available upon request

Why Open Source Hardware?

Endothelial cell response to blood pressure:• Vasoconstriction, vasodilation• Veins vs. Arteries

• Venous endothelial cells differ from arterial ones. [2]

• Why? Pressure? Or different signals during development?

• Can we use this to prevent saphenous vein graft failure during coronary bypass surgery?

Vasculogenesis/Angiogenesis during development• Once the embryonic heart starts

beating the vasculature remodels. [3] How?

Steady flow:• Outside the largest arteries, flow is

steady, not pulsatile• Except in the aorta, flow is laminar [4]• Pressure is approximately constantIn vitro studies:• Study effect of pressure in isolation• Control pressure to study other

variablesNeed: Pressure Control System that maintains steady laminar flow

References1. Davies, P. & Tripathi, S. Mechanical stress mechanisms and the cell. An endothelial paradigm.

Circulation Research 72, 239-245 (1993).2. dela Paz, N. & D’Amore, P. Arterial versus venous endothelial cells. Cell Tissue Res 335, 5-16 (2008).3. Mechanisms of angiogenesis. Nature 386, 671-674 (1997).4. Stein, P. & Sabbah, H. Turbulent blood flow in the ascending aorta of humans with normal and

diseased aortic valves. Circulation Research 39, 58-65 (1976).5. Klabunde, R. CV Physiology: Systemic Circulation. Cvphysiology.com (2016). at

<http://www.cvphysiology.com/Blood%20Pressure/BP019.htm>6. Standard PHD ULTRA™ CP Syringe Pump. Harvard Apparatuses (2016). at

<http://www.harvardapparatus.com/pumps-liquid-handling/syringe-pumps/constant-pressure/standard-phd-ultra-trade-cp-syringe-pump.html>

7. Wijnen, B., Hunt, E. J., Anzalone, G. C., & Pearce, J. M. (2014, September 17). Open-Source Syringe Pump Library. PlosONE, 9(9), 1-8. doi:10.1371/journal.pone.0107216

8. Tiny Planetary Gears Set by aubenc. Thingiverse.com (2012). at <http://www.thingiverse.com/thing:23030>

9. Zheng, Y. et al. In vitro microvessels for the study of angiogenesis and thrombosis. Proceedings of the National Academy of Sciences 109, 9342-9347 (2012).

Figure 2: Pressure in different parts of the circulation [5]

Control Systems

Figure 3: Basic Schematic of Syringe Pump-Based Constant Pressure System

Figure 4: Maintaining a constant water pressure across a flow chamber

Future Applications:Casing: To improve portability and usabilityVasculogenesis/Angiogenesis: Prepare flow chambers with collagen seeded with endothelial cells• Apply constant pressure at inlet• Observe vasculogenesis in pressurized vs. control gelVeins vs. Arteries• Make flow chambers with channels, seeded with

endothelial cells.• The vessels in “In vitro microvessels for the study of

angiogenesis and thrombosis” [9] are a starting point• Apply pressures characteristic of veins and arteries

(Figure 2) and observe differences in cell phenotype

Component Cost

Arduino Uno R3 (Atmega328 - assembled)

$24.95

3D-Printed Components (PLA filament)

<$4.00

NEMA-17 Stepper Motor $14.00

Omega Low Pressure Transducer $205.00

Polulu Adjustable Boost Regulator

$11.95

Readily Available Mechanical Components (bolts, z-couplings, nuts, resistors, wires, etc.)

<$10.00

Two-way normally closed solenoid pinch valve; 12 VDC, 1/32" ID x 3/32" OD tubing

$62.00

Adafruit Motor/Stepper/Servo Shield for Arduino v2 Kit - v2.3

$19.95

Total 351.85

Table 1: Cost of pump components

Figure 6: Geared down motor 3D printed prototype. Derived from [8]

Figure 5: Clockwise from top left: 1: Circuit Diagram of Control

System, 2: Valve on Outlet, 3: Flow validation via fluorescence

microscopy 4: Pump during flow validation.

Figure 7: In vitro microvascular networks are the specialty of the Zheng

Lab [9]

Acknowledgements: We acknowledge the support from the Zheng lab and NIH awards (1DP2DK102258 and UH2/UH3 TR000504)