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. 2026 Jul 14;11(29):44275–44283. doi: 10.1021/acsomega.6c04488

3D Printing of Mechanically Robust Elastomers: Molecular Design and Fabrication with Urea-Containing Photocurable Monomers

Guohong Shi †,‡, Jiexiang Tong †,‡,*, Ren Liu †,‡,*
PMCID: PMC13425311  PMID: 42540199

Abstract

The mechanical properties of UV-cured elastomers for digital light processing (DLP) 3D printing are essential for their practical applications. However, it remains challenging for printed elastomers to achieve both a high mechanical strength and excellent ductility. In this work, a series of novel photocurable monomers containing urea groups were synthesized via a simple one-step method and then used to fabricate mechanically robust elastomers through DLP 3D printing. The UV-cured elastomer systems showed high photopolymerization activity, which was compatible with the DLP 3D printing process. The as-prepared elastomers exhibited a high elongation at break (326%) while maintaining a high mechanical strength (20.7 MPa). The robust mechanical performances are attributed to the presence of urea groups in the molecular structure of photocurable monomers, which could act as physical cross-linking points to effectively dissipate the mechanical energy. In addition, the honeycomblike elastomers printed by DLP printing demonstrated excellent energy absorption capacity and could support a heavy weight (480 times their own weight) without any collapse. This study provides a simple and effective strategy for preparing mechanically robust elastomers for DLP-3D printing.

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1. Introduction

3D printing is a booming fabrication technology that enables the fabrication of elastomers with intricate architectures and novel functionalities, which far surpass those of their bulk counterparts. − Among various 3D printing technologies, digital light processing (DLP) 3D printing has attracted increasing attention, benefiting from its high efficiency and resolution. − Superior mechanical properties are essential for elastomers to ensure reliable long-term service. However, photocurable elastomers for DLP printing generally face a trade-off between strength and ductility, which significantly restricts their practical applications. − Therefore, photocurable elastomers with outstanding mechanical performance for DLP 3D printing need to be developed.

The photocurable monomers for DLP printing systems are typically (meth)­acrylic monomers. In general, the printed elastomers fabricated from monofunctional photocurable monomers exhibit high ductility but low strength owing to low cross-linking density. In contrast, the adoption of difunctional or multifunctional photocurable monomers results in elastomers with low ductility but high strength because of elevated cross-linking density. Therefore, it is difficult for commonly used photocurable monomers to balance the strength and ductility of printed elastomers. To address this challenge, introducing hydrogen bonds into the molecular structure of photocurable monomers is one of the important strategies. , Specifically, substantial mechanical energy or impact energy can be efficiently dissipated by the rupture and reformation of hydrogen bonds, which leads to the improvement of mechanical performance.

While supramolecular interactions such as hydrogen bonding have been widely employed to toughen photocurable elastomers, current strategies primarily fall into two established categories: (i) modifying oligomeric or polymeric backbones with hydrogen-bonding moieties, and (ii) incorporating functional additives into multicomponent resin formulations. The former often involves multistep synthesis and purification, whereas the latter may introduce undesired phase separation or structural heterogeneity. In contrast, the direct design of reactive small-molecule monomers to precisely engineer supramolecular networks remains comparatively underexplored.

Urea groups are well-known for their ability to form strong, reversible dual hydrogen bonds, which have been extensively leveraged in polymer science to enhance material properties. − In elastomers, these hydrogen bonds can act as dynamic physical cross-links. Under external stress, their continuous dissociation and recombination effectively dissipate mechanical energy, thereby significantly improving toughness. Concurrently, the robust hydrogen-bonding interactions inherently contribute to increased mechanical strength. − This dynamic character further leads to a unique strain-adaptive stiffening effect, endowing the materials with excellent damage resistance.

Herein, a series of urea-containing photocurable monomers were synthesized via a facile method (Figure a), and complex-structured elastomers were successfully fabricated using DLP 3D printing technology (Figure b–c). The effects of urea-containing monomers on the viscosity and photocuring process of the UV-curable elastomer systems were systematically investigated. It was demonstrated that the reversible breakage and reformation of hydrogen bonds during deformation effectively enhance both strength and ductility (Figure d). Furthermore, the printed honeycomb-structured elastomers exhibited remarkable energy absorption capacity, attributed to the synergistic effect between the excellent mechanical properties of the elastomer and the rationally designed honeycomb architecture. This work breaks the strength–ductility trade-off bottleneck in UV-curable elastomers for DLP 3D printing, thereby advancing the practical application of 3D printed elastomers.

1.

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(A) The synthesis route of the urea-containing photocurable monomer. (b) Chemical structure of photocurable monomers and photocurable oligomers for DLP 3D printing. (c) Schematic diagram of the DLP 3D printing. (d) Schematic illustration of energy dissipation via sacrificial hydrogen bonds.

2. Experimental Section

2.1. Materials

Cyclohexylamine (CA, 99%), 2-isocyanatoethyl acrylate (IA, 97%), n-butylamine (BA, 99%), 2,5-bis­(5-tert-butyl-2-benzoxazolyl) thiophene (BBOT, 99%), and 2-furfurylamine (FA, 99%) were purchased from Macklin. 4-Methoxyphenol (MEHQ) was bought from Adamas. Polyurethane acrylate (PUA) DR-U096 and isobornyl acrylate (IBOA) were supplied by Changxing Materials Industry Co., Ltd. DR-U096 had a number-average molecular weight (M n) of approximately 1500–2500 g·mol–1 and a weight-average molecular weight (Mw) of approximately 3000–5000 g·mol–1. 1,6-hexanediol diacrylate (HDDA) was provided by Kailin Ruiyang Chemical Co., Ltd. Trichloromethane (AR, 99.5%) and petroleum ether (AR, 99.5%) were acquired from Sinopharm Chemical Reagent Co. Ltd. Phenylbis­(2,4,6-trimethylbenzoyl) phosphine oxide (819) was supplied by Changxing Materials Industry Co.

2.2. Synthesis of Urea-Containing Photocurable Monomers

The synthesis route is shown in Figure . IA (14.805 g, 0.105 mol) and chloroform (20 mL) were added into a 100 mL three-necked flask, and the mixture was cooled to approximately 5 °C. Then, BA (7.3 g, 0.1 mol) was added to the mixture while continuously stirring, followed by a 2 h reaction at 5 °C. Upon completion of the reaction, the solution was dropped into petroleum ether to precipitate white solids from the solution. The product was washed repeatedly with petroleum ether, and this purified monomer was designated as IB. Following the identical synthetic protocol and reaction conditions, the other urea-containing photocurable monomers (IC and IF) were also synthesized. Meanwhile, a structurally analogous carbamate-containing photocurable monomer (IO) was prepared for comparison.

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Synthesis route of urea-containing photocurable monomers. (a) Monomer IB was synthesized by reacting IA with butylamine (BA) in chloroform at 5 °C for 2 h. Monomers IC (b) and IF (c) were prepared following the same procedure using the corresponding amines.

2.3. Preparation of UV-Curable Systems and DLP 3D Printing

UV-curable systems for DLP 3D printing were composed of 10% IB, 70 wt % PUA (PUA refers to the urea group-containing PUA network obtained via photopolymerization of urea-containing monomers under 405 nm UV light), 19 wt % IBOA, 1 wt % PI-819, and 0.05 wt % BBOT. The system for the gel content test, split Hopkinson pressure bar test, dynamic mechanical analysis test, and tensile test was cured by Fusion’s crawler F300S with an irradiation energy of 1200 mJ cm–2. DLP 3D Printer TC-1 (Zhejiang Xunshi Technology Co., Ltd., light intensity: 1250–1350 μW/cm2) is equipped with a 405 nm LED projector. The critical printing control parameters were optimized as follows: the single-layer thickness was set to 50 μm, and the exposure time per layer was 8 s. Subsequently, a 2 min post-UV curing step was performed under a dose of 1200 mJ/cm2 to obtain fully cross-linked and dimensionally stable networks.

2.4. Characterization and Measurement

The molecular structure of photocurable monomers was characterized by Fourier-transform infrared spectroscopy (FTIR, Thermo Scientific Nicolet 6700) over a scanning range from 4000 to 600 cm–1. 1H NMR spectra were collected by a Bruker AVANCE III 400 MHz Digital NMR spectrometer, with CDCl3 serving as the solvent. Viscosity of the system was measured using a TA Discovery DHR-3 rheometer at 25 °C, with the shear rate varied from 0 to 100 rad/s. Photo-DSC (DSC 204 F1 Phoenix-Netzsch) was employed to characterize the photopolymerization reaction kinetics. The light intensity at the sample plane was set to 8 mW/cm2. The degree of double bond conversion was monitored continuously in real time by ATR-FTIR (Nicolet iS10 series, Thermo Fisher).

Real-time infrared (RTIR) spectroscopy was employed to monitor the reaction. Specifically, the decrease in the integrated area of the double-bond peak (1660–1610 cm–1) was recorded. The carbonyl peak (1760–1680 cm–1), which remains unreactive throughout the process, was used as an internal reference to normalize the data and account for any physical variations. The conversion was then calculated according to eq

Conversion(%)=(1−AX,tAX,0·AST,0AST,t)×100% 1

where A X,t and A X,0 represent the integrated peak areas of the functional group (double bond) at time t and the initial state, respectively; A ST,0 and A ST,t denote the integrated peak areas of the nonreactive reference group (carbonyl) at time t and the initial state, respectively, used to correct for physical variations.

Tensile properties were tested using a universal mechanical testing machine (Instron 5976) at different tensile speeds. The dimensions of dumbbell-shaped specimens were 35 mm × 2 mm × (0.07–0.13) mm. For each formulation, at least five independent dumbbell-shaped specimens (n = 5) were tested to ensure statistical reproducibility. The baseline mechanical parameters are reported as mean ± standard deviation (SD). Static tensile testing was conducted under conditions of 25 °C and 10 mm/min crosshead speed.

The gel content of the cured film was determined by a dissolution-elution experiment. A certain mass (m1) of cured film was placed into a filter paper bag with a mass of m2, followed by refluxing with acetone for 24 h. Subsequently, the filter paper bag was removed and dried in a vacuum oven at 50 °C until a constant mass (m3) was achieved. The gel content of the cured film was then calculated according to the change in mass of the filter paper bag before and after acetone extraction, using eq

Gelcontent(%)=(m3−m2m1)×100% 2

3. Results and Discussion

3.1. Synthesis and Characterization of Photocurable Monomers Containing the Urea Group

The monomers were simply synthesized from the reaction of 2-isocyanatoethyl acrylate (IA) with amino compounds. It should be noted that both the double bond and isocyanate in IA are capable of reacting with amino groups. Fortunately, we found that the reaction between amino groups and isocyanate groups could rapidly yield urea groups at low temperatures (below 10 °C) without any catalyst, while the reaction of the amino group with a double bond normally took place at room temperature. Therefore, urea-containing photocurable monomers were successfully synthesized via the priority reaction of amino groups with isocyanate of IA at low temperatures (about 5 °C). By varying the molecular structure of amino compounds, a series of urea-containing photocurable monomers with distinct chemical structures (IB, IC, and IF) were obtained. In the molecular structure of IB, IC, or IF, double bonds involved in photopolymerization can form covalent cross-linking points, while urea groups that provided double hydrogen bonds can function as physical cross-linking points, rendering these monomers analogous to difunctional photocurable monomers. Meanwhile, HDDA contains two double bonds, and photocurable monomer containing carbamate (IO) was used as control monomers to investigate the effects of the urea group on the properties of the resulting elastomers (Figure S1).

The chemical structures of urea-containing photocurable monomers were determined by FTIR spectra and 1H NMR. It can be observed that the characteristic peak of –NCO at 2280 cm–1 disappeared (Figure S2b). However, the peaks of CO and –NH– in the urea group appeared at 1640 cm–1 and 3340 cm–1, respectively. At the same time, the characteristic absorption peaks of CC at 1410 cm–1 and 810 cm–1 remained intact. In the 1H NMR spectrum of IB (Figure a), the peaks at 5.81–6.45 ppm belonged to the protons (Ha and Hb) on the CC bond; the peaks at 5.15–5.56 ppm were ascribed to the protons (He and Hf) in the urea group; the peak at 4.23 ppm was attributed to the protons (Hc), and the peaks at 3.46 and 3.14 ppm belonged to Hd and Hg, respectively. Other peaks were derived from the protons (Hh, Hi, and Hj) in the alkyl chain. The 1H NMR spectra of IC and IF were similar to those of IB. Specifically, in the 1H NMR spectrum of IC, the peaks at 1.01–1.96 ppm were attributed to the protons (Hh, Hi, Hj, Hm, and Hn) on the aliphatic ring (Figure b). In the 1H NMR spectrum of IF, the peaks at 5.81–6.45 ppm correspond to the protons (Ha and Hb) on the CC bond and the protons (Hh, Hi, and Hj) on the furan ring (Figure c). These results demonstrated the successful synthesis of IB, IC, and IF.

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1H NMR spectra of (a) IB, (b) IC, and (c) IF.

Because of the strong hydrogen-bonding interactions of the urea groups, the as-prepared urea-containing photocurable monomers existed as solids. Therefore, a solubility test was first performed. Specifically, mixtures were prepared by mixing 70 wt % photocurable oligomer, 19 wt % IBOA, and 10 wt % urea-containing photocurable monomers, and the resultant mixtures were visually observed after standing for 24 h (Figure a). All mixtures incorporating the urea-containing photocurable monomers appeared clear and transparent without any precipitation or turbidity, which was similar to the mixture with HDDA, thus confirming the excellent solubility of the urea-containing photocurable monomers in the formulated elastomer system.

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(A) The digital photographs of the mixtures incorporating different photocurable monomers. (b) Double-bond conversion of UV-curable systems with different photocurable monomers. (c) Photo-DSC curves of UV-curable systems with different photocurable monomers. (d) Gel content of UV-curable systems with different photocurable monomers.

Viscosity is a critical process parameter for DLP 3D printing. The influence of different photocurable monomers on the viscosity of the resin systems was investigated via a rheometer. As illustrated in Figure S3, the viscosity of the systems incorporating urea-containing photocurable monomers was notably higher than that of the HDDA-based reference system. The higher viscosity of IB, IC, and IF systems was attributed to the presence of double hydrogen bonds formed by urea groups. Moreover, the three urea-containing photocurable monomers with distinct molecular structures exhibited differential effects on the system viscosity. Specifically, the IB system exhibited the lowest viscosity, followed by the IC system, while the IF system showed the highest viscosity among the three. This maximum viscosity of the IF system was caused by the π–π stacking interactions derived from the furan ring moieties in the monomer structure.

The rapid liquid-to-solid transition of a UV-curable system under light irradiation is a prerequisite for DLP 3D printing. The UV-curing behavior of the formulated systems was first characterized by RTIR spectroscopy. As shown in Figure b, the final double-bond conversion of the IB and IC systems was 95% and 93%, respectively, which was even slightly higher than that of the HDDA system (91%), suggesting high polymerization activity of the IB and IC systems. Despite the high viscosity of the IF system, its final double-bond conversion still reached 86%. Such favorable polymerization reactivity is well-suited for DLP 3D printing applications. The main reason for the high polymerization activity may be the presence of hydrogen bonds that reduced the activation energy of the photopolymerization reaction, thereby accelerating the photopolymerization rate and increasing the double-bond conversion rate.

To further investigate the UV-curing behavior, we measured the heat flux during the photopolymerization process of the elastomer systems with different photocurable monomers (Figure c). The maximum heat flux of the IB and IC systems emerged at about 35 s, and the heat flux decayed to zero within 200 s, which was comparable to that of the HDDA system, indicating a similar photopolymerization process. In contrast, the maximum heat flux of the IF system occurred at 54 s, and the heat flux did not decline to zero until 250 s, suggesting that the IF system had the slowest photopolymerization speed, which was consistent with the results of double-bond conversion.

During the DLP process, the printed elastomers need to maintain their shape to enable the precise layer-by-layer fabrication of three-dimensional constructs. Therefore, the gel content is an important factor for DLP 3D printing, which influences the accuracy of printed objects. As shown in Figure d, the gel content of IB, IC, and IF systems was 95%, 96%, and 97%, respectively, which was close to that of the HDDA system (97%), indicating that the systems with urea-containing photocurable monomers were well-suited for high-precision DLP 3D printing.

It is important to clarify that while the final gel contents of all elastomer systems are highly comparable (∼95%–97%), indicating similar radical conversion and covalent network integrity, their mechanical behaviors differ significantly. This distinction highlights that the observed variations in toughness and ductility among the IB, IC, and IF series are not attributable to differences in chemical cross-linking efficiency. Instead, they originate from the dynamic, reversible hydrogen-bonding network introduced by the urea groups. Under deformation, the covalent network ensures structural recovery, while the dynamic dissociation and reformation of hydrogen bonds enable chain slippage and efficient energy dissipation, thereby decoupling high toughness from excessive chemical cross-linking.

3.2. Mechanical Properties of the Printed Elastomers

The mechanical properties of UV-curable elastomers were systematically investigated. As depicted in Figure a, under the condition of 10 wt % monomer loading, the elongation at break of IB, IC, IF, and HDDA elastomers was 326%, 278%, 185%, and 83%, respectively. Notably, the elongation at break values of the IB, IC, and IF elastomers were significantly higher than that of the HDDA elastomer. The excellent ductility of these urea-containing elastomers was attributed to the hydrogen bonds introduced by urea groups, which act as dynamic physical cross-linking sites. These hydrogen bonds can be reversibly broken and reformed during deformation, thereby dissipating substantial amounts of energy and effectively retarding the accumulation of local stress (Figure d). In contrast, the HDDA elastomer dissipates energy primarily through the irreversible cleavage of covalent cross-links, which account for its relatively low elongation at break.

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(A) Stress–strain curves of UV-curable elastomers prepared with different photocurable monomers at 10 wt % loading. (b) Stress–strain curves of 10 wt % IB elastomers at various tensile speeds. (c) Cyclic loading–unloading tensile curves of IB elastomers under sequential cycles. (d) Schematic diagram of the split Hopkinson pressure bar (SHPB) apparatus. (e) Compressive stress–strain curves of IB elastomers at different strain rates.

In addition, the mechanical strengths of IB, IC, IF, and HDDA elastomers were 20.7, 20.4, 21.1, and 18.6 MPa, respectively. These results clearly demonstrate that the incorporation of urea groups as physical cross-linking sites not only significantly enhances the ductility of the elastomers but also enables them to retain high mechanical strength. Such a combination of high strength and ductility is highly favorable for their applications. IO elastomers also had a high elongation at break of 296% (Figure a). However, the strength of IO elastomers was only 13.3 MPa due to the weak hydrogen bonding of carbamates, demonstrating the advantages of the dual hydrogen bonds of urea groups.

The chemical structure difference among urea-based monomers directly caused distinct mechanical properties in the printed elastomers. IF contains a phenyl ring adjacent to the urea group, introducing additional π–π stacking interactions. This forms a denser, more rigid physical network, giving IF the highest tensile strength (21.1 MPa) but lower elongation (185%) compared to IB (326%), which relies only on hydrogen bonds. Rubbery plateau modulus analysis shows similar covalent cross-link densities for IB, IC, and IF. Thus, the higher stiffness and strength of IF arise from π–π reinforcement, not from increased covalent cross-linking. More importantly, the overall mechanical enhancement originates from dynamic physical cross-links (hydrogen bonds and π–π interactions) acting as reversible sacrificial bonds for energy dissipation, rather than from higher covalent cross-link density. This is confirmed by the IB vs IO comparison: with the same covalent network, introducing urea groups alone simultaneously improves both strength and ductility.

Unlike covalent cross-linking points, the physical cross-linking points undergo continuous recombination during tensile experiments. Consequently, the mechanical properties of UV-curable elastomers with urea groups are strongly dependent on the strain speed; Figure b shows the stress–strain curves of the elastomer with 10 wt % IB loading, tested at various tensile speeds ranging from 2 mm/min to 150 mm/min. It can be observed that, as the tensile speed increases, the elongation at break continuously decreases, accompanied by an increase in elastic modulus. The IB elastomer had the highest elongation at break (355%) at the strain speed of 2 mm/min, while at the strain speed of 150 mm/min, the elongation at break of the elastomer decreased to 218%. The primary underlying mechanism is that hydrogen bonds could rupture and reform sufficiently at low strain rates, which resulted in high ductility and low elastic modulus. In contrast, there was no sufficient time for the rupture and reformation of hydrogen bonds at high strain speed, which led to the decrease of ductility and the increase of modulus. At a tensile rate of 10 mm/min, the material exhibits optimal elongation at break (326%) and tensile strength (20.7 MPa). The trends of stress–strain curves of IC or IF elastomers at different tensile speeds are similar to those of the IB elastomer (Figure S4). By comparison, the elongation at break of the HDDA elastomer is almost unchanged with the increase of tensile speed, along with increasing elastic modulus.

The energy dissipation capability of the UV-curable elastomer was evaluated by the hysteresis loop (the area enclosed in sequential cyclic tensile tests). The cyclic loading–unloading behavior was evaluated at 10 mm/min. As illustrated in Figure c, a pronounced hysteresis loop appeared at the loading–unloading curve of the IB elastomer, and the area of these hysteresis loops increased consistently with rising tensile strain. The variation trends of loading–unloading curves of IC and IF elastomers at different tensile strains were similar to those of the IB elastomer. For the HDDA elastomer, a large hysteresis loop was detected at a strain of 50%. Nevertheless, further increases in strain would induce fracture of the HDDA elastomer, which is attributed to its high cross-linking density (Figure S5). Besides, the IB elastomer could be easily twisted into a spiral shape without any damage (Figure S6), which vividly demonstrated its excellent mechanical performance.

The strain-rate-dependent mechanical properties render them an ideal impact-resistant material. The capacity of impact resistance and energy absorption of the IB elastomer was further investigated. A split Hopkinson pressure bar (SHPB) test was carried out, and the schematic diagram of the device is shown in Figure d. The representative stress–strain curves of the IB elastomer at a strain rate range of 1500 to 10,000 s–1 are presented in Figure e. The compression stress of the IB elastomer increased with increasing strain rate. These results indicate that the IB elastomer exhibits strain-hardening behavior at high strain rates, a property that is indispensable for impact protection applications.

The effect of the urea group incorporation on the thermomechanical properties of elastomers was also investigated. As shown in Figure a, the HDDA elastomer exhibited the highest initial elastic modulus (3200 MPa) at −20 °C due to its high cross-linking density. It was noteworthy that the initial elastic moduli of IB elastomer (2600 MPa) and IC elastomer (2900 MPa) at −20 °C did not decrease significantly compared with HDDA elastomer, which benefited from the reinforcing effect of the double hydrogen bond of urea groups. In particular, the initial elastic modulus of IF elastomer (3100 MPa) was nearly identical to HDDA elastomer because of the strong hydrogen bond interaction of the urea group and the π–π interaction of the furan ring. In addition, as illustrated in Figure b, the HDDA elastomer possessed the highest glass transition temperature (T g, determined as the peak temperature of the tan δ–temperature curve), followed by IC and IF elastomers, while IB elastomer had the lowest T g.

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(A) Storage modulus–temperature curves and (b) tan δ–temperature curves of UV-curable elastomers.

To demonstrate the significance of our work, we compared the mechanical performance of the as-prepared elastomer with that of the recently reported DLP-printed counterparts (Table S1). Unlike existing photocurable systems that compromise tensile strength (<6 MPa) for high stretchability (>500%) or require complex multistep synthesis and high-viscosity processing to achieve high strength, our elastomer bridges this gap. Benefiting from the hydrogen-bonded urea groups introduced via a facile one-step monomer synthesis, it simultaneously achieves a robust tensile strength of 20.7 MPa and a 326% elongation at break without ex situ nanoreinforcement.

3.3. Printed Honeycomblike Structure as an Impact-Absorption Element

Due to low viscosity, high photopolymerization activity, and superior mechanical performance, the IB system was selected for DLP printing. In addition, photoabsorber (BBOT) was incorporated into the system to improve the accuracy of printed objects. Compared with solid bulk materials, certain 3D printed elastomers possess tailorable mechanical properties and enhanced energy absorption capabilities, thus finding extensive applications in diverse engineering fields. Honeycomb and other porous materials can guide deformation and gradually buckle under load. This allows them to absorb energy across a wide range. By combining this with urea-based elastomerswhich are sensitive to impact speed and can stiffen on their ownwe can design advanced lattice structures. This approach is very promising for creating lightweight, high-performance protective cushions. A honeycomblike structure and high-precision model components were fabricated via 3D printing to validate the printability of the developed system (Figure a). Furthermore, compression tests were conducted on the lattice structures to characterize their mechanical performance (Figure b). At the initial compression stage, the printed lattice showed relatively low compression stress. As the strain increased to the range of 20%–50%, the compressive stress curve appeared to plateau. When the strain exceeded 50%, the compressive stress of the lattice rose sharply due to tightly compacted lattice (Figure S7). This characteristic compression behavior demonstrates that the printed lattice serves as an efficient impact-absorption unit, benefiting from both its rational lattice topology and the excellent intrinsic properties of the base material.

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(A) Digital photographs of the printed objects. (b) Digital photographs of the compression process. (c–d) Digital photographs of the printed honeycomblike structure serving as a buffer device. (e) The printed honeycomblike elastomer withstands a weight of 1 kg. (f–g) The encapsulated egg and bare egg being dropped from a height of 1 m onto the ground.

This study designed a honeycomb-structured elastomer based on the excellent energy absorption capacity of 3D-printed IB elastomer for egg protection, where a honeycomblike elastomer was printed to encapsulate an egg serving as a cushioning component (Figure c–d). Furthermore, the printed honeycomblike elastomer can easily withstand a weight of 1 kg (480 times its own weight) without any structural collapse (Figure e). Subsequently, the encapsulated egg was dropped from a height of 1 m. The egg remained intact without sustaining any damage, whereas the bare egg dropped from the same height shattered completely upon impact with the ground (Figure g–f). These results demonstrate that the honeycomblike elastomers possess remarkable energy absorption capabilities, which are attributed to the synergistic effect of the honeycomblike architecture and the robust mechanical properties of the IB elastomer itself.

4. Conclusion

In summary, a series of urea-containing photocurable monomers suitable for DLP 3D printing were successfully synthesized via a one-step method. The resin systems formulated with these monomers exhibited high photopolymerization activity, which is fully compatible with the DLP printing processes. Elastomers incorporating urea groups as physical cross-links (IB, IC, and IF) showed significantly higher toughness than the covalently cross-linked HDDA elastomer, with the IB elastomer reaching an extremely high elongation at break of 326%. Notably, the enhancement in the ductility did not compromise the mechanical strength. Moreover, 3D-printed honeycomb-structured IB samples demonstrated efficient impact energy dissipation, benefiting from the synergy between the porous architecture and the intrinsic properties of the elastomer. The novel monomer design strategy proposed in this work provides a universal and effective route for fabricating DLP-printable elastomers that combine high strength, high toughness, and excellent energy absorption capability, showing broad application potential in fields such as soft robotics and flexible wearable devices that demand stringent mechanical performance. Despite the promising mechanical performance of the obtained elastomers, the long-term cyclic fatigue resistance and mechanical durability under repeated loading still need to be further investigated. Future work will focus on evaluating the fatigue behavior and optimizing material formulations to improve long-term service reliability.

Supplementary Material

ao6c04488_si_001.pdf (528.2KB, pdf)

Acknowledgments

The authors acknowledge the financial support provided by the National Natural Science Foundation of China (Grant No.: 52373057), the Jiangsu Funding Program for Excellent Postdoctoral Talent (Grant No.: 2025ZB865), and Postgraduate Research & Practice Innovation Program of Jiangsu Province (KYCX25_2673).

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.6c04488.

  • Synthetic routes of IO, FTIR spectra, viscosity vs shear rate, stress–strain curves at various tensile speeds, cyclic loading–unloading curves, digital photograph of a twisted IB elastomer, compressive force–strain curve of printed lattice, and a comparison of mechanical properties with related references (PDF)

The authors declare no competing financial interest.

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