Metal Oxide-Functionalized Photopolymers: A Perspective in 3D Printing

Vat photopolymerization is a widely adopted additive manufacturing technique valued for its high resolution, smooth surface finish, and rapid production speed. Recently, it has gained prominence in the fabrication of polymer nanocomposites, as liquid photopolymer resins allow efficient incorporation and dispersion of nanoparticles. Current research in vat 3D printing of polymer nanocomposites is directed toward creating materials with enhanced functionalities, enabling the development of advanced functional components. Among different nanofillers, semiconducting metal oxide nanoparticles (MOx NPs) such as TiO₂, ZnO, Fe₃O₄, Cu₂O, and ZrO₂ are of particular interest. These NPs act not only as functional additives but also as photocatalysts, directly influencing photopolymerization kinetics, cross-linking density, and final properties. Mechanical performance is enhanced through nanoreinforcement, provided that homogeneous NP dispersion is achieved. This enables lightweight, high-performance parts for aerospace, automotive, and biomedical engineering. MOx NPs also improve thermal stability, supporting applications in electronics, automotive systems, and energy devices. Adjustments in electrical and dielectric properties open further potential in power electronics, high-voltage insulation, and wearable devices. Incorporation of superparamagnetic Fe₃O₄ introduces magnetic functionality, useful for microactuators, sensors, and graded materials. Optical properties can likewise be tailored, with MOx/polymer nanocomposites enabling photodetectors, optoelectronic components, and functional thin films. In the biomedical field, biofunctional performanceranging from antimicrobial activity to tissue compatibilityhas been exploited in dentistry, tissue scaffolds, and micromachines for drug delivery. Despite these advances, challenges such as nanoparticle aggregation, viscosity increase, light scattering, and altered reaction kinetics still limit the achievable filler loadings and overall performance of vat-printed nanocomposites. This review therefore emphasizes both the potential and the limitations of incorporating MOx nanoparticles into vat photopolymerization, outlining the current state of knowledge and key challenges that must be addressed to enable application-oriented functional materials.