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A simple Matrigel cooling setup for optimal cell seeding of microfluidic devices

Torben Roy

MeBioS biomimetics group, KU Leuven, Willem de Croylaan 42, 3001 Leuven, Belgium

Why is this useful?

Some organ-on-a-chip models require seeding of cells suspended in an extracellular matrix (ECM) such as Matrigel.1-3 When seeded inside microfluidic channels, cells experience shear stresses due to mechanical forces of the fluid which can have a negative effect on the viability of the cells.

Matrigel starts to polymerize at a temperature above 10 °C, which hinders the injection of the ECM inside microfluidic channels due to an increase in viscosity. An increase in pressure from the pipette or pump is then required and if not met, the microfluidic channel will not be fully deposited as intended (Figure 1). Precautions including the cooling of the ECM solution, pipette tips and microfluidic chip need to be taken to ensure proper deposition.

A study by Kane et al. found that a temperature between 8 °C and 10 °C is ideal for cell seeding as in this temperature range a minimal shear stress is observed.4 Below 8 °C an increase in shear stress is observed due to temperature induced liquefaction, while above 10 °C polymerization induces a higher rate of shear stress. Thus to ensure maximum cell viability, it is recommended to seed a microfluidic device with a cell-Matrigel solution in the 8 – 10 °C range. The use of an ice bath or current commercial coolers does not allow for stable cooling in that temperature range.

A new method is presented that allows for cooling of a cell-Matrigel solution in the optimal temperature window (8 – 10 °C). The cooling setup is composed out of a heating block (from a dry block heater) (or CoolRack™ from Corning), ice packs and a thermometer. Ice packs are less efficient at cooling compared to the ice bath and can be added and removed until a desired stable temperature is obtained. While the metal heating block (common lab equipment) allows for a homogeneous spread of the temperature.

Figure 1 – Unsuccessful deposition of a microfluidic chip with Matrigel. The Matrigel solution did not fill the entire main channel as intended due to premature polymerization.

 

What do I need?

  • Heating block (e.g. modular heating block for vials, VWR) or CoolRack™ (Corning)
  • Ice packs
  • Cooling element
  • Thermometer
  • Matrigel® Basement Membrane Matrix, Phenol Red-Free, LDEV-Free (356237, Corning)
  • Eppendorf tube
  • Pipette
  • Pipette tips

 

How do I do it?

  1. Prepare the cell-Matrigel solution in a sterile environment, aliquot in an Eppendorf tube and place on ice.
  2. Place the heating block, (autoclaved) pipette tips and (autoclaved) microfluidic chip inside the fridge to cool to 4°C.
  3. Remove the heating block from the fridge, place it on a cooling element (stable surface) and surround the heating block with ice packs.
  4. Place the Matrigel-cell solution and thermometer inside the heating block holes.
  5. Add or remove ice packs until a stable temperature in the 8 – 10°C range is achieved.
  6. Remove the microfluidic chip from the autoclave insert and place it on a cooling element. Inject the Matrigel-cell solution using cooled pipette tips.

 

Figure 2 – Cooling setup. A heating block is surrounded by ice packs to reach a stable temperature in the 8 – 10°C temperature range.

References

  1. Wang Y, Wang L, Guo Y, Zhu Y, Qin J. Engineering stem cell-derived 3D brain organoids in a perfusable organ-on-a-chip system. RSC Advances. 2018;8(3):1677-1685.
  2. Trietsch S, Israëls G, Joore J, Hankemeier T, Vulto P. Microfluidic titer plate for stratified 3D cell culture. Lab on a Chip. 2013;13(18):3548.
  3. Moreno E, Hachi S, Hemmer K, Trietsch S, Baumuratov A, Hankemeier T et al. Differentiation of neuroepithelial stem cells into functional dopaminergic neurons in 3D microfluidic cell culture. Lab on a Chip. 2015;15(11):2419-2428.
  4. Kane K, Moreno E, Lehr C, Hachi S, Dannert R, Sanctuary R et al. Determination of the rheological properties of Matrigel for optimum seeding conditions in microfluidic cell cultures. AIP Advances. 2018;8(12):125332.
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A simple, efficient, and cost-effective spin coater: A waste to wealth approach

S.J.Samuel Justin1, P.Wilson1

1Department of Chemistry, Madras Christian College

Email: sam310just@gmail.com, wilson@mcc.edu.in

 

Why is this useful?

Spin-coating is a highly reproducible, simple, time-efficient, and cost-effective coating technique is widely employed technique for the fabrication of thin-film coatings over large areas with smooth and homogeneous surfaces [1]. It has been widely used for the production of monolayer- and multilayer-thin coatings, freestanding (FS) nanosheets and membranes, for various industrial and biomedical applications, e.g. mitigation of corrosion [2], wound dressings, cell culture substrates, and as drug delivery devices.

A tip to develop portable spin coaters by recycling computer fans and mobile phone wall chargers was previously presented [3]. Using adhesive strips to secure a metal alloy sample on the center of the computer fan often slips and knocked down while trying to remove the sample after the coating process. This affects the coating and thereby a proper substitute to hold the sample tight during the spin and at the same time easier to remove it after the coating is essential. In addition, the sample spinning at high rpm levels expels the excess coating substrate away from the system which has to be addressed in order to prevent the contamination of the surroundings. In this regard an improved form of portable spin coater is proposed and presented.

 

What do I need?

Parts for the spin coater

  1. Polycarbonate container, Dimensions 155 X 155 X 60 mm
  2. Panel cooling fan 120 x 120 x 38 mm with 2800 rpm
  3. Acrylic support rod of length 15 mm and diameter of 12 mm
  4. Faucet water tap adapter
  5. Black cap of 5mL clear round glass bottle – 4 pieces
  6. 8 pieces set of 3mm diameter round head 20 mm bolt and nut
  7. Power cable

Parts and chemicals for the specific examples

  • Nitro cellulose lacquer
  • Aluminium alloy 15mm x15mm x6mm

 

What do I do?

Assembling of spin coater

  1. The acrylic rod is fixed at the centre of the fan using instant cyanoacrylate ester adhesive (Fig.a)

 

  1. A hole of 15 mm dia. is drilled at the centre of the container base and 2.8 mm hole at the four corners of the container (Fig.b).
  2. The container is placed over the fan and the corners are fixed using bolt and nut (Fig.c)
  3. The stem of the faucet water tap adapter was cut and the hole is enlarged to 12mm dia. It is then fixed using instant adhesive on the top of the acrylic rod (Fig.d, e & f)

  1. The black caps were drilled at the center to create a hole of 2.8mm dia. The bolt is inserted from below each cap and then tightened with the base of the cooling fan at the four corners (Fig. g and h).
  2. The power cable is attached to the fan (Fig. i)

  1. The lid of the container is drilled at the center to 15mm dia. which acts as a space for dropping the coating material (Fig. j and k) and the final product is displayed in (Fig. l).
  2. The liquid containing the coating material (pigmented nitrocellulose lacquer) is placed on top of                 the substrate (Aluminium alloy) (Fig. m) by using a (micro) pipette (Fig. n.)
  3. The fan is turned on and the substrate is spin coated for about 30 seconds (Fig. o) (time can vary    depending on the substrate viscosity and coating thickness required). The coated substrate (Fig. p) is subjected to further evaluation.

 

References:

 

[1] Moreira, Joana, A. Catarina Vale, and Natália M. Alves. “Spin-coated freestanding films for biomedical applications.” Journal of materials chemistry B 9, no. 18 (2021): 3778-3799.

[2] Telmenbayar, Lkhagvaa, Adam Gopal Ramu, Daejeong Yang, Minjung Song, Tumur-Ochir Erdenebat, and Dongjin Choi. “Corrosion resistance of the anodization/glycidoxypropyltrimethoxysilane composite coating on 6061 aluminum alloy.” Surface and Coatings Technology 403 (2020): 126433.

[3] A second life for old electronic parts: a spin coater for microfluidic applications, https://blogs.rsc.org/chipsandtips/2018/04/25/a-second-life-for-old-electronic-parts-a-spin-coater-for-microfluidic-applications/ (accessed August 2020)

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The Name is Bond – Heat Bond: Using a Heated Lamination Press for Thermoplastic Thin Film Bonding

Travis Swaggard1, Johanna Bobrow1, Peter Carr, Isabel Smokelin1, Todd Thorsen1, Christina Zook1, David Walsh1

1MIT-Lincoln Laboratory, 242 Wood St, Lexington, MA 02421

 

Why is this useful?

Have you ever tried to bond a thin clear bottom to your custom thermoplastic microfluidic device for high magnification microscopy? The bonding process can be cumbersome and relies on the heating temperature, the pressure placed on the device assembly, surface chemistry, as well as many other factors.1 We have developed a method that utilizes a heated laminator press and a UVO oven, which together cost less than hiring an external vendor who will likely charge per design and item manufactured. Currently, manufacturing bonded devices in-house can be difficult, expensive, and time consuming.

The new paradigm in microfluidic device prototyping using high-resolution 3D-printing has significantly reduced the barrier to participate in microfluidics, which traditionally required dedicated infrastructure and specialized expertise.2 However, once the design-build-test prototyping cycle has gone beyond the 3D-printing stage, additional prototyping in thermoplastics (e.g. CNC milling) is typically required for eventual scale-up using traditional hot embossing or injection molding manufacturing techniques. One of the critical challenges at this stage is placing optically-clear bottoms below the thermoplastic microfluidic device for optical interrogation, while withstanding fluidic flow and pressure. For example, adhesive bonding such as using double-sided tape can be tricky and tedious to align, and solvent-based adhesives can be messy or challenging to avoid impacting thin-film clarity, and even pose environmental safety concerns.

We have developed an inexpensive bonding protocol which can utilize almost any commercially available heated machine press to mitigate the aforementioned drawbacks, and bond layers of thin (125 micrometer) acrylic film to any flat acrylic microfluidic device surface. This allows for a strong bond that can provide a clear bottom for high-resolution optical interrogation, such as using a confocal microscope, for example. New low-cost commercial UVO ovens (Jelight Model 18 – $3,000) and heated laminated presses (Nugsmasher $500 [Mini] – $7,000 [Pro Touch]) have helped enable democratization of the thermoplastic film bonding process.

Here is a detailed walkthrough for the preparation and assembly of these devices. We have included photos and figures from each step for reference and convenience.

What do I need?

  • Thin, optically clear acrylic film (e.g. Röhm GmbH Acrylite Film 99524 or similar)
  • Microfluidic device from cast acrylic (e.g. Protolabs – CNC Machined)
  • Scissors
  • Oven mitts (or equivalent)
  • Multipurpose Neoprene rubber sheet 6”x 6” x 1/16” (or equivalent heat-safe separator)
  • Heated lamination press (Premiere Manufacturing SKU: 714343996295 or similar)
    • Must apply pressures between 30 and 50 PSI (roughly finger-tight, part won’t move if pushed by a finger)
    • Must be able to heat up to 118 °C

How do I do it?

  1. Using scissors, cut piece(s) of thin, optically clear acrylic film slightly larger than your acrylic device (this will eliminate any alignment steps, you can cut the remaining excess after the device has been pressed). Your film should be about half an inch oversized on all edges of the device to ensure that it is completely covered
  2. Place the cutout of acrylic film(s) and plastic device(s) into the UVO oven so they are not touching and run for eighty minutes (see Fig.1). You can also perform oxygen plasma bonding alternatively; however, as that bond weakens over time, it’s important to perform the bonding immediately before the treatment. (Note: Be sure to put the bonding surfaces face-up in the UVO machine for best results.)
  3. Preheat laminated press to 118 °C (or about 250 °F). It may take up to twenty minutes to get up to temperature and an hour total to stabilize at the set point (see Fig.2).
  4. Very carefully (press will be very hot) place thin film on bottom plate and plastic device on top of film (use oven mitts or tongs for safety).
  5. Place a neoprene cover sheet over plastic coupon/film assembly. This will provide cushioning between the top press and your device and prevent any possible cracking or pitting from the top press (see Fig.3).
  6. Using the lever crank in the back, apply manual pressure until the machine registers a reading of 30-50 PSI (or roughly finger-tight, so the part won’t move if pushed by a finger or tong).
  7. Let device sit at steady pressure and heat, hold for ten minutes.
  8. Turn off heat but keep the device under pressure.
  9. Once heat returns to near room temperature, release pressure and remove device (Note: This may be overnight). Once complete, the devices should be effectively bonded and show optically clear bottoms with no aberrations (see Fig.4).

What Else Should I Know?

Before running this protocol, check your heated laminator press for scratches or pitting that could imprint on your film. If there are any significant scratches, these might become imprinted on your film and cause uneven bonding later in the process. A steel stainless steel sheet with a polished finish can be added on top of the bottom plate using thermal paste.

UVO treatment of plastics will create an oxide layer on the surface, rendering it more hydrophilic. The generation of oxygen species on the surface of plastics will reach a plateau after about sixty minutes.3

Almost any thermoplastic material4 can be bonded to the same type of material using the rule-of-thumb of heat being 5 °C over glass temperature, however it is worth noting that identical materials will bond most effectively, for example cyclic olefin polymer (COC) bonds to COC material straightforwardly, whereas COC will not bond as well to dislike material such as polycarbonate.

Do not overexpose your film and device to UVO (>sixty min) as this may cause significant yellowing and irreversible changes to the chemical makeup of the acrylic. Apply UVO as directed in this protocol. Some yellowing may happen, but in our hands, this does not create any noticeable background shading or autofluorescence.

Make sure not to put too much pressure on the film and device during the bonding process to ensure that devices are not warped, deformed or cracked, use only the pressure recommended in this protocol.

Always allow the heat from the laminated press to return back to room temperature, do not try to remove the device from the press before returning to room temperature as this will potentially produce an incomplete bonding.

If the pressure required for this bond causes deformation of critical features, consider applying ethanol to reduce surface glass temperature for a lighter pressure bond.5

 

While this publication discusses bonding to CNC-milled devices, there is potential for devices made from alternative fabrication techniques such as xurography or laser cutting to be bonded using a modified version of this protocol as well.6

 

Acknowledgements

We would like to acknowledge Chris Phaneuf, Ph.D. from Sandia National Laboratories as well as Edge Embossing (Charlestown, MA) for their assistance and expertise with helping us create this protocol. This work was funded by NIH/NCATS through an Interagency Agreement with MIT-Lincoln Laboratory as well as by NIH/NIBIB via grant award number 1R01EB025256-01A1.

© 2022 Massachusetts Institute of Technology.
Delivered to the U.S. Government with Unlimited Rights, as defined in DFARS Part 252.227-7013 or 7014 (Feb 2014). Notwithstanding any copyright notice, U.S. Government rights in this work are defined by DFARS 252.227-7013 or DFARS 252.227-7014 as detailed above. Use of this work other than as specifically authorized by the U.S. Government may violate any copyrights that exist in this work.

 

 

References

  1. Putting the Lid on Microfluidics [Internet]. Microfluidics. 2017 [cited 2022 Jan 7]. Available from: https://microfluidics.technicolor.com/wp-content/uploads/2021/12/Microfluidic-Chip-Bonding-Considerations-and-Case-Studies.pdf
  2. Bhattacharjee N, Urrios A, Kang S, Folch A. The upcoming 3D-printing revolution in microfluidics. Lab on a Chip. 2016;16(10):1720-42.
  3. Lin TY, Pfeiffer TT, Lillehoj PB. Stability of UV/ozone-treated thermoplastics under different storage conditions for microfluidic analytical devices. RSC advances. 2017;7(59):37374-9.
  4. Jiang J, Zhan J, Yue W, Yang M, Yi C, Li CW. A single low-cost microfabrication approach for polymethylmethacrylate, polystyrene, polycarbonate and polysulfone based microdevices. RSC Advances. 2015;5(45):36036-43.
  5. Harriet Riley, Development Editor. (2017, November 1). A solvent-based method to fabricate PMMA microfluidic devices – Chips and Tips. https://blogs.rsc.org/chipsandtips/2017/11/01/a-solvent-based-method-to-fabricate-pmma-microfluidic-devises/?doing_wp_cron=1625578271.8969628810882568359375 (Accessed November 2021)
  6. Burgoyne, F. (2010, May 17). Fast-iteration prototyping and bonding of complex plastic microfluidic devices – Chips and Tips. https://blogs.rsc.org/chipsandtips/2010/05/17/fast-iteration-prototyping-and-bonding-of-complex-plastic-microfluidic-devices/?doing_wp_cron=1625578517.8055989742279052734375 (Accessed November 2021)
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INTERFACING MICROFLUIDIC CHIPS: DUAL CONNECTOR-RESERVOIR FIXTURE

Daniel Alcaide Martín, Jean Cacheux, Sergio Dávila & Isabel Rodríguez

Madrid Institute for Advanced Studies in Nanoscience (IMDEA Nanoscience), Ciudad Universitaria de Cantoblanco, C/Faraday 9, Madrid 28049, Spain

1- Why is this useful?

Microfluidic devices need to be connected to fluidic pumps for regulation of the flow during the device operation1. Connecting and disconnecting devices is a tedious and time-consuming operation that often causes air bubbles which are detrimental for the fluidic experiment and a real nuisance for the time it takes to eliminate them.

Furthermore, in microfluidic experiments dealing with biomolecules or cell cultures, volumes are of concern as these materials are typically limited and/or costly. Hence, it will be very useful if the reagent filling or replacement process and the connecting and disconnecting operations to microchips are minimized to avoid both bubbles and reagents waste. Reducing the reservoir volume to the volumes needed for the experiment minimizing dead volumes will also allow saving expensive reagents.

With this aim, we have designed a fixture to make practical fluidic connections to a microchip from a pressure controller for fluidic control and device operations. It allows for easy opening and closing operations and for easy re-filling or replacement of the reagents into the microchannels without moving any tubing connection.

Here, we present a dual connector cum reservoir fixture as a practical and effective means to making fluidic connections onto polydimethylsiloxane (PDMS) microfluidic based chips. The fixture is completely built by stereolithography (SLA) 3D printing and includes two components: a piece including a reservoir with an O-ring slit and a cone shaped outlet as chip connector and, another piece that closes the reservoir and has a cone shaped inlet or air pressure connector.

This Chips and Tips builds on a previous approach,2 dealing with microchip fluidic fixtures using magnets. However, in this case, the reservoirs and release connection are moved off the chip which would be more practical to work with the chip on the microscope stage for real time observations. Moreover, it is adaptable for any chip design and particularly for microchips made in soft PDMS.

 

2- What do I need?

  • 3D design software.
  • SLA 3D printer.
  • Cubic magnets.
  • O-rings.

 

3 – What do I do?

We first digitally design the parts of the dual connector: the reservoir-chip connector and the reservoir-seal air pressure adaptor. See the drawing in Figure 1. The corresponding F3D files can be here downloaded.

In our design, the reservoir sits aside from the PDMS chip and it is connected to it through a standard tube fitted on to the connecting outlet. The reservoir-seal encloses the reservoir. Four permanent magnets are inserted in each of the two components to produce a magnetic compressive force onto the O-ring and a tight seal to allow for applying a controlled pressure to cause the reagent to flow at the desired rate into the microfluidic chip.

Once the components are printed, the magnets are inserted into the lateral slots. Then, the plastic tubes are connected to the chip inlets and outlets and to the reservoir chip connector. The reservoir is filled with the correct volume of reagent (in this design is 0.2 ml) and the reservoir- seal piece is placed on top. Finally, through the air pressure inlet, tubing is connected to a pressure controller. When air pressure is applied, the reagent flows through the chip. The closing system formed by the O-ring seal and magnet force is able to handle at least 1 bar working pressure without any leakage.

Figure 2 – Fluidic system set-up showing .two dual connector-reservoir fixtures connected to a microchip and to a pressure controller.

Acknowledgements

This work was performed within the framework of the EVONANO project funded by the European Union’s Horizon 2020 FET Open programme under grant agreement No. 800983.

References

  1. Interfacing of microfluidic devices – Chips and Tips. https://blogs.rsc.org/chipsandtips/2009/02/27/interfacing-of-microfluidic-devices/.
  2. Reusable magnetic connector for easy microchip interconnects – Chips and Tips. https://blogs.rsc.org/chipsandtips/2011/06/27/reusable-magnetic-connector-for-easy-microchip-interconnects/.

 

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Solvent Extraction of 3D Printed Molds for Soft Lithography

Jonathan Tjong1, Alyne G. Teixeira1 and John P. Frampton1,2

1School of Biomedical Engineering, Dalhousie University, Halifax, NS, Canada

2Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, NS, Canada

Why Is This Tip Useful?

Casting polydimethylsiloxane (PDMS) in molds produced from additive manufacturing (i.e., 3D printing) enables rapid prototyping of parts with microscale features without the need for conventional photolithography. Whereas conventional photolithography followed by soft lithography involves the use of silicon substrates and photomasks, which can be costly and may require special preparation and processing (e.g., application and removal of photoresist in a clean room environment), the emergence of stereolithographic 3D printers allow for the rapid manufacture of masters for PDMS casting in almost any laboratory space. Stereolithographic 3D printers use photopolymer resins that when cured can withstand temperatures as a high as 200 °C without plastic deformation, which occurs with thermoplastics such as polystyrene that have glass transition temperature around 95-105 °C (Lerman et al.). The ability to withstand such high temperatures opens the possibility for PDMS and other silicone elastomers to be cured quickly and also provides the possibility for greater control of the mechanical properties of the elastomers (Johnston et al.). However, the components within the 3D printed resin mold such as residual photoinitiators and unreacted oligomers may interfere with the curing of PDMS, resulting in incomplete curing at the interface of the printed mold and the PDMS part. Here, we demonstrate a simple treatment to remove these unwanted materials through solvent extraction.

What Do I Need?

  • Stereolithographic 3D printer and appropriate resin
  • Leak-proof, sealable container large enough to hold the 3D-printed mold
  • Dishwashing detergent
  • 95% ethanol or isopropanol
  • Orbital shaker table
  • Uncured PDMS base and curing agent (10:1 w/w)
  • Post-curing UV lightbox

What Do I Do?

  1. After cleaning and post-curing of the 3D-printed mold in the UV lightbox, place the mold in the container and add enough solvent to submerge the part.
  2. Seal the container and leave on a shaker table for 24 hours.
  3. Discard the old solvent and add new solvent. Seal and agitate for another 24 hours.
  4. Remove the part from the solvent and allow to air dry at room temperature.

What else should I know?

The exact composition of photopolymer resins for stereolithography may vary significantly between different manufacturers; therefore, it may be necessary to adjust the protocol (e.g., the type of solvent). In addition, larger prints will likely require more solvent and a longer duration of solvent extraction to account for the increased migration time of unwanted components from the print to the free solvent.

To demonstrate our procedure, we printed two sets of 5 identical molds with basic geometric features. One set used 1 mm thick outer walls, while the other set used 3 mm thick outer walls (Figure 1). The molds were designed using Onshape (Onshape, Cambridge, MA) CAD software and printed using a B9Creator v1.2 (B9Creations, Rapid City, SD) stereolithographic 3D printer. For all prints, we used B9-R2-Black resin from B9Creations. This resin is documented by the manufacturer as having a heat deflection temperature of 65 °C at 0.45 MPa determined through ISO 75-1/2:2013 standards (B9Creations). As no significant mechanical load would be placed on the resin molds (with a maximum depth of 6 mm for the PDMS chamber), we decided this resin was suitable for our test molds. After printing, excess resin was removed from the molds by submerging and agitating in an approximately 1:10 mixture of Dawn dishwashing detergent and water in a 1 L container. This was followed with additional cleaning by rinsing with excess isopropanol using a wash bottle until no visible evidence of uncured resin was present on the surface (approximately 10-20 mL per part). The molds were then post-cured in a UV lightbox for 20 minutes.

Once post-cured, the molds were each placed in new, 15 mL polypropylene centrifuge tubes (Falcon® Corning, Corning, NY) with 10 mL of the test solvents (reverse osmosis-treated (RO) water, isopropanol, 95% ethanol, or methanol), and exposed to the two 24-hour extraction procedures listed in the “What Do I Do” section. After extraction, the molds were briefly rinsed with RO water and allowed to air dry for 1 hour. Then, approximately 0.4 mL or 1 mL of premixed 10:1 uncured PDMS and curing agent were added to the 1 mm and 3 mm molds, respectively. The PDMS parts were heat-cured in a dry oven at 65 °C overnight. The cured PDMS parts were then carefully removed from the mold using a stainless-steel spatula. Images were taken using the default settings on an iPhone 7 camera.

Resin molds that did not undergo extraction or that underwent extraction in water or methanol produced PDMS parts with major defects. For these extraction conditions, fragments of semi-cured and traces of uncured PDMS remained at the PDMS-mold interface (Figure 2A-C). Extraction with methanol appeared to weaken the cured resin, with significant softening and the appearance of cracks on these molds (Figure 2C), and while the cured PDMS easily released from the methanol-extracted molds, this left artifacts on the PDMS surface. We found that resin parts pretreated with either isopropanol or 95% ethanol performed well as molds for PDMS. The cured PDMS parts easily released from the substrates, with no visible traces of uncured PDMS (Figure 2D-E), and the PDMS parts we retrieved cleanly replicated the features of the resin mold (Figure 3). In addition to producing defects in the mold itself, extraction with methanol also led to bubbles forming in the PDMS as it cured (Figure 3C). Overall, PDMS casts were most easily released from the 1 mm-thick molds compared to the 3 mm-thick molds, but this may simply be due to the lower aspect ratio (h/l) of the 1 mm-thick molds.

Take Home Message

When casting PDMS parts from molds produced by stereolithography, incomplete curing and defects in the PDMS part can be minimized by extracting residual photo-initiators and oligomers present in the mold using either isopropanol or 95% ethanol.

 

 

 

References

B9Creations. Black Resin Material Properties. 2018, pp. 9–11, https://cdn2.hubspot.net/hubfs/4018395/Material Data Sheets/B9Creations Black Material Properties.pdf.

Johnston, I. D., et al. “Mechanical Characterization of Bulk Sylgard 184 for Microfluidics and Microengineering.” Journal of Micromechanics and Microengineering, vol. 24, no. 3, 2014, doi:10.1088/0960-1317/24/3/035017.

Lerman, Max J., et al. “The Evolution of Polystyrene as a Cell Culture Material.” Tissue Engineering – Part B: Reviews, vol. 24, no. 5, 2018, pp. 359–72, doi:10.1089/ten.teb.2018.0056.

 

 

 

Figures and Legends

 

Figure 1. Design features of molds produced by stereolithography. Top panels in (A) and (B) are the Onshape renderings. Bottom panels in (A) and (B) are parts printed in the B9Creations B9-R2-Black resin.

Figure 2. Molds produced by stereolithography following extraction in various solvents. Fragments of partially cured PDMS and uncured PDMS remain on the surface of molds that have not undergone extraction, as well as those extracted in RO-water and methanol. Isopropanol and 95% ethanol extraction produce molds that can be re-used numerous times for PDMS curing.

Figure 3. PDMS parts obtained from curing in resin molds extracted using various solvents. Extraction of residual photo-initiators and oligomers present in the mold prior to soft lithography using either isopropanol or 95% ethanol results in clean PDMS parts that are free of defects.

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