Building bridges—with 3D printing in mid-air
Our new research article in Elsevier’s Additive Manufacturing is online!
2025/11/07 by Alexander A. Altmann
Researchers at Measurement and sensor technology Group and partners present a simple recipe for printing self-supporting, single-layer polypropylene spans in mid-air that enclose cavities cleanly—and a model to predict the resulting surface quality before you print.
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![Schematic of the mid-air printed single-layer PP cap: 3D model with top and bottom surfaces and toolpath, extrusion spacing vs overlap, YZ cross-section of layers, and lateral profile showing overlap-controlled spacing and bonding.]()
Schematic of the mid-air printed single-layer PP cap: 3D model with top and bottom surfaces and toolpath, extrusion spacing vs overlap, YZ cross-section of layers, and lateral profile showing overlap-controlled spacing and bonding. -
![Nozzle-induced smoothing of the mid-air top layer during deposition—the tip flattens adjacent lines and reduces peak roughness (scale bar: 500 µm).]()
Nozzle-induced smoothing of the mid-air top layer during deposition—the tip flattens adjacent lines and reduces peak roughness (scale bar: 500 µm). -
![Top and bottom surfaces with cross section of a mid-air printed single-layer PP cap, showing a sealed cavity with enclosed air gap and ~200 µm layer thickness]()
Top and bottom surfaces with cross section of a mid-air printed single-layer PP cap, showing a sealed cavity with enclosed air gap and ~200 µm layer thickness (scale bars: 5 mm and 1 mm). -
![Overview of applications enabled by 3D-printed embedded cavity structures—spanning bioengineering, metamaterials, and sensor–actuator systems—from microfluidics and tissue scaffolds to antennas, energy harvesting, and acoustic/optical devices.]()
Overview of applications enabled by 3D-printed embedded cavity structures—spanning bioengineering, metamaterials, and sensor–actuator systems—from microfluidics and tissue scaffolds to antennas, energy harvesting, and acoustic/optical devices. -
![Model validation: predicted vs measured surface roughness and material distribution across flow rates, showing height partitioning (top/core/bottom) and A–F parameters (C̄, S̄, Rpk, Rk, Rvk) capturing intralayer bonding, surface material, and void volume trends.]()
Model validation: predicted vs measured surface roughness and material distribution across flow rates, showing height partitioning (top/core/bottom) and A–F parameters (C̄, S̄, Rpk, Rk, Rvk) capturing intralayer bonding, surface material, and void volume trends.
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Building bridges—in a special way: 3D printing in mid-air that cleanly seals cavities
Bridges matter—especially now. Our team shows how to print self-supporting, single-layer polypropylene spans in mid-air that enclose cavities cleanly on an off-the-shelf printer. We also provide a predictive model so you can pick parameters for the surface quality and bonding you want before you hit “print.”
What’s new Predictive model:
- Links flow rate, nozzle geometry, and line overlap to geometry, material distribution, and roughness of a mid-air top layer. It enables forward predictions and inverse parameter tuning.
- Validated on a standard printer: Using a Prusa i3 MK3S+ and PP, the team varied flow from 20 to 100 percent at 105 percent overlap to achieve fully closed surfaces without cracks.
- Surface you can dial in: With lower flow, the top “bridge” gets flatter and smoother—down to Ra = 4.52 ± 0.49 μm at 20% flow—while higher flow introduces waviness.
Why it matters
Enclosed air cavities are functional building blocks for microfluidics, sensors, and lightweight metamaterials. A mid-air, single-layer approach reduces stiffness and still achieves airtight closure with strong intralayer bonding (up to ~70 percent), enabling compact channels and sensitive membranes.
How to use it
1. Set overlap to ~105% for sealed surfaces,
2. choose a zigzag path with constant spacing,
3. lower flow (≤60%) to suppress roughness peaks via nozzle-induced smoothing, and
4. use the model to target a desired Ra or bonding level.
Paper details
The paper, titled “Self-supporting mid-air 3D printing of single-layer polypropylene structures: Flow rate-dependent analytical modeling and surface characterization,” appears in Elsevier’s Additive Manufacturing, Volume 113, 5 September 2025, 105010.
Link
Read the paper: Link
Citation
Altmann A. A., Suppelt S., Wüst P., Dörsam J. H., Latsch B., Flachs D., Blaeser A., Zhang X., Thielemann C., von Seggern H., Kupnik M. Additive Manufacturing, 113 (2025) 105010.
