The promise of 3D printing has always been control, not just of shape but of substance. A new open-source tool from the University of Colorado Boulder moves that promise closer to reality by letting engineers design and fabricate continuous material gradients inside a single object.
The software, called OpenVCAD, compiles code that specifies both geometry and material fields, then hands those instructions to a gradient-aware slicer. In a peer-reviewed study published October 13 in Additive Manufacturing, the team describes how their approach converts complex volumetric gradients directly into printer-ready G-code, removing a major bottleneck. The work comes out of the Matter Assembly Computation Lab led by mechanical engineering professor Robert MacCurdy, with lead author and computer science PhD student Charles Wade.
In plain terms, the team is tackling a long-standing limitation of conventional CAD and slicing. Standard tools assume that everything inside a boundary is uniform. That is fine for single-material parts, but it breaks down for functionally graded materials, such as a shoe sole that transitions from stiff to soft, or a surgical model that blends cartilage-like and bone-like regions. OpenVCAD represents those gradients as mathematical functions in space, then a new slicer plans how to print them.
“In this work we present the first fully automated, functionally graded materials slicing framework that converts arbitrarily complex three-dimensional material fields directly into printer-ready G-code.”
The system offers two strategies. Strategy 1 keeps familiar perimeters, skins, and infill, but subdivides them by mixture ratio and applies automated seam “zippering” to avoid weak points where materials meet. Strategy 2 prints concentric iso-contours against the gradient to maximize fidelity, eliminating purge towers and reducing waste at the cost of discarding some traditional toolpath structures. Both strategies adapt printing parameters on the fly, including mixed filament ratios, toolhead changes, and nozzle temperature for foaming filaments.
That flexibility matters across printers. In demonstrations, the researchers generated graded parts on a two-material mixing hotend, a five-head tool-changer, and even a single-material system that uses temperature to alter density. In tensile tests, the team reports that Strategy 1 with zippering can reach strengths comparable to single-material prints, despite containing gradients.
The result is a design and manufacturing workflow that is both programmable and reproducible. Engineers can define a gradient once, then re-slice the same design for different machines with only minor changes to the G-code writer. That portability opens doors for soft robotics, impact-absorbing lattices, medical models that emulate tissue feel, and printed devices whose electromagnetic behavior depends on precise spatial blends of conductive and dielectric materials.
A shift from surfaces to volumes
Traditional CAD is surface-first. You draw boundaries, export meshes, and let the slicer fill the interior. OpenVCAD flips the hierarchy. It treats the object as a volume where any point can carry a material value or a temperature setpoint. The slicer samples those fields with iso-contouring, then assigns paths and process parameters that respect both the shape and the gradient. In practice, that means less hand-tuned G-code and more consistent prints across complex transitions.
It also means faster iteration. Change one variable and the entire material distribution updates. In the lab’s color palette demos, for example, gradients curve and twist through space like braided taffy, yet the printed parts track those paths cleanly. For lattice structures, designers can tune stiffness locally by varying mixture ratios at the strut scale, rather than designing separate subparts.
“This work provides a robust, open-source, and automated framework for designing and fabricating advanced FGMs, accelerating research in multi-material additive manufacturing.”
Open toolchain, immediate use
OpenVCAD is available for researchers and industry to try today. It includes a Python implementation so users can import the package, write functions that describe geometry and material fields, and export printer-ready files. The team emphasizes that the slicer targets any G-code-based system; adapting to a new platform often involves only tweaking command syntax in the output writer.
The stakes are practical. Multi-material printing is moving from novelty to necessity in fields like prosthetics, robotics, and device packaging. Continuous gradients can reduce stress concentrations, merge disparate functions in one build, and cut waste from purging. By providing a common language to describe and fabricate those gradients, OpenVCAD shifts multi-material printing from manual craft to repeatable engineering.
Journal reference and DOI:
Additive Manufacturing: 10.1016/j.addma.2025.104963
ScienceBlog.com has no paywalls, no sponsored content, and no agenda beyond getting the science right. Every story here is written to inform, not to impress an advertiser or push a point of view.
Good science journalism takes time — reading the papers, checking the claims, finding researchers who can put findings in context. We do that work because we think it matters.
If you find this site useful, consider supporting it with a donation. Even a few dollars a month helps keep the coverage independent and free for everyone.