Controlled light masking and tuned platinum catalysts make it possible to volumetrically 3D print silicone devices with open channels, eliminating molds and reducing fabrication time to minutes.
(Nanowerk Spotlight) Silicone elastomers are central to many technologies that bridge chemistry, biology, and engineering. They stretch without tearing, withstand heat and ultraviolet light, and stay chemically stable in contact with living tissues. These traits make them indispensable for microfluidic devices that handle tiny liquid volumes in medical diagnostics, drug development, and cell culture. Despite these advantages, fabricating silicone into intricate three-dimensional structures remains cumbersome.
Traditional fabrication methods rely on molding. Liquid silicone is poured onto rigid templates created by photolithography, a process that can replicate fine detail but is expensive, labor-intensive, and limited to mostly flat geometries. Each design iteration demands a new mold, delaying experiments and raising costs.
Layer-by-layer 3D printing approaches offer more freedom but introduce other flaws. Layers leave seams that scatter light and weaken parts. Some resins use acrylate chemistry that can damage cells if any unreacted material remains after curing.
A new technique called volumetric additive manufacturing (VAM) aims to bypass those limits. Instead of stacking layers, it cures an entire object at once by projecting a sequence of two-dimensional images through a rotating cylinder of liquid resin. Where the combined light dose reaches a threshold, the resin solidifies.
This process, also called computed axial lithography, is conceptually similar to medical CT imaging run in reverse: the computer calculates light projections that will create the desired shape. It can build solid parts within minutes and works well with viscous or light-scattering materials that frustrate standard printers.
Silicone chemistry should suit this method, yet a key obstacle has persisted. Many silicones cure by hydrosilylation, a platinum-catalyzed reaction that links silane and vinyl groups into flexible networks. When the catalyst is activated by light, it keeps working in the dark. This continuing or dark cure erases the boundary between the printed object and the liquid resin around it, closing tiny channels and distorting edges. Without precise control of where and how the catalyst activates, volumetric printing of silicone could not yield clear internal features.
The study presents a strategy to confine light activation and regulate cure timing. It introduces a projection design that keeps unexposed regions fully dark and a resin formulation whose gelation can be measured and predicted. Together, these methods make it possible to print silicone devices with open channels and to create instant molds in a matter of minutes.
Representative diagram of the volumetric additive manufacturing printers and the photocatalyzed hydrosilylation chemistry mechanism. (Image: Reprinted from DOI:10.1002/advs.202512300, CC BY)
In volumetric printing, each projected image contributes a small portion of the total light absorbed at every point within the rotating vat. A mathematical tool called the Radon transform converts the 3D model into the 2D projections required for this process.
Conventional optimization assumes that low light doses outside the target object are harmless because most photopolymers stop reacting as soon as exposure ends. Catalytic silicone resins violate that assumption. Even slight illumination in a nominally empty region can generate active platinum that continues curing in darkness.
To solve this, the researchers created a zero-dose mask. The algorithm calculates all light paths that pass through regions intended to stay liquid and sets their intensity to zero. These masked projections ensure that no light activates the catalyst in the voids. The approach prevents dark cure in channels and cavities while maintaining exposure in solid regions. A tradeoff appears near concave surfaces where light paths are blocked, leading to slight underexposure and minor feature distortion, which the authors quantify later.
The second part of the work focuses on the resin itself. The team tested three platinum catalysts and three photosensitizers under violet light at 405 nanometers, using photorheology to monitor the transition from liquid to gel. Photorheology measures how the resin’s mechanical stiffness changes during illumination, providing a direct readout of the point when the material first solidifies. Platinum acetylacetonate cured without added sensitizers but was unstable in ambient light. Trimethyl methylcyclopentadienyl platinum reacted too slowly even with sensitizers. The most effective system combined trimethyl pentamethylcyclopentadienyl platinum—known as PtCp*—with the sensitizer isopropylthioxanthone (ITX).
At 100 parts per million of PtCp* and 200 parts per million of ITX, the resin gelled in about 110 seconds under continuous 405-nanometer light. This composition provided rapid but controllable curing and remained stable until exposure. By varying light doses, the researchers determined that a total absorbed energy of roughly 500 millijoules per cubic centimeter ensured full solidification after a brief dark period. Lower doses gave incomplete curing; higher doses made little difference. This measured volumetric dose threshold became the operational target for scaling all projection intensities.
Using the optimized resin and masked projections, the team produced both millimeter-scale and micrometer-scale silicone structures. The millifluidic system used a digital light projector with a 14-micrometer pixel size and peak intensity of 58 milliwatts per square centimeter. The microfluidic setup used a focused laser with 5-micrometer pixels and 32 milliwatts per square centimeter at maximum intensity. Each resin-filled glass vial rotated inside a silicone oil bath with a matched refractive index to minimize light distortion.
Because the cured and uncured silicones have nearly identical refractive indices, the curing front was invisible. The operators relied entirely on the predicted dose map from the projection algorithm. After illumination, the samples rested for four to six minutes to let dark cure complete in the solid regions while the masked voids remained liquid. The parts were then extracted and rinsed. Tests with dyed water confirmed that the channels were open and continuous.
The same process was used to print negative molds for quick metal casting. A printed silicone cavity filled with molten gallium yielded a metallic screw, showing that the material’s heat resistance and elasticity were sufficient for temporary mold applications.
Resolution testing involved printing molds with channels of different diameters and filling them with wax to measure actual dimensions. Channels wider than 0.89 millimeters printed accurately. The 0.89-millimeter channel was present but narrowed to about two-thirds of its design size. Smaller channels failed to open completely, establishing a lower size limit for this configuration.
X-ray computed tomography provided a non-destructive view of internal geometry. Comparing scans with the original 3D models showed that deviations mostly followed the predicted dose distribution. For a representative millifluidic part, the average deviation from the model was −0.40 millimeters, while deviation from the predicted dose map was only −0.13 millimeters. Spiral artifacts visible inside the channels corresponded to shadows created as the rotating projection path passed behind dense regions.
Mechanical tests compared volumetric-printed silicone bars with cast controls made from the same resin. Both acted as flexible elastomers, but printed samples broke earlier and showed slightly lower tensile strength. The study attributes this difference to small deformations during removal from the viscous vat and to localized material buildup at narrow points. Because the process requires quick extraction to stop further dark curing nearby, mechanical uniformity remains a challenge for refinement.
The experimental outcomes demonstrate several key principles. Masking projections to enforce zero light dose in voids stops unwanted catalyst activation and prevents dark cure. A known volumetric energy threshold ensures consistent solidification across the object. The technique works with both projector-based and laser-based setups. Predictable distortions appear near concave or shadowed areas but match theoretical predictions, meaning they can be corrected by improved projection algorithms or modified rotation paths.
This work situates volumetric printing as a practical alternative to soft lithography and layer-based additive methods. Soft lithography remains reliable for flat microfluidic devices but demands clean-room fabrication and repeated mold production. Layer-based printing can build three-dimensional silicone architectures but often replaces the native silicone chemistry with acrylate systems that introduce unwanted reactivity. The method reported in Advanced Science preserves the hydrosilylation chemistry and yields fully cured, biologically compatible parts within minutes.
Remaining limitations are quantitative rather than conceptual. The current smallest channel size is just under one millimeter, spiral artifacts appear in shadowed regions, and mechanical properties trail those of cast samples. These weaknesses point to clear engineering tasks: refining projection optimization, extending real-time monitoring, and stabilizing the resin with inhibitors that delay unwanted cure. Adding fillers could further strengthen the elastomer without altering printability.
Volumetric printing that manages light exposure and catalyst behavior opens a realistic path to rapid silicone device fabrication. The ability to form entire structures at once rather than layer by layer can shorten design cycles for microfluidic experiments, soft robotic components, and biomedical test platforms.
By demonstrating that catalytic chemistries once thought incompatible with bulk illumination can be controlled through light management and energy thresholds, this study redefines what volumetric additive manufacturing can achieve. Silicone devices that once required molds or clean-room facilities may soon be produced directly in liquid form, fully cured and ready for use within minutes.
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Johanna J. Schwartz (Lawrence Livermore National Laboratory)
, 0000-0002-3709-6478 corresponding author
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