3D-printed core–shell scaffolds with a biphasic calcium phosphate core and GelMA hydrogel shell for bone tissue engineering

Bone tissue engineering requires scaffolds that simultaneously provide mechanical stability, controlled biodegradation, and bioactivity to support bone regeneration. In this study, a novel core-shell composite scaffold was developed by integrating an extrusion-based 3D-printed alginate/ceramic lattice core with a bioactive gelatin methacrylate (GelMA) hydrogel shell. Biphasic calcium phosphate (BCP) systems with different hydroxyapatite (HA)/β-tricalcium phosphate (β-TCP) ratios were incorporated into alginate-based bioinks and fabricated via robocasting to achieve well-defined, interconnected porous architectures. Following ionic crosslinking and lyophilization, the printed scaffolds were uniformly coated with GelMA and photo-crosslinked to form a stable hydrogel shell. Morphological analyses confirmed the preservation of interconnected porosity with pore sizes in the range of 450-650 µm, suitable for bone tissue ingrowth. Mechanical testing revealed that the incorporation of ceramic phases significantly enhanced scaffold stability, while GelMA coating further improved compressive performance, increasing the elastic modulus from 37.35 ± 0.73 MPa for pure alginate scaffolds to 82.04 ± 0.50 MPa for GelMA-coated BCP scaffolds. In vitro degradation studies demonstrated a controlled, time-dependent mass loss profile, indicating favorable scaffold stability under physiological-like conditions. Bioactivity evaluation in simulated body fluid (SBF) showed pronounced calcium phosphate deposition on BCP-containing scaffolds, particularly those coated with GelMA, as confirmed by FESEM and EDS analyses. Accordingly, the synergistic combination of a mechanically reinforced ceramic-polymer core and a bioactive GelMA shell resulted in scaffolds with enhanced mechanical integrity, tunable degradation behavior, and superior in vitro bioactivity. These findings highlight the potential of GelMA-coated BCP composite scaffolds as promising candidates for bone tissue engineering applications.