open-source wax reprap 3-d printer for rapid prototyping paper-based microfluidics

Pre-Print: J. M. Pearce, N. C. Anzalone, and C. L. Heldt. Open-source Wax RepRap 3-D Printer for Rapid Prototyping Paper-Based Microfluidics, Journal of Laboratory Automation 21(4) 510–516 (2016). DOI: http://dx.doi.org/10.1177/2211068215624408

Open-source Wax RepRap 3-D Printer for Rapid Prototyping Paper-Based Microfluidics

J. M. Pearce1,2,*, N. C. Anzalone3, and C. L. Heldt4

1. Department of Materials Science & Engineering, Michigan Technological University, MI

2. Department of Electrical & Computer Engineering, Michigan Technological University, MI

3. Department of Mechanical Engineering & Engineering Mechanics, Michigan Technological

University, MI

4. Department of Chemical Engineering, Michigan Technological University, MI

*Corresponding author: Michigan Technological University, 601 M&M Building, 1400 Townsend

Drive, Houghton, MI 499311295 ([email protected]) ph: 9064871466

Keywords: 3-D printing, wax, paper-based microfluidics, lab-on-a-chip, electrochemical detection

Abstract

The opensource release of selfreplicating rapid prototypers (RepRaps), has created a rich opportunity

for lowcost distributed digital fabrication of complex three dimensional objects such as scientific

equipment. For example, 3D printable reactionware devices offer the opportunity to combine open

hardware microfluidic handling with lab on a chip reactionware to radically reduce costs and increase

the number and complexity of microfluidic applications. To further drive down the cost while

improving the performance of labonachip paperbased microfluidic prototyping this study reports on

the development of a RepRap upgrade capable of converting a Prusa Mendel RepRap into a wax 3D

printer for paperbased microfluidic applications. An opensource hardware approach is used to

http://dx.doi.org/10.1177/2211068215624408


demonstrate a 3D printable upgrade for the 3D printer, which combines a heated syringe pump with

the RepRap/Arduino 3D control. The bill of materials, designs, basic assembly and use instructions are

provided along with a completely free and open source software tool chain. The open source hardware

device described here accelerates the potential of the nascent field of electrochemical detection

combined with paperbased microfluidics by dropping the marginal cost of prototyping to nearly zero

while accelerating the turnover between paperbased microfluidic designs.

Introduction

Bowyer's opensource release of selfreplicating rapid prototypers (RepRaps) [13], has created

a rich opportunity for lowcost distributed digital fabrication of complex three dimensional objects.

There has been a surge of interest among scientists from a wide swath of fields in using RepRap 3D

printers to design, manufacture and share the opensource digital designs of scientific equipment [46].

As these opensource digitally replicable scientific tools are freely distributed and thus widely

accessible for the cost of materials, 3D printing components or entire devices results in substantial

economic savings – generally 9099% less than proprietary commercial equipment [5]. Preliminary

analysis of the economic value of an open hardware approach [7] indicates scientific funders can obtain

a return on such investments in the hundreds or thousands of percent [8]. This has resulted in an

explosion of highquality 3D printable lab tools for: biology labs [9] and biotechnological and

chemical labwares [1012], optics and optical system components [13], colorimetery [14],

nephelometer [15] and turbidimeter [16], nitrate testing [17], liquid autosampling [18] with robot arms

[19], automated sensing arrays [20] and compatible components for medical applications [21]. Not only

are relatively inexpensive 3D printed parts being used to replace conventional scientific tools, they are

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also being used to create new scientific opportunities for investigation. For example, utilizing a 3D

printer in the lab makes it easier for researchers to design and build laboratory tools faster and more

closely aligned to specific research needs. For example, a highly configurable reaction vessel made

with a 3D printer can integrate reagents, catalysts and a purification apparatus into a single

reactionware [22,23], which can significantly simplify multistep reactions by integrating equipment

into a single component. These 3D printable reactionware devices offer the opportunity to combine

open hardware microfluidic handling [24] with simple “labonachip” reactionware [25].

There is a large interest in creating such inexpensive labonachip devices for rapid detection of

health-related biomarkers [26,27], explosives [28,29], and gas components [30]. The goal of such

applications is to save lives by detecting molecules in short periods of time, typically less than one

hour. While the field of microdevices is currently exploding, cost is a constant concern with these

devices. In 2008, the Whitesides group pioneered paper microfluidics [31]. This discovery was quickly

followed by other complex 3-D structures made in paper that controlled the capillary flow of biological

liquids by creating channels bordered with hydrophobic wax [32-34]. Such paper microfluidic devices

have reduced or eliminated the need for pumping of fluids, and this reduces both the footprint and cost

of the overall device. The paper base is also inexpensive and readily available throughout the world,

making it an ideal point of care platform. Originally, groups were creating wax channels using

lithography [32], but this is time consuming and expensive. Recently, wax printing has been developed

that provides more flexibility in design and reduces the cost of device creation [33].

To further drive down the cost while improving the performance of lab on a chip paper

microfluidic prototyping this study reports on the development of a RepRap upgrade capable of

converting a Prusa Mendell RepRap into a wax 3D printer for paperbased microfluidic applications.

An opensource hardware approach is used to demonstrate a 3D printable upgrade for the 3D printer,

http://dx.doi.org/10.1177/2211068215624408


which combines a heated syringe pump with the RepRap/Arduino 3D control. The bill of materials,

designs, basic assembly and use instructions are provided along with a completely free and open source

software tool chain. The results of this approach are discussed.

Materials and Methods

The mechanical and electrical design of the wax 3-D printer upgrade followed standard RepRap

design methods for scientific equipment outlined in detail elsewhere [5], thus relying on only open

source electronics, RepRap printable custom parts, off-the-shelf globally available non-printed parts

(referred to as vitamins in the RepRap literature), and a completely open source software tool chain.

The designs are released under a CC-BY-SA license. In addition, no expensive tools, specialty

equipment or advanced skills are needed for assembly.

Both the custom 3-D printed parts as well as the wax print designs are created in OpenSCAD

[35]. Open-source and freely available OpenSCAD is a script-based, parametric CAD program

possessing powerful 3-D modeling capabilities. 3-D models are created by adding and subtracting

primitive objects created by code to produce the desired complex shapes. The script language is based

upon C++. As only a small number of methods are required to produce very complex designs the

learning curve is short for students with programming experience even if they are not familiar with

conventional CAD. The scripts are written such that designs are parametric, thus by changing the

values of a single variable the design can easily be altered. Models rendered in OpenSCAD are saved

as a (.scad) file and are also exported as a stereolithography (.stl) file for the slicing process. Slicing

converts an stl file into layers of equal thickness in the z direction in G-code, a human-readable file

format specifying the path the print head must follow to produce a physical object. Cura, an open

source and freely available package, was used to slice the stl models [36].

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The mass of the printed parts was calculated with Cura Lulzbot Edition 14.09-1.18 using

normal quality setting for polylactic acid (PLA) for the syringe carriage and the remainder of the parts

were printed in acrylonitrile butadiene styrene (ABS) for its relatively higher temperature resistance.

Results and Discussion

The syringe design was derived from the Wijnen et al. open-source 3-D printable syringe pump

library [37]. There are five 3-D printed custom parts needed for the conversion including a motor

mount (Figure 1), syringe carriage (Figure 2), x carriage (Figure 3) and two syringe retainers (Figure

4). The 3-D printed parts can be printed in about 5 hours on any standard RepRap 3-D printer

consuming $3.11 of commercial PLA filament. The entire bill of materials including part, count, cost

and source totals $87.49 as seen in Table 1. This BOM assumes that only a single conversion kit is

purchased and it should be pointed out that there are discounts for most of the components when

purchased in bulk (e.g. fasteners). The conversion kit assembly follows the basic steps outlined by

Wijnen et al. [37] for syringe pumps and is shown completed without the syringe in Figure 5.

The Prusa Mendell RepRap [38], which can be fabricated for less than $600 and assembled in

24 hours [39], is itself capable of printing all of the conversion components (Figures 1-4). After

printing the ABS and PLA components with the standard direct drive head, the mechanical components

of the syringe depressor are assembled as shown in Figure 5 and the heater made up of the copper pipe

and nichrome heating element wrapped in Kapton polyimide tape for the syringe is installed (Figure 6).

Then the syringe is placed into position along with the temperature feedback provided by the thermistor

and the assembly is insulated as shown in Figure 7. Finally, the extruder driver and standard hot end is

removed to be replaced by the assembled syringe pump (Figure 8). It should be noted that similar

conversions can be made for all other RepRap designs using a direct drive extruder, although further

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work is needed to convert delta style 3-D printers with Bowden sheaths.

The wax printer, can then be fully assembled, utilizing a Prusa Mendel open source RepRap 3-D

printer for the frame and electronics as shown in Figure 8. The resultant wax 3-D printer has a

horizontal print area of 150 mm width by 200 mm length, and about 30 mm in height. The printer uses

an open source electronics prototyping platform of the Arduino Atmega 2560 [40], with a RepRap

Arduino Mega Pololu Shield (RAMPS) to control the motors and heating element [41]. The glass

syringe is then filled with a wax and heated to melting and the wax is printed on a paper substrate as

shown in Figure 9 at 5mm/s.

Similar to the design of the conversion kit, the design of the microfluidic device takes place in

OpenSCAD using parametric variables (e.g. changing the gap width variable alters the distance

between the two lines of wax in a test print). The design is then exported as an stl in order to be sliced

with Cura into several layers of G-code, a language that is understood and controls the movements of

the 3-D printer. Thus complex geometries for the wax print can be easily designed and printed as

shown in the example in Figure 10. The settings for Cura, that are used to dictate the boundaries and

how the motors move, are specific to each printer. With the wax printer, Cura is set up to produce slow

moving prints, around 5 mm/s, with an extrusion rate less than 0.5 mm/s for the wax (as compared to

conventional RepRap printing materials), in order to maintain print quality. The print is meant to be

printed, hot enough to melt the wax, but is close enough to the phase transition temperature to have the

wax solidify shortly after it is deposited on the print bed. In the example shown in Figures 9 and 10 the

Cerita wax (normally used for investment casting) is printed at 70oC. The G-code is then imported into

one of several printer control software packages such as Repetier [42], Printrun [43] or Franklin [44]),

which provides a user interface to control the printer. This software is used to load the G-code into the

control board on the printer, which is then used to control the 3-D printer during the print. In this way

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the marginal cost of changing a paper-based microfluidic design is reduced to the cost of the substrate

paper and the wax used for the experiment. The far more time consuming and expensive lithography-

based prototyping steps, including transparency mask fabrication, SU-8 photoresisit for the channels,

wafer cleaning, lithography, developing, sealing, and vacuum degassing, are eliminated.

Conservatively, creating a single new microfluidic design using lithography based methods costs more

than the wax printer conversion kit capable of unlimited design options for nearly zero marginal cost. It

however, should be noted that there are other lower cost methods of microfluidic design available, such

as the paper-based methods in [33]. Future work is needed to compare these two methods, which would

involve first optimizing the printing of the 3-D wax printer described. This is accomplished for each

specific wax in a short power vs velocity study. First, an approximate extrusion temperature is found

by ramping up the temperature while printing a constant velocity spiral. When this is done a simple zig

zag pattern is designed that increases the print head velocity at each corner. Then this pattern is

repeatedly printed with a small x-offset while varying the extrusion temperature and extrusion rate in a

systematic fashion. After the optimal print head velocity and extrusion rate are found a final set of runs

are made while adjusting the temperature again by small increments to obtain optimal printing

parameters. These parameters are then used in printing identical microfluidic devices using the two

methods and the resultant devices are tested.

The Prusa has an x-y position accuracy of 20 microns and a minimum z accuracy of 0.4

microns. The heated bed on the Prusa can also be used to anneal the wax and/or further drive it into the

paper substrate to obtain channel widths that the printer itself is not capable of obtaining. This,

however, can only be achieved for a subset of geometries. Future work is needed to improve this

resolution, by for example moving to finer pitched lead screws and belts, higher-quality stepper motors,

and finer syringe needles. In addition, future improvements on the design could enable both retraction

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and easy removal of the plunger for wax filling; multi material printing with multiple heads, and

indirect automated head swapping.

In addition, to wax printing to replicate the work that has been accomplished in the past [33] for

lower costs so that experiments are more accessible to a greater selection of scientists [45], this 3D

printer also enables fabrication of fully integrated microdevices using a single tool and the creation of

complex 3D geometries for yet unexplored microdevice applications. For example, The most common

detection method for paper microfluidic devices is colorimetric [46,47] and there are already well

established techniques for utilizing Arduinobased open source electronics and RepRap 3D printing to

make handheld detection devices [14,15,17]. However, colorimetric detection works well for yes/no

detection, but is difficult to calibrate to a quantitative measures in microfluidic applications. For a

microfluidic device this is the difference between a pregnancy test and a blood glucose level test. A

more quantitative measure uses electrochemical detection. Electrochemical paperbased devices have

been created to detect the oxidation of glucose with an indiumdoped tin oxide electrode [47] and a

more standard glassy carbon electrode [48]. Other examples include human tears being analyzed for

ion detection [49] and the detection of cholesterol levels in human serum [50]. While electrochemical

detection combined with paperbased microfluidics is still in its infancy, it has a high potential to

become a useful and cost effective microdevice platform for many different analytes, as well as serving

to detect environmental hazards. The open source hardware device described in this paper accelerates

this potential by dropping the marginal cost of prototyping microdevices to nearly zero, while

accelerating the turnover between paperbased microfluidic designs.

Acknowledgements

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The authors would like to acknowledge NSF (CBET-1159425 and CBET-1510006) for funding of this

work.

Declaration of Conflicting Interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or

publication of this article.

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Tables and table legends

Table 1. Bill of materials for wax 3-D printer conversion kit.

Part Name Quantity $/unit Cost $ Source

Glass Syringe, 3 ml 1 $ 9.93

$ 9.93 Zoro.com

30 RW x 2" Blunt Needle 1 $ 14.00

$ 14.00 Labemco.com

LM6UU Linear Bearing 2 $ 0.65

$ 1.30 Robotdigg.com

Semitec 104-GT2 Thermistor 1 $ 1.12

$ 1.12 Mouser.com

1" x 24" Copper Pipe 1 $ 4.89

$ 4.89 HomeDepot.com

Nema 11 Motor 1 $ 15.50

$ 15.50 Kysanelectronics.com

5 mm x 5 mm Shaft Coupling 1 $ 2.98

$ 2.98 Adafruit.com

625zz Ball Bearing 1 $ 7.77

$ 7.77 VXB.com

M5 Hex Nut 2 $ 0.17

$ 0.34 McMasterCarr.com

M5 Washer 1 $ 0.14


M3 Hex Nut 8 $ 0.30


M3 x 16 mm socket head cap screw 8 $ 0.82


M2.5 x 12mm socket head cap screw 4 $ 0.17


Stainless Steel M5 Threaded Rod 150mm 1 $ 2.61


6 mm A2 Tool Steel Smooth Rod 150mm 2 $ 6.83


Ni-Chrome Wire 150mm 1 $ 0.48


insulation 1 scavenged

Vitamin subtotal $ 84.38

Printed Parts mass (g)

Motor mount (ABS) 39 $ 42.95

$ 1.68 Lulzbot.com

Syringe carriage (PLA) 18 $ 24.95

$ 0.45 Lulzbot.com

Syringe retainers (ABS) 6 $ 42.95

$ 0.26 Lulzbot.com

X carriage (ABS) 17 $ 42.95

$ 0.73 Lulzbot.com

Printed part subtotal $ 3.11

Total $ 87.49

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Figure Legends

Figure 1. Cura rendering of motor mount.

Figure 2. Cura rendering of syringe carriage.

Figure 3. Cura rendering of x carriage.

Figure 4. Cura rendering of the small and large syringe retainers.

Figure 5. Assembled conversion kit without syringe.

Figure 6. Assembled conversion kit with heater and copper pipe installed.

Figure 7. Fully assembled conversion kit with syringe, thermistor wiring and insulation.

Figure 8. Prusa Mendel open source RepRap Converted Wax 3-D printer.

Figure 9. Wax printing on paper substrate.

Figure 10. As printed wax clover leaf pattern before drive in.

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Fig 10

open-source wax reprap 3-d printer for rapid prototyping paper-based microfluidics

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