Early-stage stability and degradation of patient-specific biodegradable 3D-printed implants for critical mandibular reconstruction

This study aimed to develop patient-specific biodegradable mandibular implants composed of polycaprolactone (PCL) reinforced with 30 wt% β-tricalcium phosphate (β-TCP) using fused deposition modeling (FDM), and to evaluate how gradient lattice structural designs influence early postoperative mechanical stability and degradation behavior in critical-sized mandibular defects, thereby establishing practical design criteria for reliable reconstruction. Gradient lattice architectures were designed by finite element–based topology optimization, assigning dense lattices (P06, ∼1000 μm pores) to high-stress regions and larger pores (P08, ∼1500 μm) to low-stress zones. Two implant spans were investigated: RI-2, with an arc length approximately twice the average bone width, and RI-3, with an arc length about three times the bone width. Mechanical properties were characterized by tensile and four-point bending tests, and a dual-mode platform applied hydrolytic degradation and cyclic loading (20–200 N, 1 Hz) to replicate early postoperative oral conditions. The PCL/β-TCP composite showed an elastic modulus of 450 ± 20 MPa and cell viability of average 84.5 %. Four-point bending revealed that the RI-2 design achieved a proof load of 83.8 ± 5.3 N and bending strength of 1466 ± 92 N·mm, 2.35-fold higher than RI-3. Under dual hydrolysis–loading, all RI-2 implants maintained structural integrity for one month, whereas RI-3 failed after 14.4 ± 1.2 days. Micro-CT confirmed greater dimensional stability of P06 versus P08 lattices. This work demonstrates that high-content PCL/β-TCP composites can be reliably 3D printed into stress-adaptive mandibular implants, and establishes quantitative design thresholds for balancing early mechanical support with degradation in oral and maxillofacial reconstruction. • High-content PCL+ 30 % β-TCP filaments enabled stable FDM printing of large implants. • Topology optimization guided gradient lattice balancing stress with degradation. • Implants spanning 2 × bone width showed 2.35-fold higher bending strength vs. 3 × width. • Dual hydrolysis–dynamic loading platform simulated early postoperative conditions. • Design rule: arc length ≤ 2 × stump width ensures stability in mandibular implants.