Addressing these challenges, an innovative research team led by Professor Keun Park and Associate Professor Soonjae Pyo at Seoul National University of Science and Technology has pioneered the fabrication of highly stretchable and electrically conductive CNT nanocomposites using vat photopolymerization (VPP)-based additive manufacturing. VPP is a sophisticated 3D printing technique that leverages selective light curing within a resin vat to create finely detailed, complex structures. The researchers expertly overcame traditional issues related to CNT agglomeration and ink curing, achieving a formidable balance between stretchability, conductivity, and print resolution—factors that usually exhibit trade-offs in composite materials.

The core strategy employed involved dispersing multi-walled carbon nanotubes (MWCNTs) within an aliphatic urethane diacrylate (AUD) photopolymer matrix. This required meticulous ultrasonic agitation to achieve a homogeneous mixture, which is essential for ensuring consistent electrical pathways and mechanical reinforcement throughout the printed material. Ranging from 0.1 to 0.9 weight percent MWCNTs, the polymer nanocomposite inks were rigorously evaluated to determine optimal properties for 3D printing, including viscosity, curing kinetics, and compatibility with VPP’s photopolymerization process.

Key to their breakthrough was the identification of the 0.9 weight percent MWCNT concentration as the sweet spot that balanced conductivity and mechanical resiliency. Test specimens exhibited remarkable stretchability, enduring elongations up to 223% of their original length without failure, an exceptional value that far exceeds typical CNT nanocomposite performance benchmarks. Concurrently, the electrical conductivity reached an impressive 1.64 × 10^−3 S/m, surpassing earlier reports of similar 3D printable composite materials. This dual achievement of high stretchability and conductivity while maintaining a print resolution of 0.6 mm signifies a new frontier in material science and engineering.

Leveraging the optimized nanocomposite formulations, the team fabricated triply periodic minimal surface (TPMS) structures—complex 3D lattice geometries known for their outstanding mechanical properties and lightweight architectures. These structures functioned as piezoresistive sensors characterized by high sensitivity to mechanical deformation, which is vital for accurate detection of pressure and strain in wearable devices. Incorporating these sensors into a flexible insole demonstrated practical application potential, whereby the pressure distribution exerted by a user’s foot could be monitored in real time. This capability paves the way for advanced health monitoring systems that can detect gait anomalies or postural changes with high spatial and temporal resolution.

The integration of the CNT-based piezoresistive sensors into wearable platforms, such as smart insoles, embodies the intersection of materials innovation and human-centric design. The use of additive manufacturing allows for the precise tailoring of sensor architectures, enabling bespoke designs optimized for sensitivity, durability, and wearer comfort. Moreover, the piezoresistive effect in CNT nanocomposites offers a promising alternative to conventional rigid sensors, which often suffer from limited flexibility and poor adaptability to dynamic human motion.

Beyond the sensor application, the researchers underscore the broader implications of their work for fields ranging from soft robotics to smart textiles. The tailored VPP-based synthesis of CNT nanocomposites can lead to next-generation electronic components that combine mechanical compliance with conductive functionality, a crucial requirement for devices embedded in flexible and deformable substrates. This advance fundamentally changes how we conceive the design and manufacture of wearable health monitors by integrating sensing capabilities directly into customized 3D-printed form factors.

While prior approaches struggled with CNT dispersion and UV-light induced curing limitations, this study’s methodical optimization allowed the preservation of photopolymerization efficiency despite the presence of electrically conductive fillers. The ultrasonication technique effectively broke down CNT bundles, facilitating homogenous dispersion and minimizing light scattering during the VPP curing process. This breakthrough enables a radical enhancement in print fidelity for complex geometries, pushing the envelope of what additive manufacturing can achieve with multifunctional nanocomposites.

This development arrives at a time when the demand for wearable health devices is surging, fueled by the growing population of health-conscious and aging individuals. The ability to manufacture stretchable, conductive, and highly sensitive sensors affordably and at scale could democratize advanced healthcare monitoring, providing continuous, real-time data to both patients and healthcare providers. This would allow early detection of abnormalities and personalized interventions outside clinical settings, significantly impacting patient outcomes and healthcare economics.

Professor Keun Park emphasizes that their optimized CNT nanocomposites are not only suited for piezoresistive sensor fabrication but also open avenues for creating architectured materials with tunable mechanical and electrical properties. Such materials can be tailored to specific application requirements, enhancing the functionality and integration capacity of flexible devices. The research demonstrates critical progress in the feasibility of 3D printing these complex materials in forms that were previously impossible due to material or process constraints.

Associate Professor Soonjae Pyo highlights the multidisciplinary synergy required to realize these advancements, combining expertise in nanoscale material science, additive manufacturing technology, and sensor engineering. Their collaborative efforts embody the future trajectory of materials innovation, where precise control at multiple length scales—from molecular dispersion of CNTs to large-scale device architecture—enables transformative device capabilities.

The significance of this study extends beyond academia, potentially impacting industries such as healthcare, consumer electronics, athletics, and even aerospace, where lightweight, multifunctional, and flexible materials are in high demand. The scalable VPP-based process for these CNT nanocomposites also implies cost-effective manufacturability, critical for commercial viability. As flexible and wearable electronics continue to push boundaries, the materials enabling these devices must evolve. This research provides a key technological leap, signaling a paradigm shift in how conductive, stretchable materials are created and utilized.

In summary, the team at Seoul National University of Science and Technology has successfully demonstrated a photopolymerization additive manufacturing method that fabricates highly stretchable, electrically conductive CNT nanocomposites with exceptional mechanical and electrical performance. Their ability to create complex, architectured sensors using 3D printing marks a significant advancement in wearable technology. By embedding these sensors into smart insoles capable of real-time pressure monitoring, they exemplify the practical impact and transformative potential of their materials innovation. As the field advances, such breakthroughs will undoubtedly accelerate the development of next-generation smart, flexible devices vital for personalized health monitoring and beyond.

Subject of Research: Not applicable

Article Title: Photopolymerization additive manufacturing of highly stretchable CNT nanocomposites for 3D-architectured sensor applications

News Publication Date: 15-Nov-2025

References: DOI: 10.1016/j.compstruct.2025.119614

Image Credits: Seoul National University of Science and Technology

Keywords: Nanotechnology, Additive manufacturing, Carbon nanotubes, Conductive polymers, Wearable devices, Health and medicine, Sensors, Materials science

Silicon nitride, a non-oxide ceramic renowned for its exceptional mechanical strength, thermal stability, and resistance to wear and corrosion, is highly sought after in aerospace, biomedical, and automotive industries. Yet, integrating silicon nitride within vat photopolymerization—the technology underpinning high-resolution stereolithography—is a highly complex endeavor. The fundamental challenge arises from the necessity to balance the ceramic powder loading with the resin’s flow behavior, ensuring consistent layer formation and subsequent structural integrity post-sintering.

The study’s core focus revolves around modifying the slurry rheology to optimize printability and final part density. Traditionally, ceramic slurries face a trade-off between viscosity and ceramic content; higher ceramic loadings increase viscosity, complicating the vat photopolymerization printing process and sometimes leading to defects such as incomplete layer curing or delamination. The researchers tackled this issue by developing a tailored dispersant system that enhances particle suspension and homogeneity without excessively increasing viscosity, permitting higher ceramic loadings while retaining print fidelity.

Through careful experimentation, the team formulated resin ceramic slurries comprising silicon nitride particles dispersed within photocurable resins, then systematically adjusted dispersant concentrations and particle size distributions. Their innovative approach resulted in slurries that maintained shear-thinning behavior, crucial for smooth recoating during printing, and rapid viscosity recovery post-shear, reducing the likelihood of sedimentation—a notorious problem in dense ceramic slurries.

Moreover, the researchers utilized advanced rheometry to characterize the non-Newtonian flow behavior of the slurries, quantifying parameters such as yield stress and thixotropy. Obtaining an optimal balance of these parameters ensured that the material would not flow uncontrollably post-application yet would spread evenly to form ultra-thin layers essential for high-resolution vat photopolymerization. This controlled rheological profile ultimately afforded superior layer stacking and curing uniformity, key to achieving dense, crack-free ceramic parts after sintering.

Following the printing stage, the debinding and sintering protocols were finely tuned to minimize residual stresses and prevent warping, which are frequent obstacles in ceramic additive manufacturing. The precise control over slurry composition and print parameters directly influenced the microstructural evolution during sintering, encouraging grain growth in a manner that preserved mechanical strength and avoided abnormal densification patterns.

The impact of this research transcends mere material formulation. By establishing a robust link between slurry rheology and 3D printing capability, the findings provide a scalable pathway toward producing complex silicon nitride components with geometries previously unattainable by traditional manufacturing. This leap is particularly transformative for industries requiring bespoke parts with intricate internal architectures, such as turbine blades with internal cooling channels or custom biomedical implants with optimized porosity for bone ingrowth.

From a technological standpoint, the incorporation of appropriately engineered dispersants modifies interparticle interactions, promoting steric stabilization that deters agglomeration, thereby maintaining resin transparency necessary for effective UV curing. This transparency is vital in vat photopolymerization, where light penetration depth dictates cure thickness and fidelity. The researchers’ method ensures that high ceramic loads do not impede polymerization kinetics, a fine balance critical for successful layer-by-layer photopolymerization.

In addition to rheological modifications, the study highlights the importance of particle surface chemistry in compatibility with the resin matrix. Functionalizing silicon nitride surfaces enhanced resin bonding, contributing to the final composite’s mechanical properties. This insight illuminates the broader principle that surface engineering of ceramic particles is integral to optimizing composite slurry systems for additive manufacturing.

Coupling these material advances with precision printing controls results in ceramic parts exhibiting mechanical properties rivaling traditionally manufactured counterparts. The tensile strength, fracture toughness, and hardness measurements performed on sintered samples underscore the viability of the developed process as a candidate for industrial adoption, especially where high-performance ceramic materials are indispensable.

Industry analysts assert that this kind of breakthrough will catalyze wider acceptance of vat photopolymerization for ceramic additive manufacturing, moving beyond prototyping toward functional end-use components. The scalability inherent in this process, alongside improvements in process speed and dimensional accuracy, aligns with manufacturing’s broader shift towards digitalization and on-demand production.

Notably, this research may accelerate the integration of silicon nitride ceramics in sectors demanding ultra-high-performance materials fabricated with minimal waste and maximal design freedom. Combining traditional ceramics’ robustness with the geometric creativity enabled by additive manufacturing could revolutionize design paradigms and product lifecycles.

Furthermore, the environmental implications are compelling. Optimizing slurry rheology to facilitate higher ceramic solids loading without sacrificing print printability directly reduces reliance on organic resins and supports more efficient sintering cycles. This improvement could decrease the carbon footprint associated with ceramic component manufacturing, complementing sustainability goals increasingly prioritized by manufacturers worldwide.

One cannot overlook the ripple effect this research may have on adjacent fields such as electronics, where silicon nitride’s dielectric properties are invaluable, or in energy applications including fuel cells and battery components. The capacity to fabricate finely featured ceramic structures with enhanced mechanical integrity opens new avenues for device miniaturization and performance enhancement.

Ultimately, Cramer and colleagues’ work exemplifies the symbiotic relationship between material science innovations and additive manufacturing technology. By meticulously engineering the complex interplay between particle dispersion, resin chemistry, and process mechanics, they have forged pathways that unlock the latent potential of ceramics in vat photopolymerization, reshaping the future of high-performance manufacturing.

As further investigations build on these findings, we can anticipate progressively sophisticated slurry formulations tailored to a broader range of ceramics and photopolymer resins, pushing the frontier of precision, performance, and application scope in 3D-printed ceramic components. This research not only charts a course for silicon nitride but heralds a new era in additive manufacturing technology whereby ceramic materials achieve unprecedented manufacturability and functionality.

Subject of Research: Rheology optimization of silicon nitride and resin slurries for vat photopolymerization and subsequent sintering in ceramic additive manufacturing.

Article Title: Rheology improvement for silicon nitride and resin slurries for vat photopolymerization printing and sintering.

Article References:

Cramer, C.L., Hmeidat, N.S., Mitchell, D.J. et al. Rheology improvement for silicon nitride and resin slurries for vat photopolymerization printing and sintering.
npj Adv. Manuf. 2, 36 (2025). https://doi.org/10.1038/s44334-025-00051-y

Image Credits: AI Generated