Lötters, Joost Conrad

Sanders, Remco G.P.

Veltkamp, Henk-Willem

Wiegerink, Remco J.

Zhao, Yiyuan

English

3D-printing in microfluidics is a relatively new approach. However, most of the applications are printed in polymeric material, limiting the use in high temperature applications. This paper describes the first steps towards a 3D printed microfluidic device in α-alumina. This material could potentially be used in applications with temperatures up to 1000°C. In this paper we shortly discuss the history of 3D printing and microfluidics, the material properties of α-alumina, the theory on membrane deflection, and proposed structures to test this theory, gas-tightness, metal adhesion properties of α-alumina

University of Twente Research Information

3. Interfaces PosterTOWARDS 3D PRINTED MICROFLUIDIC DEVICES IN α-ALUMINAH.-W. Veltkamp1, Y. Zhao1, R.G.P. Sanders1, R.J. Wiegerink1, and J.C. Lötters1,21 MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands2 Bronkhorst High-Tech BV, Ruurlo, The NetherlandsABSTRACT3D-printing in microfluidics is a relatively new approach.However, most of the applications are printed inpolymeric material, limiting the use in high temperatureapplications. This paper describes the first steps towardsa 3D printed microfluidic device in α-alumina. Thismaterial could potentially be used in applications withtemperatures up to 1000 ◦C. In this paper we shortlydiscuss the history of 3D printing and microfluidics,the material properties of α-alumina, the theory onmembrane deflection, and proposed structures to testthis theory, gas-tightness, metal adhesion properties ofα-alumina.KEYWORDSLaminated object manufacturing, 3D printing inα-alumina, high temperature microfluidicsINTRODUCTION3D printingAfter the Second (electricity and assembly linemanufacturing) Industrial Revolution the world wasmainly based on Fordism, a concept of mass productionoriginally based on the large-scale manufacturing ofcars. However, the demand for customized goods isincreasing, goods that no longer can be made withconventional methods. Additive manufacturing (AM)is, in contrast to subtractive (e.g. milling, turning,grinding) and equivalent manufacturing (e.g. casting,forging), a relatively new field (roughly 40 yearscompared to centuries), and sometimes referred to asthe third industrial revolution [1]. It is defined by theAmerican Society for Testing and Materials (ASTM) asthe “process of joining materials to make objects from3D model data, usually layer upon layer, as opposed tosubtractive manufacturing methodologies” [2].One major technique in AM, and often used as asynonym for AM, is 3D printing. Though the first patentis from almost 10 years earlier [3], this technique emergedin the early 1980s with a patent on the first commercialstereolithography (SLA) machine [4]. After SLA, thefield of 3D printing evolved and matured, making thatmore 3D printing techniques were developed. Withthe expiration of the first patents, 3D printing becameopen-source, which greatly reduced the costs andboosted the development of each printing technique andeven hybrid techniques. A 2010 Gartner’s Hype CycleReport [5] identified 3D Printing as a transformationaltechnology in the Technology Trigger phase of the HypeCycle [6]. According to the ASTM F42 subcommitteeon Additive Manufacturing Technologies, establishedin 2009, the field encompasses 7 distinct printingmethods [2], which are nowadays used in all kinds ofindustries, ranging from aerospace to automotive andmedical equipment. This makes the prediction that itwas only 5 to 10 years away from mass adoption, backin 2010 [5] a quite valid prediction. The seven distinct3D print methods are listed in table 1 together with areference to their first patent.Table 1: The seven distinct 3D printing techniques with theircorresponding first patents and date of filing.3D printing technique U.S. patent no. Date of filingMaterial extrusion [3] 4,078,229 Jan. 27, 1975Directed energy deposition [7] 4,323,756 Oct. 29, 1979Material jetting [8] 4,665,492 Jul. 2, 1984Vat photopolymerication [9] 4,575,330 Aug. 8, 1984Sheet lamination [10] 4,752,352 Apr. 17, 1987Powder bed fusion [11] 5,121,329 Oct. 30, 1989Binder jetting [12] 5,204,055 Dec. 8, 1989MicrofluidicsAnother relatively new field is microfluidics.Starting in the 1950s with the development of modernink-jet printing technology [13]. The real revolutioncame when the first miniaturized gas chromatographwas realized in 1979 by Terry et al. [14]. Manz etal. extended this principle to the concept of micrototal analysis system in 1990 [15] (nowadays knownas lab-on-a-chip devices). With the support of theDefense Advanced Research Projects Agency (DARPA)of the US Department of Defence, the developmentof field-deployable microfluidic systems that can beused for the detection of chemical and biological threatswas boosted [16]. The next revolution in microfluidicscame with the development of soft lithography [17].However, this method uses molds/stamps which are2019The 4th Conference on MicroFluidic Handling Systems, 2–4 October 2019, Enschede, The Netherlands156often fabricated using a microfabrication line and theused materials are not industry compatible, preventinglarge-scale manufacturing [18].3D printing in microfluidicsWith 3D printing no molds/stamps are required andmore complex 3D structures can be fabricated. Since2012, this is being used for direct manufacturing ofmicrofluidic reaction-ware [19]. Although, the efficiencyof the microfluidic device depends largely on the chosen3D printing method [18], all reported applications inmicrofluidics lack the possibility for being used at hightemperatures and in harsh chemical conditions. Thisis solved by using α-alumina. In table 2 a comparisonbetween α-alumina and two commonly used materialsin (high temperature) micro-electro mechanical systems,i.e. silicon and silicon-rich silicon nitride (SiRN), isgiven.Table 2: Comparison α-alumina with traditional MEMSmaterials.Property [unit] Si SixNy α-Al2O3Density2.28-2.38 2.37-3.25 3.00-3.98[g cm−3]Thermal conductivity84-100 10-43 12-38.5[W m−1 K−1]Heat capacity668-715 673-1100 451-955[J kg−1 K−1]Thermal expansion7-8 1.4-3.7 4.5-10.9[10−6 K−1]Melting temperature1700-1723 2661-2769 2277-2369[K]Young’s modulus140-180 297 215-413[GPa]Poisson’s ratio0.265-0.275 0.28 0.21-0.33[-]Resistivity106-1010 1016-1021 1018-1024[10−8 Ω m]α-Alumina can be printed by using a patentedtechnique based on digital light processing (DLP)and laminating object manufacturing (LOM) [20]. Inthis LOM technique, photosensitive resin mixed withα-alumina particles (i.e. the ‘slurry’) is transported tothe building platform using a foil roll. The buildingstage is pressed onto the foil and is patterned withDLP. Repeating this, allows layers to be built ontop of each other, as is shown in figure 1. Insubsequent post-processing the resin is evaporated andthe α-alumina particles are sintered.Figure 1: Working principle of the patented DLP-LOMprinting method for ceramics [20]. Picture taken fromAdmaflex 130 flyer of Admatex [21].PROPOSED EXPERIMENTAL WORKThe use of α-alumina and this printing techniqueis a new approach in microfluidics. Therefore, thereare still quite some unknowns in the development of amicrofluidic device. Examples of these unknowns are:1. How good is the leak-tightness of the printedmaterial after sintering as function of wallthickness;2. What is the maximum operating pressure asfunction of wall thickness;3. How good is the adhesion between sinteredα-alumina and glue when tubing/capillaries areglued into the inlets;4. How good is the adhesion between sinteredα-alumina and deposited thin-film resistive metaltracks for heaters/temperature sensors;5. What is the surface roughness of sinteredα-alumina;6. What is the optical transparency of sinteredα-alumina;7. How to incorporate heaters in a 3D printed system;8. How to incorporate temperature sensors in a 3Dprinted system.Unknowns 1, 2, 3, and 5 can all be examinedwith one test structure, shown in figure 2. This teststructure has cylindrical chambers with a diameter of1 cm with varying top and bottom wall thicknesses(0.5mm, 1.0mm, 1.5mm, and 2.0mm) and an inletchannel on the long side of the cylinder for an 1/16 inchtubing, which can be glued into this channel. Schematicsof the chambers are shown in figure 2. These chamberswill be printed both parallel and perpendicular to theprinting direction. He-leakage tests will be performed inorder to check the porosity of different wall thicknesses2019The 4th Conference on MicroFluidic Handling Systems, 2–4 October 2019, Enschede, The Netherlands157and the adhesion of glue between the α-alumina and thetubing. As final tests on these chambers, the maximumoperating pressure will be determined, while monitoringthe deflection of the thin α-alumina wall. The deflectionof this wall can be approximated by the deflection of athin clamped circular plate loaded by a uniform pressure(see also figure 3) [22]:w(r) =P64D(a2 − r2)2 (1)where, w(r) is the deflection under pressure P at pointr of radius a. D is the flexural rigidity, and is given byEh3/(12(1− ν2)), where E is Young’s modulus, h themembrane thickness, and ν Poisson’s ratio.Figure 2: Designed pressure chambers for He leakage testsand failure pressure tests. The chambers are 1 cm indiameter.Figure 3: Deflection of a 0.5 mm thick membrane with aradius of 1 cm, a Young’s modulus of 215 GPa and aPoisson’s ratio of 0.21 according to the clamped thin circularplate with uniform pressure theory [22].Unknown number 4 can be investigated using thesame device. Metal can be deposited using eitherDC magnetron sputtering or e-beam physical vapordeposition (evaporation). Metals of interest are, forexample, Au and Pt, which are commonly used metalsin microfluidics [23]. Adhesion properties can be studiedusing the Scotch tape test [24], and the resistance versustemperature behavior in the range 20 ◦C – 1000 ◦C.CONCLUSIONAll above mentioned experiments are purelyconceptual. The printing of the test structures didnot proceed yet, as there are a lot of design rules forsintering. However, once these results are obtained,it becomes evident whether 3D printing of α-aluminais an applicable method for the fabrication of hightemperature microfluidic structures.ACKNOWLEDGMENTSThis work is part of the research program IntegratedWobbe Index Meter under project number 13952 whichis co-financed by the Netherlands Organization forScientific Research (NWO).REFERENCES[1] B. Lu, D. Li, and x. Tian. Development trends in additivemanufacturing and 3d printing. Engineering, 1(1):85–89, 2015.doi: 10.15302/J-ENG-2015012.[2] American Society for Testing and Materials Committee F42on Additive Manufacturing Technologies. Standardterminology for additive manufacturing technologies. (ASTMstandard F2792-10), June 2010. doi: 10.1520/F2792-10.[3] S.S. Crump. Apparatus and method for creatingthree-dimensional objects. (U.S. Patent 5,121,329), Oct.30, 1989. URL https://patents.google.com/patent/US5121329A/en. [Last accessed: Jun. 5, 2019].[4] C.W. Hull. 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[Last accessed: Jun. 5, 2019].2019The 4th Conference on MicroFluidic Handling Systems, 2–4 October 2019, Enschede, The Netherlands158[9] W.K. Swanson and S.D. Kremer. Three dimensional systems.(U.S. Patent 4,078,229), Jan. 27, 1975. URL https://patents.google.com/patent/US4078229A/en.[Last accessed: Jun. 5, 2019].[10] M. Feygin. Apparatus and method for forming an integralobject from laminations. (U.S. Patent 4,752,352), Apr.17, 1987. URL https://patents.google.com/patent/US4752352A/en. [Last accessed: Jun. 5, 2019].[11] C.R. Deckard. Method and apparatus for producingparts by selective sintering. (U.S. Patent 4,863,538), Oct.17, 1986. URL https://patents.google.com/patent/US4863538A/en. [Last accessed: Jun. 5, 2019].[12] E.M. Sachs, J.S. Haggerty, M.J. Cima, and P.A.Williams. Three dimensional printing techniques.(U.S. Patent 5,204,055), Dec. 8, 1989. URL https://patents.google.com/patent/US5204055A/en.[Last accessed: Jun. 5, 2019].[13] N. Convery and N. 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Malloggi, and M. C. Jullien. A reviewof heating and temperature control in microfluidic systems:techniques and applications. Diagnostics, 3(1):33–67, 2013.doi: 10.3390/diagnostics3010033.[24] I. F. Silvera, K. R. Stewart, G. M. Whitesides, H. P. Godfried,and F. Silvera. Improved adhesion of thin conformal organicfilms to metal surfaces. Review of Scientific Instruments, 57(7):1381–1383, 1986. doi: 10.1063/1.1138605.CONTACTHenk-Willem Veltkamp, h.veltkamp@utwente.nl2019The 4th Conference on MicroFluidic Handling Systems, 2–4 October 2019, Enschede, The Netherlands159

Towards 3D printed microfluidic devices in α-alumina

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Towards 3D printed microfluidic devices in α-alumina

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