Volumetric additive manufacturing (VAM) — the technique that projects a rotating series of light patterns into a spinning vat of resin to solidify an entire object at once, rather than layer by layer — has always had a dirty secret: it runs hot enough to cook itself. A new paper published in Nature Communications on July 9, 2026 by researchers at the University of Nottingham and UC Berkeley says they've found a fix, and it comes not from better optics or smarter software, but from rethinking the resin's chemistry itself.

The team, led by Research Fellow Eduards Krumins and Professor of Materials Chemistry Derek Irvine at Nottingham's Additive Manufacturing Research Group, added a small amount of a RAFT (reversible addition-fragmentation chain transfer) polymerization agent to standard VAM resin. The additive acts, in Krumins' words, as a "regulator" on the runaway polymerization reaction that has limited how fine and how fast volumetric printing can go. In testing, it cut the resin's internal temperature rise from over 60°C down to a fraction of that — and let the team print separate parts sitting just 150 micrometers apart without those parts melting into a single fused blob.

The Trommsdorff Problem

To understand why this matters, it helps to know what volumetric printing has been fighting ever since the arrival of computed axial lithography (CAL), the specific volumetric method used here. Unlike SLA or DLP, where a laser or projector cures one thin layer at a time and the heat from each exposure has time to dissipate, CAL delivers a full 3D dose of light energy into the vat almost simultaneously, from many angles, to solidify an entire object in one continuous pour. That speed is the whole appeal: no layer lines, no support structures for many geometries, and print times measured in tens of seconds rather than hours.

But concentrating that much photopolymerization into one volume at once creates a chemistry problem called the Trommsdorff effect, also known as autoacceleration or the gel effect. As acrylate resin — commonly pentaerythritol tetraacrylate in these formulations — begins to polymerize, the growing polymer chains make the liquid more viscous. That rising viscosity physically traps the reactive radical ends of growing chains, preventing them from finding each other and terminating the reaction normally. With termination throttled, but new chains still being initiated by light, the reaction accelerates rather than dying down. And an accelerating exothermic reaction generates heat faster than it can escape, which further speeds the reaction — a feedback loop that, according to the VoxelMatters report by Joseph Caron-Dawe published July 10, pushed standard CAL resin's temperature up 59°C in the team's tests. That's enough heat to keep curing resin well outside the intended light pattern, a phenomenon printmakers call overcuring: features blur, fine gaps between parts fill in and fuse, and the crisp geometric control that's supposed to be CAL's selling point falls apart.

What RAFT Actually Does

RAFT polymerization isn't new chemistry — it's a well-established method for controlling how polymer chains grow in conventional plastics and coatings manufacturing. What's novel here is applying it inside a light-cured VAM resin during the print itself. A RAFT agent works by reversibly capping growing polymer chains: instead of a chain either propagating uncontrolled or terminating permanently, RAFT lets chains repeatedly deactivate and reactivate. That reversible capping effectively caps the rate at which the reaction can run away, acting as the "regulator" Krumins describes — smoothing out the exotherm instead of letting it spike.

The numbers from VoxelMatters' account of the paper are stark. Standard resin with no RAFT agent saw temperatures climb 59°C during the volumetric exposure. Adding just 0.1% of the RAFT agent CPBD to the pentaerythritol tetraacrylate resin cut that rise to 27°C. Pushing the loading to 0.3% brought the temperature rise down to just 3.5°C — roughly a 94% reduction from baseline. Thermal and shadowgraph imaging backed up the numbers visually: the standard resin showed overcuring artifacts within minutes of exposure, while the RAFT-modified resin showed none, even after two minutes under the same light dose.

What It Means for Makers

None of this shows up as a new machine you can buy this year — CAL and other volumetric printing systems remain largely research-lab and industrial hardware, not desktop units. But it matters for anyone tracking where fast, layerless printing is headed, for a few concrete reasons.

First, resolution and part density. The 150-micrometer separation the team demonstrated between adjacent parts is a meaningful number for volumetric printing specifically, because CAL's big promise has always been the ability to print multiple free-floating or interlocking parts in a single vat in one shot — think nested mechanisms, lattices, or assemblies that never need supports because they're surrounded by uncured liquid resin the whole time. Overcuring has been the thing standing between that promise and reality; if neighboring geometry keeps fusing, you can't pack a build volume densely. A chemistry fix that solves this without touching the optics or the printer hardware is the kind of unglamorous, foundational fix that tends to unlock everything built on top of it.

Second, it's a resin formulation change, not a hardware change, which historically means it's easier and cheaper to propagate once a photoinitiator/monomer supplier picks it up — no new light engines, no new rotation stages, no firmware changes, just a different bottle of resin with a RAFT agent mixed in at low single-digit-percent loading.

Third — and this is the part likely to matter most for bioprinting and multi-material work down the road — the researchers note that RAFT chemistry leaves reactive end groups on the finished polymer chains, rather than fully quenching them the way conventional free-radical cure does. That opens the door to post-print chemical modification: grafting on antibacterial coatings, functional surface chemistry, or additional material layers after the object has already been solidified. For bioprinting in particular, where printed scaffolds often need functionalization after the fact to support cell growth or deliver drugs, having chemically "live" end groups built into the base resin rather than added in a separate step is a genuinely useful capability, not just a curiosity.

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