Method Article

Fabrication of Circular Cross-section Microchannels with Stenosis via DLP 3D Printing and PDMS Membrane Inflation for Microfluidic Vascular Models

DOI:

10.3791/69706

⸱

March 6th, 2026

 ,  ,  , 
1School of Biomedical Engineering, International University, 2Vietnam National University Ho Chi Minh City

In This Article

Summary

$$\rightleftharpoonup{xx}$$ $$\longleftharp{xx}$$, $$\longrightharp{xx}$$,

This article presents a simple and low-cost fabrication method for creating circular microchannels using digital light processing (DLP) 3D printing and polydimethylsiloxane (PDMS) membrane inflation. The method produces smooth, controllable, and biomimetic channels suitable for vascular-on-chip or organ-on-chip applications.

Abstract

$$\rightleftharpoonup{xx}$$ $$\longleftharp{xx}$$, $$\longrightharp{xx}$$,

Microfluidic models mimicking the complex architecture of biological vessels require circular cross-sectional channels to accurately simulate hemodynamic conditions, shear stress, and cell behavior in native vasculature. Traditional soft lithography techniques typically yield rectangular channels, leading to non-physiological flow patterns and poor mimicry of the human circulatory system. Herein, we present an accessible hybrid fabrication method that integrates Digital Light Processing (DLP) 3D-printed master molds with a polydimethylsiloxane (PDMS) membrane inflation technique to produce high-fidelity circular microchannels. The primary goal of this protocol is to provide a cleanroom-free strategy for creating biomimetic vascular models with tunable stenosis geometries.

The proposed protocol comprises four essential stages: (1) Computer-Aided Design (CAD) of master molds incorporating a 10% height compensation to account for material shrinkage, (2) DLP 3D printing and post-processing of resin molds, (3) PDMS casting and oxygen plasma-assisted bonding to a thin elastic membrane, and (4) controlled pneumatic membrane inflation followed by a second PDMS casting to seal the circular structure. We demonstrated that this approach enables the precise tuning of channel diameters, which range from 300 µm to 1000 µm, by carefully modulating the internal inflation pressure. The performance of the resulting microchannels was evaluated through structural characterization, including cross-sectional circularity analysis, surface roughness measurement via scanning electron microscopy (SEM), and pneumatic burst testing to ensure bonding stability. Our findings indicate that this method supports the accessible and reproducible fabrication of circular microchannels, offering a robust platform for future research in vascular physiology, thrombosis modeling, and drug screening applications.

Introduction

$$\rightleftharpoonup{xx}$$ $$\longleftharp{xx}$$, $$\longrightharp{xx}$$,

Microfluidic systems mimicking biological blood vessels are vital for future research on vascular physiology, disease mechanisms, and drug interactions in vitro1,2. Among many existing structures in the body, circular cross-sectional geometries are crucial for accurately replicating hemodynamic conditions such as shear stress and flow patterns found in native vasculature3. Conventional fabrication methods, such as soft lithography or sacrificial molding using wires or needles, often yield rectangular channels or incomplete circular geometries, leading to flow distortion and poor physiological relevance4,5,6. Additionally, these approaches are time-consuming, prone to misalignment during multilayer assembly, and offer limited scalability when designing complex vascular-assembled microchannel networks with more than two branches7. However, recent advancements in additive manufacturing, especially digital light processing (DLP) 3D printing, have opened new opportunities for rapid and precise microchannel mold fabrication of complex structures, including circular microchannels8. In addition, DLP allows the printing of customized mold geometries with exceptional resolution, despite requiring no cleanroom facilities.

In this study, we present a novel, cleanroom-free fabrication strategy that integrates DLP 3D-printed molds, accompanied by the inflation of the polydimethylsiloxane (PDMS) membrane. Briefly, this hybrid protocol consists of: (1) design and fabrication of a half-channel mold to produce a semi-circular PDMS layer, and (2) bonding of this layer to a thin plastic membrane, followed by pneumatic inflation and second-layer casting to form a complete circular microchannel. This experimental procedure offers a straightforward, low-cost, and misalignment-free approach, which is more effective compared to other techniques in multilayer microfluidic assembly. Furthermore, the circularity of the obtained channels can be precisely controlled by adjusting the inflation pressure.

Besides these advantages, the proposed protocol also offers a rapid fabrication time (less than 4 hours). The obtained circular constructs are highly consistent across channel lengths with small diameters (e.g., 300 µm). In addition, experimental results in this work (i.e., surface roughness measurement, optical imaging, contact angle measurement, and pressure burst testing) have confirmed the structural integrity and fluidic compatibility, offering a promising future in fabricating complex vascular microchannel networks with astonishing reproducibility and adaptability. Finally, the proposed method is especially suitable for laboratories with limited access to cleanroom infrastructure and holds great potential for future advancements of vascular-on-chip, thrombosis modeling, and drug screening applications.

Access restricted. Please log in or start a trial to view this content.

Protocol

$$\rightleftharpoonup{xx}$$ $$\longleftharp{xx}$$, $$\longrightharp{xx}$$,

1. Fabrication of the master mold

  1. Master mold design
    NOTE: The microchannel master mold design was conducted using Fusion 360, which can be downloaded from the official website.
    1. Design the mold base.
      1. Open Fusion 360 and create a new sketch on the Oxy plane.
      2. Sketch an Origin-based corner rectangular outline (e.g., 30 mm × 30 mm) as the mold platform.
      3. Use the Fillet tool to fillet all the corners with a 3 mm radius.
      4. Use the Offset tool to offset the base outline inward 3 mm to create a wall outline.
      5. Use the Extrude tool to extrude all the base platform surface upward 2 mm to create a base. Extrude the wall platform upward 4 mm.
      6. Use the Chamfer tool with the Two Distance option in the Modify section to create a slope.
      7. Select the inner wall edges and set the first and second offset distances to 0.5 mm and 4 mm, respectively.
        NOTE: This step facilitates the PDMS chip demolding process later.
    2. Design the circular microchannel.
      1. Construct two offset planes that are 5 mm and 15 mm from the Oyz plane.
      2. On the 5 mm offset plane, draw a circle with a diameter of 1 mm with the center 2 mm offset from the Oxy plane.
        NOTE: The center of the circle should align with the upper surface of the base.
      3. Extrude the circular profile for 8 mm toward the inner side of the base to obtain the first side of the regular section of the microchannel.
      4. On the 15 mm offset plane, draw a circle with a diameter of 0.5 mm (or desired stenosis diameter) with the center 2 mm offset from the Oxy plane.
      5. Extrude the circular stenosis profile for 0.25 mm toward the regular section to obtain half of the stenosis of the microchannel.
      6. Use the Loft tool in the Create section to connect the regular section and the stenosis section to obtain a full half of the stenosis-regular circular microchannel.
      7. Use the Mirror tool with the 15 mm offset plane as the mirror plane to create the other half of the circular microchannel.
      8. Select the whole obtained circular microchannel body > right-click > select the Move/Copy option.
      9. Translate the microchannel body by 0.05 mm upward (or 10% of the stenosis diameter) along the Z-axis.
        NOTE: This step provides compensation height for the printing tolerance and results in an improved circular-shaped microchannel.
      10. Create four additional circular microchannels using the same method to decrease stenosis from 0.4 mm to 0.1 mm.
      11. Use the Pattern tool in the Create section to duplicate four additional regular sections and 4 additional circular stenosis profiles.
      12. Adjust the stenosis diameter profiles in sketches and apply the Loft tool for each microchannel.
      13. Translate the microchannel bodies to the 10% compensation height position.
    3. Export the microchannel master mold design as .STL file.
  2. DLP 3D printing
    1. Set up the machining parameters.
      1. Open Chitubox Software, select Open on the toolbar, and choose the master mold in .STL file
      2. Place the mold horizontally as the default on the software printing platform.
        NOTE: Check for Z-distance = 0, Angle = 0°.
        NOTE: Use the Make a copy option to place and print multiple molds in one go.
      3. Open the Print option on the toolbar and set Layer Thickness to 25 µm.
      4. Select the Slice option and wait for the slicing process to complete at the estimated printing time. Then select Print to proceed.
    2. Post-process the master mold.
      NOTE: There are two steps of washing with alcohol to remove all of the resin residue and achieve a less defective mold surface: (1) washing with ethanol, and (2) washing with isopropyl alcohol.
      1. Demold the master mold from the 3D printer base.
      2. Wipe off the printed construct with a paper towel, and then wash with 70% ethanol in a cup for 10 min.
      3. Fine-wash with 99% ethanol for 15 min at the washing station.
      4. Dry the mold at room temperature for at least 10 min.
        NOTE: Check for white irregular spots on the inner mold surface. If there is still white residue around the microchannels, repeat the fine-wash step one or two additional times.
      5. Expose the molds to UV light at an intensity of 20 mW/cm2 for 5 min for complete surface curing.
      6. Dry the molds in the oven at 65 °C for at least 12 h to evaporate any chemical residue and stabilize the surface.

2. PDMS casting and mold assembly

NOTE: PDMS-based microchannel fabrication is comprised of three primary stages: (1) PDMS casting of the first-half circular microchannels, (2) Membrane inflation, and (3) PDMS casting of the second-half circular microchannels.

  1. PDMS preparation
    1. Mix PDMS base and curing agent (e.g., SYLGARD 184) at a 10:1 weight ratio.
    2. Degas the mixture in a vacuum chamber for 10 min or until all bubbles are removed.
  2. Casting the First half-circular PDMS chip
    1. Place the 3D-printed mold on a level surface inside a Petri dish.
    2. Pour the degassed PDMS mixture over the mold until fully submerged (4 mm thickness above the half-circular channel).
    3. Cure the PDMS at 90 °C for 40 min9.
    4. Carefully remove the cured PDMS layer from the mold and trim edges if needed.
      NOTE: The PDMS chip now contains concave half-circular microchannels.
  3. Membrane bonding
    1. Cut out the plastic 25 µm-thick membrane as a 5 mm x 25 mm rectangle and remove the upper layer of the membrane.
    2. Clean the PDMS chip surface multiple times with transparent tape.
    3. Make an inlet near the tip of the microchannel using a 1 mm biopsy puncher.
    4. Place the PDMS chip and the membrane facing forward on the aluminium foil-covered platform. Gently put the platform inside the plasma cleaner.
    5. Turn on the vacuum pump for 60 s and then set the oxygen plasma level to 30 W with a pressure level of 0.3 Torr for 75 s.
    6. Turn off the plasma level and the vacuum pump.
      NOTE: Carefully detach the vacuum pump to prevent spillage caused by a sudden pressure change.
    7. Immediately align the microchannel on the PDMS chip and the treated face of the membrane.
      NOTE: Carefully position the two components to ensure proper alignment.
    8. Gently press the PDMS chip and membrane together.
      NOTE: Ensure that the microchannel is fully sealed beneath the membrane. Use tweezers or marks to help manually align. Do not delay more than 60 s post-plasma, or bonding efficiency might drop
    9. Place the bonded device in an oven at 90 °C for 20 min to stabilize the surface and enhance bonding strength.
  4. Membrane Inflation
    1. Set up the pressure recording system.
      NOTE: The pressure recording system is comprised of three components: (1) the electric syringe pump, (2) a laptop, and (3) the Arduino Mega 2560. The syringe is a 50 mL Luer-lock.
      1. Download the sensor reading code available in Supplementary File 1 and upload it to the Arduino board.
        NOTE: Check if the code is successfully compiled.
      2. Open the Tera Term Software to record the pressure log. From Setup > Serial Port > Speed > 115200.
      3. From File, choose Log to start recording the pressure over time.
      4. Select New/Overwrite to record a new log, and check the Timestamp box to write the pressure log with time marks.
      5. Select Browse to select the folder to save the pressure log.
      6. Hold the On/Off button on the electric syringe pump to turn it on, and press << to start setting up the pressure level.
      7. Connect a 1.1 mm diameter needle to the inlet of the PDMS chip and use flexible silicone tubes to connect to the outlet of the syringe pump.
      8. Set the pressure level at 30 mL/h and press the << to start the inflation process.
    2. Perform Membrane inflation and PDMS casting of the second-half circular microchannels.
      1. Start the inflation and monitor the pressure level in the microchannel via the Tera Term log.
      2. Stop the inflation process when the inner pressure reaches the desired level.
        NOTE: It is recommended that the inflation pressure range should be 0.0-17.5 kPa, since pressure levels exceeding 20 kPa may cause membrane rupture.
      3. Cast a 2-3 mm-thick layer of PDMS over the inflated membrane-PDMS structure.
      4. Apply continuous heating at 90 °C for 40 min to stabilize the inflated structure.
      5. Select Stop Logging on Tera Term to stop recording the pressure level when the second PDMS layer is completely cured.
      6. Save the pressure log file for experimental records and further investigation.

3. Characterization of the obtained PDMS vascular microfluidic chips

  1. Surface roughness characterization
    1. Perform digital 3D microscopy of mold and channel surfaces
      1. Use a 3D digital microscope system to characterize the surface topography of the fabricated PDMS chips and their corresponding DLP 3D-printed molds.
      2. Identify and mark three specific analysis regions for each sample.
        NOTE: Stenosis section of the microchannel (A1), regular channel section (A2), and external flat surface of the chip (control).
      3. Mount the sample on the microscope stage and adjust the focus to capture high-resolution 3D topography at each location.
      4. Acquire surface profile data using built-in software to generate roughness maps and extract average surface roughness (Sa) and peak-to-valley height variation (Sz).
      5. Export the topographic data and 3D visualization for comparison across varying printing conditions (e.g., orientation and layer thickness).
        NOTE: Pay attention to the sloped wall within the stenosis region, as surface features in this zone can significantly affect downstream flow behavior and shear stress distributions.
    2. Perform scanning electron microscopy (SEM).
      1. Use SEM to analyze the detailed surface morphology and microstructural fidelity of the PDMS-based microchannels.
      2. Carefully section the microchannel region using a sharp blade and mount the sample on aluminum stubs with conductive tape.
      3. Sputter-coat with gold or platinum for 60 s to reduce charging artifacts.
      4. Capture SEM images at multiple magnifications (e.g., 200× and 400×), targeting the stenosis region.
      5. Compare layer line visibility, wall smoothness, and contour transitions between vertically and horizontally printed mold-derived chips.
        NOTE: Stair-step artifacts in horizontally printed samples and directional ridges in vertically printed molds are important indicators of fabrication quality and flow fidelity.
  2. Geometric characterization of half and full-circular microchannels
    1. Prepare cross-sectional samples by cleanly slicing the PDMS chip perpendicular to the microchannel axis using a razor blade.
    2. Use a fluorescence microscope to capture the cross-sectional view of the microchannels.
    3. Load the images into the ImageJ software and use the line tool to measure H1, H2, and Wo manually.
      NOTE: H1: Height of the molded half-circular channel (bottom); H2: Membrane inflation height (top). Wo: Channel width at the base.
    4. Calculate geometric ratios (H1 + H2≈ Wo) to assess circularity and validate mold design versus inflation behavior.
      NOTE: Ideally, H1 and H2 are equal, and their sum should approximate Wo in a fully circular profile. Deviations signal inflation insufficiency or membrane overextension.
  3. Perform pneumatic bonding strength test
    NOTE: A pneumatic burst test is composed of five components: (1) an electric syringe pump, (2) a pressure sensor, (3) an Arduino Mega 2560 microcontroller, (4) a Serial communication cable, and (5) a laptop.
    1. Connect the pressure sensor to the PDMS microchannel inlet via a flexible silicone tube.
    2. Initialize the Arduino by uploading a serial data reading script.
    3. Launch the Tera Term software for pressure monitoring.
    4. Begin applying pressure incrementally by running the syringe pump (e.g., 40 mL/h).
    5. Record pressure data in real time. Continue until delamination, rupture, or visible leakage occurs.
    6. Define the burst pressure as the final recorded pressure value before structural failure. This value represents the bonding strength between the membrane and the molded PDMS chip.
  4. Measure the contact angle.
    1. Assemble a contact angle measurement setup using a digital side-mounted camera, a ring LED light source, and a laptop for image capture.
    2. Place a cured PDMS chip on a level glass platform under the camera.
    3. Dispense a 2 µL droplet of deionized water onto the PDMS surface using a micropipette.
    4. Capture the droplet profile immediately using the camera. Export the image for analysis.
    5. Open the image in ImageJ software, select Drop Analysis - LB-ADSA plugin in the Analyze section.
    6. Adjust the curve fitting to determine the contact angle.

Access restricted. Please log in or start a trial to view this content.

Results

$$\rightleftharpoonup{xx}$$ $$\longleftharp{xx}$$, $$\longrightharp{xx}$$,

This study presents a cleanroom-free protocol for fabricating full-circular PDMS microchannels using DLP 3D-printed molds and membrane inflation. The design of half-circular microchannel molds with varying stenosis diameters is illustrated in Figure 1, while the effect of printing orientation on mold resolution is outlined in Figure 2. A complete fabrication workflow from mold printing to inflation and second-layer PDMS casting is shown in F...

Access restricted. Please log in or start a trial to view this content.

Discussion

$$\rightleftharpoonup{xx}$$ $$\longleftharp{xx}$$, $$\longrightharp{xx}$$,

In this work, we developed a cleanroom-free fabrication protocol for circular PDMS microchannels using DLP 3D printing and membrane inflation. A critical step within this protocol is the integration of 10% height compensation in the CAD mold design to account for the inherent isotropic shrinkage of PDMS during thermal curing. Furthermore, the selection of printing orientations, specifically vertical orientation, is vital for minimizing the "stair-stepping" artifacts common in additive manufacturing. By printing v...

Access restricted. Please log in or start a trial to view this content.

Disclosures

$$\rightleftharpoonup{xx}$$ $$\longleftharp{xx}$$, $$\longrightharp{xx}$$,

The authors have nothing to declare.

Acknowledgements

$$\rightleftharpoonup{xx}$$ $$\longleftharp{xx}$$, $$\longrightharp{xx}$$,

The authors would like to thank International University, Vietnam National University, Ho Chi Minh City, for laboratory equipment and material support.

Access restricted. Please log in or start a trial to view this content.

Materials

List of materials used in this article
NameCompanyCatalog NumberComments
3D printerElegoo Saturn 3N/ADLP-based mold printing
3D printing resinJAMG HE, KoreaN/AResin for general DLP printing
Arduino microcontrollerArduino Mega 2560N/AUsed for burst test pressure monitoring
Digital 3D microscopeKeyence, USAVHX-7100Surface roughness characterization
Digital camera system Custom-madeN/AUsed for contact angle imaging
Electric syringe pumpFresenius SE & Co. KGaA, GermanyPILOT A2 CE2RS232Used for inflation during membrane shaping
Fluorescence microscopeNikon Eclipse Ti, USAN/AGeometric measurement of microchannel
Fusion 360 softwareAutodesk, USAhttps://www.autodesk.com/asean/products/fusion-360Design software
ImageJ softwareNational Institutes of Health, USAhttps://imagej.net/ij/Image analysis
PDMS base and curing agentDowhitech, Koreahttps://www.dow.com/en-us/pdp.sylgard-184-silicone-elastomer-kit.01064291zUsed for chip casting
PolydimethylsiloxaneSYLGARD 184 Silicone Elastomer Kit1330-20-7Used for chip fabrication
Pressure sensorNXPMPX5700APMeasures internal pressure during burst test
RAPID resinElegoo, China—Used for master mold fabrication
Scanning electron microscope (SEM)Jeol, JapanJSM T-100Surface morphology imaging
Silicone membrane (25 µm)——Used for membrane inflation

References

$$\rightleftharpoonup{xx}$$ $$\longleftharp{xx}$$, $$\longrightharp{xx}$$,
  1. Inagaki, S., Ishida, T. Fabrication of irregularity-free, highly circular cross-sectional microchannel. Micro. 2 (2), 325-333 (2022).
  2. Ma, Q., Ma, H., Xu, F., Wang, X., Sun, W. Microfluidics in cardiovascular disease research: state of the art and future outlook. Microsyst Nanoeng. 7 (1), 19(2021).
  3. Fleischer, S., Tavakol, D. N., Vunjak-Novakovic, G. From arteries to capillaries: approaches to engineering human vasculature. Adv Funct Mater. 30 (37), 1910811(2020).
  4. Li, Z., Hui, J., Yang, P., Mao, H. Microfluidic organ-on-a-chip system for disease modeling and drug development. Biosensors. 12 (6), 370(2022).
  5. Zhang, H., Yang, J., Sun, R., Han, S., Yang, Z., et al. Microfluidics for nano-drug delivery systems: from fundamentals to industrialization. Acta Pharm Sin B. 13 (8), 3277-3299 (2023).
  6. Oh, K. W. Microfluidic devices for biomedical applications: biomedical microfluidic devices 2019. Micromachines. 11 (4), 370(2020).
  7. He, Y., Wu, Y., Fu, J. Z., Gao, Q., Qiu, J. J. Developments of 3D printing microfluidics and applications in chemistry and biology: a review. Electroanalysis. 28 (8), 1658-1678 (2016).
  8. Qiu, J., et al. 3D printing of individualized microfluidic chips with DLP-based printer. Materials. 16 (21), 6984(2023).
  9. Miranda, I., et al. Properties and applications of PDMS for biomedical engineering: a review. J Funct Biomater. 13 (1), (2022).
  10. Kumar, P., Harvie, D. J. E. Energy dissipation during Wenzel wetting via roughness scale interface dynamics. Langmuir. 40 (31), 16190-16207 (2024).
  11. Pandian, N. K. R., Mannino, R. G., Lam, W. A., Jain, A. Thrombosis-on-a-chip: prospective impact of microphysiological models of vascular thrombosis. Curr Opin Biomed Eng. 5 (1), 29-34 (2018).
  12. Nguyen, T. Q., et al. Fabrication method of multi-depth circular microchannels for investigating arterial thrombosis-on-a-chip. Sens Actuators B Chem. 321 (1), 128590(2020).
  13. Nguyen, T. Q., et al. low-cost fabrication of circular microchannels by air expansion into partially cured polymer. Sens Actuators B Chem. 235 (1), 302-308 (2016).

Access restricted. Please log in or start a trial to view this content.

Reprints and Permissions

Request permission to reuse the text or figures of this JoVE article

Request Permission

Tags

Circular MicrochannelsStenosis FabricationOxygen Plasma BondingPneumatic Membrane InflationChannel Diameter TuningScanning Electron MicroscopyVascular Physiology

Related Articles