Open Source 3-D Printed Nutating Mixer

applied sciences

Article Open Source 3-D Printed Nutating Mixer

Dhwani K. Trivedi 1 and Joshua M. Pearce 1,2,3,* ID

1 Department of Electrical & Computer Engineering, Michigan Technological University, Houghton, MI 49931, USA; [email protected] 2 Department of Electronics and Nanoengineering, School of Electrical Engineering, Aalto University, 02150 Espoo, Finland 3 Department of Materials Science & Engineering, Michigan Technological University, Houghton, MI 49931, USA * Correspondence: [email protected]; Tel.: +1-906-487-1466

Received: 30 August 2017; Accepted: 11 September 2017; Published: 13 September 2017

Abstract: As the open source development of additive manufacturing has led to low-cost desktop three-dimensional (3-D) printing, a number of scientists throughout the world have begun to share digital designs of free and open source scientific hardware. Open source scientific hardware enables custom experimentation, laboratory control, rapid upgrading, transparent maintenance, and lower costs in general. To aid in this trend, this study describes the development, design, assembly, and operation of a 3-D printable open source desktop nutating mixer, which provides a fixed 20◦ platform tilt angle for a gentle three-dimensional (gyrating) agitation of chemical or biological samples (e.g., DNA or blood samples) without foam formation. The custom components for the nutating mixer are designed using open source FreeCAD software to enable customization. All of the non-readily available components can be fabricated with a low-cost RepRap 3-D printer using an open source software tool chain from common thermoplastics. All of the designs are open sourced and can be configured to add more functionality to the equipment in the future. It is relatively easy to assemble and is accessible to both the science education of younger students as well as state-of-the-art research laboratories. Overall, the open source nutating mixer can be fabricated with US$37 in parts, which is 1/10th of the cost of proprietary nutating mixers with similar capabilities. The open source nature of the device allow it to be easily repaired or upgraded with digital files, as well as to accommodate custom sample sizes and mixing velocities with minimal additional costs.

Keywords: mixing; nutating mixer; shaker; stirrer; open hardware; 3-D printing; scientiﬁc hardware; open source hardware; chemical mixing

1. Introduction Open source three-dimensional (3-D) printing developed from the self-replicating rapid prototype (RepRap) project [1–3], has widened the doors for innovation and excellence in varied domains [4]. Combining 3-D printing with off the shelf and easily available electrical mechanisms has provided cost effective opportunities to design and build customized scientific equipment [5,6]. This equipment ranges from an automatic feeder for animal experiments [7] and time-sorting pitfall traps for sampling arthropods [8], to electronics to provide big data like IoT meter devices for smart and energy-efficient buildings [9] and even entire smart cities [10]. Open hardware has also been developed for more conventional scientific tools in biology labs [11], optics labs [12], and even DNA nanotechnology labs, which can fabricate DNA-coated for up to 90% less than commercially offered tools [13]. This trend in cost savings from 90–99% is seen in a wide variety of open hardware tools for science and their outputs [5,6,11,12]. Moreover, the open source design platform has provided the opportunity for distributed manufacturing [14–18]—specifically to download the designs and print them anywhere at

Appl. Sci. 2017, 7, 942; doi:10.3390/app7090942 www.mdpi.com/journal/applsci Appl. Sci. 2017, 7, 942 2 of 14 any time, which can provide additional savings from avoided shipping costs as well as various taxes and tariffs. These savings are perhaps most stark when distributed manufacturing using 3-D printing (which enables material minimization coupled to free complexity) is tied to some form of automation. For example, radial stretching systems with force sensors [19] or a sample rotator mixer [20] can save hundreds of dollars per scientific tool, a mobile water quality testing platform [21] or a syringe pump [22] saves thousands per tool, and a robot-assisted mass spectrometry assay platform [23] and an automated peptide synthesizer [24] can save over $25,000. Scientists can now design, share and build on one another’s work to develop advanced scientific tools [25], such as devices to enable digital microfluidics [26,27], large stage probing [28], and microscopy [29]. These tools can all be easily maintained, modified, upgraded, or repaired because the full assembly instructions and bill of materials (BOM) are included. To continue this development of low-cost open hardware tools, this paper describes the development of a desktop nutating mixer, which provides a fixed 20◦ platform tilt angle for a gentle three-dimensional (gyrating) agitation of samples. Such devices agitate liquids for chemical or biological scientific procedures by repetitively moving the vessels holding the liquids. Although, open hardware methods to mix samples have been developed in the past (e.g., rotating mixing and shaking [20], orbital shaker [5,6], as well as using a 3-D platform for stirring and custom shaking [30]), they were either too violent to ensure foam free mixing in tubes or too large for conventional portable use. Proprietary nutating mixers cost hundreds of dollars and lack the ability to either repair or upgrade with digital files, as well as to accommodate custom sample sizes and mixing velocities. These shortcomings are overcome here with the development of an open source nutating mixer, which can be fabricated with a conventional fused filament 3-D printer capable of printing both hard and flexible thermoplastics and off the shelf electrical components. This study describes how the system was designed and manufactured in way that is universally replicable. The operation of the mixer is tested, and the technical performance is compared to conventional systems and an economic comparison is made with the closest commercial alternatives. Finally, future work will be detailed to enhance the performance of the system.

2. Materials and Methods As open source hardware for science [31,32], the full BOM, manufacturing, assembly, and operation instructions are provided.

2.1. Bill of Materials The full BOM is shown in Table1 for the 3-D printed components, and Table2 for the remaining components. First in Table1, the 3-D printed components are listed for fabrication with a hard thermoplastic polymer (e.g., polylactic acid (PLA)) or an elastomer (e.g., NinjaFlex). The filament used was 1.75 mm diameter filament at a cost of US$18.33/kg for PLA [33] and US$86.67/kg for the more expensive 3 mm diameter filament of NinjaFlex for flexible components [34]. The open source CAD software, FreeCAD and STL files (STereoLithography format is a file format that describes only the surface geometry of a three-dimensional object used for 3-D printing) for the 3-D printed components are available at the Open Science Framework [35] under a GNU General Public License 3.0 license and are detailed below. The ordered components from Table2 are readily available online. Prices shown in Table2 were all sourced from Amazon and shipping was not included as free Amazon Prime was assumed. Appl. Sci. 2017, 7, 942 3 of 14

Table 1. Bill of materials (BOM) for three-dimensional (3-D) printed components including material, mass and cost.

Sr. No. Component 3-D Printing Material Quantity Mass (g) Cost (US$) 1 Rod PLA 1 7 0.15 2 Bearing holder PLA 1 8 0.18 3 Base PLA 1 60 1.32 4 Cover PLA 1 126 2.77 5 Platform PLA 1 76 1.67 6 Dimpled Bed Ninja Flex 1 67 5.80 7 Slit Ninja Flex 1 4 0.34 Total Filament Cost 12.23

Table 2. BOM for ordered components.

Sr. No. Component Qty Cost (US$) 1 Skateboard bearing [36] 1 0.73 2 DC barrel connector [37] 1 1.00 3 Switch DPDT [38] 1 1.19 4 12 Volt DC Motor—25 RPM [39] 1 13.95 5 DC adapter [40] 1 6.99 M3 Fasteners (2 M3 7 mm, 2 6 mm, 3 M3 16 6 1 <1.00 mm and 1 M3 10 mm and bolts) Total Ordered Material Cost 24.86 Total Cost of Equipment (Tables1 and2) 37.09

2.2. Design The design and fabrication followed a completely free and open source software toolchain, which maximizes the ability for the replication of the results. All of the 3-D printable components are designed by using the open source CAD software, FreeCAD [41], and can be further edited to customize the equipment for any scientific lab. They were designed to provide the mechanical integrity necessary for the component while still being 3-D printable without support. Exported STL files were sliced with the open source slicer, Cura [42]. Most of the components are printed using PLA, which is the most popular 3-D printing material, being available for the majority of 3-D printing supplies vendors. PLA has been shown to be a safer alternative to toxic acrylonitrile butadiene styrene (ABS) plastic fumes, the second most widely available 3-D printing material [43,44]. PLA has a relatively low melting point (150 ◦C to 160 ◦C), so it may not be appropriate for high temperature applications. For such applications, a higher melting point thermoplastic such as ABS or polycarbonate can be substituted and printed in a fume hood or a well-ventilated area by using the same designs shown here. All of the PLA filament designs were printed using a MOST Delta 3-D printer [45] running Franklin [46], which is a RepRap [1–3]. All of the PLA components were built with the following print settings: infill 25%, layer height 0.25 mm, shell thickness 1 mm, print temperature 185 ◦C, and 70 mm/s print speed (with the exception of the rod that was printed with 0.15 mm layer height and 35% infill to improve the mechanical properties). The slit and dimpled mat were printed using Ninja Flex on a commercial RepRap, the Lulzbot Mini with a Flexystruder Extruder (Aleph Objects, Loveland, CO, USA) [47,48], with print settings: infill 20%, layer height 0.325 mm, shell thickness 0.6 mm, print speed 14 mm/s, and print temperature 230 ◦C. The final design for the 3-D printable components focused on minimizing the filament quantity used while still achieving high torque despite the offset of the rotating axis. If the design needs to be scaled up, all of the components can be scaled, as well until the limit of the DC motor is reached and then will need to be substituted for a higher torque DC motor. Figure1 shows all of the 3-D printed parts that are required for the open source nutating mixer. Appl. Sci. 2017, 7, 942 4 of 14

Appl. Sci. 2017, 7, 942 4 of 14 Appl. Sci. 2017, 7, 942 4 of 14

Appl. Sci. 2017, 7, 942 4 of 14

Figure 1. Disassembled 3-D printed components of the open source nutating mixer. Figure 1. Disassembled 3-D printed components of the open source nutating mixer. Figure 1. Disassembled 3-D printed components of the open source nutating mixer. The functionality for each 3-D printed component is described below:

The(1) functionalityThe Base functionality (Figure for2): forThe each each base 3-D 3-D of printed the printed equipment component component holds the is described described12 V 25 RPM below: below: DC geared motor, which is the mainFigure load 1.bearing Disassembled component 3-D printed of the componentsequipment. of the open source nutating mixer. (1) (1)Base Base (Figure (Figure2): The 2): The base base of theof the equipment equipment holds holds the the 12 12 V V 25 25 RPM RPM DC DC gearedgeared motor, which which is is the mainthe loadThe main functionality bearing load bearing component for eachcomponent 3-D of printed the ofequipment. the component equipment. is described below: (1) Base (Figure 2): The base of the equipment holds the 12 V 25 RPM DC geared motor, which is the main load bearing component of the equipment.

Figure 2. Base of the open source nutating mixer printed with PLA and showing the 12 V 25 RPM DC geared motor mounted in place. Figure 2. Base of the open source nutating mixer printed with PLA and showing the 12 V 25 RPM DC Figure(2) 2.BearingBase of holder the open (Figure source 3): The nutating bearing mixer holder printed is designed with PLAat a 20-degree and showing tilt angle. the 12A skateboard V 25 RPM DC geared motor mounted in place. geared motorbearing mounted is mounted in place. on the top on a flat surface, which further holds the rod and the platform, Figurehence 2.enabling Base of the 3-D open rotation source of nutating platform mixer at 20 pr degrees.inted with PLA and showing the 12 V 25 RPM DC (2) Bearinggeared holdermotor mounted (Figure in 3): place. The bearing holder is designed at a 20-degree tilt angle. A skateboard (2) Bearingbearing holder is mounted (Figure 3on): the The top bearing on a flat holder surface, is designed which further at a 20-degreeholds the rod tilt and angle. the Aplatform, skateboard (2) Bearing holder (Figure 3): The bearing holder is designed at a 20-degree tilt angle. A skateboard hence enabling 3-D rotation of platform at 20 degrees. bearingbearing is mounted is mounted on theon the top top on on a a ﬂat flat surface,surface, which which further further holds holds the rod the and rod the and platform, the platform, hence enablinghence enabling 3-D 3-D rotation rotation of of platform platform atat 20 degrees.

(a) (b)(c) Figure 3. Bearing holder printed with polylactic acid (PLA). (a) in base; (b) detail; (c) FreeCAD side view showing 20° tilt angle.

(3) Rod (Figure 4): The(a) rod is mounted on the( bbearing)( holder and fits in thec) bore of the bearing, so Figurethat 3.when Bearing the holdermotor(a) printedrotates, withthe rod polylactic rotates(b acid)(at 20 (PLA). degrees (a) within base; some (bc) offset.) detail; The(c) FreeCAD slit hole inside the viewFigurerod showing is designed3. Bearing 20° tilt specificallyholder angle. printed for with 20-degree polylactic angle acid and (PLA). calculated (a) in base; based (b )on detail; the height (c) FreeCAD of intersection side Figure 3.viewofBearing the showing rod with holder 20° thetilt printed angle.center of with the rotating polylactic shaft. acid It (PLA).should (bea) noted in base; that (b the) detail; FreeCAD (c) FreeCAD model can side ◦ view(3) Rod showingbe (Figure adjusted 20 4):tilt for The angle.different rod is angles,mounted but on if the the mixer bearing needs ho lderto be and customized fits in the at abore different of the angle, bearing, the so (3)that Rodslit when hole (Figure positionthe 4):motor The in therotates,rod rod is mounted will the change, rod on rotates therespectively. bearing at 20 degrees ho 30%lder infill, and with fitswith some in a the lower offset. bore layer ofThe the height slit bearing, hole results in so the that when the motor rotates, the rod rotates at 20 degrees with some offset. The slit hole in the (3) Rodrod (Figure is designed4): The specifically rod is mounted for 20-degree on the bearingangle and holder calculated and fitsbased in on the the bore height of the of intersection bearing, so that of rodthe isrod designed with the specifically center of for the 20 rotating-degree angleshaft. and It should calculated be noted based thaton the the height FreeCAD of intersection model can when theof the motor rod with rotates, the center the rodof the rotates rotating at shaft. 20 degrees It should with be noted some that offset. the FreeCAD The slit model hole can in the rod be adjusted for different angles, but if the mixer needs to be customized at a different angle, the be adjusted for different angles, but if the mixer needs to be customized at a different angle, the is designedslit hole position specifically in the for rod 20-degree will change, angle respectively. and calculated 30% infill, based with on a lower the height layer height of intersection results of the rodslit with hole theposition center in the of therod will rotating change, shaft. respectively. It should 30% be infill, noted with that a lower the layer FreeCAD height modelresults can be adjusted for different angles, but if the mixer needs to be customized at a different angle, the slit hole position in the rod will change, respectively. 30% infill, with a lower layer height results in the Appl.Appl. Sci. Sci.2017 2017, 7,, 9427, 942 5 of5 14 of 14 Appl. Sci. 2017, 7, 942 5 of 14 in the mechanical strength needed for this component that has a relatively small cross-sectional mechanicalinarea the at mechanical the strength top. Polymer strength needed use forneeded could this componentfor also this be component reduced that has by that ausing relatively has a a slicer relatively small capable cross-sectional small of cross-sectionalvariable area height at the Appl.top.areainfill Sci. Polymer at2017 settings. the, 7, 942top. use Polymer could also use be could reduced also by be using reduced a slicer by using capable a slicer of variable capable height of variable infill5 settings. heightof 14 infill settings. in the mechanical strength needed for this component that has a relatively small cross-sectional area at the top. Polymer use could also be reduced by using a slicer capable of variable height infill settings.

FigureFigure 4. 4.Rod Rod design design forfor thethe open source nutating nutating mixer. mixer. Figure 4. Rod design for the open source nutating mixer. (4) Cover (Figure 5): The shell of the mixer is a functional component and is thus designed to fit on (4) Cover (Figure5): The shell of the mixer is a functional component and is thus designed to ﬁt (4) Coverthe base (Figure as well 5): as The holdFigure shell the of4. rotating Rodthe designmixer rod foris exactly a the functi open atonal sourcethe componentcenter nutating of themixer. and slit ishole thus position. designed Hence, to fit theon on the base as well as hold the rotating rod exactly at the center of the slit hole position. Hence, theneck base on asthe well cover as holdconsists the ofrotating a slit hole rod exactlyto accommodate at the center a rubber of the (NinjaFlexslit hole position. slit), which Hence, passes the

(4)theneckthrough neckCover on on the (Figurethe the cover cover cover 5): consists andThe consists throughshell of of ofa theslit athe slit mixer hole rotating hole tois toaaccommodate functirod accommodate suchonal that component a it rubber aprevents rubber and (NinjaFlex (NinjaFlexthe is thus rod designedfrom slit), slit), rotatingwhich which to fit passes abouton passes the base as well as hold the rotating rod exactly at the center of the slit hole position. Hence, the throughthroughits own the theaxis. cover cover The and andheight through through of the thethe equipment rotating rodis rod determined such such that that it itbased prevents prevents on thisthe the rodslit rod fromheight from rotating as rotating it must about about be neck on the cover consists of a slit hole to accommodate a rubber (NinjaFlex slit), which passes itsitsaligned own own axis. axis.with The Thethe height rodheight slit of ofhole thethe after equipmentequipment the assembly. is is determined determined Thus, again based based for on oncustomizing, this this slit slit height height the asdesign asit must it mustof thebe be through the cover and through the rotating rod such that it prevents the rod from rotating about alignedalignedcover will with with need the the rod torod be slitslit modified holehole afterafter in FreeCAD. the assembly. Thus, Thus, again again for for customizing, customizing, the the design design of ofthe the covercoverits will own will need axis.need toThe to be be heightmodiﬁed modified of the inin equipment FreeCAD. is determined based on this slit height as it must be aligned with the rod slit hole after the assembly. Thus, again for customizing, the design of the cover will need to be modified in FreeCAD.

Figure 5. Cover design (left) and 3-D printed cover assembled detail (right). FigureFigure 5. 5.Cover Coverdesign design (left)(left) and 3-D printed cover cover assembled assembled detail detail (right). (right). (5) Platform (FigureFigure 6): 5. The Cover platform design (left) of the and mixer 3-D printed is designed cover assembled to provide detail a solid (right). base for the dimpled (5) Platform (Figure 6): The platform of the mixer is designed to provide a solid base for the dimpled (5) Platformmat, which (Figure is printed6): The in platform flexible material of the mixer to hold is designed the test tubes. to provide To reduce a solid the baseamount for theof filament dimpled (5)mat, Platform which (Figureis printed 6): Thein flexible platform material of the mixer to hold is designedthe test tubes. to provide To reduce a solid the base amount for the ofdimpled filament mat,consumed, which is it printed is designed in ﬂexible as a mesh, material which to hold is strong the test enough tubes. to To hold reduce the dimpled the amount mat of and ﬁlament the consumed,testmat, tubes. which Theit is printedplatformdesigned in is flexibleas attached a mesh, material to which the to rod hold is strongwith the testthe enough M3tubes. nuts Toto andreducehold bolts. the the dimpled amount ofmat filament and the consumed,testconsumed, tubes. itThe is it designed platformis designed is as attached aas mesh, a mesh, whichto whichthe rod is is strong withstrong the enough enough M3 nutsto to holdandhold bolts. thethe dimpleddimpled mat mat and and the the test tubes.test The tubes. platform The platform is attached is attached to the to rod the withrod with the the M3 M3 nuts nuts and and bolts. bolts.

Figure 6. Platform printed with black PLA. The underside of the platform showing the attachment of Figure 6. Platform printed with black PLA. The underside of the platform showing the attachment of FiguretheFigure rod 6. Platform with 6. Platform M3 nuts printed printed andwith bolts withblack is black shown PLA. PLA. onThe Thethe undersideundersidleft and thee ofof platform the the platform platform mounted showing showing on thethe theattachmentmixer attachment assembly of of thethe rod rod with with M3 M3 nuts nuts and and bolts bolts is is shown shown on on the the leleftft and the platformplatform mounted mounted on on the the mixer mixer assembly assembly thewithout rod with the M3 dimpled nuts and mat bolts is shown is shown on the on right. the left and the platform mounted on the mixer assembly withoutwithout the the dimpled dimpled mat mat is is shown shown on on the the right. right. without the dimpled mat is shown on the right. Appl. Sci. 2017, 7, 942 6 of 14

Appl.Appl. Sci. Sci. 2017 2017, 7, ,942 7, 942 6 of6 14 of 14 (6) Dimpled mat (Figure7): The dimpled mat is built using NinjaFlex, which provides flexibility to (6)hold (6)Dimpled testDimpled tubes mat mat of (Figure various(Figure 7): 7): sizes.The The dimpled dimpled The shown matmat isis designbuilt using can NinjaFlex,NinjaFlex, hold the which testwhich tubes provides provides with flexibility flexibility 13 mm, to 16to mm, andhold 20hold mm test test diameter. tubes tubes of of various Thevarious design sizes. sizes. The canThe shown beshown easily design modified can holdhold for the the any test test custom tubes tubes with with tube 13 13 sizemm, mm, (or16 16mm, assortment mm, andand 20 20mm mm diameter. diameter. The The design design can can be be easilyeasily modified forfor any any custom custom tube tube size size (or (or assortment assortment of tube sizes) by changing the location of the cylinders as per the requirement and test tube sizes. of tubeof tube sizes) sizes) by by changing changing the the lo locationcation of of thethe cylinders asas per per the the requirement requirement and and test test tube tube sizes. sizes. Finally, the diameter of the dimpled mat, as shown is 200 mm, and can be modified to a larger Finally,Finally, the the diameter diameter of of the the di dimpledmpled mat,mat, asas shown is 200200 mm,mm, and and can can be be modified modified to toa largera larger or smalleror orsmaller smaller size size tosize accommodateto to accommodate accommodate more more more samplessamples samples or or to to savesave save onon on equipment equipment equipment costs costs costs (as (as this this (as is thisisthe the most is most the most expensiveexpensiveexpensive 3-D 3-D printed 3-D printed printed component component component as as as shownshown shown in in Ta Tableble 1),1),1), respectively.respectively. respectively. Thus, Thus, Thus, the the dimpled the dimpled dimpled mat mat can matcan can be customizedbe becustomized customized for anyfor for typeany any oftype type vessel ofof vessel includevessel includinclud glasse orglass plastic oror plasticplastic tubes, tubes, bottles,tubes, bottles, bottles, flasks, flasks, andflasks, microplates.and and microplates. microplates.

Figure 7.FigureDimpled 7. Dimpled mat 3-D mat printed 3-D printed with with NinjaFlex. NinjaFlex. The The spacing spacing ofof thethe dimplesdimples can can be be adjusted adjusted to to hold hold various tube sizes. variousFigure tube 7. sizes. Dimpled mat 3-D printed with NinjaFlex. The spacing of the dimples can be adjusted to (7)hold Slit various (Figure tube 8): sizes.The flexible slit is built using NinjaFlex so that it not only holds the rod in place (7) Slit (Figureand prevents8): The ﬂexibleit from rotating slit is builtabout using its own NinjaFlex axis, but soalso that acts it as not a damper only holds to give the smooth rod in place (7)and Slit preventsrotation (Figure itto 8): from the The mixer. rotating flexible This slit aboutcomponent is built its own usingneeds axis, NinjaFlexto be but added also so to actsthat the as itmixer not a damper onlyafter holdsit is to assembled. give the rod smooth in place rotation and prevents it from rotating about its own axis, but also acts as a damper to give smooth to the mixer. This component needs to be added to the mixer after it is assembled. rotation to the mixer. This component needs to be added to the mixer after it is assembled.

Figure 8. NinjaFlex slit design.

2.3. Assembly and Testing Figure 8. NinjaFlex slit design. Figure 8. NinjaFlex slit design. 2.3.1. Procedure to Assemble the 3-D Printed Open Source Nutating Mixer 2.3. Assembly and Testing 2.3. Assembly(1) Print and all Testing of the components listed in the BOM (Table 1) for the mixer, which can be downloaded 2.3.1. Procedureat the Open to ScienceAssemble Framework the 3-D Printed [35]. Acquire Open the Source remaining Nutating BOM Mixer components from Table 2. 2.3.1. Procedure to Assemble the 3-D Printed Open Source Nutating Mixer (1) Print all of the components listed in the BOM (Table 1) for the mixer, which can be downloaded (1) Printat all the of Open the componentsScience Framework listed [35]. in the Acquire BOM the (Table remaining1) for the BOM mixer, components which canfrom be Table downloaded 2. at the Open Science Framework [35]. Acquire the remaining BOM components from Table2. (2) Assemble the motor to the base, as shown in Figure9. Use only two 6 mm M3 hex bolt screws to ﬁt the motor to the base, as mentioned below. Adding the all 4 hex bolts restricts the movement of the bearing holder. Appl. Sci. 2017, 7, 942 7 of 14 Appl. Sci. 2017, 7, 942 7 of 14 (2)Appl. Sci.Assemble 2017, 7, 942 the motor to the base, as shown in Figure 9. Use only two 6 mm M3 hex bolt screws7 of 14 Appl. Sci. 2017, 7, 942 7 of 14 (2) toAssemble fit the motorthe motor to theto the base, base, as asmentioned shown in Figurebelow. 9.Adding Use only the two all 64 mm hex M3 bolts hex restricts bolt screws the (2) movementAssembleto fit the the motorof themotor bearingto theto the base,holder. base, as as mentioned shown in Figurebelow. 9.Adding Use only the two all 64 mm hex M3 bolts hex restricts bolt screws the Next,tomovementNext, fit fit ﬁtthe M3 M3 motor of nuts nuts the on onbearingto all allthe three three base, holder. blocks, blocks, as mentioned as as shown shown belo below.below.w. A AAdding little little glue glue the can can all be be 4 used usedhex to tobolts prevent prevent restricts slipping slipping the ifmovementNext,if necessary. necessary. fit M3 of nuts the onbearing all three holder. blocks, as shown below. A little glue can be used to prevent slipping Next,if necessary. fit M3 nuts on all three blocks, as shown below. A little glue can be used to prevent slipping if necessary.

FigureFigure 9. 9. BaseBase assembly. assembly. Figure 9. Base assembly. Figure 9. Base assembly. (3)(3) FitFit the the bearing bearing holder holder to to the the motor motor shaft shaft using using 10 10 mm mm M3 M3 hex hex bolt. bolt. (4)(3) FitFit thethe doublebearing pole holder double to the throw motor (DPDT) shaft using switch 10 and mm DC M3 barrel hex bolt. connector on the printed cover. (4) Fit the double pole double throw (DPDT) switch and DC barrel connector on the printed cover. (3)(4) Note:Fit the Do bearingdouble not solder poleholder double it beforeto the throw motorassembling (DPDT) shaft usingit switch to the 10 cover. andmm DC M3 barrelhex bolt. connector on the printed cover. Note: Do not solder it before assembling it to the cover. (5)(4) SolderFitNote: the Do thedouble not DPDT solder pole switch double it before to throwthe assembling barrel (DPDT) connector it switch to the and andcover. the DC DC barrel motor connector following on the printedcircuit shown cover. (5) Solder the DPDT switch to the barrel connector and the DC motor following the circuit shown in (5) inNote:Solder Figure Do the 10.not DPDT solder switch it before to the assembling barrel connector it to the and cover. the DC motor following the circuit shown (5) SolderinFigure Figure the10 10.. DPDT switch to the barrel connector and the DC motor following the circuit shown in Figure 10.

Figure 10. Circuit for DC motor with double pole double throw (DPDT) switch and power connector. Figure 10. Circuit for DC motor with double pole double throw (DPDT) switch and power connector. Figure 10. Circuit for DC motor with double pole double throw (DPDT) switch and power connector. (6) FigureTighten 10. the Circuit cover for to DC the motor base with using double three pole 16 doublemm M3 throw hex (DPDT)screws. switch Make and sure power that connector.the wires are (6) outTighten of the the way cover of the to bearingthe base hold usinger orthree else 16 it mmmight M3 mess hex up screws. when Make the bearing sure that holder the rotates.wires are (6) Tighten the cover to the base using three 16 mm M3 hex screws. Make sure that the wires are out (7)(6) AssembleTightenout of the the theway cover 3-D of theprintedto thebearing base platform holdusinger with threeor else the 16 it pr mmmightinted M3 messrod hex using upscrews. when M3 Make 7the mm bearing sure hex thatscrews, holder the as wiresrotates. shown are of the way of the bearing holder or else it might mess up when the bearing holder rotates. (7) inoutAssemble Figure of the 11. waythe Two 3-D of the screwsprinted bearing should platform hold beer enoughwith or else the itfor pr might intedthe assembly. mess rod usingup when M3 the7 mm bearing hex screws, holder asrotates. shown (7) AssembleinAssemble Figure 11. the Two 3-D screws printed should platformplatform be withwithenough thethe printedforpr intedthe assembly. rod rod using using M3 M3 7 7 mm mm hex hex screws, screws, as as shown shown in inFigure Figure 11 11.. Two Two screws screws should should be be enough enough for for the the assembly. assembly.

Figure 11. Rod assembled to the platform. Figure 11. Rod assembled to the platform. Figure 11. Rod assembled to the platform. (8) Important: Turn on the mixerFigure using 11. Rod the assembled adapter and to the make platform. sure that the bearing holder is in (8) parallelImportant: position Turn to on the the base mixer as shown using inthe Figure adapter 12. andThis makestep is sure important that the so bearingthat the holderrod and is slit in (8) Important:parallel position Turn toon the the base mixer as shown using inthe Figure adapter 12 . andThis make step is sure important that the so bearing that the holderrod and is slit in parallel position to the base as shown in Figure 12. This step is important so that the rod and slit Appl. Sci. 2017, 7, 942 8 of 14

(8)Appl. Sci.Important: 2017, 7, 942 Turn on the mixer using the adapter and make sure that the bearing holder8is of in14 Appl. Sci.parallel 2017, 7, position 942 to the base as shown in Figure 12. This step is important so that the rod and8 of slit 14 cancan be be assembled with with ease. It It should should be be noted that if the bearing holder is not in this positionposition can be assembled with ease. It should be noted that if the bearing holder is not in this position while assembling the rod, the rod might break or it might not assemble properly. while assembling the rod, the rod might break or it might not assemble properly.

Figure 12. Bearing holder position should be parallel to the base and the motor. Figure 12. Bearing holder position should be parallel to the base and the motor. (9) Assemble the rod platform assembly to the cover such that the rod tip fits exactly at the center (9) AssembleAssemble the rod platform assemblyassembly toto thethe covercover such such that that the the rod rod tip tip ﬁts fits exactly exactly at at the the center center of of the bearing bore. ofthe the bearing bearing bore. bore. (10) Make sure that the rod fits properly in the bearing bore by aligning the slit hole of the cover with (10) MakeMake sure sure that that the the rod rod fits ﬁts properly properly in the the bearing bearing bore by aligning the slit hole of the cover with the rod hole, as shown in Figure 13. thethe rod rod hole, hole, as as shown shown in in Figure Figure 13.13.

Figure 13. Visual check needed to determine if the rod hole is aligned with the cover holes. FigureFigure 13. VisualVisual check needed to determine if the rod hole is aligned withwith the cover holes. (11) Install the slit passing it through the cover and through the rod. (11) Install the slit passing it through the cover and through the rod. (11)(12) PlaceInstall the the dimpled slit passing mat it on through top of the the cover cover. and If through required the use rod. some glue to fix it firmly to the (12) Place the dimpled mat on top of the cover. If required use some glue to fix it firmly to the (12) platform.Place the dimpled mat on top of the cover. If required use some glue to fix it firmly to the platform. platform. 2.3.2. Testing 2.3.2. Testing The systemsystem was was timed timed for for 100 100 rotations rotations three three times times to determine to determine the rotation the rotation speed in speed the forward in the The system was timed for 100 rotations three times to determine the rotation speed in the andforward reverse and directions.reverse directions. In addition, In addition, mass was mass applied was applied to the to system the system until until failure failure to determine to determine the forward and reverse directions. In addition, mass was applied to the system until failure to determine maximumthe maximum mixing mixing capacity. capacity. the maximum mixing capacity. 3. Results 3. Results After printing,printing, allall ofof thethe partsparts and and assembling assembling following following the the instructions instructions in in Section Section3, the3, the mixer mixer is After printing, all of the parts and assembling following the instructions in Section 3, the mixer finishedis finished as seenas seen inFigure in Figure 14a and14a and is capable is capable to mixing to mixing samples samples of various of various sizes (Figure sizes (Figure 14b). The 14b). switch The is finished as seen in Figure 14a and is capable to mixing samples of various sizes (Figure 14b). The usedswitch to used turn theto turn equipment the equipment on/off is on/off a double is a pole double double pole throw double (DPDT), throw which (DPDT), allows which clockwise allows switch used to turn the equipment on/off is a double pole double throw (DPDT), which allows andclockwise counter and clockwise counter clockwise rotation of rotation the platform. of the pl Theatform. motor The used motor is 25used RPM is 25 DC RPM motor, DC whichmotor, canwhich be clockwise and counter clockwise rotation of the platform. The motor used is 25 RPM DC motor, which changedcan be changed to a different to a different RPM motor RPM usually motor available usually fromavailable 6 RPM from to 456 RPM RPM to based 45 RPM on the based application. on the can be changed to a different RPM motor usually available from 6 RPM to 45 RPM based on the Theapplication. operation The of theoperation open source of the nutating open source mixer cannutating be seen mixer in the can Supplemental be seen in Informationthe Supplemental video. application. The operation of the open source nutating mixer can be seen in the Supplemental InformationThe open video. source nutating mixer can rotate successfully at 25 RPM with up to a 3 kg mass applied. Information video. The dimpledThe open matsource design nutating can mixer be modified can rotate in successfully FreeCAD by at changing 25 RPM with the up X valuesto a 3 kg of mass the dimplesapplied. The open source nutating mixer can rotate successfully at 25 RPM with up to a 3 kg mass applied. The dimpled mat design can be modified in FreeCAD by changing the X values of the dimples The dimpled mat design can be modified in FreeCAD by changing the X values of the dimples (cylinders) to fit the test tube sizes as per any experimental requirements. The current design can hold (cylinders) to fit the test tube sizes as per any experimental requirements. The current design can hold 13 mm, 16 mm, and 20 mm test tubes, and the dimpled mat can be removed for cleaning with soap 13 mm, 16 mm, and 20 mm test tubes, and the dimpled mat can be removed for cleaning with soap and water. The part which is the most likely to need replacement over a long time period of usage and water. The part which is the most likely to need replacement over a long time period of usage Appl. Sci. 2017, 7, 942 9 of 14

(cylinders) to ﬁt the test tube sizes as per any experimental requirements. The current design can hold 13 mm, 16 mm, and 20 mm test tubes, and the dimpled mat can be removed for cleaning with soap Appl. Sci. 2017, 7, 942 9 of 14 and water. The part which is the most likely to need replacement over a long time period of usage would be the NinjaFlex slit, and it can be 3-D printed and replaced at a cost of US$0.34. In In addition, addition, thethe entire mixer is easily disassembled/re-assembled to to replace replace any any other other broken broken part part or or to to upgrade thethe apparatus, as discussed below.

(a) (b) Figure 14. (a) Fully-assembld 3-D printed open source nutating mixer; (b) with samples of various sizes.Figure 14. (a) Fully-assembld 3-D printed open source nutating mixer; (b) with samples of various sizes.

4. Discussion Discussion

4.1. Performance Performance and Future Work The open source nutating mixer is designed to perform the basic gentle 3-dimensional nutating rotation in both CW and CCW directions. The The mixi mixingng provided by the nutating mixer is thorough yet gentle mixing that prevents foaming. This This func functionalitytionality is is enough enough for for most most basic basic mixing mixing needs, needs, such as mixing blood samples or biological DNA samples. Both Both the the speed speed and and the the tilt tilt angle of the open source nutating mixer are fixed fixed to provide appropriate agitation for mixing samples in small containers. However, However, some laboratories may want other tilt angles, as discussed above, or may need thethe ability to vary the speed of mixing. This This open open source source system system can can be be modified modified to a variable speed adjustable mixermixer inin thethe future future by by adding adding a potentiometera potentiometer to theto the circuit. circuit. In this In this case, case, a 45 ora 45 higher or higher RPM RPMmotor motor can be can used, be used, and theand potentiometer the potentiometer can can adjust adjust the the speed speed from from 0 RPM 0 RPM to 45to 45 RPM RPM according according to tothe the requirements requirements of of the the experiments. experiments. This This modification modification would would have have onlyonly aa modestmodest additionaladditional cost associated with the cost of the motor (

4.2. Cost Analysis The overall cost of the 3-D printed and purchased equipment based on the BOM in shown in Tables1 and2 is US$37, which can be compared to other nutating mixers commercially available on the market, as summarized in Table3. The closest available commercial products on both instrument suppliers’ websites and Amazon cost on average US$373, which is 10 times the cost of the open source nutating mixer, thus saving 90% of the commercial cost. These cost savings are in agreement with the savings observed in other scientiﬁc tools in past studies [6,11,12,31]. Finally, a point should be made about the range in costs of the commercial systems shown in Table3. The most expensive system also included variable speed, which are not included in the lowest cost models. As noted above, this functionality could be added to the open source system, while maintaining the same cost advantage in percent for the materials costs.

Table 3. Commercial nutating mixers cost and cost saving percent for the use of the open source nutating mixer.

Commercial Proprietary Product Cost (US$) Cost Savings for OS Nutating Mixer (%) Labnet GyroMini Nutating Mixer [49] 291.65 87.3 Benchmark BlotBoy 3-Dimensional Rockers [50] 381.65 90.3 Benchmark Scientiﬁc B3D1008 Mini [51] 322.15 88.5 Boekel 201100 Mini Orbitron [52] 491.00 92.4 Globe Nutating Mixer [53] 443.03 91.6 Globe Scientiﬁc 522-230 Nutating Mixer II [54] 420.60 91.2 Benchmark Mini BioMixer 3-D Shakers [55] 313.65 88.2 Chemglass CLS-4029-100 3D Nutating Mixer [56] 325.00 88.6 Average 373.59 90.1

These cost savings, however, assume that there is no labor cost for the purchasing of components, 3-D printing, and assembly. Zero labor costs are relevant in the following situations: (1) where the 3-D printing and the assembly of the device is used as a learning tool in order to provide students with experience in the construction of scientific equipment or open hardware [57,58]; (2) where the labor is provided by unpaid interns or volunteers (e.g., undergraduates volunteering for research to gain experience and improve their resume/CVs); or, (3) where there is no opportunity cost to using existing salaried employee (e.g., the use of a lab manager or RA, TA, or other position that is paid a fixed cost, and for which there is no opportunity cost for them working on the fabrication of the device. In general, in academic institutions these conditions can be readily met in most labs. In the labs, however, where this is not the case (e.g., industrial labs) it is instructive to look at the potential cost of labor for the fabrication of the open source desktop nutating mixer. The labor involved is represented by three tasks: (1) purchasing the six primary components, as outlined in Table2; (2) 3-D printing the seven 3-D printed parts listed in Table1; and, (3) assembling the device when all of the components have been gathered. The labor for each of these tasks will be analyzed separately. First, purchasing the components is a low-skill task, particularly when the Amazon hyperlinks in references [36–40] are still active and purchasing is occurring in the United States (U.S.). The total time for this task would be about 5 min for anyone with an existing Amazon account and shipping is free for those with Amazon prime. In the future, if these components are no longer available on these hyperlinks than they will need to be sourced from other websites, which will have an additional time cost. It should also be pointed out that it may be possible to decrease the cost of the device by careful comparison shopping for the components, and many of the components are probably already available for no cost at institutional Fablabs [59,60]. Regardless, this subtask can be undertaken by the lowest-cost worker in an organization (e.g., a receptionist at a company) and represents a trivial or non-existent cost. Next, the 3-D printing of the components listed in Table1 can be considered a moderate skilled task (although FFF 3-D printing is a rapidly expanding skill set seen in young workers in a wide array Appl. Sci. 2017, 7, 942 11 of 14 of disciplines). However, it would appear challenging for those with no experience in 3-D printing. For those with experience and access to a basic RepRap or similar the time investment for setting up a print again is trivial. For example, although only the two flexible components were printed out on a Lulzbot Mini here, all of the components could have been. The first five components can be printed on any such hard plastic FFF 3-D printer using default settings, or the settings recommended here. There are hundreds of thousands of these 3-D printers deployed globally, which are thus readily accessible to most labs. A tuned DIY RepRap or a commercial self-bed leveling 3-D printer can be left unattended after the file has been sent to print just as long as 2-D print jobs can be left to print without the printer being monitored by a user. Thus, although the actual 3-D print time is much longer, the time that labor is focused only on printing is less than half an hour. The two flexible 3-D prints must be made on an advanced (or upgraded) 3-D printer (e.g., the Lulzbot Mini with the Flexystruder) and may not be available even in every workshop with a 3-D printer. In these cases, the local FabLab [59,60], makerspaces [61], hackerspaces [62], and even public libraries [63] often have 3-D printing services available either for free, or for the cost of materials. Most universities now have at least basic 3-D printing capabilities somewhere on campus. For researchers wishing to fabricate the open source desktop nutating mixer with no access to 3-D printers locally, an on demand quasi-local 3-D print service can be used, such as MakeXYZ [64]. The costs for a 3-D printing service will be more than the costs of the materials alone, but in general reasonable, because of the high degree of competition, quotes are available immediately for users in any given area. Lastly, once all of the components are gathered they must be assembled. Having designed the system, the researchers in this study could build the device in about 10 min. To remain conservative, it is estimated that for a novice builder the build time would be under 30 min. (with the assembly instructions in this paper). Thus, the overall cost in labor to source, print, and assemble a 3-D printable open source desktop nutating mixer is about 1 h. This indicates that it is profitable for an organization to use the open source version if their labor costs are under $250/h, even for the least expensive commercial equivalent (or under $330/h for the average commercial system). Finally, a point should be made about the life cycle cost advantages of the open source mixer. As all of the files are shared and the BOM is known, regardless of the failure mode of the device it is easily repaired from readily available components (e.g., reprint a broken plastic component or replace the DC motor). This ease of repair and upgrading is simply not available for all of the commercial systems, which would demand the purchasing of a replacement device. Thus, the value of the open source tool can be considered higher than the commercial functional equivalent, even though the open source tool costs less money to build upfront.

5. Conclusions This study successfully described the development, design, assembly, and operation of a 3-D printable open source desktop nutating mixer, which provides a ﬁxed 20◦ platform tilt angle for a gentle three-dimensional (gyrating) agitation of chemical or biological samples. The device can be fabricated from US$37 in parts, which is 1/10th of the cost of proprietary nutating mixers with similar capabilities. In addition, the open source nutating mixer was found to operate under 3 kg loads, which provides the opportunity to expand the sample carrying capacity of the device in the future. The open source nature of the device allows it to be easily repaired or upgraded with digital ﬁles, as well as to accommodate custom sample sizes and mixing velocities with minimal additional costs.

Supplementary Materials: The following are available online at https://osf.io/bqysc/, Video S1: Open Source 3-D Printed Nutating Mixer demonstration video. Acknowledgments: This project was supported by the Michigan Tech Open Sustainability Technology Laboratory and Fulbright Finland. The authors would also like to thank Aubrey Woern for technical assistance. Author Contributions: D.K.T. and J.M.P. conceived and designed the experiments; D.K.T. performed the experiments; D.K.T. and J.M.P. analyzed the data; J.M.P. contributed materials; D.K.T. and J.M.P. wrote and edited the paper. Appl. Sci. 2017, 7, 942 12 of 14

Conﬂicts of Interest: The authors declare no conﬂict of interest.

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