Cryogenic 3D-printed gelatin-chondroitin sulfate scaffold embedded with PCA/Cu2+/ε-polylysine-functionalized chitosan microspheres for simultaneous antibacterial, anti-inflammatory, angiogenic, and osteogenic bone regeneration.

Abstract

3D-printed gelatin scaffolds are widely explored for bone regeneration due to their excellent biocompatibility and biodegradability, yet their clinical translation is severely hindered by several inherent defects, including weak mechanical stability, fast in vivo biodegradation, limited osteogenic capability, and the absence of anti-infective functions. Globally, it remains a key challenge in bone tissue engineering to develop integrated scaffold systems that simultaneously satisfy mechanical matching, long-term biological activity, and anti-pathogenic requirements. To address this challenge, a multifunctional CHm/PCA/Cu2+/ε-PL@Gel-OCS scaffold with enhanced mechanical properties, outstanding antibacterial, anti-inflammatory, pro-vascularization and osteogenic activities was developed via cryogenic 3D printing of a gelatin (Gel)/oxidized chondroitin sulfate (OCS) composite ink loaded with chitosan microspheres surface-functionalized by protocatechuic aldehyde (PCA), copper ions (Cu2+) and ε-polylysine (ε-PL). Scanning electron microscopy and energy-dispersive X-ray analysis confirmed uniform dispersion of the microspheres and sustained release of therapeutic agents as the scaffold degraded. Rheological and mechanical testing demonstrated excellent print fidelity, interconnected porosity (161 ± 37 μm pores), and compressive strengths (100-200 MPa) suitable for cortical bone repair. Such porous structure and mechanical performance are highly compatible with human cortical bone microenvironment, which facilitates cell infiltration, nutrient exchange and mechanical load bearing. In vitro release studies revealed a sequential sustained release profile (OCS > Cu2+ > ε-PL), ensuring a sustainable osteogenic, angiogenic, anti-inflammatory and antibacterial activity. The scaffold achieved 100% bactericidal efficiency against both Staphylococcus aureus and Escherichia coli, suppressed protein denaturation (anti-inflammation), and promoted neovascularization in a chick chorioallantoic membrane assay. Biocompatibility assays using MC3T3-E1 osteoblasts showed enhanced cell adhesion, proliferation, and live/dead viability over 5 days. Osteogenic potential was significantly elevated on the multifunctional scaffold, as evidenced by time-dependent increases in ALP activity, mineral deposition (Alizarin Red S), and upregulated expression of ALP, RUNX2, OPN, and OCN genes compared with Gel and Gel-OCS controls. Taken together, our cryogenic 3D-printed Gel-OCS scaffold incorporating PCA/Cu2+/ε-PL-functionalized chitosan microspheres provides a single-step, customizable platform that combines robust mechanical properties with multi-modal therapeutic functionalities. Different from conventional single-function bone scaffolds reported in most international studies, this multi-component synergistic design successfully realizes the integration of mechanical reinforcement, antibacterial, anti-inflammatory, vascularization and osteogenesis functions in one system. These promising preclinical results highlight a novel therapeutic strategy for bone defect regeneration, it solves the common bottlenecks of traditional gelatin-based bone scaffolds, provides a feasible and universal fabrication strategy for high-performance multifunctional bone repair materials, and offers new insights for the global development and clinical translation of 3D-printed bone tissue engineering scaffolds.