High-Fidelity 3D bioprinting of soft hydrogel structures via spatio-temporal femtosecond laser focusing

Hydrogel materials are excellent biocompatible materials with numerous applications in biomedical devices. However, their low viscosity and high fluidity pose significant challenges to achieving high fidelity in biofunctional structures during additive manufacturing. In this paper, we present a femtosecond laser processing system based on simultaneous spatial and temporal focusing (SSTF), which employs coordinated regulation of temporal pulse stretching via blazed gratings and spatial energy gradients to generate a super-Gaussian optical field at the focal plane. Through optical simulations and experimental validation, the physical mechanism by which the super-Gaussian energy distribution of the SSTF optical field suppresses material flow and enables uniform curing is revealed. Experimental results demonstrate that, compared to traditional Gaussian laser processing, the SSTF technology significantly enhances surface smoothness (Ra < 0.5 μm) and interlayer bonding quality (interlayer thickness variation ± 0.5 μm), successfully fabricating various biofunctionalized structures. In vitro validation experiments demonstrate that the functional structures printed exhibit surfaces capable of supporting cells, maintaining high viability, and forming complete cytoskeletal networks, while significantly promoting cell proliferation and osteogenic differentiation. This three-dimensional controllable polymerization process, which relies on radial energy gradients to inhibit material flow and axial localization control, provides a high-fidelity, biosafe manufacturing strategy for medical applications.