Researchers 3D Print New Structures Directly Onto Existing Objects in Seconds

Printing onto what is already there

Most 3D printers start from a blank build plate. A team of researchers has now demonstrated a system that can print new structures directly onto existing objects made of metal, glass, or even assembled electronics, all in a matter of seconds.

The breakthrough relies on an upgraded form of tomographic volumetric additive manufacturing, or TVAM. Instead of laying down material layer by layer, the system projects calculated light patterns into a rotating vat of photosensitive resin. The entire object solidifies at once, so centimeter-scale parts can emerge in seconds rather than hours.

The light-modeling problem

Volumetric printing has always struggled with overprinting, the act of adding new material onto something that is already inside the resin vat. Existing objects block, scatter, or bend incoming light. Previous software treated those objects as either fully transparent or fully opaque, which produces blurry or failed prints in realistic scenarios.

The team, led by researchers from several institutions, built a new computational framework called Dr.TVAM. It uses physically based ray tracing to model how light reflects, refracts, scatters, and absorbs as it passes through different materials. The software also accounts for the shape of the container holding the resin.

With that model in place, the printer can calculate light patterns that successfully build around metal rods, glass spheres, and preassembled microfluidic chambers without ruining the geometry.

What they demonstrated

The researchers ran four proof-of-concept experiments. First, they printed microscopic fluid channels inside sealed, preassembled square chambers. The channels included straight paths, branching networks, and spiral shapes. Colored dye flowed through the finished structures, confirming they were leak-free.

Second, they embedded two tiny glass spheres inside a hydrogel-filled chamber. Two camera images located the spheres in three dimensions, and the software generated custom print patterns in under a minute. The printer then built hollow channels connecting each sphere to inlet and outlet ports, plus protective cavities around the spheres themselves. From detection to finished print, the whole workflow took less than three minutes.

Third, they printed a precision gear directly onto a polished steel rod. When the software ignored light scattering from the metal, the gear's fine holes came out over-polymerized and poorly defined. When the realistic optical model was enabled, the gear preserved its features with much higher fidelity.

Fourth, they printed a miniature lens and a small cross-shaped symbol directly onto the surface of a working red LED. When the LED illuminated, the lens projected the symbol onto a screen, turning the component into a tiny optical projector without any extra assembly.

Why it matters

The work remains laboratory-scale, but the implications are broad. Biomedical researchers could eventually print sterile microfluidic channels inside pre-assembled diagnostic devices without introducing contamination during manual assembly. Optical engineers might integrate lenses directly onto light sources during manufacturing. Repair crews could add custom brackets or fittings to existing metal parts without redesigning the entire component.

The software is open source, released with configuration files and experimental data so other labs can reproduce and extend the work. The researchers plan to add further physical effects, including changes in refractive index during polymerization and chemical inhibitor diffusion, to improve accuracy on more complex prints.

The study appears in Nature Communications under the title "Overprinting with tomographic volumetric additive manufacturing."