3D Photoprintable Bismuth Methacrylate Resins: From Formulation to Printed Polymers

Abstract

Vat photopolymerization enables the fabrication of complex geometries with high resolution, but incorporating high-density metal compounds into photocurable resins remains challenging due to sedimentation, limited dispersion, and reduced dimensional accuracy. In this work, we report 3D photoprintable resins incorporating bismuth(III) methacrylate [Bi(MA)3], as an alternative strategy for incorporating a high-Z element into photopolymer networks, enabling a largely homogeneous distribution at the bulk scale while mitigating dispersion and processing limitations associated with particulate fillers. Resin formulations included N,N-dimethylacrylamide (DMAA) as a solvent and monomer, either urethane dimethacrylate (UDMA) or poly(ethylene glycol) diacrylate (PEGDA), a photoinitiator, and photoabsorbers. Cure depth experiments and Jacob’s working curves guided the optimization of exposure parameters and component ratios, yielding resins with reliable curing behavior at a layer thickness of 100 μm. The influence of Bi content (0–25 wt %) as Bi(MA)3 or its polymerized form was systematically assessed. Increasing the Bi(MA)3 content reduced overpolymerization in both UDMA and PEGDA systems, improving z-axis fidelity in printed structures. Mechanical testing revealed an optimal Bi loading of 10 wt % for UDMA and 20 wt % for PEGDA at which stiffness, tensile strength, and toughness were maximized. At higher Bi contents, embrittlement caused reduced toughness and lower strain at break. Scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed a largely homogeneous bismuth distribution within the printed networks at the bulk scale, while higher Bi contents led to the formation of localized Bi-rich regions at interlayer interfaces aligned with the printing direction. These microstructural features correlate with the observed changes in mechanical behavior at elevated Bi loadings. At moderate Bi loadings, thermogravimetric analysis revealed lower decomposition temperatures, with partial recovery at higher Bi contents, while residual mass increased with Bi content, consistent with the initial Bi loading. Differential scanning calorimetry revealed glass transition temperatures of approximately 125 °C for both Bi-free and 5 wt % Bi UDMA materials, but no such transitions were observed at higher Bi contents. While polymer films without Bi and 100 μm-thick films with 10 and 20 wt % Bi content exhibited high transparency, increasing film thickness (200–500 μm) and Bi(MA)3 content led to increased opacity. Collectively, these results demonstrate that Bi(MA)3 enables the incorporation of high bismuth loadings into photocurable resins, resulting in a largely homogeneous distribution at the bulk scale. This yields materials with tunable mechanical and thermal properties while preserving printability, enhancing z-axis fidelity, and mitigating the sedimentation and dispersion issues typical of particulate fillers.