Borate-Based Bioactive Glass Powders for 3D Printing of Biomimetic Resorbable Bone Implants

As the population ages, the demand for customizable, resorbable bone implants in tissue engineering has intensified, outstripping the limitations of traditional autografts and allografts. While silicate-based bioactive glasses dominate bioactive glass research, borate-based bioactive glasses (BBGs) present distinct biomimetic advantages due to their accelerated degradation kinetics and superior ion-release profiles. However, producing highly pure, homogeneous BBG powders tailored for additive manufacturing remains a severe bottleneck. This study reports the development of a highly efficient synthesis protocol and subsequent Digital Light Processing (DLP) 3D printing of BBG scaffolds. An aqueous-based precursor mixture was processed via spray drying and a customized multi-stage thermal pretreatment sequence up to 800 °C to mitigate material loss, minimize oxide evaporation, and completely eliminate carbonates. Subsequent "flash melting" at 1150 °C for 20 min yielded an amorphous, high-purity borate-phosphate glass network (68.1B₂O₃-3.8Na₂O-18.9CaO-4.9MgO-4.3P₂O₅, in wt%). Differential scanning calorimetry (DSC) revealed a glass transition temperature (Tg) of 625 °C, while in situ X-ray diffraction localized the onset of crystal nucleation between 706 °C and 723 °C. Following fine planetary milling to achieve a highly dense particle packing distribution (D_v50 = 5.4 µm, D_n50 = 0.6 µm), the optimized BBG powder was successfully loaded into an acrylate-based photosensitive slurry (51.2 wt% solid loading) to manufacture complex 3D biomimetic gyroid scaffolds via DLP. While the structural feasibility of printing high-resolution gyroid porous architectures is validated, post-printing evaluation highlighted a narrow thermal processing window; sintering at 660 °C optimized particle coalescence while minimizing microstructural de-densification caused by closed porosity expansion (which reaches 48.4% at 675 °C). This scalable synthesis-to-printing workflow offers a crucial steppingstone toward next-generation fully resorbable bone tissue scaffolds.