Early-career researchers from around the world summarize recent developments and present visions for the future of vat photopolymerization 3D printing.

Fabrication of geometrically complex conductive carbon electrodes with micrometer-scale features via polymer 3D printing and pyrolysis enables precise control over precursor composition and structure geometry, enabling the development of a tunable electrode design space for electrochemical systems. Continuous liquid interface production 3D printing of lattices with high surface-to-volume ratios offers promise for producing polymer pyrolysis precursors with tailored microarchitected structures. Herein, a method is reported for 3D printing of polyacrylonitrile-derived carbon structures via gel infusion and subsequent pyrolysis. With optimized pyrolysis conditions, samples demonstrate high char yields of greater than 40% by mass, comparable to yields for conventionally electrospun polyacrylonitrile fibers and higher than commercial resin alternatives. Characterization of polyacrylonitrile-derived 3D carbon lattices reveals carbon crystallite sizes in the nanocrystalline to amorphous regime and capacitance values up to 1.98 F/g corresponding to an electrochemically active surface area (ECSA) of >1 m(2)/g with solid lattice beams. Increasing the pyrolysis temperature results in a higher ECSA, likely caused by increased surface roughness confirmed by microscopy. This gel infusion and pyrolysis method establishes a platform for incorporation of high char yield linear polymers into high-resolution microarchitected structures, paving a pathway for producing hierarchical 3D electrodes for energy storage, catalysis, and reactor technology applications.

THE BIGGER PICTURE Challenges and opportunities: center dot The low cost and short time frame in which parts can be manufactured through 3D printing lowers the barrier to improved electrochemical cell design, which, in turn, facilitates faster and more in-depth investigation of electrochemical systems. center dot We stress the importance and accessibility of engaging in a technological feedback loop between modeling, printing, and experimenting to inform the understanding of reaction mechanisms and the optimization of electrochemical reactor performance. center dot The development of new resin technologies expands the scope of accessible chemistries with 3D- printed electrochemical cells, although there is still room for innovation in 3D-printing techniques and materials design. SUMMARY With a recent surge in electrochemical technologies, the number of electrochemical cell designs for applications ranging from biosensors to high-current electrolyzers has grown massively. While electrode and electrocatalyst materials have been the traditional focus of electrochemistry research, the expanded experimental and computational study of dynamic conditions within electrochemical cells has revealed the importance of co-designing the cell's components. Additive manufacturing via 3D printing has historically been used to prototype parts before getting them machined out of materials with more favorable properties. However, developments in printer accuracy, filament and resin robustness, and printer accessibility in recent years have broadened the scope of the potential applications of additive manufacturing. In this perspective, we provide insight into the acceleration of reactor design and implementation for electrochemistry and catalysis facilitated by advances in vat photopolymerization.

Vat photopolymerization (VP) additive manufacturing enables fabrication of complex 3D objects by using light to selectively cure a liquid resin. Developed in the 1980s, this technique initially had few practical applications due to limitations in print speed and final part material properties. In the four decades since the inception of VP, the field has matured substantially due to simultaneous advances in light delivery, interface design, and materials chemistry. Today, VP materials are used in a variety of practical applications and are produced at industrial scale. In this perspective, we trace the developments that enabled this printing revolution by focusing on the enabling themes of light, interfaces, and materials. We focus on these fundamentals as they relate to continuous liquid interface production (CLIP), but provide context for the broader VP field. We identify the fundamental physics of the printing process and the key breakthroughs that have enabled faster and higher-resolution printing, as well as production of better materials. We show examples of how in situ print process monitoring methods such as optical coherence tomography can drastically improve our understanding of the print process. Finally, we highlight areas of recent development such as multimaterial printing and inorganic material printing that represent the next frontiers in VP methods.

Most hexagonal boron nitride (hBN) single-photon emitters (SPEs) studied to date suffer from variable emission energy and unpredictable polarization, two crucial obstacles to their application in quantum technologies. Here, we report an SPE in hBN with an energy of 2.2444 ± 0.0013 eV created via carbon implantation that exhibits a small inhomogeneity of the emission energy. Polarization-resolved measurements reveal aligned absorption and emission dipole orientations with a 3-fold distribution, which follows the crystal symmetry. Photoluminescence excitation (PLE) spectroscopy results show the predictability of polarization is associated with a reproducible PLE band, in contrast with the non-reproducible bands found in previous hBN SPE species. Photon correlation measurements are consistent with a three-level model with weak coupling to a shelving state. Our ab initio excited-state calculations shed light on the atomic origin of this SPE defect, which consists of a pair of substitutional carbon atoms located at boron and nitrogen sites separated by a hexagonal unit cell.

Using high-resolution 3D printing, a novel class of microneedle array patches (MAPs) is introduced, called latticed MAPs (L-MAPs). Unlike most MAPs which are composed of either solid structures or hollow needles, L-MAPs incorporate tapered struts that form hollow cells capable of trapping liquid droplets. The lattice structures can also be coated with traditional viscous coating formulations, enabling both liquid- and solid-state cargo delivery, on a single patch. Here, a library of 43 L-MAP designs is generated and in-silico modeling is used to down-select optimal geometries for further characterization. Compared to traditionally molded and solid-coated MAPs, L-MAPs can load more cargo with fewer needles per patch, enhancing cargo loading and drug delivery capabilities. Further, L-MAP cargo release kinetics into the skin can be tuned based on formulation and needle geometry. In this work, the utility of L-MAPs as a platform is demonstrated for the delivery of small molecules, mRNA lipid nanoparticles, and solid-state ovalbumin protein. In addition, the production of programmable L-MAPs is demonstrated with tunable cargo release profiles, enabled by combining needle geometries on a single patch.

In an era marked by a growing demand for sustainable and high-performance materials, the convergence of additive manufacturing (AM), also known as 3D printing, and the thermal treatment, or pyrolysis, of polymers to form high surface area hierarchically structured carbon materials stands poised to catalyze transformative advancements across a spectrum of electrification and energy storage applications. Designing 3D printed polymers using low-cost resins specifically for conversion to high performance carbon structures via post-printing thermal treatments overcomes the challenges of 3D printing pure carbon directly due to the inability of pure carbon to be polymerized, melted, or sintered under ambient conditions. In this perspective, we outline the current state of AM methods that have been used in combination with pyrolysis to generate 3D carbon structures and highlight promising systems to explore further. As part of this endeavor, we discuss the effects of 3D printed polymer chemistry composition, additives, and pyrolysis conditions on resulting 3D pyrolytic carbon properties. Furthermore, we demonstrate the viability of combining continuous liquid interface production (CLIP) vat photopolymerization with pyrolysis as a promising avenue for producing 3D pyrolytic carbon lattice structures with 15 μm feature resolution, paving way for 3D carbon-based sustainable energy applications.

Particle fabrication has attracted recent attention owing to its diverse applications in bioengineering 1 , 2 , drug and vaccine delivery 3 – 5 , microfluidics 6 , 7 , granular systems 8 , 9 , self-assembly 5 , 10 , 11 , microelectronics 12 , 13 and abrasives 14 . Herein we introduce a scalable, high-resolution, 3D printing technique for the fabrication of shape-specific particles based on roll-to-roll continuous liquid interface production (r2rCLIP). We demonstrate r2rCLIP using single-digit, micron-resolution optics in combination with a continuous roll of film (in lieu of a static platform), enabling the rapidly permutable fabrication and harvesting of shape-specific particles from a variety of materials and with complex geometries, including geometries not possible to achieve with advanced mould-based techniques. We demonstrate r2rCLIP production of mouldable and non-mouldable shapes with voxel sizes as small as 2.0 × 2.0 µm 2 in the print plane and 1.1 ± 0.3 µm unsupported thickness, at speeds of up to 1,000,000 particles per day. Such microscopic particles with permutable, intricate designs enable direct integration within biomedical, analytical and advanced materials applications.

Stereolithography enables the fabrication of three-dimensional (3D) freeform structures via light-induced polymerization. However, the accumulation of ultraviolet dose within resin trapped in negative spaces, such as microfluidic channels or voids, can result in the unintended closing, referred to as overcuring, of these negative spaces. We report the use of injection continuous liquid interface production to continuously displace resin at risk of overcuring in negative spaces created in previous layers with fresh resin to mitigate the loss of Z-axis resolution. We demonstrate the ability to resolve 50-μm microchannels, breaking the historical relationship between resin properties and negative space resolution. With this approach, we fabricated proof-of-concept 3D free-form microfluidic devices with improved design freedom over device material selection and resulting properties.

Abstract Additive manufacturing (AM) of metals can enable rapid development of advanced parts with complex geometries, opening potential applications in the aerospace, automotive, and biomedical fields. Most existing metal AM techniques rely on costly thermally initiated melting or sintering processes, limiting the fabrication of materials with high thermal conductivity. Alternative vat photopolymerization methods require incorporating target materials or precursors into the photoresin, leading to increased viscosity, light scattering, and the need for a different resin composition for each material fabricated. To circumvent these problems with traditional metal AM techniques, we report an AM process where we infuse aqueous metal precursors into gels formed via vat photopolymerization and subsequently calcine and reduce the gels to form metal structures. Our streamlined technique enables the use of a single photoresin composition and varied post-processing conditions to fabricate a wide variety of metals and alloys with microscale resolution and highly twinned microstructures. We demonstrate fabrication of microlattices with <50 µm beam diameters formed from copper, nickel, silver, and alloys thereof, as well as high entropy and refractory alloys. We found that during the calcination process, the rate of mass loss associated with the exothermic combustion of the gel scaffold must be controlled to form dense parts. Microcrystalline microstructures with crystallographic annealing twin densities on the order of 106 m-1 were achieved. Our simple and compositionally flexible hydrogel-based approach to metal AM provides a pathway to fabricate new classes of metals with non-equilibrium microstructures and enhanced properties. Furthermore, our method is compatible with commercially successful vat photopolymerization techniques, showing a clear path to widespread adoption of this technique.

Metal additive manufacturing (AM) enables the production of high value and high performance components1 with applications from aerospace2 to biomedical3 fields. Layer-by-layer fabrication circumvents the geometric limitations of traditional metalworking techniques, allowing topologically optimized parts to be made rapidly and efficiently4,5. Existing AM techniques rely on thermally initiated melting or sintering for part shaping, a costly and material-limited process6–8. We report an AM technique that produces metals and alloys with microscale resolution via vat photopolymerization (VP). Three-dimensional-architected hydrogels are infused with metal precursors, then calcined and reduced to convert the hydrogel scaffolds into miniaturized metal replicas. This approach represents a paradigm shift in VP; the material is selected only after the structure is fabricated. Unlike existing VP strategies, which incorporate target materials or precursors into the photoresin during printing9–11, our method does not require reoptimization of resins and curing parameters for different materials, enabling quick iteration, compositional tuning and the ability to fabricate multimaterials. We demonstrate AM of metals with critical dimensions of approximately 40 µm that are challenging to fabricate by using conventional processes. Such hydrogel-derived metals have highly twinned microstructures and unusually high hardness, providing a pathway to create advanced metallic micromaterials. An additive manufacturing technique that infuses 3D printed hydrogels with metallic precursors leads to metallic micromaterials, providing new opportunities for the fabrication of energy materials, micro-electromechanical systems and biomedical devices.

Additive manufacturing (AM) enables the fabrication of battery materials with complex geometries. When battery components can take arbitrary form factors, opportunities emerge for creating electrode configurations with improved power density, reduced weight, and excellent mechanical stability. We provide a perspective on recent progress in AM of 3D batteries, discussing relevant techniques, materials, designs, and applications. We highlight advantages and limitations associated with battery electrodes fabricated by direct ink writing, fused deposition modeling, vat photopolymerization, and selective laser sintering. Additionally, we discuss optimal geometries and compatible materials for anode, cathode, and electrolyte of fully 3D batteries. To increase transparency and utility in the field, we suggest a standardized set of reporting metrics for 3D batteries. Finally, we identify key opportunities for implementation where 3D batteries can provide critical advantages such as shape conformability and the ability to serve as multifunctional or structural components.

Lithium–sulfur batteries are poised to outcompete lithium-ion batteries in key sectors such as transportation and grid storage due to the low cost and high theoretical energy density of sulfur as a cathode material. Widespread implementation of this technology is hindered by significant degradation during cycling, including mechanical failure via cracking or detachment of insulating lithium sulfide (Li2S) from the conductive matrix in the cathode, causing irreversible capacity fade. We developed a technique to additively manufacture Li2S composites to fabricate rationally designed cathodes and demonstrate the utility of a three dimensionally architected Li2S composite cathode in a battery. We additionally measure the yet unknown material properties and deformation mechanisms of Li2S powders via in situ scanning electron microscope (SEM) nanomechanical experiments. Measuring these mechanical properties is a first step towards understanding the process of mechanical degradation and is necessary to enable the rational design of high energy density, long-cycling, and mechanically robust sulfur cathodes.

Li-S batteries are poised to outcompete Li-ion batteries in key sectors such as transportation and grid storage. Improving energy density and mitigating degradation in Li-S batteries could unlock immense impacts such as gigaton-order annual CO2 reduction. Well-designed electrolyte systems can mitigate the degradation mechanisms of electrolyte reactivity, polysulfide shuttling, and lithium dendrite growth. The most significant remaining degradation mechanism is mechanical failure and detachment of insulating Li2S from the conductive matrix in the cathode, causing irreversible capacity fade. We measure the yet unknown material properties and deformation mechanisms of Li2S powders via in situ SEM mechanical experiments. Understanding these basic properties is a first step towards rational design of high energy density, long-cycling, and mechanically robust sulfur cathodes. We also describe the development of a novel technique for additive manufacturing of Li2S composites to fabricate such rationally designed cathodes and demonstrate a 3D printed Li2S cathode with feature sizes 3x smaller than previously attainable via additive manufacturing methods for Li-S cathode materials . This work represents the most fundamental mechanical study of Li-S batteries to date and will pioneer a new design strategy for 3D-structured Li-S cathodes. Figure 1

Lithium-ion batteries are more and more widely used in portable electric applications with high power demand. Most approaches to high-power batteries gain improvement in power density on the cost of energy density. The rapid development in additive manufacturing technique in the past decade has provided a promising pathway to achieve higher power density without sacrificing energy density, where the ion diffusion distance between electrodes is minimized by improving electrode architectures. Recent approaches in 3D lithium-ion batteries with interdigitated configuration demonstrated new electrode fabrication methods through direct ink-writing. Although the power densities were improved, the large portion of organic materials in electrode inks for adhesion purpose became the “dead weight” in batteries, and also decreased the electrical conductivity of electrodes. In this work, we demonstrate a new method to fabricate 3D interdigitated lithium-ion battery with architected carbon anode, lithium cobalt oxide (LCO) cathode, and gel polymer electrolyte. An oligo(ethylene glycol)-based gel polymer electrolyte was polymerized in-situ when the resin was in direct contact with the electrodes to achieve a highly adherent interface. Stereolithography (SLA) technique was used to 3D print an architected electrode structure with feature size less than 200 μm using an acrylate-based photoresin. The printed polymer structure went through a pyrolysis process, and 3D architected carbon anode was obtained. The architected LCO anode was also fabricated using an SLA system, but through a “swell-in” — calcination method, where lithium and cobalt ions were swelled into a 3D printed hydrogel, and after a calcination process the 3D architected LCO cathode was obtained. The electrodes fabricated in this work have overcome difficulties in reducing the portion of organic materials in 3D printed electrodes, resulting to a 3D interdigitated lithium-ion battery with large percentage of active materials, high electrical conductivity in electrodes, and small ion diffusion distance between electrodes.

3D multicomponent metal oxides with complex architectures can enable previously impossible energy storage devices, particularly lithium‐ion battery (LIB) electrodes with fully controllable form factors. Existing additive manufacturing approaches for fabricating 3D multicomponent metal oxides rely on particle‐based or organic–inorganic binders, which are limited in their resolution and chemical composition, respectively. In this work, aqueous metal salt solutions are used as metal precursors to circumvent these limitations, and provide a platform for 3D printing multicomponent metal oxides. As a proof‐of‐concept, architected lithium cobalt oxide (LCO) structures are fabricated by first synthesizing a homogenous lithium and cobalt nitrate aqueous photoresin, and then using it with digital light processing printing to obtain lithium and cobalt ion containing hydrogels. The 3D hydrogels are calcined to obtain micro‐porous self‐similar LCO architectures with a resolution of ≈100 µm. These free‐standing, binder‐ and conductive additive‐free LCO structures are integrated as cathodes into LIBs, and exhibit electrochemical capacity retention of 76% over 100 cycles at C/10. This facile approach to fabricating 3D LCO structures can be extended to other materials by tailoring the identity and stoichiometry of the metal salt solutions used, providing a versatile method for the fabrication of multicomponent metal oxides with complex 3D architectures.

Graphene and other two-dimensional materials possess desirable mechanical, electrical and chemical properties for incorporation into or onto colloidal particles, potentially granting them unique electronic functions. However, this application has not yet been realized, because conventional top-down lithography scales poorly for producing colloidal solutions. Here, we develop an 'autoperforation' technique that provides a means of spontaneous assembly for surfaces composed of two-dimensional molecular scaffolds. Chemical vapour deposited two-dimensional sheets can autoperforate into circular envelopes when sandwiching a microprinted polymer composite disk of nanoparticle ink, allowing liftoff into solution and simultaneous assembly. The resulting colloidal microparticles have two independently addressable, external Janus faces that we show can function as an intraparticle array of vertically aligned, two-terminal electronic devices. Such particles demonstrate remarkable chemical and mechanical stability and form the basis of particulate electronic devices capable of collecting and storing information about their surroundings, extending nanoelectronics into previously inaccessible environments.