Early-stage mechanical stability and degradation behavior of biodegradable 3D-printed implants with topology-optimized gradient lattice design for critical mandibular defect reconstruction

Reconstruction of critical-sized mandibular defects using biodegradable load-bearing implants remains challenging due to the combined demands of high mechanical stability and controlled degradation during the early stage after surgery. This study presents a complete workflow for developing patient-specific polycaprolactone (PCL) implants reinforced with 30 wt% β-tricalcium phosphate (β-TCP) via fused deposition modeling (FDM). Achieving reliable extrusion and large-scale printing at this high ceramic content required prolonged ultrasonic dispersion, solvent-assisted blending, and optimized extrusion parameters. Finite element (FE) based topology optimization guided the design of stress-adaptive gradient lattices, combining high-density reinforcement in stress zones with larger pores in low-stress regions. Mechanical properties were evaluated by tensile and four-point bending tests, and a custom dual-mode platform applied simultaneous hydrolytic degradation and cyclic loading (20–200 N at 1 Hz) to simulate early postoperative environment. The RI-2 design, with a shorter arc length and high-density lattice in critical zones, maintained full structural integrity for one month, whereas the longer-span RI-3 failed at 14.4 days. Micro-CT and FE analyses revealed greater deformation and stress concentration in RI-3. These results highlight the crucial interplay of advanced material processing, optimized lattice geometry, and rigorous dual-condition validation in enabling clinically applicable, load-bearing resorbable implants for craniofacial reconstruction.