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.利用可降解承重植入物修复临界尺寸下颌骨缺损仍颇具挑战，因其需同时兼顾术后早期的高机械稳定性与可控降解需求。本研究提出一套完整的开发流程，用于制备经30 wt% β-磷酸三钙（β-tricalcium phosphate, β-TCP）增强的患者专属聚己内酯（polycaprolactone, PCL）植入物，制备工艺采用熔融沉积建模（fused deposition modeling, FDM）。针对该高陶瓷含量体系，要实现稳定挤出与规模化打印，需采用延长超声分散、溶剂辅助共混及优化挤出参数的工艺方案。基于有限元（finite element, FE）的拓扑优化指导了应力自适应梯度点阵的设计，该点阵在应力富集区域设置高密度增强结构，低应力区域则采用更大孔径的结构。通过拉伸试验与四点弯曲试验评估其力学性能，并借助定制化双模式平台同步开展水解降解与循环加载（1 Hz下载荷范围20–200 N），以模拟术后早期的生理环境。RI-2设计的弧长更短，且关键区域采用高密度点阵，可维持完整结构完整性达1个月；而跨度更长的RI-3则在第14.4天时发生结构失效。显微计算机断层扫描（micro-CT）与有限元分析结果显示，RI-3存在更显著的变形与应力集中现象。上述结果表明，先进材料加工工艺、优化的点阵几何结构与严格的双条件验证三者间的协同作用至关重要，这对于开发可应用于临床的承重可吸收颅面重建植入物具有关键意义。