Volumetric 3D printing of a fluoropolymer and closed-loop chemical recycling of its fluorinated content

Domain: chemistry
Published: 2026-03-19
Editorial outcome: major_revision

Abstract
Fluorinated polymers are indispensable in fields such as microfluidics, electronics, and biomedical engineering. Yet, their chemical stability leads to long-term environmental persistence, rendering end-of-life management essential. In parallel, their insolubility and lack of melt behavior complicate fabrication into complex geometries, restricting their use in 3D printing. Here, a fluorinated photoresist is introduced that enables tomographic volumetric 3D printing with closed-loop chemical recycling of its fluorinated content. The photoresist—based on an alkene-functionalized fluorinated diol and a multifunctional thiol—supports rapid fabrication of centimeter-scale objects with reproducible feature sizes down to 56 μm, among the smallest reported to date. Selective urethane hydrolysis under alkaline conditions yields ~97% recovery of the fluorinated monomer. The recovered monomer is re-functionalized and reprinted without loss of print fidelity, thermal stability, or mechanical performance. Volumetric 3D printed parts are biocompatible in vitro, supporting potential biomedical use. This represents the first demonstration of high-resolution tomographic volumetric printing of a fluoropolymer with closed-loop chemical recycling of its fluorinated content.

Introduction
Fluorinated polymers are indispensable across a broad spectrum of applications due to their unique physicochemical properties. These properties originate from the exceptional bond strength of the carbon–fluorine bond (485 kJ mol⁻¹) and the small van der Waals radii of fluorine atoms, which give rise to low surface energy, low dielectric constants, and pronounced chemical inertness. As a result, fluoropolymers exhibit outstanding resistance to chemical degradation, high thermal stability, low friction coefficients, electrical insulating behaviour, and intrinsic non-flammability.1–3 Consequently, fluorinated polymers are indispensable in sectors such as aerospace and aviation, automotive, electrical and electronic systems, medical devices, industrial coatings, microfluidic systems, semiconductor manufacturing, and cookware.4–7

At the same time, the chemical robustness that makes these materials so effective also contributes to long-term environmental persistence and bioaccumulation, underscoring the need for effective end-of-life strategies.3,8–10 Traditional recycling routes are generally ineffective, and the development of fluoropolymers that can be depolymerized or chemically reprocessed remains a significant challenge.9,11 Recent advances have demonstrated mineralization of fluorinated polymers such as PTFE under solvent-free mechanochemical conditions, enabling fluoride recovery.12 While such approaches point toward a circular fluorine economy, they remain destructive and have yet to be integrated into 3D printing.

A major barrier to integrating fluoropolymers into modern 3D printing platforms lies in their intrinsic processing limitations. Most fluorinated polymers are insoluble in common solvents and do not exhibit melt behavior, precluding both extrusion- and solution-based processing.13 For example, PTFE degrades near its softening point and cannot be thermoplastically reshaped. As a result, the fabrication of fluorinated components typically relies on subtractive methods, cold compaction, or sintering—processes that limit design freedom, generate waste, and inhibit miniaturization.14 These constraints are particularly restrictive in fields that demand precise, complex, and on-demand geometries.

3D printing offers a solution, but implementation with fluoropolymers remains limited. Strategies such as incorporating PTFE nanoparticles into thermoplastic matrices (e.g., PLA, PA12) for fused deposition modeling (FDM) or using shear-thinning suspensions for direct ink writing (DIW) have enabled partial integration of fluoropolymer-like properties into printable materials.15 However, the achievable resolution and structural fidelity remain modest, and the materials often lack the chemical performance of the parent fluoropolymer. Light-based 3D printing methods, on the other hand—including stereolithography (SLA), two-photon polymerization (2PP) and digital light processing (DLP)—have enabled sub-100 μm features in fluorinated materials by using photoresists containing fluorinated monomers or PTFE dispersions.16–20 Nonetheless, the layer-by-layer nature of these techniques imposes speed limitations and restricts the formation of isotropic geometries with high design freedom. Finally, and importantly, the highly crosslinked nature of the resulting networks has thus far precluded end-of-life strategies for recovering the fluorinated content.

To address both the processability limitations and the lack of end-of-life management associated with fluoropolymers, we introduce a fluorinated photoresist that enables tomographic volumetric 3D printing and closed-loop chemical recycling of its fluorinated content. Tomographic volumetric 3D printing—also referred to as computed axial lithography—offers a fundamentally different approach: by projecting computed light fields into a rotating resin volume, the technique enables the fabrication of centimeter-scale, geometrically complex objects within tens of seconds and with tens-of-micrometer resolution.21–25 The photoresist combines a thiol–ene crosslinkable fluorinated photoresist with a targeted hydrolytic degradation mechanism, allowing recovery of the fluorinated monomer, refunctionalization, and reprinting, without loss of performance. While we report a single-system exemplar which we follow through tomographic volumetric 3D printing, fluorinated monomer recycling, refunctionalization, and reuse, the reported workflow is modular and can be adapted by others to different fluorinated precursors. By integrating recyclability into a volumetric printing workflow, this work overcomes long-standing barriers in both fluoropolymer processing and end-of-life management, establishing a new pathway toward sustainable 3D printing of complex, and on-demand fluorinated components.

Results
1. Synthesis of alkene-functional fluorinated monomer for thiol–ene crosslinking

To enable volumetric 3D printing of fluorinated networks, a thiol-ene photoreactive precursor was synthesized from the perfluorinated diol 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluoro-1,10-decanediol (HDF-OH). The alkene-functionalized derivative (HDF-ENE) was prepared via the nucleophilic addition of the alcohols of HDF-OH to the isocyanate of allyl isocyanate using tin(II) octanoate as a catalyst (Figure 1a).

After reacting overnight at 40 °C, the product was isolated by mixed-solvent recrystallization in 80% yield. ¹H NMR spectroscopy confirmed 98.7% conversion, as evidenced by the downfield shift of the hydroxyl-adjacent methylene protons from δ = 4.0 ppm to δ = 4.8 ppm upon urethane formation (Figure 1b). Characteristic alkene resonances were observed at δ = 5.1 and 5.8 ppm (Figure 1c), confirming successful functionalization. Quantitative 1H NMR spectroscopy using dimethyl terephthalate as an internal standard determined an alkene content of 3.19 × 103 mol/g, corresponding to 100.2% substitution of the hydroxyl functionalities. Moreover, FTIR spectroscopy was used to confirm the successful functionalization of the fluorinated diol (HDF-OH) to the alkene-functionalized product (HDF-ENE) as illustrated in Figure 1d. Upon urethane formation, the broad O–H stretching band observed around 3350 cm⁻¹ in HDF-OH disappeared, indicating consumption of the hydroxyl groups. Simultaneously, the appearance of a sharp N–H stretching vibration around 3300 cm⁻¹ and a characteristic urethane carbonyl (C=O) stretch near 1700 cm⁻¹ provided clear evidence of urethane bond formation. Additionally, new C=C stretching bands associated with the alkene moieties appeared near 1645 cm⁻¹, confirming the successful incorporation of the alkene functionality required for subsequent thiol–ene crosslinking. LC–MS analysis further confirmed the successful synthesis of the alkene-functionalized fluorinated monomer (HDF-ENE). The compound eluted as a single peak at approximately 2 minutes, consistent with a well-defined molecular species (Figure 1e). The mass spectrum showed a dominant signal at m/z = 629, corresponding to the protonated molecular ion [M+H]⁺, as well as a secondary peak at m/z = 646, attributed to the ammonium adduct [M+NH₄]⁺. These results confirm the expected molar mass and purity of the functionalized product.

Allyl isocyanate end-capping was used because it is robust, operates under mild conditions, and scales well. The reaction selectively functionalizes terminal diols while avoiding the chain extension common to diisocyanate/diol couplings.26 Finally, the introduced alkene end groups enable step-growth thiol–ene crosslinking that is oxygen-tolerant, yields uniform and low-shrinkage networks with improved toughness compared to more conventional (meth)acrylate crosslinking (vide infra).

2. Development and optimization of a fluoropolymer-based photoresist for volumetric 3D printing

Following the synthesis of the alkene-functionalized fluorinated monomer (HDF-ENE), a photoresist formulation was developed specifically for tomographic volumetric 3D printing. Formulation parameters were optimized to meet the fundamental requirements of volumetric 3D printing, including photokinetics for rapid polymerization, adequate viscosity to suppress sedimentation during irradiation, and high optical transparency to ensure uniform dose delivery across the print volume.

The photocurable system was based on a thiol–ene formulation comprising HDF-ENE and the tetrafunctional thiol pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) in a stoichiometric thiol-to-ene ratio. Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) served as the radical photoinitiator, activated by exposure to 405 nm light. A small amount of high molar mass polyethylene glycol (PEG1M) was included as a viscosity modifier. The structures of all components are shown in Figure 2a.

To ensure accurate dose delivery during tomographic exposure, the photoinitiator concentration was determined using Beer–Lambert calculations together with the optical-compensation range of the printer software at 405 nm (Figure 2b). The Tomolite/Apparite reconstruction compensates attenuation up to a Napierian absorption coefficient μ = 2.0 cm⁻¹; we therefore selected a resin absorbance near this upper bound. In base-10 terms this corresponds to A = μ/ln 10 ≈ 0.87 cm⁻¹, consistent with the measured UV–Vis absorbance of ≈ 0.85–0.87 cm⁻¹ for the final formulation (Section S1.1 and S1.2). This choice maximizes photoreactivity while remaining within the instrument’s compensation envelope.

Resin viscosity was tuned to suppress gravitational sinking.22 A screening of PEG1M (Mₙ ≈ 10⁶ g mol⁻¹) from 0 to 1.25 w/v% identified 1.25 w/v% as the minimum loading that eliminated visible sedimentation over a 3 s window after volumetric 3D printing was completed (Supplementary Movies 1–6 and Supplementary Fig. S4-S5). Moreover, viscosity increased markedly, from 0.1 Pa s to ~103 Pa s, with the introduction of 1.25 w/v% PEG1M, as shown by rheological measurements (Refer to Section S1.3, Figure S5). Accordingly, 1.25 w/v% PEG1M was used for all prints to stabilize the resin during exposure (Figure 2c).

Following attenuation and viscosity optimization, the resin formulation was evaluated using photorheology to characterize its polymerization kinetics, assess its suitability for tomographic volumetric 3D printing, and determine the optimal light dose. The photorheological framework applied here is based on our previously established methodology that enables quantitative correlation between resin kinetics as determined by photo-rheology and the optimal parameters for tomographic printing.22

The time-resolved rheological response under constant irradiation at 405 nm revealed an initial latency period of approximately 10 seconds, during which the storage modulus (G′) decreased despite continuous light exposure (Figure 2d). This latency phase allows the photoresist to accumulate dose without premature network formation and is essential for achieving sharp voxel boundaries in tomographic volumetric printing. In conventional thiol-ene systems, an external radical scavenger such as TEMPO is often required to delay gelation and enhance dose contrast, due to the lack of oxygen inhibition.22,27 However, in the present formulation, the observed latency period emerged intrinsically from the resin composition, without the need for added inhibitors.

Two hypotheses were considered for the rheological latency: (i) a PEG1M-induced viscosity barrier that delays network formation, and (ii) the intrinsic gelation threshold of step-growth thiol–ene networks. Matched photorheology on formulations with and without PEG1M yielded the same latency period, excluding hypothesis (i) (Section S1.4). We therefore attribute the latency primarily to hypothesis (ii): by Flory–Stockmayer theory, an elastically percolated network forms only beyond ~58% functional-group conversion for a tetrafunctional thiol with a bifunctional alkene.28,29 However, it should be noted that the stated hypothesis should be interpreted with caution, as the onset and magnitude of the latency can be affected by other factors (e.g., fluorinated-backbone solvation, oxygen solubility, the solvent environment, local microstructure, and light intensity-dependent kinetics). Fully disentangling these contributions lies beyond the scope of the present study. Separately, the small decrease in G′ observed immediately after illumination but prior to gelation is consistent with a modest reaction exotherm that transiently raises temperature, lowers viscosity, and increases mobility.

To identify a suitable volumetric 3D printing light dose, photorhelogy and volumetric printing were wavelength- and irradiance-matched (405 nm in both cases; ≈ 9.5 mW cm⁻² at the rheology sample and 9.56 mW cm⁻² average in volumetric 3D printing). In combination with a computational contrast of 0.5–an appropriate computational contrast for most designs in tomographic volumetric 3D printing–dose thresholds, at which in-part voxels begin to gel while out-of-part voxels remain sub-gel, can be established. The middle of this range then corresponds to the selected light dose of 180 mJ cm⁻², at which in-part voxels are sufficiently cured to resist gravity-driven collapse while out-of-part voxels remain below the gelation threshold.22 This photorheological framework does not account for attenuation across the ~7 mm path during tomographic printing or for sedimentation, owing to the small rheometer gap (~300 µm) and static geometry. These two factors were therefore addressed separately before applying the photorheological window—attenuation by setting the photoinitiator concentration via Beer–Lambert calculations for the vial geometry (Section S1.1 and S1.2), and sedimentation by viscosity tuning with PEG1M (Section S1.3).22

At the established light dose of 180 mJ cm-2, the resin enabled high-resolution tomographic printing across multiple geometries. Rather than quoting a single minimum, we report condition-bound, reproducible features with explicit CAD linkage: the smallest measured features across our test set are ~56, ~66, ~97, and ~254 μm at the indicated locations (Figure 3a). Benchmarked against a curated literature screen, these values lie among the smallest polymer features reported to date for tomographic volumetric 3D printing and—within fluorinated photoresists—appear to be the smallest (Section S3).

The optimized resin formulation enables the volumetric fabrication of high-resolution fluorinated structures with potential across a broad spectrum of applications (Figure 3b). To showcase this versatility, distinct designs were fabricated that reflect the specific fields. In the biomedical context, vascular-like and porous scaffolds were printed. Aligned with these biomedical exemplars, the printed materials were shown to meet the ISO 10993 criterion for non-cytotoxicity in vitro, performing comparably to a PTFE benchmark (Supplementary Information, Section S2), supporting the use of the developed material in a biomedical context. For industrial applications, fluorinated spacers were integrated into electronic assemblies, demonstrating the potential for on-demand fabrication of custom-sized gaskets or bearings. In the microfluidics domain, optically clear microfluidic channels were produced. While these examples highlight biomedical, industrial, and microfluidic implementations, the combination of resolution, print speed, and recyclability points to broader utility across sectors requiring high-fidelity fluorinated structures.

3. Recycling of volumetrically 3D printed fluoropolymer-based constructs

The development of durable polymers must increasingly be accompanied by strategies that address their end-of-life management. To that end, hydrolytically cleavable urethane linkages were positioned adjacent to the non-degradable fluorinated backbone during functionalization. These hydrolytically cleavable handles provide the opportunity to recover the fluorinated monomer post-printing. The monomer can be re-functionalized and reintroduced into the resin formulation without loss of performance, thereby demonstrating the feasibility of a closed-loop circular material lifecycle compatible with volumetric 3D printing (Figure 4a).

Importantly, while urethane bonds are hydrolytically cleavable under strongly basic conditions (e.g., 5 M NaOH), they are known to degrade only slowly under neutral conditions, with reported degradation half-lives in the order of decades.30 In addition, the thiol crosslinker employed (PETMP) contains ester functionalities, which may also be susceptible to hydrolysis under prolonged aqueous exposure. As such, the overall hydrolytic stability of the network may depend on both environmental conditions and the specific chemical composition. The use of an alternative crosslinker lacking ester groups could further limit this susceptibility while preserving the selective degradability enabled by the urethane linkage.

The closed-loop cycle involves initial functionalization of HDF-OH into HDF-ENE, photopolymerization into a thiol–ene crosslinked network (HDF-X), and subsequent alkaline degradation to HDF-OH (Figure 4b). Under these alkaline conditions, urethane bond cleavage releases HDF-OH along with pentaerythritol and 3-((3-(carboxyamino)propyl)thio)propanoic acid, the latter of which is expected to undergo decarboxylation to form 3-((3-aminopropyl)thio)propanoic acid. These byproducts are separated from the fluorinated monomer through neutralization and subsequent solvent extraction. Since the herein reported work targets closed-loop recycling of the fluorinated content, the non-fluorinated components (crosslinker and photoinitiator) are replenished in subsequent cycles. Consequently, the recyclable mass fraction is determined by the fluorinated diol’s molar mass, amounting to ~52% for M of 462 g.mol-1 (the fluorinated mass fraction of the network) and increasing to ~82%, ~90%, ~93%, and ~95% for M 2 000, 4 000, 6 000, and 8 000 g mol⁻¹, respectively (Supplementary Information, Section S4.1).

After establishing a general workflow—alkaline reflux depolymerization, neutralization, purification, and drying— through which the fluorinated diol could be recovered from volumetrically 3D printed constructs, the degradation conditions were optimized to maximize the chemical recycling yield of the fluorinated diol (Section S5). More precisely, a condition screen at 85 °C was performed across NaOH concentrations of 1.0, 2.5, and 5.0 M and depolymerization times from 0.5–16 h, executing the complete sequence for every timepoint. The optimal condition (2.5 M NaOH for 3 h) afforded a recovery of 97.4 % ± 2.1 % (n = 3). At this per-cycle recovery, the theoretical retained fraction after ten recycle–reuse cycles is ≈76.8 % of the original fluorinated content (see Supplementary Information, Section S5, for the full data and calculations).

The recovery–time profiles delineate two regimes, depicted in Figure S10. In the kinetic regime, yield increases to a concentration-dependent maximum that is reached earlier at higher [NaOH] (5 M: ~1–1.5 h; 2.5 M: ~3 h; 1 M: no maximum within 16 h). This trend is consistent with base-catalyzed urethane cleavage in which the apparent rate scales with hydroxide activity (pseudo-first-order, 𝑘 ≈ 𝑘 [OH−]). Beyond the maximum, the isolated yield declines at 2.5–5 M and approaches a plateau. It is hypothesized that the gradual formation of crosslinked/aggregated side-product particulates during prolonged alkaline treatment physically entrap a fraction of the fluorinated diol and resist subsequent extraction. Once the population of such particulates saturates, the recovery approaches the observed plateau. The optimum at 2.5 M, 3 h therefore marks the intersection of fast cleavage kinetics with minimal secondary entrainment, resulting in a recycling yield of the fluorinated monomer of 97.4 % ± 2.1 % (n = 3).

Structural integrity of the recovered HDF-OH was confirmed by ¹H NMR spectroscopy and LC–MS (Figure 4c), and the re-functionalized HDF-ENE —obtained via reaction with additional allyl isocyanate— exhibited the expected chemical structure evidenced by FTIR, 1H-NMR, and LC-MS (Supplementary Information, Section S3). Finally, for reprinting, PETMP is reintroduced according to a 1:1 thiol-to-ene ratio.

4. Characterization of pristine and recycled volumetrically 3D printed fluoropolymer-based constructs

Since the recycling strategy restores the monomeric precursor while maintaining the molecular integrity, identical network properties are theoretically expected upon functionalization and reprinting. To experimentally verify this, both pristine and recycled volumetrically 3D printed constructs were subjected to thermogravimetric analysis (TGA) to evaluate thermal stability, differential scanning calorimetry (DSC) to determine thermal transitions and crystallinity, tensile testing and dynamic mechanical analysis (DMA) to probe mechanical performance.

Thermogravimetric analysis (TGA) demonstrated identical thermal degradation profiles within experimental resolution for both pristine and recycled materials (Figure 5a). The temperature at 2% mass loss was 294.8 ± 2.7 °C for pristine and 294.3 ± 1.9 °C for recycled constructs, indicating that thermal stability was fully retained after recycling. Differential scanning calorimetry (DSC) showed that the thermal properties of the recycled and pristine samples were statistically indistinguishable within experimental variation (Figure 5a, p > 0.05). The glass transition temperature (T ) was 1.3 ± 0.5 °C for pristine and 3.6 ± 2.7 °C for recycled samples, the melting temperature (T ) was 64.2 ± 1.8 °C and 66.3 ± 1.0 °C, and the crystallization temperature (T ) was 55.0 ± 1.0 °C and 56.0 ± 0.3 °C, respectively. The melting enthalpy (ΔH ) and crystallization enthalpy (ΔH ) were 5.58 ± 0.1 J g⁻¹ and 6.93 ± 0.7 J g⁻¹ for the pristine samples, and 4.1 ± 2.6 J g⁻¹ and 5.0 ± 3.3 J g⁻¹ for the recycled samples.

In addition to their thermal stability, the mechanical properties of the pristine and recycled volumetrically 3D printed fluoropolymer constructs were also preserved. Tensile testing confirmed that the mechanical performance of the recycled constructs matched that of the pristine counterparts within experimental variation (Figure 5b). The Young’s modulus was 32.3 ± 17.3 MPa for pristine samples and 44.3 ± 2.5 MPa for recycled samples. Ultimate tensile strength values were 6.6 ± 2.2 MPa and 8.4 ± 1.9 MPa, respectively, while elongation at break was measured at 408.7 ± 193.3 % for pristine and 446.0 ± 90.2 % for recycled samples. No statistically significant differences were observed between the two, indicating that ductility, toughness, and overall mechanical integrity were fully retained throughout the recycling and reprinting process. Finally, dynamic mechanical analysis (DMA) provided additional insight into the thermo-mechanical behavior of the pristine and recycled networks (Figure 5c,d). In both samples, the tan δ exhibited two distinct thermal transitions—one near 20 °C and another around 60 °C—corresponding to the glass transition and melting temperature, respectively, as confirmed by DSC.

To contextualize performance against the fluoropolymer state-of-the-art, we benchmarked the material against a food-grade PTFE reference (also known by the brand name Teflon). PTFE shows the expected semicrystalline thermoplastic signature with higher stiffness and ultimate strength (Young’s modulus 458.6 ± 0.2 MPa; ultimate tensile strength 27.1 ± 0.3 MPa) but a lower elongation at break (188 ± 6 %). The developed semi-crystalline fluorinated network operates above its glass transition (≈1.3 °C) and retains residual crystallinity (crystallization and melting at ≈55 °C and ≈64 °C), which—together with a homogeneous thiol–ene network topology—yields large post-yield deformation, and a very high elongation at break (409 ± 193 %). Despite a lower stiffness and ultimate tensile strength (Young’s modulus 32.3 ± 17 MPa; ultimate tensile strength 6.6 ± 2.2 MPa), the extensive ductility gives a comparable toughness (work-to-break) under our test geometry. The resulting toughness is 22.3 ± 16.1 J cm⁻³ for HDF-X and 21.6 ± 12.7 J cm⁻³ for PTFE, i.e., comparable toughness within experimental variance. In other words, our crosslinked network matches the toughness of PTFE, a high molar mass thermoplastic which is used across a wide range of applications. Thermogravimetric analysis at 2% mass loss places the degradation onset near 295 °C for the network and 547 ± 0.5 °C for PTFE; while PTFE retains the higher thermal margin, the network’s stability is sufficient for many service environments well below 300 °C. Full datasets, replicate statistics, and analysis procedures are provided in Supplementary Information S7.

Collectively, these results confirm that recovery, re-functionalization, and volumetric reprinting of the fluorinated monomer enable a fully recyclable photoresist with preserved thermal, structural, and mechanical performance.

Methods
Materials and reagents. All chemicals were used as received unless stated otherwise. 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluoro-1,10-decanediol (HDF-OH) (97%), allyl isocyanate (98%), tin(II) 2-ethylhexanoate (92.5−100%), pentaerythritol tetrakis(3- mercaptopropionate) (PETMP) (>95%), poly(ethylene oxide) 1 000 000 g .mol-1 (PEG1M) and diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide (TPO) (97%) were supplied by Sigma-Aldrich (Diegem, Belgium). Sodium hydroxide (≥98.5%), tetrahydrofuran a.r (stabilized with 250 ppm BHT, ≥99.9%), methanol p. (≥99%), diethylether (stabilized with 5−7 ppm BHT, >99%), and chloroform (stabilized with amylene, >99%) were supplied by Chem-lab NV (Zedelgem, Belgium). PTFE benchmark plate with a thickness of 1 mm (PerlaPlast, item no. 2900260001).

Synthesis of HDF-ENE. HDF-OH was functionalized under inert atmosphere following the following procedure. A 100 mL Schlenk flask equipped with an oval stirring bar was flame-dried under vacuum and filled with argon. Anhydrous tetrahydrofuran (THF, 100 mL, M = 72.11 g·mol⁻¹) was introduced into the flask, followed by the addition of HDF-OH (10 g, 15.92 mmol, M = 628.31 g·mol⁻¹). Tin(II) 2-ethylhexanoate (Sn(Oct)₂, 1.25 w/w%, 50 µL, M = 405.12 g·mol⁻¹) was subsequently added as a catalyst. Allyl isocyanate (4.01 mL, 43.28 mmol, 1.05 molar equivalents, M = 83.09 g·mol⁻¹) was added dropwise to the mixture while maintaining an argon atmosphere. The mixture was allowed to react overnight at 40 °C under magnetic stirring. Reaction progress was monitored through 1H-NMR spectroscopy until complete conversion was confirmed. Upon completion, THF was removed using a rotary evaporator. The product was then purified via mixed-solvent recrystallization. The solid was dissolved in hot methanol (MeOH, M = 32.04 g·mol⁻¹), and water was added dropwise until the solution became slightly turbid. Additional MeOH was gradually added dropwise until the solution became fully clear. The mixture was allowed to cool slowly to room temperature and placed in an ice bath for 20 minutes. The resulting crystals were dissolved in diethyl ether (Et₂O, M = 72.11 g·mol⁻¹) while still being on the filter. The solution was filtered again to recover the product as a solution in Et₂O in a 100 mL flask. Finally, the solvent was removed under reduced pressure using a rotary evaporator, and the purified product was vacuum-dried at 40 °C for 2 days. To determine the alkene content, dimethyl terephthalate (DMT, 10 mg, 0.05 mmol, 1 eq., M = 194.18 g.mol-1) was added as internal 1H-NMR standard to 10 mg of the respective HDF-E precursor and CDCl . NMR spectra were analyzed in MestReNova software and the fully automatic baseline correction (Whittaker Smoother) was applied. The alkene content was calculated as follows:
Alkene content (mol.g−1) = 𝐼(𝛿5.2)+𝐼(𝛿5.8) × 𝑁(DMT) × 𝑚(DMT) × 1 (1)
𝐼(𝛿8) 𝑁(alkene) 𝑀𝑀(DMT) 𝑚(HDF−E)
‘I’ stands for the integrated value of the peaks compared to the signal from DMT at 8 ppm. ‘N’ is the amount of protons of DMT and the alkene/acrylate functional group. ‘m’ refers to the weighed mass, and ‘MM’ refers to the molar mass.

Chemical recycling of HDF-OH from HDF-X. Prior to alkaline degradation, volumetrically printed constructs were briefly ground with a mortar and pestle to eliminate geometry-dependent effects during degradation. A condition screen was performed at 85 °C under reflux, varying [NaOH] to 1.0, 2.5, and 5.0 M, and reaction time (0.5–16 h). For each condition, the same resin mass and solution volume were used and the full workflow was executed—alkaline depolymerization → neutralization to pH ≈ 7 with 1 M HCl → solvent removal by rotary evaporation → dissolution of the residue in diethyl ether (Et₂O) → filtration of insolubles → solvent removal → drying—to isolate HDF-OH (see Supplementary Information Section S5). The optimized condition was identified as 2.5 M NaOH for 3 h at 85 °C, which afforded 97.4 % ± 2.1 % recovery (n = 3). For a representative batch, ground material (300 mg) was charged to a 50 mL round-bottom flask with 10 mL of 2.5 M NaOH and heated at 85 °C under reflux for 3 h. The reaction mixture was then neutralized to pH ≈ 7 by gradual addition of 1 M HCl. After neutralization, acetone was added to the aqueous phase (1:1 v/v water:acetone) to facilitate co-evaporation and streamline water removal during rotary evaporation. The mixture was concentrated by rotary evaporation to remove water and acetone, affording a solid residue. The residue was dissolved in diethyl ether (Et₂O), and the mixture was filtered to remove insoluble inorganic and polymeric by-products. The Et₂O-soluble fraction was collected, while the retained solids were washed thoroughly with deionized water to remove NaCl and other inorganic residues, then rinsed with hexane to displace residual water. The washed solids were subsequently re-extracted with Et₂O to recover any remaining HDF-OH. The combined Et₂O extracts were concentrated by rotary evaporation, and the resulting product was dried under vacuum at 40 °C for 2 h to afford purified HDF-OH, which was then re-functionalized as described in the preceding section.

Formulation of the photoresist for volumetric 3D printing. The concentration of the photoinitiator diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) was determined according to the Beer-Lambert law to achieve a targeted absorbance of 0.85, requiring a photoinitiator concentration of 4.159 mM. The molar absorption coefficient of TPO was measured to be 202.5 M-1 cm-1. To increase the viscosity of the resin, 1.25% w/v of polyethylene glycol 1 000 000 g/mol (PEG1M) was added. For 1 mL of resin, 300 mg of alkene-functionalized 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-hexadecafluoro-1,10-decanediol (HDF-ENE, 300 mg/mL, 0.4775 mmol) and 12.5 mg of polyethylene glycol 1 000 000 g/mol (PEG1M, 12.5 mg/mL, 12.5×10-5 mmol) were dissolved in 648.9 μL of chloroform (CHCl , 959.8 mg, 959.8 mg/mL, 8.040 mmol) in an amber vial. The mixture was heated at 40 °C and vortexed until properly dissolved. Subsequently, 72.4 μL of TPO (1.449 mg TPO, 4.159×10-3 mmol TPO, 107.1 mg CHCl , 0.8974 mmol CHCl ) from a stock solution of 20 mg mL-1 in CHCl (5.741×10-5 M TPO) and 91.1 μL of pentaerythritol tetrakis(3-mercaptopropionate) (PETMP, 116.7 mg, 116.7 mg/mL, 0.2387 mmol) were added to the mixture. The mixture was then vortexed and sonicated to ensure homogeneity.

Characterization techniques. 1H-NMR spectroscopy was conducted on a Bruker Avance 400 MHz Spectrometer, with data acquisition in Bruker TopSpin (v4.4.1). 128 scans were recorded with a relaxation delay of 1 s and a spectral width of 14.7 ppm. Unless otherwise specified, deuterated DMSO was used as the solvent. The resulting spectra were analyzed using MestReNova (v6.0.2-5475), with fully automatic baseline correction applied using the Whittaker Smoother method. Liquid chromatography-mass spectrometry (LC-MS) analyses were performed using an Agilent Technologies 1100 series LC/MSD system equipped with a diode array detector and a single quadrupole MS detector (VL) featuring an electrospray ionization source (ESII-MS). Data acquisition was performed in Agilent ChemStation (Edition B.03.04), and the spectra were recorded using acetonitrile solutions of the compounds and analyzed with ACD/Spectrus Processor 2015 Pack 2 (file version S40S41, build 81783). FTIR spectra were recorded on a PerkinElmer Frontier FTIR spectrometer combined with an MK2 Golden Gate setup equipped with a diamond crystal from Specac, using PerkinElmer Spectrum software (v10.4.2.279). The spectra were recorded at room temperature, between 600 and 4000 cm-1 at a resolution of 4 cm-1, accumulating eight scans per test. UV-VIS spectrophotometry was performed using a UV-1900i (Shimadzu) with data acquisition in LabSolutions UV-Vis (v1.12.2). The absorbance was measured from 600 to 250 nm with an interval of 1 nm and at medium scan speed at 25 °C referenced to a cuvette containing chloroform. Photorheology was performed using the Anton Paar Physica MCR 302 with a parallel plate setup (PP25 as the top plate, diameter: 25 mm), equipped with a LED light source M405LP1-C5 from Thorlabs (405 nm, 9.5 mW cm-2). The activation and deactivation of light irradiation were controlled through an in-house shutter setup.22 The light intensity was measured using a Power Meter Console PM120VA and a Photodiode Power Sensor S120VC from Thorlabs. Measurements were performed at a wavelength of 405 nm, considering that the light was hitting the total area of the sensor (9.5 mm in diameter), with a circular shape for the light beam and a Gaussian profile. Measurements were performed at 20 °C with a strain amplitude of 0.1 % and an oscillation frequency of 1 Hz. A 200 μL mixture (HDF-ENE, PETMP, PEG1M, TPO, and CHCl ) was placed between the parallel plates with a gap of 300 μm. UV light was turned on after 20 s, exposing the sample to UV light for 120 s (unless another exposure time is stated). Data acquisition and data analysis were performed in RheoCompass (v1.26.22; Anton Paar). Rheology was performed using the Anton Paar Physica MCR 302 with a parallel-plate setup (PP25 as the top plate, 25 mm diameter). Measurements were performed at 40 °C with a constant shear rate of 0.1Hz. An 80 μL mixture (HDF-ENE, PETMP, PEG1M, and CHCl3) was placed between the parallel plates with a 50 μm gap. Data acquisition and data analysis were performed in RheoCompass (v1.26.22; Anton Paar). Thermogravimetric analyses (TGA) were carried out on a Mettler-Toledo TGA/SDTA 851 device under nitrogen atmosphere from 30 °C to 600 °C at a heating rate of 10 °C min⁻¹. The degradation temperature was defined as the temperature corresponding to a mass loss of 2 wt%. Cross-linked samples weighing 6–10 mg were used for each analysis. Data recording and analysis were performed using STARe software (version 18.00d; Mettler Toledo). Differential Scanning Calorimetry (DSC) measurements were conducted using a DSC Q2300 (TA Instruments) equipped with an RSC 500 cooler (Zellik, Belgium). Approximately 5 mg of cross-linked sample was used for each analysis. Heating and cooling rates of 2 °C min⁻¹ were applied. The thermal properties discussed are based on the second heating and first cooling ramps. Data collection was performed using TA Instruments Thermal Advantage Release 5.5.24 and TA Instruments Universal Analysis 2000 (Version 4.5A, Build 4.5.0.5) for data analysis. Dynamic Mechanical Analysis (DMA) was conducted using a DMA/SDTA 861e from Mettler-Toledo (Switzerland) in shear mode. The tests were performed using a displacement amplitude of 2 µm and a force amplitude of 5 N at a frequency of 1 Hz, while the samples were subjected to a heating rate of 3 °C/min over a temperature range from -50 °C to 100 °C. Data recording and analysis were performed using STARe software (version 18.00d; Mettler Toledo). Tensile tests were conducted using a Tinius Olsen Model 1 ST apparatus equipped with a 500 N load cell, with data acquisition and analysis performed through Horizon UTM Software (v10.2.3.0; Tinius Olsen). Bars with a length of 10 mm, a thickness of 1 mm, and a width of 4 mm, were volumetrically 3D printed and evaluated. For the PTFE benchmark, dogbones with a thickness of 1 mm, width of 4 mm and a gage length of 27 mm were used. The initial strain rate was set to 1 mm min⁻¹ until a force of 0.1 N was reached, after which the strain rate was increased to 10 mm min⁻¹. Gel fraction and swelling properties were assessed using discs with a diameter of 4 mm and a thickness of 1 mm, which were volumetrically 3D printed. The discs were immersed in excess CHCl (5 mL) at room temperature for one day. The initial dry mass of the discs (W ), their mass in the swollen state (W ), and their mass after drying post-swelling (W) were measured. All measurements were performed in triplicate to ensure reproducibility. The gel fraction and swelling ratio were calculated using the following equations:
𝑊
𝐺𝑒𝑙 𝐹𝑟𝑎𝑐𝑡𝑖𝑜𝑛 (%) = f ×100 (2)
𝑊
d
𝑆𝑤𝑒𝑙𝑙𝑖𝑛𝑔 𝑟𝑎𝑡𝑖𝑜 (%) = 𝑊s−𝑊
f×100 (3)
𝑊
d
Statistical analysis was performed in GraphPad Prism 8 for Windows (v8.0.2 (263)) using unpaired two-tailed t-tests with Welch’s correction or two-way ANOVA with Sidak’s multiple comparisons, as indicated in the figure legends. Full test statistics, including exact P values, are reported in Supplementary Information Sections S2 and Section S7.

Volumetric 3D Printing. Tomographic volumetric prints were produced on a Tomolite v2.0 (Readily3D, 405 nm source; nominal voxel pitch 25 µm) with projection and continuous rotation controlled in Apparite 1.2.4. CAD files and nominal dimensions for all resolution-test geometries are provided in Section S3 of the Supplementary Information. In Apparite, the refractive index was set to 1.450—chosen to match the dominant solvent (chloroform) and consistent with related fluorinated monomers (e.g., poly(trifluoroethyl methacrylate, n ≈ 1.44). The absorption setting was 2.00 cm⁻¹, which corresponds to a base-10 absorbance of ~0.87 cm⁻¹ (conversion A = μ/ln 10); this matches the measured UV–Vis absorbance of ~0.85–0.87 cm⁻¹ for the final formulation. “Bulk Length” and “Bulk Strength” were set to Off. The vial profile was measured in situ (glass type BK7, outer diameter 7.49 mm, wall thickness 0.92 mm). After printing, parts were rinsed with acetone to remove uncured resin and post-cured under UVA (365 nm, 5 mW cm⁻², 2 h), then air-dried.

Cell culture and live dead assay. Human foreskin fibroblasts (HFF; ATCC SCRC-1041, passage 4) were cultured in high-glucose DMEM (Merck, D6429) supplemented with 10% fetal bovine serum (Sigma Aldrich, F7524) and 1% penicillin-streptomycin (Thermo Fisher, 15140122) at 37 °C and 5% CO₂. For direct-contact assays, cells were seeded in 96-well tissue culture plates (Thermo Fisher, 167008) at 10,000 cells/cm² (3,200 cells/well in 100 µL) and allowed to adhere for 10 h before material placement. Sterile 6 mm discs of the volumetrically 3D printed HDF-X and PTFE (benchmark) were prepared by 2 × 12 h ethanol sterilization, washed three times in DPBS, and pre-wetted in complete medium for 6 h prior to use. Discs were gently placed centrally on fibroblast monolayers using sterile forceps, while uncovered wells served as cell controls (CTRL). Cell viability was assessed at 1, 3, and 7 days post-seeding. Calcein-AM (Thermo Fisher, 65-0853-78) and propidium iodide (Thermo Fisher, P3566) were diluted to 2 µL/mL each in Fluorobrite DMEM (Thermo Fisher, A1896701). Wells were washed with DPBS, incubated with 100 µL of staining solution for 15 min at room temperature in the dark, and imaged using a Zeiss confocal microscope controlled with ZEISS ZEN Imaging Software. Images were processed in Fiji (ImageJ, v1.54) under identical exposure conditions across groups. For each condition and timepoint, three independent experiments were performed (n = 3). Data are presented as mean ± standard deviation. Statistical significance was determined using two-way ANOVA with post hoc tests, with p-values indicated as ***p < 0.001 and ****p < 0.0001.

Reproducibility. Key quantitative experiments were independently replicated as indicated for each assay.

Sample size determination. No prospective power analysis was performed. Sample sizes were selected a priori based on standard practice for screening assays and materials characterization, as well as practical experimental throughput.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This manuscript focuses on a closed-loop strategy integrating volumetric 3D printing with chemical recycling for fluoropolymers. Selective urethane hydrolysis under alkaline conditions then affords 77% fluorinated monomer recovery. The application of high-concentration alkali reduces the practical application value of this work. Although this work focuses on the recycling of fluorinated materials, it essentially relies on the dissociation of urethane bonds by high-concentration alkali, and the process is cumbersome. However, there are many questions and a more detailed description is lacking in this manuscript. See the following for details:\n1. In HDF-ENE synthesis, the reaction of allyl isocyanate with HDF-OH is used to form a urethane bond. Similar reactions have been presented in a number of papers and the authors are required to elaborate on this approach and the advantages of this material.\n2. The generality of this work is insufficient: the recycling process was only demonstrated for one specific fluorinated material, HDF-OH, rendering the conclusions less generalizable.\n3. The explanation for the latency period in photorheology needs to be verified by experiments and requires deeper interpretation.\n4. The chemical recovery section mentions the condition “5 M NaOH/85 °C/2 h” without stating the basis or showing data on the effect of different base concentrations or temperatures on the recovery. Additional experimental results are recommended to illustrate the process of optimizing the conditions.\n5. Printing microfluidic devices (Figure 3b) requires biocompatibility, but the cytotoxicity of HDF-X was not mentioned. Please add cytotoxicity testing. There are no in vivo or in vitro experimental results.", "reviewer_2": "The manuscript reports a strategy to enable 3D printing of a fluoropolymer material using radical thiol-ene photochemistry. Importantly, the authors go on to show that these materials can be deconstructed into their constituent monomer pre-cursors, which is an important goal with respect to recovery of these environmentally harmful molecules. This contribution focuses on the use of volumetric 3D printing. This method can overcome some of the challenges that other printing methods entail such as layer-to-layer adhesion. The chemistry applied in this study does not deviate greatly from that of many printing resins, relying on creating an allyl end capped fluorinated monomer that is subsequently crosslinked with a multi arm thiol. The study is thoroughly conducted and there are some nice innovations such as the removal of inhibitors which present an advantage to the methods reported. The print resolution is impressive and the recycling studies are great to see. There are however a few amendments to the paper that should be considered prior to publication:\n1) It is important to compare the materials' properties to existing fluoropolymer materials, both printed and molded so the significance of this contribution can be properly assessed.\n2) I would disagree that the term 'closed loop' is appropriate to describe these materials, the fluorinated alcohol can be recovered but all other components will need to be added to a new resin to create a printable formulation and hence ca. 45% of the original chemicals are recovered to be reused and a large volume of additional chemicals is required to be added.\n3) In figure 4, why is the 475 peak absent in the recycled HDF-OH?\n4) Additionally, a yield of 77% of the fluorinated monomer is also not ideal as the remainder will be lost - have the authors optimized this process?", "reviewer_3": "The authors report the synthesis of an alkene-functional fluorinated monomer for thiol–ene crosslinking and its use for volumetric 3D printing. While the introduction of fluoropolymer for tomographic volumetric 3D printing has never been attempted, from my opinion, this is not sufficient in term of novelty to be considered for publication in a journal such as Nature Communications. Indeed, since the emergence of volumetric additive manufacturing (VAM), most of the photoresists developed for SLA/DLP printers have been successfully transferred to volumetric 3D printer (Bernal et al. Nature Review Materials 2025, https://doi.org/10.1038/s41578-025-00785-3, The road ahead in materials and technologies for volumetric 3D printing). The challenge, if any, to successfully 3D print fluorinated monomer regarding the condition of VAM photopolymerization is not clearly discussed.\nHowever, the authors also introduced a cleavable urethane linkage in the non degradable fluorinated precursor, allowing chemical recycling of the fluorinated monomer. This aspect is scarcely addressed for 3D printed fluoropolymer and consequently deserved to be highlighted.\nFinally, some of the conclusions that the authors draw from the data appear in their current form overstated. For instance, can we really say “closed-loop volumetric 3D printing” when more than half of the chemical should be replaced to make a new print? Besides, some aspects request additional experiments or explanation to obtain a comprehensive manuscript. In its current form the manuscript appears therefore too premature for publication in Nature communications.\nPlease check out my comments below.\n1/ Evidence of the influence of PEG1M.\nFirstly, the authors have mentioned the role of PEG1M to suppress the sedimentation during printing, but no experimental evidence is given to illustrate this drawback and to explain how the authors have selected the optimal concentration (movie showing the sedimentation for different concentrations of PEG1M). See for instance SI Movie 1 & 2 of Loterie, D., Delrot, P. & Moser, C. High-resolution tomographic volumetric additive manufacturing. Nat Commun 11, 852 (2020). https://doi-org.inc.bib.cnrs.fr/10.1038/s41467-020-14630-4). Besides, the viscosity of the photoresists should be determined for concentrations of PEG1M ranging from 0 to 1.25 w% since it is a key parameter in the optimization step. The scheme depicted in Figure 2d is not sufficient to support the statement made by the authors.\nSecondly, the built-in inhibition is partially attributed by the authors to the presence of PEG1M, in particularly due to the modification of the viscosity. To confirm this hypothesis, photorheology experiment has to be performed in absence of PEG1M.\n2/ Origin of the delayed gelation\nBeyond viscosity issue (see previous point), another hypothesis proposed by the authors to explain the intrinsic inhibition of the photoresist without adding radical scavenger (such as TEMPO) is the fact that thiol-ene polymerization occurs through a step-growth mechanism. However, in their previous work with different precursors (Adv. Mater. 2023, 35 (19), e2210136. DOI: 10.1002/adma.202210136), step-growth thiol-ene polymerization was involved and the use of TEMPO was requested. I do not understand why in this specific case, step-growth will lead to delayed gelation (difference in the viscosity, photoreactivity of fluoropolymer vs its hydrogen-based counterpart?).\n3/ Determination of the optimal printing dose for volumetric\nPhotorheological experiments are used to determine the optimal printing dose. However, the comparison between the light intensities used during photorheology experiments and those used in volumetric printing is not clearly established. This information is crucial, as photoreactivity and polymerization kinetics can be strongly influenced by light intensity and exposure time (or here manufacturing time). Moreover, experimental configuration should also influence the results: while in photorheology, the thickness is set to few hundred micrometers with continuous irradiation, for volumetric printing, the length is around 7 mm.\nClarification on this point is necessary in order to assess the transposability of results between the two experimental contexts. And light intensity and manufacturing time should be specified, the latter being also important to assess if sedimentation can occur in this time scale.\n4/ Optical properties of the photoresists\nThe authors indicate that the absorbance value of 0.85 was chosen because, according to the Beer-Lambert law, it corresponds to a light intensity drop of about 20%. However, it is not explained why this 20% loss is considered acceptable. This threshold appears to have been set arbitrarily, without experimental or theoretical justification. It is important to explain the criteria on which this limit was based, and how it aligns with the requirements of the printing process.\nFurthermore, the Tomolite printer is supposed to incorporate an optical compensation function. In the section regarding fabrication parameters, an absorption value of 2.00 cm-1 is indicated. This choice is not sufficiently explained: why was this specific value selected? In addition, the relationship between this absorption value (2.00 cm-1) and the absorbance of 0.85 is not clearly established. The correspondence between these two quantities is neither detailed nor referenced, which leads to confusion in data interpretation. A clarification on this point would be welcome.\nAnother aspect concerns the refractive index (1.45). It should be indicated how it has been determined and for which wavelength ?\n5/ Resolution issue – feature size\nThe authors report feature sizes down to 15.5 µm (negative one) as the “smallest negative features reported to date for volumetric 3D printing” and highlight this fact in the abstract. How the authors can explained such resolution? Is it due to the chemistry (and why)? Or is it due to the optical system? Can they give details about the optical configuration of their printer?\nAccording to the current experimental data, this statement is overexaggerated. The provided optical microscopic images do not allow reliable conclusions to be drawn regarding the resolution achieved. It is difficult to determine whether this is due to an actual resolution limitation, a fabrication artefact, or surface defects. It is recommended to acquire higher-quality images, particularly using a scanning electron microscope (SEM), in order to confirm the observations. CAD model should be provided to discuss printing fidelity and state on the merit of the chemistry or optical set-up.\nThe choice of the « Klein bottle » object for evaluating resolution appears to be poorly suited. It would be preferable to use a standardized test object, such as a grid pattern or regularly spaced lines, to allow a more rigorous and objective assessment of resolution performance. More interesting/convincing will be the printing of the microfluidic chip with internal channel of 15.5 µm width and few millimetres length (see Gong et al. Lab Chip, 2017, 17, 2899, DOI: 10.1039/c7lc00644f, Custom 3D printer and resin for 18 μm × 20 μm microfluidic flow channels)\n6/ Printing fidelity\nIn a general manner, the CAD models should be provided with the expected dimension to assess the printing fidelity. For instance, in Figure 3b, the microfluidic system seems to be distorted (inhomogeneous geometry). Is this an expected phenomenon or a fabrication defect? Printing fidelity to be discussed.\n7/ Chemical recycling\nThe study does not evaluate the effect of multiple recycling cycles on monomer purity, side product accumulation, or long-term property retention. Only one recycling/reprint cycle is rigorously characterized. The environmental benefit of the closed-loop system is asserted 77% monomer recovery (vs. theoretical maximum) implies significant loss after multiple recycling.\nThus, life cycle assessment may be required.\nSince degradability is design-dependent owing to diffusion issue, could you indicate the shape and dimension of the volumetric printed object for such test?\nWhat are the shape / dimension of the printed object used for the mechanical test (before and after recycling)?\nSome minor Points\n• The equation in page 20 mention PCL but PCL has not been used in this work. See also in the text, PCL to be removed.\n• Both References 26 and 28 are identical", "reviewer_4": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts."}, "author_response": "Response to the reviewer comment:\nThank you for asking us to elaborate on the HDF-ENE design and the choice of the allyl-isocyanate urethane coupling. The functionalization route is intentional rather than novel. Using a mono- functional isocyanate avoids any chain extension during end-group installation, which can occur with diisocyanate/diol couplings. Moreover, installing allyl groups enables thiol–ene crosslinking, which follows a step-growth polymerization that is oxygen-tolerant, exhibits lower shrinkage stress, and forms more homogeneous networks with significantly increased toughness (due to the combined effect of increased crystallinity, higher ultimate strength, and larger elongation at break) relative to more commonly used (meth)acrylates. Embedding alkenes via a urethane- forming reaction also provides an alkaline-cleavable handle that releases the initial fluorinated diol, which forms the basis for the recovery of the fluorinated content of the network, as you noted in your general assessment of our work. Rather than providing a novel functionalization route, our claim of novelty lies in the integration of the reported thiol-ene fluoronetwork into volumetric printing and in closed-loop chemical recycling of its fluorinated content at very high yield (i.e., 97.4%).\nHowever, in order to provide insight to the reader related to our choice of functionalization and the unique attributes of our developed material, we have introduced the following paragraph in the synthesis section of the main article:\n“Allyl isocyanate end-capping was used because it is robust, operates under mild conditions, and scales well. The reaction selectively functionalizes terminal diols while avoiding the chain extension common to diisocyanate/diol couplings.26 Finally, the introduced alkene end groups enable step-growth thiol–ene crosslinking that is oxygen-tolerant, yields uniform and low-shrinkage networks with improved toughness compared to more conventional (meth)acrylate crosslinking (vide infra).”\n2. The generality of this work is insufficient: the recycling process was only demonstrated for one specific fluorinated material, HDF-OH, rendering the conclusions less generalizable.\nResponse to the reviewer comment:\nThank you for foregrounding generality. The study was designed as an integrated proof-of-concept that follows one system through the full arc of material development → tomographic volumetric printing → chemical recycling → re-functionalization → re-use. Prompted by your comment, we have made the scope explicit and reframed the paper as a single, carefully documented exemplar rather than a broad survey across different fluorinated polymers. Extending the workflow to additional fluoropolymers would require de novo optimization of solubility and work-up, optical attenuation and dose windows, resin rheology, and alkaline depolymerization for each precursor; those are substantive, independent efforts that fall beyond the scope of the present study. We therefore chose depth over breadth and tightened the claims accordingly, while emphasizing the aspects that are transferable (workflow, analysis, and documentation).\nConcretely, we narrowed the language throughout the article so readers see at a glance what is— and is not—being claimed.\nThe title now reflects the singular exemplar “Volumetric 3D Printing of a Fluoropolymer and Closed-Loop Chemical Recycling of its Fluorinated Content.”\nThe abstract’s final sentence has been revised to: “This represents the first demonstration of high- resolution tomographic volumetric printing of a fluoropolymer with closed-loop chemical recycling of its fluorinated content.”\nIn the introduction has been revised to: “While we report a single-system exemplar which we follow through tomographic volumetric 3D printing, fluorinated monomer recycling, refunctionalization, and reuse, the reported workflow is modular and can be adapted by others to different fluorinated precursors.”\nWe believe this framing clarifies contribution and generality: the paper offers a complete, reproducible template that others can adapt to different fluorinated systems, while avoiding over- generalization in the current work.\n3. The explanation for the latency period in photorheology needs to be verified by experiments and requires deeper interpretation.\nResponse to the reviewer comment:\nThank you for pressing us to verify the origin of the photorheological latency—this was an important check. We repeated the measurements on matched formulations with and without PEG1M under identical conditions. Interestingly, the latency period and the transient dip in G′ were essentially unchanged, which does not support a PEG1M-driven viscosity origin. We therefore withdraw that explanation in the main text and now attribute the delay primarily to step- growth gelation in the bifunctional-ene/multifunctional-thiol network: gelation—and thus the rise in G′—is expected only at comparatively high functional conversion (consistent with Flory– Stockmayer considerations for tetrafunctional thiol with bifunctional ene). A small initial decrease in G′ is plausibly due to the exothermicity of the reaction. We note, however, that formulation-specific factors (solvation of the fluorinated backbone, oxygen solubility, solvent environment and local microstructure, and light intensity/exposure history) can modulate latency even in oxygen-tolerant thiol–ene systems. Fully disentangling these influences is beyond the scope here; we present step-growth gelation as the leading explanation and document the control data so readers can judge the assignment, but prompt readers to approach the current hypothesis with caution.\nWe have incorporated these new experiments and insights into the main article as follows:\n“Two hypotheses were considered for the rheological latency: (i) a PEG1M-induced viscosity barrier that delays network formation, and (ii) the intrinsic gelation threshold of step-growth thiol–ene networks. Matched photorheology on formulations with and without PEG1M yielded the same latency period, excluding hypothesis (i) (Section S1.4). We therefore attribute the latency primarily to hypothesis (ii): by Flory–Stockmayer theory, an elastically percolated network forms only beyond ~58% functional-group conversion for a tetrafunctional thiol with a bifunctional alkene.28,29 However, it should be noted that the stated hypothesis should be interpreted with caution, as the onset and magnitude of the latency can be affected by other factors (e.g., fluorinated-backbone solvation, oxygen solubility, the solvent environment, local microstructure, and light intensity-dependent kinetics). Fully disentangling these contributions lies beyond the scope of the present study. Separately, the small decrease in G′ observed immediately after illumination but prior to gelation is consistent with a modest reaction exotherm that transiently raises temperature, lowers viscosity, and increases mobility.”\nAdditionally, we have included the photo-rheological data in Section S1.4 of the Supporting Information as shown below:\n“S1.4 Influence of PEG1M on the inhibition period in photo-rheology\nTo test whether the rheological latency originates from PEG1M-induced viscosity effects, we repeated photorheology on matched formulations with and without PEG1M under identical irradiation; the latency and G′ trajectory were unchanged.\nFigure S6. Photorheology with/without PEG1M at 405 nm, 10 mW cm⁻²; light on at t = 10 s. Solid line: storage modulus (G′); dashed line: loss modulus (G″). Both traces show similar latency and rise, indicating PEG1M is not the origin.”\n4. The chemical recovery section mentions the condition “5 M NaOH/85 °C/2 h” without stating the basis or showing data on the effect of different base concentrations or temperatures on the recovery. Additional experimental results are recommended to illustrate the process of optimizing the conditions.\nResponse to the reviewer comment:\nThe authors agree that rigor around the recycling step is essential. Because all three reviewers independently raised this point, we executed a full condition matrix and were able to increase the recovery of the fluorinated monomer to 97.4 % ± 2.1 %. Thus, 97.4% of the fluorinated monomer is recovered after the first recycle–reuse loop, and that retained fraction compounds with each additional loop. In practice, this means that about 88% remains after five cycles and about 77% remains after ten cycles.\nWe systematically screened NaOH concentrations of 1.0, 2.5, and 5.0 M at 85 °C across hydrolytic degradation times ranging from 0.5 to 16 h. For each condition, we executed the complete workflow—alkaline reflux depolymerization, neutralization, purification, and drying—with identical resin mass and solution volume. This investigation, initiated by the reviewers’ comments, increased the fluorinated-monomer recovery to 97.4% ± 2.1% at 2.5 M NaOH for 3 h, and is now used throughout the manuscript. Finally, repeatability at this condition was confirmed in triplicate (s.d. = 2.1%), significantly reducing cumulative loss over multiple reuse cycles.\nWe have included the following discussion related to the parameter screening into the main manuscript:\n“After establishing a general workflow—alkaline reflux depolymerization, neutralization, purification, and drying— through which the fluorinated diol could be recovered from volumetrically 3D printed constructs, the degradation conditions were optimized to maximize the chemical recycling yield of the fluorinated diol (Section S5). More precisely, a condition screen at 85 °C was performed across NaOH concentrations of 1.0, 2.5, and 5.0 M and depolymerization times from 0.5–16 h, executing the complete sequence for every timepoint. The optimal condition (2.5 M NaOH for 3 h) afforded a recovery of 97.4 % ± 2.1 % (n = 3). At this per-cycle recovery, the theoretical retained fraction after ten recycle–reuse cycles is ≈76.8 % of the original fluorinated content (see Supporting Information, Section S5, for the full data and calculations).\nThe recovery–time profiles delineate two regimes, depicted in Figure S10. In the kinetic regime, yield increases to a concentration-dependent maximum that is reached earlier at higher [NaOH] (5 M: ~1–1.5 h; 2.5 M: ~3 h; 1 M: no maximum within 16 h). This trend is consistent with base-catalyzed urethane cleavage in which the apparent rate scales with hydroxide activity (pseudo-first-order, 𝑘 ≈ 𝑘 [𝑂𝐻−]). Beyond the maximum, the 𝑜𝑏𝑠 𝑏 isolated yield declines at 2.5–5 M and approaches a plateau. It is hypothesized that the gradual formation of crosslinked/aggregated side-product particulates during prolonged alkaline treatment physically entrap a fraction of the fluorinated diol and resist subsequent extraction. Once the population of such particulates saturates, the recovery approaches the observed plateau. The optimum at 2.5 M, 3 h therefore marks the intersection of fast cleavage kinetics with minimal secondary entrainment, resulting in a recycling yield of the fluorinated monomer of 97.4 % ± 2.1 % (n = 3).”\nMoreover, we have included the actual data in Section S5 of the Supporting Information, ‘Optimization of chemical recycling conditions and multi-cycle retention of the fluorinated content’ as shown below:\n“S5. Optimization of chemical recycling conditions and multi-cycle retention of the fluorinated content\nRecovery of the fluorinated diol was optimized by varying NaOH concentration (1.0, 2.5, and 5.0 M) and depolymerization time (0.5–16 h) at 85 °C. For each condition, the whole workflow was carried out (alkaline reflux depolymerization, neutralization, purification, drying) with identical resin mass and solution volume. The optimal point (2.5 M, 3 h) was repeated in triplicate to obtain mean ± s.d. (97.4 % ± 2.1 %).\nFigure S10. (a) Recovery of HDF-OH versus time for NaOH concentrations of 1.0, 2.5, and 5.0 M. The optimal condition (2.5 M, 3 h) yielded 97.4% ± 2.1%. (b) Projected multi-cycle retention of the fluorinated content, calculated as 𝑓 = 𝑟𝑁with 𝑟 = 0.974.\n𝑁\nCalculation of the multi-cycle retention of the fluorinated content\nLet 𝑟 be the single-cycle recovery fraction (𝑟 = 0.974). After 𝑁 recycle–reuse cycles, the retained fraction of the original fluorinated content is\n𝑓 = 𝑟𝑁,\n𝑁\nand the cumulative loss is\n𝐿 = 1−𝑟𝑁.\n𝑁\nUsing the optimized recovery (𝑟 = 0.974), the retained fraction after 𝑁 = 10 cycles is\n𝑓 = 0.97410 ≈ 0.768(76.8%).”\n“Chemical recycling of HDF-OH from HDF-X. Prior to alkaline cleavage, volumetrically printed constructs were briefly ground with a mortar and pestle to eliminate geometry- dependent effects during degradation. A condition screen was performed at 85 °C under reflux, varying [NaOH] to 1.0, 2.5, and 5.0 M, and reaction time (0.5–16 h). For each condition, the same resin mass and solution volume were used and the full workflow was executed—alkaline depolymerization → neutralization to pH ≈ 7 with 1 M HCl → solvent removal by rotary evaporation → dissolution of the residue in diethyl ether (Et₂O) → filtration of insolubles → solvent removal → drying—to isolate HDF-OH (see Supporting Information Section S5). The optimized condition was identified as 2.5 M NaOH for 3 h at 85 °C, which afforded 97.4 % ± 2.1 % recovery (n = 3). For a representative batch, ground material (300 mg) was charged to a 50 mL round-bottom flask with 10 mL of 2.5 M NaOH and heated at 85 °C under reflux for 3 h. The reaction mixture was then neutralized to pH ≈ 7 by gradual addition of 1 M HCl. After neutralization, acetone was added to the aqueous phase (1:1 v/v water:acetone) to facilitate co-evaporation and streamline water removal during rotary evaporation. The mixture was concentrated by rotary evaporation to remove water and acetone, affording a solid residue. The residue was dissolved in diethyl ether (Et₂O), and the mixture was filtered to remove insoluble inorganic and polymeric by-products. The Et₂O-soluble fraction was collected, while the retained solids were washed thoroughly with deionized water to remove NaCl and other inorganic residues, then rinsed with hexane to displace residual water. The washed solids were subsequently re- extracted with Et₂O to recover any remaining HDF-OH. The combined Et₂O extracts were concentrated by rotary evaporation, and the resulting product was dried under vacuum at 40 °C for 2 h to afford purified HDF-OH, which was then re-functionalized as described in the preceding section.”\n5. Printing microfluidic devices (Figure 3b) requires biocompatibility, but the cytotoxicity of HDF-X was not mentioned. Please add cytotoxicity testing. There are no in vivo or in vitro experimental results.\nResponse to the reviewer comment:\nThank you for underscoring the value of documenting cytocompatibility alongside the biomedical exemplars. Prompted by this comment, we performed in-vitro testing on volumetrically 3D printed samples in accordance with ISO 10993 using human foreskin fibroblasts, employing both Live/Dead imaging and MTS assays with a positive control and PTFE as a benchmark. Across 1, 3, and 7 days, HDF-X satisfied the ISO 10993 non-cytotoxicity criterion (viability ≥70%) and performed comparably to PTFE under identical conditions. These results substantiate the relevance of the printed biomedical designs in the manuscript and have been incorporated into the manuscript as noted below.\nWe introduced the following text module into Section S2 of the Supporting Information related to the newly performed biocompatibility experiments:\n“S2. In vitro biocompatibility of volumetric 3D printed constructs\nUnder ISO 10993, a material is considered non-cytotoxic when cell viability is ≥70% relative to an untreated control under the test conditions. Across all time points (D1, D3, D7), HDF-X maintained viabilities above this threshold and comparable to the PTFE benchmark (Figure S7a). Live/Dead micrographs acquired at the material interface show dense, confluent monolayers with the expected elongated fibroblast morphology and alignment (Figure S7b). No qualitative signs of cytotoxic response—such as widespread rounding, detachment, or pericellular clearing—were observed over the 7-day period.\nTaking together, these results indicate that volumetrically printed, post-cured HDF-X meets the ISO 10993 criterion for non-cytotoxicity in direct-contact assays.\nFigure S7. In vitro cytocompatibility of HDF-X (direct contact, human fibroblasts). Live/dead viability (%) at days 1, 3, and 7 for cell-only control (CTRL), PTFE benchmark, and HDF-X. All conditions remain above the ISO 10993 viability criterion (70%; dashed line). (b) Representative live/dead fluorescence micrographs (Calcein-AM, green; propidium iodide, red) at days 1, 3, and 7 for CTRL, PTFE, and HDF-X. Confluent green monolayers with sparse red nuclei are observed across conditions. Scale bars are 200 µm.”\nMoreover, we introduced the following discussion into the main manuscript:\n“In the biomedical context, vascular-like and porous scaffolds were printed. Aligned with these biomedical exemplars, the printed materials were shown to meet the ISO 10993 criterion for non-cytotoxicity in vitro, performing comparably to a PTFE benchmark (Supporting Information, Section S2), supporting the use of the developed material in a biomedical context.”\nAdditionally, we introduced the following sentence to the abstract of the article:\n“Volumetric 3D printed parts are biocompatible in vitro, supporting potential biomedical use.”\nFinally, we introduced the following description to the experimental section of the paper:\n“Cell culture and live dead assays. Human foreskin fibroblasts (HFF; ATCC SCRC-1041, passage 4) were cultured in high-glucose DMEM (Merck, D6429) supplemented with 10% fetal bovine serum (Sigma Aldrich, F7524) and 1% penicillin-streptomycin (Thermo Fisher, 15140122) at 37 °C and 5% CO₂. For direct-contact assays, cells were seeded in 96-well tissue culture plates (Thermo Fisher, 167008) at 10,000 cells/cm² (3,200 cells/well in 100 µL) and allowed to adhere for 10 h before material placement. Sterile 6 mm diameter discs of the volumetrically 3D printed HDF-X and PTFE (benchmark) were prepared by 2 × 12 h ethanol sterilization, washed three times in DPBS, and pre-wetted in complete medium for 6 h prior to use. Discs were gently placed centrally on fibroblast monolayers using sterile forceps, while uncovered wells served as cell controls (CTRL). Cell viability was assessed at 1, 3, and 7 days post-seeding. Calcein-AM (Thermo Fisher, 65-0853-78) and propidium iodide (Thermo Fisher, P3566) were diluted to 2 µL/mL each in Fluorobrite DMEM (Thermo Fisher, A1896701). Wells were washed with DPBS, incubated with 100 µL of staining solution for 15 min at room temperature in the dark, and imaged using a Zeiss confocal microscope under identical exposure conditions across groups. For each condition and timepoint, three independent replicates were obtained per readout (n = 3). Data are presented as mean ± standard deviation. Statistical significance was determined using two-way ANOVA with post hoc tests, with p-values indicated as ***p < 0.001 and ****p < 0.0001.”\n6. The authors should include a supplementary table comparing resolution metrics of volumetric 3D printing technologies, explicitly demonstrating that their 15.5 μm negative feature size represents the smallest reported to date.\nResponse to the reviewer comment:\nThank you for recommending a comparative resolution summary. Given that both you and Reviewer 3 raised concerns about our earlier single-value emphasis, we have revised the way we report feature size throughout the article. Rather than highlighting one minimum, we now report condition-bound feature sizes with explicit CAD linkage across several demanding geometries, while keeping the central contribution—volumetric 3D printing of a fluorinated network together with closed-loop chemical recycling of the fluorinated content—front and center.\nIn tomographic volumetric printing, the smallest reliably formed feature is not dictated by optics alone. It reflects the design-dependent computational contrast in back-projection, resin kinetics around gelation, viscosity with associated diffusion and sedimentation during and after exposure, polymerization shrinkage, and post-processing choices such as wash solvent and time. Because these factors couple, assigning a particular small feature to a single cause would be speculative and lies beyond the scope of the present work. Rather than advancing an ultimate resolution limit, we document what is reproducibly achieved under clearly specified conditions and provide the information needed for others to interpret those outcomes.\nTo position the results, the Supporting Information now includes a curated overview of reported feature sizes in tomographic volumetric printing derived from a screen of 37 studies; fourteen papers that list explicit numerical values were retained. Table S1 collates those minima to indicate what has been achieved in the field and to contextualize the condition-bound features reported here. Many publications present a single “best-case” feature size without linking back to design. In tomographic volumetric 3D printing, such single-feature reporting is not adequate due to its relatively low computational contrast (i.e., the difference between the light dose that in-part and out-of-part voxels receive), as compared to stereolithography (SLA) or digital light processing (DLP), where out-of-part voxels typically don’t receive any light (i.e., perfect computational contrast). As a result, the out-of-part voxels fundamentally limit the dose that in-part voxels can receive, and, as a result, the apparent feature size can depend strongly on the washing step. In the revised manuscript, we make this linkage explicit.\nWe also strengthened the experimental evidence underlying our values. The single-geometry showcase has been replaced by a multi-geometry presentation. For each design, we report the measured feature size alongside the corresponding CAD dimension at that exact location, so any deviation is explicit. The images show continuous features rather than surface artefacts, and the CAD files with nominal dimensions are provided so readers can assess fidelity directly. Firstly, related to the aforementioned discussion, the following text has been added to the Supporting Information:\n“S3. Feature-size in tomographic volumetric 3D printing. In tomographic volumetric printing, the smallest reliably formed feature is not dictated by optics alone. It is governed by the design-dependent computational contrast in back-projection, resin kinetics around gelation, viscosity together with diffusion and sedimentation during and after exposure, polymerization shrinkage, and post-processing choices such as wash solvent and time. Rather than advancing an ultimate resolution limit, we document what is reproducibly achieved under fixed conditions and provide the information needed for others to interpret those outcomes.\nS3.1 Literature positioning of volumetric 3D printing resolution. To contextualize the obtained feature sizes in the current work, we screened 37 publications on tomographic volumetric 3D printing and retained 14 that report explicit numerical values (restricted to tomographic volumetric 3D printing and excluding post-sintered ceramics). Table S1 collates these reported minima. Only two papers provide a direct design-to- measurement comparison: Kelly et al. (2019) report a 200 µm tail-fin tip radius versus a 400 µm design (sharper than intended), and Orth et al. (2023) report 195–200 µm versus ~180 µm for a gyroid wall and 580 µm versus ~500 µm for a pore. Most articles list single ‘best-case’ values with little to no linkage to CAD or reproducibility. The purpose of Table S1 is transparency: to position achievable feature sizes in tomographic volumetric printing and to provide readers with context for interpreting the condition-bound feature sizes reported here.\nS3.2 Experimental and theoretical feature sizes of volumetric 3D printed constructs. Figure S8 pairs each CAD model with its simulated back-projection contrast and a micrograph at the narrowest measured element. Across the four designs shown, the smallest observed features are ~56 µm, ~66 µm, ~97 µm, and ~254 µm; the corresponding CAD dimensions at those exact locations are indicated in the contrast panels. Set against the survey in Table S1, these values sit among the smallest polymer features reported for tomographic volumetric printing. Only a few studies approach this scale with comparable clarity of reporting; notably, Toombs et al. (2022) demonstrate ~20 µm polymer features on a different platform. It should be noted that the very small ‘positive’ values reported by Bernal et al. (2022) and by Falandt et al. (2023) correspond to the outermost tip of a star-shaped element; such apex measurements are highly sensitive to washing and do not represent generally reproducible line or strut widths.\nThe gap between CAD and experiment is expected. In tomographic exposure, the achievable width at a given location is governed by local computational contrast from back-projection, the resin’s conversion profile near gelation, and the subsequent washing step, which can remove weakly crosslinked material at feature edges. Additional contributors include polymerization shrinkage and any swelling or surface relaxation during post-processing. Because most papers in the field report single ‘best-case’ numbers without CAD-to-measurement linkage—Kelly et al. (2019) and Orth et al. (2023) are rare exceptions—Figure S8 provides that linkage explicitly so that readers can interpret the condition-bound features observed here.\nTable S1. Reported feature sizes in tomographic volumetric 3D printing. Minimum feature sizes as stated in the cited publications, restricted to tomographic volumetric methods and to papers that report explicit numerical values (studies without clear values are not included). Positive = solid features (e.g., struts/walls); negative = open features (e.g., channels/voids). Ceramics (post-sintered) are excluded. Values were distilled from a screen of 37 publications; only entries meeting the criteria above are listed.\nPaper Geometry Feature size\nKelly et al, 2019 [1] Airplane tail-fin tip radius 200 µm (positive)\nBernal et al, 2019 [2] Trabecular bone model and microfluidic channel 144.7 µm (positive) and 200 µm (negative)\nLoterie et al, 2020 [3] Notre Dame model and 3DBenchy chimney aperture 80 µm (positive) and 500 µm (negative)\nToombs et al, 2022 [4] Cubic lattice 20 µm (positive)\nBernal et al, 2022 [5] Outermost tip of a star and microfluidic channel 41.5 (positive) and 104.0 (negative)\nThijssen et al, 2023 [6] Lattice struts 100 µm (positive)\nChansoria et al, 2023 [7] Auxetic mesh (second layer) ≈289 μm (positive)\nFalandt et al, 2023 [8] Outermost tip of a star and microfluidic channel 23.7 µm (positive) and 176.0 µm (negative)\nOrth et al, 2022 [9] Gyroid top-surface pore and Gyroid interior walls 195–200 μm (positive) and 580 μm (negative)\nXie et al, 2023 [10] Solid bar 45.9 μm (positive)\nOrth et al, 2023 [11] Spacing between lattice struts 0.465 mm (negative)\nLian et al, 2024 [12] Solid rod with bars and cube array ≈79 μm (positive) and ≈137 μm (negative)\nDuquesne et al, 2025 [13] Prism tips and Swiss cylinder holes 138.83 µm (positive) and 198.97 µm (negative)\nThijssen et al, 2025 [14] TPMS I WP lattice ~300–400 µm (positive)\nFigure S8. (a) CAD design of each test geometry with the measured feature location indicated. (b) Computational contrast from tomographic back-projection at the corresponding cross-section; circles mark the positions used for measurement. (c) Optical micrographs of the same locations showing the smallest reproducible feature; measured widths are annotated (scale bars as shown). (d) Side-by-side comparison of theoretical (CAD) versus experimental feature size for each geometry, highlighting the expected disparity arising from local contrast, conversion near gelation, and wash-driven removal of partially converted material.”\nIn addition, the Methods now provide the optical resolution of the volumetric 3D printing used in this work, as shown: “Volumetric 3D Printing. Tomographic volumetric prints were produced on a Tomolite v2.0 (Readily3D, 405 nm source; nominal voxel pitch 25 µm) with projection and continuous rotation controlled in Apparite 1.2.4. CAD files and nominal dimensions for all resolution-test geometries are provided in SI §3.”\nRevised abstract line: “The photoresist—based on an alkene-functionalized fluorinated diol and a multifunctional thiol—supports rapid fabrication of centimeter-scale objects with reproducible feature sizes down to 56 μm, among the smallest reported to date.”\nRevised text related to resolution in the main manuscript: “By means of this photorheological framework, a suitable light dose of 180 mJ cm⁻² was determined.22 At this dose, the optimized resin enabled high-resolution tomographic printing across multiple geometries. Rather than quoting a single minimum, we report condition-bound, reproducible features with explicit CAD linkage (see SI §3): the smallest measured widths across our test set are ~56, ~66, ~97, and ~254 μm at the indicated locations. Benchmarked against a curated literature screen, these values lie among the smallest polymer features reported to date for tomographic volumetric 3D printing and—within fluorinated photoresists—are the smallest reported to date (Section S3 of the Supporting Information).”\nRevised Figure 3 and caption:\n“Figure 1. (a) High-resolution tomographic printing. Several demanding geometries are shown; the smallest reproducible features span ~56–254 μm. Detailed information is provided in Section S3 of the Supporting Information. (b) Demonstration of structural versatility across application domains. In the biomedical context, vascular-like and porous scaffold architectures were printed. In industrial settings, custom-fitted fluorinated spacers were integrated into electronic assemblies, illustrating potential for chemically resistant, precisely dimensioned parts. For microfluidics, transparent channel structures with embedded flow paths were produced.”\nRevised discussion: “Features among the smallest reported for tomographic volumetric printing of polymers were reproducibly obtained under fixed conditions and reported with explicit CAD linkage (see SI §3).”\nAltogether, the manuscript now combines a fair positioning of feature sizes within the tomographic literature, clear, condition-bound evidence of fine, reproducible features across multiple geometries, and the core advance of closed-loop chemical recycling of the fluorinated content with near-quantitative recovery.\n7. The keywords “volumetric 3D printing” and “volumetric additive manufacturing” have the same meaning. And the meaning of “PFOS”.\nResponse to the reviewer comment:\nThank you for flagging the redundancy and the undefined abbreviation. We agree that “volumetric 3D printing” and “volumetric additive manufacturing” are synonymous; we retain the former and remove the latter to avoid duplication. We also remove “PFOS” as a keyword because it is not the subject of our experiments and would misdirect indexing toward pollutant toxicology; replacing it with “fluoropolymers” better reflects the scope on fluorinated polymer networks.\nThe revised manuscript keywords now list: “chemical recycling; volumetric 3D printing; fluoropolymers; thiol-ene photopolymerization; hydrolysis.”\nReviewer #2\nThe manuscript reports a strategy to enable 3D printing of a fluoropolymer material using radical thiol-ene photochemistry. Importantly, the authors go on to show that these materials can be deconstructed into their constituent monomer pre-cursors, which is an important goal with respect to recovery of these environmentally harmful molecules. This contribution focuses on the use of volumetric 3D printing. This method can overcome some of the challenges that other printing methods entail such as layer-to-layer adhesion. The chemistry applied in this study does not deviate greatly from that of many printing resins, relying on creating an allyl end capped fluorinated monomer that is subsequently crosslinked with a multi arm thiol. The study is thoroughly conducted and there are some nice innovations such as the removal of inhibitors which present an advantage to the methods reported. The print resolution is impressive and the recycling studies are great to see. There are however a few amendments to the paper that should be considered prior to publication:\n1. It is important to compare the materials' properties to existing fluoropolymer materials, both printed and molded so the significance of this contribution can be properly assessed.\nResponse to the reviewer comment:\nThank you for asking for a benchmark—this was an important gap in our initial submission, as we had mainly focused on showing property retention before and after chemical recycling. Your point helped us reframe the contribution in terms of where the material sits among established, gold- standard fluoropolymers. We have now benchmarked our material against a gold-standard fluoropolymer (molded, high–molar-mass PTFE).\nThe developed system is a crosslinkable, semi-crystalline fluorinated thermoset that operates above T at room temperature. Under tension, it shows a broad elastic window and large post- g yield ductility, yielding a work-to-break of 22.3 ± 13.2 J cm⁻³ versus 21.6 ± 10.4 J cm⁻³ for PTFE— statistically indistinguishable under our test geometry. In other words, our crosslinked network matches the toughness of PTFE, a high molar mass thermoplastic which is used across a wide range of applications. We attribute this toughness to a synergy between crystallinity coupled with a homogeneous thiol–ene network topology.\nRegarding ‘printed vs molded,’ because light-based 3D-printable fluorinated resins are not commercially available, and extrusion introduces process-dependent microstructures, we opted for a material benchmark to enable a fair comparison by class (i.e., thermoplastic vs thermoset).\nRelated to the benchmark, we have included the following discussion in the main manuscript\n“To contextualize performance against the fluoropolymer state-of-the-art, we benchmarked the material against a food-grade PTFE reference (also known by the brand name Teflon). PTFE shows the expected semicrystalline thermoplastic signature with higher stiffness and ultimate strength (Young’s modulus 458.6 ± 0.1 MPa; ultimate tensile strength 27.0 ± 0.3 MPa) but a lower elongation at break (188 ± 5 %). The developed semi- crystalline fluorinated network operates above its glass transition (≈1.3 °C) and retains residual crystallinity (crystallization and melting at ≈55 °C and ≈64 °C), which—together with a homogeneous thiol–ene network topology—yields large post-yield deformation, and a very high elongation at break (409 ± 108 %). Despite a lower stiffness and ultimate tensile strength (Young’s modulus 32.3 ± 14 MPa; ultimate tensile strength 6.6 ± 1.8 MPa), the extensive ductility gives a comparable toughness (work-to-break) under our test geometry. The resulting toughness is 22.3 ± 13.2 J cm⁻³ for HDF-X and 21.6 ± 10.4 J cm⁻³ for PTFE, i.e., comparable toughness within experimental variance. In other words, our crosslinked network matches the toughness of PTFE, a high molar mass thermoplastic which is used across a wide range of applications. Thermogravimetric analysis at 2% mass loss places the degradation onset near 295 °C for the network and 547 ± 0.4 °C for PTFE; while PTFE retains the higher thermal margin, the network’s stability is sufficient for many service environments well below 300 °C. Full datasets, replicate statistics, and analysis procedures are provided in Supporting Information §7.”\nAdditionally, we have included the actual data that was performed in a new section of the supporting information, as can be seen below:\n“S7. Benchmarking of the HDF-X against PTFE\nFigure S15 summarizes differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and uniaxial tensile data for the crosslinked fluorinated network (pristine and recycled) alongside a food-grade PTFE reference. The network operates above its glass transition (Tg ≈ 1.3 °C) and retains residual semicrystallinity, with Tc ≈ 55 °C and Tm ≈ 64 °C and enthalpies ΔHc = 6.9 J g⁻¹ and ΔHm = 5.6 J g⁻¹. PTFE exhibits the expected semicrystalline thermal signature under our DSC conditions, with Tc = 315 ± 2.7 °C and Tm = 328.7 ± 1.9 °C; a Tg was not observed in our measurement window. TGA (2% mass loss) places the degradation onset at 295 °C for the network and 547 ± 0.4 °C for PTFE. While PTFE retains a higher thermal margin, the network’s stability is adequate for many service environments with operating temperatures well below 300 °C.\nMechanical tests at ambient conditions show distinct class characteristics. The network has a modulus of 32.3 ± 14 MPa and an ultimate tensile strength of 6.6 ± 1.8 MPa, coupled to a substantial elongation at break of 409 ± 108 %. PTFE is stiffer and stronger with a Young’s modulus of 458.6 ± 0.1 MPa and an ultimate tensile strength of 27.0 ± 0.3 MPa, but breaks at a lower strain of 188 ± 5 %. The combination of moderate strength with very large ductility in the network indicates high energy absorption to failure (toughness). The toughness is 22.3 ± 13.2 J cm⁻³ for HDF-X and 21.6 ± 10.4 J cm⁻³ for PTFE, confirming comparable energy absorption to failure under the same test conditions.\nTaken together, the thermal and mechanical datasets capture the intended class-aware benchmark: a densely crosslinked, semi-crystalline fluorinated network whose residual crystallinity and homogeneous thiol–ene topology enable high toughness—uncommon for thermosets—while PTFE maintains the higher stiffness and higher thermal margin.\nFigure S15. Thermal and mechanical benchmarking of HDF-X versus PTFE. Side-by-side comparison of the thermal and tensile metrics for pristine and recycled HDF-X (left) and PTFE (right): TGA 2% mass-loss temperature, DSC transitions (T , T , T ), enthalpies (ΔH , g c m c ΔH ), modulus, ultimate stress, total elongation, and toughness. Shown data are mean ± m standard deviation based on triplicate measurements.”\nFinally, we included the following sentence in the material section of the paper related to the purchased benchmark materials.\n“PTFE benchmark: plate with a thickness of 1 mm (PerlaPlast, item no. 2900260001).”\nTaken together, the comparison shows a crosslinked fluorinated network with PTFE-level toughness (work-to-break 22.3 ± 13.2 vs 21.6 ± 10.4 J cm⁻³) while retaining the processing advantages of photopolymerization.\n2. I would disagree that the term 'closed loop' is appropriate to describe these materials, the fluorinated alcohol can be recovered but all other components will need to be added to a new resin to create a printable formulation and hence ca. 45% of the original chemicals are recovered to be reused and a large volume of additional chemicals is required to be added.\nResponse to the reviewer comment:\nThank you for the careful point on terminology. We agree that “closed loop” should be used with a clear system boundary. In our work, the loop is closed for the fluorinated content: alkaline urethane cleavage releases HDF-OH, which is re-functionalized and re-used; the non-fluorinated auxiliaries are replenished each cycle. To remove any ambiguity, we have made this explicit throughout the article and revised its title to: “Volumetric 3D Printing of a Fluoropolymer and Closed-Loop Chemical Recycling of its Fluorinated Content.” This wording makes clear that the closed loop pertains to the fluorinated fraction of the network.\nThe reviewer is also right that, in the current formulation, approximately 52 wt.% of the network is fluorinated content; the remainder must be replenished upon reprinting. Per cycle, however, the fluorinated monomer is recovered at 97.4% ± 2.1%, and we report the corresponding multi- cycle retention in the manuscript and the Supporting Information (refer to our reply to your 4th comment). Importantly, the recyclable fraction can be increased by raising the molar mass of the fluorinated diol, which directly increases the weight fraction of fluorinated content in the network. We therefore added a short analysis showing how the overall recyclable fraction increases to 82, 90, 93, and 94%, when the diol molar mass is increased to 2 000, 4 000, 6 000, and 8 000 g mol⁻¹, respectively (calculations and assumptions are provided below).\nWe chose, however, not to broaden the present study to multiple fluoropolymer backbones with different molar masses because our aim here is an integrated and detailed proof-of-concept that runs the full arc: material development → volumetric printing → chemical recycling → refunctionalization → reuse. Extending to additional precursors would require de novo optimization of the synthesis and workup, volumetric 3D printing, depolymerization parameters as well as purification, and full characterization—which was considered beyond the scope of the current contribution.\nRelated calculations linking diol molar mass to the recyclable fraction are provided in the Supporting Information:\n“S4.1 Scaling of the recyclable fraction with the molar mass of the fluorinated diol\nThe theoretically recyclable material fraction (%) increases with the molar mass of the fluorinated diol as follows;\n𝑅(𝑀 ) =\n2 𝑀𝐹\nEq. 6\n𝐹\n2 𝑀𝐹+873.38\nwhere 873.38 𝑔 𝑚𝑜𝑙⁻¹= 4𝑀 +𝑀 +𝑛 𝑀 for the resin used here.\n𝐴𝐼𝐶 𝑃𝐸𝑇𝑀𝑃 𝑃𝐸𝐺1𝑀 𝑃𝐸𝐺1𝑀\nTable S2. Recyclable material fraction as a function of fluorinated diol molar mass computed from equation 6.\nMolar mass fluorinated diol (g.mol-1) Recyclable material fraction (%)\n462 51.4\n2000 82.1\n4000 90.2\n6000 93.2\n8000 94.8\nTo reflect these important insights related to how the recyclable fraction scales with the molar mass of the fluorinated diol, we have included the following text in the main manuscript:\n“Since the herein reported work targets closed-loop recycling of the fluorinated content, the non-fluorinated components (crosslinker and photoinitiator) are replenished in subsequent cycles. Consequently, the recyclable mass fraction is determined by the fluorinated diol’s molar mass, amounting to ~52% for M of 462 g.mol-1 (the fluorinated n mass fraction of the network) and increasing to ~82%, ~90%, ~93%, and ~95% for M 2 n 000, 4 000, 6 000, and 8 000 g mol⁻¹, respectively (Supporting Information, Section S4.1).”\n3. In figure 4, why is the 475 peak absent in the recycled HDF-OH?\nResponse to the reviewer comment:\nThank you for asking us to clarify the LC–MS assignments. For HDE-OH (neutral exact mass 462.1305), the peak at 461 corresponds to the deprotonated ion [M–H]⁻ (calc. 461.1227). The signals at 507 and 521 are common anion-adducts formed in negative-mode ESI from trace mobile-phase acids: [M+HCOO]⁻ (formate; calc. 507.1282) and [M+CH₃COO]⁻ (acetate; calc. 521.1438); 522 is the M+1 isotope of the acetate adduct.\nHowever, the ∼475 signal does not seem to match any obvious adduct of HDE-OH. Yet, the functionalized material was recrystallized, and after recycling, it is therefore much purer than the pristine commercial sample; at LC–MS sensitivity, the 475 feature is consistent with a trace side component present only in the pristine lot. Our working hypothesis is a trifluoroacetate adduct of a lower-mass homolog (e.g., HDF-OH, neutral 362.1148): [homolog + CF₃COO – H]⁻ calc. 475.0999 m/z. Recrystallization is assumed to remove this minor homolog, resulting in the absence of the 475 peak in the recycled HDE-OH.\n4. Additionally, a yield of 77% of the fluorinated monomer is also not ideal as the remainder will be lost - have the authors optimized this process?\nResponse to the reviewer comment:\nThe authors agree that rigor around the recycling step is essential. Because all three reviewers independently raised this point, we executed a full condition matrix and were able to increase the recovery of the fluorinated monomer to 97.4 % ± 2.1 %. Thus, 97.4% of the fluorinated monomer is recovered after the first recycle–reuse loop, and that retained fraction compounds with each additional loop. In practice, this means that about 88% remains after five cycles and about 77% remains after ten cycles.\nWe systematically screened NaOH concentrations of 1.0, 2.5, and 5.0 M at 85 °C across hydrolytic degradation times ranging from 0.5 to 16 h. For each condition, we executed the complete workflow—alkaline reflux depolymerization, liquid–liquid extraction, aqueous washing/neutralization, and drying— with identical resin mass and solution volume. This investigation, initiated by the reviewers’ comments, increased the fluorinated-monomer recovery to 97.4% ± 2.1% at 2.5 M NaOH for 3 h, and is now used throughout the manuscript. Finally, repeatability at this condition was confirmed in triplicate (s.d. = 2.1%), significantly reducing cumulative loss over multiple reuse cycles.\nWe have included the following discussion related to the parameter screening into the main manuscript:\n“After establishing a general workflow—alkaline reflux depolymerization, neutralization, purification, and drying— through which the fluorinated diol could be recovered from volumetrically 3D printed constructs, the degradation conditions were optimized to maximize the chemical recycling yield of the fluorinated diol (Section S5). More precisely, a condition screen at 85 °C was performed across NaOH concentrations of 1.0, 2.5, and 5.0 M and depolymerization times from 0.5–16 h, executing the complete sequence for every timepoint. The optimal condition (2.5 M NaOH for 3 h) afforded a recovery of 97.4 % ± 2.1 % (n = 3). At this per-cycle recovery, the theoretical retained fraction after ten recycle–reuse cycles is ≈76.8 % of the original fluorinated content (see Supporting Information, Section S5, for the full data and calculations).\nThe recovery–time profiles delineate two regimes, depicted in Figure S10. In the kinetic regime, yield increases to a concentration-dependent maximum that is reached earlier at higher [NaOH] (5 M: ~1–1.5 h; 2.5 M: ~3 h; 1 M: no maximum within 16 h). This trend is consistent with base-catalyzed urethane cleavage in which the apparent rate scales with hydroxide activity (pseudo-first-order, 𝑘 ≈ 𝑘 [𝑂𝐻−]). Beyond the maximum, the 𝑜𝑏𝑠 𝑏 isolated yield declines at 2.5–5 M and approaches a plateau. It is hypothesized that the gradual formation of crosslinked/aggregated side-product particulates during prolonged alkaline treatment physically entrap a fraction of the fluorinated diol and resist subsequent extraction. Once the population of such particulates saturates, the recovery approaches the observed plateau. The optimum at 2.5 M, 3 h therefore marks the intersection of fast cleavage kinetics with minimal secondary entrainment, resulting in a recycling yield of the fluorinated monomer of 97.4 % ± 2.1 % (n = 3).”\nMoreover, we have included the actual data in Section S5 of the Supporting Information, ‘Optimization of chemical recycling conditions and multi-cycle retention of the fluorinated content’ as shown below:\n“S5. Optimization of chemical recycling conditions and multi-cycle retention of the fluorinated content\nRecovery of the fluorinated diol was optimized by varying NaOH concentration (1.0, 2.5, and 5.0 M) and depolymerization time (0.5–16 h) at 85 °C. For each condition, the whole workflow was carried out (alkaline reflux depolymerization, neutralization, purification, drying) with identical resin mass and solution volume. The optimal point (2.5 M, 3 h) was repeated in triplicate to obtain mean ± s.d. (97.4 % ± 2.1 %).\nFigure S10. (a) Recovery of HDF-OH versus time for NaOH concentrations of 1.0, 2.5, and 5.0 M. The optimal condition (2.5 M, 3 h) yielded 97.4% ± 2.1%. (b) Projected multi-cycle retention of the fluorinated content, calculated as 𝑓 = 𝑟𝑁with 𝑟 = 0.974.\n𝑁\nCalculation of the multi-cycle retention of the fluorinated content\nLet 𝑟 be the single-cycle recovery fraction (𝑟 = 0.974). After 𝑁 recycle–reuse cycles, the retained fraction of the original fluorinated content is\n𝑓 = 𝑟𝑁,\n𝑁\nand the cumulative loss is\n𝐿 = 1−𝑟𝑁.\n𝑁\nUsing the optimized recovery (𝑟 = 0.974), the retained fraction after 𝑁 = 10 cycles is\n𝑓 = 0.97410 ≈ 0.768(76.8%).”\n“Chemical recycling of HDF-OH from HDF-X. Prior to alkaline cleavage, volumetrically printed constructs were briefly ground with a mortar and pestle to eliminate geometry- dependent effects during degradation. A condition screen was performed at 85 °C under reflux, varying [NaOH] to 1.0, 2.5, and 5.0 M, and reaction time (0.5–16 h). For each condition, the same resin mass and solution volume were used and the full workflow was executed—alkaline depolymerization → neutralization to pH ≈ 7 with 1 M HCl → solvent removal by rotary evaporation → dissolution of the residue in diethyl ether (Et₂O) → filtration of insolubles → solvent removal → drying—to isolate HDF-OH (see Supporting Information Section S5). The optimized condition was identified as 2.5 M NaOH for 3 h at 85 °C, which afforded 97.4 % ± 2.1 % recovery (n = 3). For a representative batch, ground material (300 mg) was charged to a 50 mL round-bottom flask with 10 mL of 2.5 M NaOH and heated at 85 °C under reflux for 3 h. The reaction mixture was then neutralized to pH ≈ 7 by gradual addition of 1 M HCl. After neutralization, acetone was added to the aqueous phase (1:1 v/v water:acetone) to facilitate co-evaporation and streamline water removal during rotary evaporation. The mixture was concentrated by rotary evaporation to remove water and acetone, affording a solid residue. The residue was dissolved in diethyl ether (Et₂O), and the mixture was filtered to remove insoluble inorganic and polymeric by-products. The Et₂O-soluble fraction was collected, while the retained solids were washed thoroughly with deionized water to remove NaCl and other inorganic residues, then rinsed with hexane to displace residual water. The washed solids were subsequently re- extracted with Et₂O to recover any remaining HDF-OH. The combined Et₂O extracts were concentrated by rotary evaporation, and the resulting product was dried under vacuum at 40 °C for 2 h to afford purified HDF-OH, which was then re-functionalized as described in the preceding section.”\nReviewer #3 (Remarks to the Author)\nThe authors report the synthesis of an alkene-functional fluorinated monomer for thiol–ene crosslinking and its use for volumetric 3D printing. While the introduction of fluoropolymer for tomographic volumetric 3D printing has never been attempted, from my opinion, this is not sufficient in term of novelty to be considered for publication in a journal such as Nature Communications. Indeed, since the emergence of volumetric additive manufacturing (VAM), most of the photoresists developed for SLA/DLP printers have been successfully transferred to volumetric 3D printer (Bernal et al. Nature Review Materials 2025, https://doi.org/10.1038/s41578-025-00785-3, The road ahead in materials and technologies for volumetric 3D printing). The challenge, if any, to successfully 3D print fluorinated monomer regarding the condition of VAM photopolymerization is not clearly discussed.\nHowever, the authors also introduced a cleavable urethane linkage in the non degradable fluorinated precursor, allowing chemical recycling of the fluorinated monomer. This aspect is scarcely addressed for 3D printed fluoropolymer and consequently deserved to be highlighted.\nFinally, some of the conclusions that the authors draw from the data appear in their current form overstated. For instance, can we really say “closed-loop volumetric 3D printing” when more than half of the chemical should be replaced to make a new print? Besides, some aspects request additional experiments or explanation to obtain a comprehensive manuscript. In its current form the manuscript appears therefore too premature for publication in Nature communications.\nPlease check out my comments below.\n1. Evidence of the influence of PEG1M. Firstly, the authors have mentioned the role of PEG1M to suppress the sedimentation during printing, but no experimental evidence is given to illustrate this drawback and to explain how the authors have selected the optimal concentration (movie showing the sedimentation for different concentrations of PEG1M). See for instance SI Movie 1 & 2 of Loterie, D., Delrot, P. & Moser, C. High-resolution tomographic volumetric additive manufacturing. Nat Commun 11, 852 (2020). https://doi-org.inc.bib.cnrs.fr/10.1038/s41467-020-14630-4). Besides, the viscosity of the photoresists should be determined for concentrations of PEG1M ranging from 0 to 1.25 w% since it is a key parameter in the optimization step. The scheme depicted in Figure 2d is not sufficient to support the statement made by the authors.\nResponse to the reviewer comment:\nThank you for this insightful point. As requested, we quantified the role of PEG-1M on viscosity and sedimentation during printing by recording time-lapse videos during volumetric printing at PEG-1M loadings of 0, 0.25, 0.5, 0.75, 1, and 1.25 wt.% to visualize sedimentation during a print of 210 mJ.cm-2, with a printing time of 24 seconds. From these videos, we have exported the timeframes at 27 seconds, which is 3 seconds after the print has finished. The respective timeframes show that only the resin containing 1.25 wt.% is able to prevent sedimentation within this time window. In addition, we included viscosity measurements for the resin without and with the optimal concentration of 1.25 wt.% PEG1M.\nIn order to address the current comment, the authors have included the following new measurements and discussion to the supporting information:\n“S1.3 Influence of PEG1M on the viscosity\nTo visualize sedimentation during tomographic printing, back-lit time-lapse videos were recorded for formulations containing PEG1M at 0, 0.25, 0.5, 0.75, 1.0, and 1.25 w/v%. All prints used a total dose of 210 mJ cm⁻² with a 24 s irradiation; single frames at t = 27 s (i.e., 3 s after irradiation ended) are shown in Figure S4. Horizontal contrast bands that translate downward over time indicate settling within the print window. Pronounced band migration is evident for ≤1.0 w/v% PEG1M, whereas no discernible migration is observed at 1.25 w/v% within the same observation window, identifying 1.25 w/v% as the minimum loading that suppresses visible sedimentation under these conditions.\nFigure S4. Effect of PEG1M on sedimentation during volumetric 3D printing. Back-lit frames captured at t = 27 s (3 s after a 24 s print; total dose 210 mJ cm⁻²) for formulations containing 0, 0.25, 0.5, 0.75, 1.0, and 1.25 w/v% PEG1M. Boxes mark the region of interest used to score sedimentation. Visible band migration is observed for ≤1.0 w/v%, whereas no discernible sedimentation is seen at 1.25 w/v% within the observation window. Time- lapse sequences are provided in Supplementary Movies S1–S6; viscosity data across PEG1M loadings are reported in Figure S5.\nFigure S5. Viscosity measured by rheology (shear rate of 0.1 Hz) for the base resin (magenta) and the resin containing PEG1M at 1.25 w/v% (blue). The PEG1M addition produces a marked increase in viscosity across the measurement window, providing the targeted viscosity boost used to suppress sedimentation during volumetric printing.”\nFurthermore, the respective discussion was updated to include these additional experiments as shown below:\n“Resin viscosity was tuned to suppress gravitational sinking and within-print diffusion.22 A screening of PEG1M (Mₙ ≈ 10⁶ g mol⁻¹) from 0 to 1.25 w/v% identified 1.25 w/v% as the minimum loading that eliminated visible sedimentation over a 3 s window after volumetric 3D printing was completed (Supporting Information, Movies and Figure S4-S5). Moreover, viscosity increased markedly, from 0.1 Pa s to ~103 Pa s, with the introduction of 1.25 w/v% PEG1M, as shown by rheological measurements (Refer to Section S1.3, Figure S5). Accordingly, 1.25 w/v% PEG1M was used for all prints to stabilize the resin during exposure (Figure 2d).”\nMoreover, the following text was included in the experimental section:\n“Rheology was performed using the Anton Paar Physica MCR 302 with a parallel-plate setup (PP25 as the top plate, 25 mm diameter). Measurements were performed at 40 °C with a constant shear rate of 0.1Hz. An 80 μL mixture (HDF-ENE, PETMP, PEG1M, and CHCl3) was placed between the parallel plates with a 50 μm gap.”\nAdditionally, the videos from which the screenshot were taken are uploaded as supporting information, similarly to the work of Loterie et al., which was referenced in the comment.\n2. Origin of the delayed gelation. Secondly, the built-in inhibition is partially attributed by the authors to the presence of PEG1M, in particularly due to the modification of the viscosity. To confirm this hypothesis, photorheology experiment has to be performed in absence of PEG1M. Beyond viscosity issue (see previous point), another hypothesis proposed by the authors to explain the intrinsic inhibition of the photoresist without adding radical scavenger (such as TEMPO) is the fact that thiol-ene polymerization occurs through a step-growth mechanism. However, in their previous work with different precursors (Adv. Mater. 2023, 35 (19), e2210136. DOI: 10.1002/adma.202210136), step-growth thiol-ene polymerization was involved and the use of TEMPO was requested. I do not understand why in this specific case, step-growth will lead to delayed gelation (difference in the viscosity, photoreactivity of fluoropolymer vs its hydrogen-based counterpart?).\nResponse to the reviewer comment:\nThank you for pressing us to verify the origin of the photorheological latency—this was an important check. We repeated the measurements on matched formulations with and without PEG1M under identical conditions. Interestingly, the latency period and the transient dip in G′ were essentially unchanged, which does not support a PEG1M-driven viscosity origin. We therefore withdraw the earlier viscosity-based explanation and retain PEG1M only to mitigate sedimentation during printing (see Comment 1).\nOur current hypothesis is that the apparent delay reflects step-growth gelation in the tetra- thiol/bis-allyl formulation: an elastically percolated network—and thus a rise in G′—is expected only after a comparatively high functional-group conversion (≈58% for an ideal 4/2 system, Flory– Stockmayer). As correctly noted by the reviewer, this conversion threshold is also present in our earlier thiol–ene work (Adv. Mater. 2023, 35, e2210136), where we added TEMPO to deliberately extend the pre-gel window. The difference in practice between the two systems likely stems from resin-specific factors: in the present resin, the bifunctional alkene has a much lower molar mass (≈462 g mol⁻¹ versus 2 000–8 000 g mol⁻¹ previously), leading to shorter strands between crosslinks and different kinetics; the fluorinated backbone also differs from poly(ε-caprolactone) in polarity and oxygen/solvation behavior; and the volumetric dose schedule and employed photo-initiator are not identical. Together, these effects plausibly shift the time required to reach percolation so that an added inhibitor is unnecessary here. We emphasize that this mechanistic assignment should be interpreted with caution; fully deconvolving backbone, oxygen partitioning, solvent environment, and local microstructure lies beyond the present scope. In the revision, we include the +/− PEG1M datasets, withdraw the viscosity hypothesis, and present step-growth gelation as the leading explanation, while highlighting that the reported hypothesis should be interpreted with caution.\nWe have incorporated these new insights into the main article as follows:\n“Two hypotheses were considered for the rheological latency: (i) a PEG1M-induced viscosity barrier that delays network formation, and (ii) the intrinsic gelation threshold of step-growth thiol–ene networks. Matched photorheology on formulations with and without PEG1M yielded the same inhibition period, excluding hypothesis (i) (Section S1.4). We therefore attribute the latency primarily to hypothesis (ii): by Flory–Stockmayer theory, an elastically percolated network forms only beyond ~58% functional-group conversion for a tetrafunctional thiol with a bifunctional alkene.28,29 However, it should be noted that the stated hypothesis should be interpreted with caution, as the onset and magnitude of the latency can be affected by other contributions (e.g., fluorinated- backbone solvation, oxygen solubility, the solvent environment, local microstructure, and light intensity-dependent kinetics). Fully disentangling these contributions lies beyond the scope of the present study. Separately, the small decrease in G′ observed immediately after illumination but prior to gelation is consistent with a modest reaction exotherm that transiently raises temperature, lowers viscosity, and increases mobility.”\nAdditionally, we have included the photo-rheological data in the Supporting Information as shown below:\n“S1.4 Influence of PEG1M on the inhibition period in photo-rheology\nTo test whether the rheological latency originates from PEG1M-induced viscosity effects, we repeated photorheology on matched formulations with and without PEG1M under identical irradiation; the latency and G′ trajectory were unchanged.\nFigure S6. Photorheology with/without PEG1M at 405 nm, 10 mW cm⁻²; light on at t = 10 s. Solid line: storage modulus (G′); dashed line: loss modulus (G″). Both traces show similar latency and rise, indicating PEG1M is not the origin.”\n3. Determination of the optimal printing dose for volumetric. Photorheological experiments are used to determine the optimal printing dose. However, the comparison between the light intensities used during photorheology experiments and those used in volumetric printing is not clearly established. This information is crucial, as photoreactivity and polymerization kinetics can be strongly influenced by light intensity and exposure time (or here manufacturing time). Moreover, experimental configuration should also influence the results: while in photorheology, the thickness is set to few hundred micrometers with continuous irradiation, for volumetric printing, the length is around 7 mm. Clarification on this point is necessary in order to assess the transposability of results between the two experimental contexts. And light intensity and manufacturing time should be specified, the latter being also important to assess if sedimentation can occur in this time scale.\nResponse to the reviewer comment:\nThank you for this careful and expert comment. You are absolutely right that light intensity and attenuation govern transposability, and our original text did not make that mapping explicit enough. In the present work, photorheology is used to define a kinetic light-dose window under conditions that match volumetric printing in wavelength and irradiance: both setups use 405 nm, and the irradiance at the sample is comparable (photorheology ≈ 9.5 mW cm⁻²; volumetric 3D printing average ≈ 9.56 mW cm⁻², measured radiometrically). The optimal rheological dose is identified by the computational contrast (i.e., the ratio of the light dose that the out-of-part voxels receive to the light dose that the in-part voxels receive) and the gelation light dose.\nWe do not convert this delivered rheology dose into a tomographic “absorbed dose.” Instead, the two volumetric 3D printing-specific factors that differ from rheology are handled separately: attenuation across the ~7 mm path is addressed during resin design by Beer–Lambert calculations used to set the photoinitiator concentration at 405 nm, and sedimentation is addressed by increasing viscosity with PEG1M and verifying—by time-lapse videos—that no visible settling occurs over the 24 s manufacturing time used here.\nWe have revised the manuscript to state explicitly the wavelength, irradiances, and manufacturing time; to clarify that photorheology yields the kinetic window while attenuation and sedimentation are treated separately. We would like to note, however, that this framework builds on prior published work where these crucial considerations are discussed in much greater depth, and, for readers interested in the full methodology that links photorheology to tomographic printing (kinetic modelling, FTIR validation on dose-stopped rheology samples, and a discussion of reciprocity and geometric limits), we have made the reference to our previously published framework more clear throughout the manuscript.\nThe following text was introduced to the manuscript to address the reviewer’s comment:\n“To identify a suitable volumetric 3D printing light dose, photorhelogy and volumetric printing were wavelength- and irradiance-matched (405 nm in both cases; ≈ 9.5 mW cm⁻² at the rheology sample and 9.56 mW cm⁻² average in volumetric 3D printing). In combination with a computational contrast of 0.5–an appropriate computational contrast for most designs in tomographic volumetric 3D printing–dose thresholds, at which in-part voxels begin to gel while out-of-part voxels remain sub-gel, can be established. The middle of this range then corresponds to the selected light dose of 180 mJ cm⁻², at which in-part voxels are sufficiently cured to resist gravity-driven collapse while out-of-part voxels remain below the gelation threshold.22 This photorheological framework does not account for attenuation across the ~7 mm path during tomographic printing or for sedimentation, owing to the small rheometer gap (~300 µm) and static geometry. These two factors were therefore addressed separately before applying the photorheological window—attenuation by setting the photoinitiator concentration via Beer–Lambert calculations for the vial geometry (Section S1.1 and S1.2), and sedimentation by viscosity tuning with PEG1M (Section S1.3). For full methodological details underpinning this framework refer to the cited work.22”\n4. Optical properties of the photoresists. The authors indicate that the absorbance value of 0.85 was chosen because, according to the Beer-Lambert law, it corresponds to a light intensity drop of about 20%. However, it is not explained why this 20% loss is considered acceptable. This threshold appears to have been set arbitrarily, without experimental or theoretical justification. It is important to explain the criteria on which this limit was based, and how it aligns with the requirements of the printing process. Furthermore, the Tomolite printer is supposed to incorporate an optical compensation function. In the section regarding fabrication parameters, an absorption value of 2.00 cm-1 is indicated. This choice is not sufficiently explained: why was this specific value selected? In addition, the relationship between this absorption value (2.00 cm-1) and the absorbance of 0.85 is not clearly established. The correspondence between these two quantities is neither detailed nor referenced, which leads to confusion in data interpretation. A clarification on this point would be welcome. Another aspect concerns the refractive index (1.45). It should be indicated how it has been determined and for which wavelength ?\nResponse to the reviewer comment:\nThank you for this careful observation. You are right that our wording around “~20% drop” reads as arbitrary. In practice, the attenuation setting was chosen to sit within the optical- compensation envelope of the Tomolite/Apparite reconstruction at 405 nm. The software compensates through-volume attenuation reliably up to a Napierian absorption coefficient μ = 2.0 cm⁻¹. We therefore set the initiator loading so that the resin’s attenuation is at (but not above) this limit. In base-10 terms, this corresponds to an absorbance per centimetre of A = μ/ln 10 ≈ 2.0/2.303 ≈ 0.87, which matches the A ≈ 0.85 cm⁻¹ we report by UV–Vis. Selecting this value balances photoreactivity (high photoinitiator concentration) with the attenuation compensation and is not an arbitrary “percentage loss” rule. We have revised the discussion in the main manuscript as shown below:\n“To ensure accurate dose delivery during tomographic exposure, the photoinitiator concentration was determined using Beer–Lambert calculations together with the optical-compensation range of the printer software at 405 nm. The Tomolite/Apparite reconstruction compensates attenuation up to a Napierian absorption coefficient μ = 2.0 cm⁻¹; we therefore selected a resin absorbance near this upper bound. In base-10 terms this corresponds to A = μ/ln 10 ≈ 0.87 cm⁻¹, consistent with the measured UV–Vis absorbance of ≈ 0.85–0.87 cm⁻¹ for the final formulation (Section S1.1 and S1.2). This choice maximizes photoreactivity while remaining within the instrument’s compensation envelope.”\nFinally, regarding the refractive index used in reconstruction, we set n = 1.45 at 405 nm. This value was chosen by reference to the dominant liquid component in the formulation (chloroform) and cross-checked against literature values for closely related fluoropolymers (e.g., poly(trifluoroethyl methacrylate), reported n ≈ 1.44). We have added this clarification to the manuscript as shown below:\n“Volumetric 3D Printing. Volumetric 3D printing was performed using the Tomolite v2.0 (405 nm light source) from Readily 3D. In Apparite 1.2.4, the following settings were applied: “Refractive Index” set to 1.450 (chosen to match the dominant solvent, chloroform, and consistent with related fluorinated monomers such as poly(trifluoroethyl methacrylate, n ≈ 1.44)), “Absorption” set to 2.00 cm⁻¹ (base-10 absorbance A ≈ μ/ln 10 = 0.87 cm⁻¹, consistent with UV–Vis A ≈ 0.85–0.87 cm⁻¹), “Bulk Length” set to “Off,” and “Bulk Strength” set to “Off.” The test tube was measured for the vial profile, with the “Glass” type set to BK7, an “Outer Diameter” of 7.49 mm, and a “Thickness” of 0.92 mm. After volumetric printing, the print was rinsed with acetone to remove uncured resin, followed by post-curing with UV-A light (365 nm, 5 mW cm⁻², 2 h). After post-curing, the prints were air-dried.”\n5. Resolution issue – feature size. The authors report feature sizes down to 15.5 µm (negative one) as the “smallest negative features reported to date for volumetric 3D printing” and highlight this fact in the abstract. How the authors can explained such resolution? Is it due to the chemistry (and why)? Or is it due to the optical system? Can they give details about the optical configuration of their printer?\nAccording to the current experimental data, this statement is overexaggerated. The provided optical microscopic images do not allow reliable conclusions to be drawn regarding the resolution achieved. It is difficult to determine whether this is due to an actual resolution limitation, a fabrication artefact, or surface defects. It is recommended to acquire higher-quality images, particularly using a scanning electron microscope (SEM), in order to confirm the observations. CAD model should be provided to discuss printing fidelity and state on the merit of the chemistry or optical set-up. The choice of the « Klein bottle » object for evaluating resolution appears to be poorly suited. It would be preferable to use a standardized test object, such as a grid pattern or regularly spaced lines, to allow a more rigorous and objective assessment of resolution performance. More interesting/convincing will be the printing of the microfluidic chip with internal channel of 15.5 µm width and few millimetres length (see Gong et al. Lab Chip, 2017, 17, 2899, DOI: 10.1039/c7lc00644f, Custom 3D printer and resin for 18 μm × 20 μm microfluidic flow channels).\n6. Printing fidelity. In a general manner, the CAD models should be provided with the expected dimension to assess the printing fidelity. For instance, in Figure 3b, the microfluidic system seems to be distorted (inhomogeneous geometry). Is this an expected phenomenon or a fabrication defect? Printing fidelity to be discussed.\nCombined response to reviewer comments 5 and 6:\nThank you for the thoughtful critique of the feature-size claim and the request for clearer evidence of fidelity. We agree that the earlier abstract gave undue weight to a single minimum value relative to the evidence shown—a tendency that is common in reports on tomographic volumetric printing. In the revision, the claim is reframed: we report reproducible feature sizes with explicit CAD linkage across several demanding geometries, while keeping the central contribution—volumetric 3D printing of a fluorinated network together with closed-loop chemical recycling of the fluorinated content—front and center.\nIn tomographic volumetric printing, the smallest reliably formed feature is not dictated by optics alone. It reflects the design-dependent computational contrast in the back-projection, resin kinetics around gelation, viscosity with associated diffusion and sedimentation during and after exposure, polymerization shrinkage, and post-processing choices such as wash solvent and time. Because these factors couple, assigning a particular small feature to a single cause would be speculative and lies beyond the scope of the present work. Rather than advancing an ultimate resolution limit, we document what is reproducibly achieved under clearly specified conditions and provide the information needed for others to interpret those outcomes.\nTo position the results, the Supporting Information now includes a curated overview of reported feature sizes in tomographic volumetric printing derived from a screen of 37 studies; fourteen papers that list explicit numerical values were retained. Table S1 collates those minima to indicate what has been achieved in the field and to contextualize the condition-bound features reported here. As noted in your comment, many publications present a single “best-case” feature size without linking back to design. In tomographic volumetric 3D printing, such single-feature reporting is not adequate due to its relatively low computational contrast (i.e., the difference between the light dose that in-part and out-of-part voxels receive), as compared to stereolithography (SLA) or digital light processing (DLP), where out-of-part voxels typically don’t receive any light (i.e., perfect computational contrast). As a result, the out-of-part voxels fundamentally limit the dose that in-part voxels can receive, and, therefore, the apparent feature size can depend strongly on the washing step. In the revised manuscript, we make this linkage explicit.\nWe also strengthened the experimental evidence underlying our values. The single-geometry showcase has been replaced by a multi-geometry presentation. For each design, we report the measured feature size alongside the corresponding CAD dimension at that exact location, so any deviation is explicit. The images show continuous features rather than surface artefacts, addressing the fidelity concern, and the CAD files with nominal dimensions are provided so readers can assess fidelity directly. Optical microscopy is retained because the features are clearly resolved at the stated scales; SEM is not required to substantiate the widths we report.\nThe following text has been added to the Supporting Information:\n“S3. Feature-size in tomographic volumetric 3D printing. In tomographic volumetric printing, the smallest reliably formed feature is not dictated by optics alone. It is governed by the design-dependent computational contrast in back-projection, resin kinetics around gelation, viscosity together with diffusion and sedimentation during and after exposure, polymerization shrinkage, and post-processing choices such as wash solvent and time. Rather than advancing an ultimate resolution limit, we document what is reproducibly achieved under fixed conditions and provide the information needed for others to interpret those outcomes.\nS3.1 Literature positioning of volumetric 3D printing resolution. To contextualize the obtained feature sizes in the current work, we screened 37 publications on tomographic volumetric 3D printing and retained 14 that report explicit numerical values (restricted to tomographic volumetric 3D printing and excluding post-sintered ceramics). Table S1 collates these reported minima. Only two papers provide a direct design-to- measurement comparison: Kelly et al. (2019) report a 200 µm tail-fin tip radius versus a 400 µm design (sharper than intended), and Orth et al. (2023) report 195–200 µm versus ~180 µm for a gyroid wall and 580 µm versus ~500 µm for a pore. Most articles list single ‘best-case’ values with little to no linkage to CAD or reproducibility. The purpose of Table S1 is transparency: to position achievable feature sizes in tomographic volumetric printing and to provide readers with context for interpreting the condition-bound feature sizes reported here.\nS3.2 Experimental and theoretical feature sizes of volumetric 3D printed constructs. Figure S8 pairs each CAD model with its simulated back-projection contrast and a micrograph at the narrowest measured element. Across the four designs shown, the smallest observed features are ~56 µm, ~66 µm, ~97 µm, and ~254 µm; the corresponding CAD dimensions at those exact locations are indicated in the contrast panels. Set against the survey in Table S1, these values sit among the smallest polymer features reported for tomographic volumetric printing. Only a few studies approach this scale with comparable clarity of reporting; notably, Toombs et al. (2022) demonstrate ~20 µm polymer features on a different platform. It should be noted that the very small ‘positive’ values reported by Bernal et al. (2022) and by Falandt et al. (2023) correspond to the outermost tip of a star-shaped element; such apex measurements are highly sensitive to washing and do not represent generally reproducible line or strut widths.\nThe gap between CAD and experiment is expected. In tomographic exposure, the achievable width at a given location is governed by local computational contrast from back-projection, the resin’s conversion profile near gelation, and the subsequent washing step, which can remove weakly crosslinked material at feature edges. Additional contributors include polymerization shrinkage and any swelling or surface relaxation during post-processing. Because most papers in the field report single ‘best-case’ numbers without CAD-to-measurement linkage—Kelly et al. (2019) and Orth et al. (2023) are rare exceptions—Figure S8 provides that linkage explicitly so that readers can interpret the condition-bound features observed here.\nTable S1. Reported feature sizes in tomographic volumetric 3D printing. Minimum feature sizes as stated in the cited publications, restricted to tomographic volumetric methods and to papers that report explicit numerical values (studies without clear values are not included). Positive = solid features (e.g., struts/walls); negative = open features (e.g., channels/voids). Ceramics (post-sintered) are excluded. Values were distilled from a screen of 37 publications; only entries meeting the criteria above are listed.\nPaper Geometry Feature size\nKelly et al, 2019 [1] Airplane tail-fin tip radius 200 µm (positive)\nBernal et al, 2019 [2] Trabecular bone model and microfluidic channel 144.7 µm (positive) and 200 µm (negative)\nLoterie et al, 2020 [3] Notre Dame model and 3DBenchy chimney aperture 80 µm (positive) and 500 µm (negative)\nToombs et al, 2022 [4] Cubic lattice 20 µm (positive)\nBernal et al, 2022 [5] Outermost tip of a star and microfluidic channel 41.5 (positive) and 104.0 (negative)\nThijssen et al, 2023 [6] Lattice struts 100 µm (positive)\nChansoria et al, 2023 [7] Auxetic mesh (second layer) ≈289 μm (positive)\nFalandt et al, 2023 [8] Outermost tip of a star and microfluidic channel 23.7 µm (positive) and 176.0 µm (negative)\nOrth et al, 2022 [9] Gyroid top-surface pore and Gyroid interior walls 195–200 μm (positive) and 580 μm (negative)\nXie et al, 2023 [10] Solid bar 45.9 μm (positive)\nOrth et al, 2023 [11] Spacing between lattice struts 0.465 mm (negative)\nLian et al, 2024 [12] Solid rod with bars and cube array ≈79 μm (positive) and ≈137 μm (negative)\nDuquesne et al, 2025 [13] Prism tips and Swiss cylinder holes 138.83 µm (positive) and 198.97 µm (negative)\nThijssen et al, 2025 [14] TPMS I WP lattice ~300–400 µm (positive)\nFigure S8. (a) CAD design of each test geometry with the measured feature location indicated. (b) Computational contrast from tomographic back-projection at the corresponding cross-section; circles mark the positions used for measurement. (c) Optical micrographs of the same locations showing the smallest reproducible feature; measured widths are annotated (scale bars as shown). (d) Side-by-side comparison of theoretical (CAD) versus experimental feature size for each geometry, highlighting the expected disparity arising from local contrast, conversion near gelation, and wash-driven removal of partially converted material.”\nIn addition, the Methods now provide the optical resolution of the volumetric 3D printing used in this work, as shown: “Volumetric 3D Printing. Tomographic volumetric prints were produced on a Tomolite v2.0 (Readily3D, 405 nm source; nominal voxel pitch 25 µm) with projection and continuous rotation controlled in Apparite 1.2.4. CAD files and nominal dimensions for all resolution-test geometries are provided in SI §3.”\nRevised abstract line: “The photoresist—based on an alkene-functionalized fluorinated diol and a multifunctional thiol—supports rapid fabrication of centimeter-scale objects with reproducible feature sizes down to 56 μm, among the smallest reported to date.”\nRevised text related to resolution in the main manuscript: “By means of this photorheological framework, a suitable light dose of 180 mJ cm⁻² was determined.22 At this dose, the optimized resin enabled high-resolution tomographic printing across multiple geometries. Rather than quoting a single minimum, we report condition-bound, reproducible features with explicit CAD linkage (see SI §3): the smallest measured widths across our test set are ~56, ~66, ~97, and ~254 μm at the indicated locations. Benchmarked against a curated literature screen, these values lie among the smallest polymer features reported to date for tomographic volumetric 3D printing and—within fluorinated photoresists—are the smallest reported to date (Section S3 of the Supporting Information).”\nRevised Figure 3 and caption:\n“Figure 2. (a) High-resolution tomographic printing. Several demanding geometries are shown; the smallest reproducible features span ~56–254 μm. Detailed information is provided in Section S3 of the Supporting Information. (b) Demonstration of structural versatility across application domains. In the biomedical context, vascular-like and porous scaffold architectures were printed. In industrial settings, custom-fitted fluorinated spacers were integrated into electronic assemblies, illustrating potential for chemically resistant, precisely dimensioned parts. For microfluidics, transparent channel structures with embedded flow paths were produced.”\nRevised discussion: “Features among the smallest reported for tomographic volumetric printing of polymers were reproducibly obtained under fixed conditions and reported with explicit CAD linkage (see SI §3).”\nAltogether, the manuscript now combines a fair positioning of feature sizes within the tomographic literature, clear, condition-bound evidence of fine, reproducible features across multiple geometries, and the core advance of closed-loop chemical recycling of the fluorinated content with near-quantitative recovery.\n7. Chemical recycling. The study does not evaluate the effect of multiple recycling cycles on monomer purity, side product accumulation, or long-term property retention. Only one recycling/reprint cycle is rigorously characterized. The environmental benefit of the closed-loop system is asserted 77% monomer recovery (vs. theoretical maximum) implies significant loss after multiple recycling. Thus, life cycle assessment may be required. Since degradability is design-dependent owing to diffusion issue, could you indicate the shape and dimension of the volumetric printed object for such test? What are the shape / dimension of the printed object used for the mechanical test (before and after recycling)?\nResponse to the reviewer comment:\nThe authors agree that rigor around the recycling step is essential. Because all three reviewers independently raised this point, we executed a full condition matrix and were able to increase the recovery of the fluorinated monomer to 97.4 % ± 2.1 %. Thus, 97.4% of the fluorinated monomer is recovered after the first recycle–reuse loop, and that retained fraction compounds with each additional loop. In practice, this means that about 88% remains after five cycles and about 77% remains after ten cycles.\nWe systematically screened NaOH concentrations of 1.0, 2.5, and 5.0 M at 85 °C across hydrolytic degradation times ranging from 0.5 to 16 h. For each condition, we executed the complete workflow—alkaline reflux depolymerization, liquid–liquid extraction, aqueous washing/neutralization, and drying— with identical resin mass and solution volume. This investigation, initiated by the reviewers’ comments, increased the fluorinated-monomer recovery to 97.4% ± 2.1% at 2.5 M NaOH for 3 h, and is now used throughout the manuscript. Finally, repeatability at this condition was confirmed in triplicate (s.d. = 2.1%), significantly reducing cumulative loss over multiple reuse cycles.\nWe have included the following discussion related to the parameter screening into the main manuscript:\n“After establishing a general workflow—alkaline reflux depolymerization, neutralization, purification, and drying— through which the fluorinated diol could be recovered from volumetrically 3D printed constructs, the degradation conditions were optimized to maximize the chemical recycling yield of the fluorinated diol (Section S5). More precisely, a condition screen at 85 °C was performed across NaOH concentrations of 1.0, 2.5, and 5.0 M and depolymerization times from 0.5–16 h, executing the complete sequence for every timepoint. The optimal condition (2.5 M NaOH for 3 h) afforded a recovery of 97.4 % ± 2.1 % (n = 3). At this per-cycle recovery, the theoretical retained fraction after ten recycle–reuse cycles is ≈76.8 % of the original fluorinated content (see Supporting Information, Section S5, for the full data and calculations).\nThe recovery–time profiles delineate two regimes, depicted in Figure S10. In the kinetic regime, yield increases to a concentration-dependent maximum that is reached earlier at higher [NaOH] (5 M: ~1–1.5 h; 2.5 M: ~3 h; 1 M: no maximum within 16 h). This trend is consistent with base-catalyzed urethane cleavage in which the apparent rate scales with hydroxide activity (pseudo-first-order, 𝑘 ≈ 𝑘 [𝑂𝐻−]). Beyond the maximum, the 𝑜𝑏𝑠 𝑏 isolated yield declines at 2.5–5 M and approaches a plateau. It is hypothesized that the gradual formation of crosslinked/aggregated side-product particulates during prolonged alkaline treatment physically entrap a fraction of the fluorinated diol and resist subsequent extraction. Once the population of such particulates saturates, the recovery approaches the observed plateau. The optimum at 2.5 M, 3 h therefore marks the intersection of fast cleavage kinetics with minimal secondary entrainment, resulting in a recycling yield of the fluorinated monomer of 97.4 % ± 2.1 % (n = 3).”\nMoreover, we have included the actual data in Section S5 of the Supporting Information, ‘Optimization of chemical recycling conditions and multi-cycle retention of the fluorinated content’ as shown below:\n“S5. Optimization of chemical recycling conditions and multi-cycle retention of the fluorinated content\nRecovery of the fluorinated diol was optimized by varying NaOH concentration (1.0, 2.5, and 5.0 M) and depolymerization time (0.5–16 h) at 85 °C. For each condition, the whole workflow was carried out (alkaline reflux depolymerization, neutralization, purification, drying) with identical resin mass and solution volume. The optimal point (2.5 M, 3 h) was repeated in triplicate to obtain mean ± s.d. (97.4 % ± 2.1 %).\nFigure S10. (a) Recovery of HDF-OH versus time for NaOH concentrations of 1.0, 2.5, and 5.0 M. The optimal condition (2.5 M, 3 h) yielded 97.4% ± 2.1%. (b) Projected multi-cycle retention of the fluorinated content, calculated as 𝑓 = 𝑟𝑁with 𝑟 = 0.974.\n𝑁\nCalculation of the multi-cycle retention of the fluorinated content\nLet 𝑟 be the single-cycle recovery fraction (𝑟 = 0.974). After 𝑁 recycle–reuse cycles, the retained fraction of the original fluorinated content is\n𝑓 = 𝑟𝑁,\n𝑁\nand the cumulative loss is\n𝐿 = 1−𝑟𝑁.\n𝑁\nUsing the optimized recovery (𝑟 = 0.974), the retained fraction after 𝑁 = 10 cycles is\n𝑓 = 0.97410 ≈ 0.768(76.8%).”\n“Chemical recycling of HDF-OH from HDF-X. Prior to alkaline cleavage, volumetrically printed constructs were briefly ground with a mortar and pestle to eliminate geometry- dependent effects during degradation. A condition screen was performed at 85 °C under reflux, varying [NaOH] to 1.0, 2.5, and 5.0 M, and reaction time (0.5–16 h). For each condition, the same resin mass and solution volume were used and the full workflow was executed—alkaline depolymerization → neutralization to pH ≈ 7 with 1 M HCl → solvent removal by rotary evaporation → dissolution of the residue in diethyl ether (Et₂O) → filtration of insolubles → solvent removal → drying—to isolate HDF-OH (see Supporting Information Section S5). The optimized condition was identified as 2.5 M NaOH for 3 h at 85 °C, which afforded 97.4 % ± 2.1 % recovery (n = 3). For a representative batch, ground material (300 mg) was charged to a 50 mL round-bottom flask with 10 mL of 2.5 M NaOH and heated at 85 °C under reflux for 3 h. The reaction mixture was then neutralized to pH ≈ 7 by gradual addition of 1 M HCl. After neutralization, acetone was added to the aqueous phase (1:1 v/v water:acetone) to facilitate co-evaporation and streamline water removal during rotary evaporation. The mixture was concentrated by rotary evaporation to remove water and acetone, affording a solid residue. The residue was dissolved in diethyl ether (Et₂O), and the mixture was filtered to remove insoluble inorganic and polymeric by-products. The Et₂O-soluble fraction was collected, while the retained solids were washed thoroughly with deionized water to remove NaCl and other inorganic residues, then rinsed with hexane to displace residual water. The washed solids were subsequently re- extracted with Et₂O to recover any remaining HDF-OH. The combined Et₂O extracts were concentrated by rotary evaporation, and the resulting product was dried under vacuum at 40 °C for 2 h to afford purified HDF-OH, which was then re-functionalized as described in the preceding section.”\nOn the request for multiple recycle–reuse loops: our closed-loop design targets chemical recycling to the identical fluorinated monomer (HDF-OH). Given the fact that we verified chemical identity (NMR/MS) and property parity upon reprinting (thermal/mechanical metrics within statistical variation), running additional physical cycles does not probe a changing material state (unlike vitrimers or mechanical reprocessing, where properties can drift with each pass); it primarily tests process robustness. We therefore report the analytically grounded cumulative retention fₙ = rⁿ (with r measured at the optimized condition) and perform only one cycle experimentally.\nRegarding geometry and diffusion limits during degradation: prior to alkaline cleavage, all printed parts were ground to a powder. As a result, the original object shape and dimensions do not govern recovery time in our protocol; kinetics are controlled by solution conditions and the extraction sequence. The following sentence is stated in the experimental part of the paper: “Prior to alkaline degradation, volumetrically printed constructs were briefly ground with a mortar and pestle to eliminate geometry-dependent effects during degradation.”\nFinally, we have now specified the shapes/dimensions of the printed objects used for recycling and for mechanical testing in the Experimental section, as shown: “Bars with a length of 10 mm, a thickness of 1 mm, and a width of 4 mm, were volumetrically 3D printed and evaluated.”\nSome minor Points\n1. The equation in page 20 mention PCL but PCL has not been used in this work. See also in the text, PCL to be removed.\nResponse to the reviewer comment:\nMany thanks for noting this mistake. We have rectified the mistake as shown below:\n“To determine the alkene content, dimethyl terephthalate (DMT, 10 mg, 0.05 mmol, 1 eq., M = 194.18 g.mol-1) was added as internal 1H-NMR standard to 10 mg of the respective HDF-E precursor and CDCl . NMR spectra were analyzed in MestReNova software and 3 the fully automatic baseline correction (Whittaker Smoother) was applied. The alkene content was calculated as follows:\n𝐴𝑙𝑘𝑒𝑛𝑒 𝑐𝑜𝑛𝑡𝑒𝑛𝑡 (𝑚𝑜𝑙.𝑔−1) = 𝐼(𝛿5.2)+𝐼(𝛿5.8) ∗ 𝑁(𝐷𝑀𝑇) ∗ 1 Eq. 1\n𝐼(𝛿8) 𝑁(𝑎𝑙𝑘𝑒𝑛𝑒) 𝑀𝑀(𝐷𝑀𝑇) 𝑚(𝐻𝐷𝐹−𝐸)\n‘I‘ stands for the integrated value of the peaks compared to the signal from DMT at 8 ppm. ‘N’ is the amount of protons of DMT and the alkene functional group. ‘m’ refers to the weighed mass and ‘MM’ refers to the molar mass.”\n2. Both References 26 and 28 are identical\nResponse to the reviewer comment:\nMany thanks for noting this. We have removed the reference duplicate.\nReviewer #4 (Remarks to the Author)\nI co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have addressed all of our questions in the revised manuscript. Additionally, since Reviewer #2 is not available to comment on the revised version, and with the editor's approval, I have taken another careful look at the revision myself. In my opinion, the issues raised by Reviewer #2 have also been adequately addressed.", "reviewer_3": "The authors have adequately addressed all comments and incorporated the necessary revisions into the reorganized manuscript.The manuscript is now considered ready for publication in Nature Communications.\nQuentin Bauerlin and Arnaud Spangenberg", "reviewer_4": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts."}, "author_response": ""}]

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