Triply Periodic Minimal Surface Architecture Improves Bone Growth in 3d-Printed Polycaprolactone Scaffolds

Critical-sized bone defects often require bone grafting, and tissue-engineered scaffolds are increasingly used to enhance bone healing.[1] Polycaprolactone (PCL), a biocompatible and biodegradable polymer, has been used for bone reconstruction due to its printable nature and tunable properties. [2] Triply periodic minimal surface (TPMS), such as gyroid, feature interconnected pores and high surface – all which support cell growth. This study evaluates PCL scaffolds with varying architectures (TPMS gyroid and honeycomb) and infill percentage (40% and 60%, Fig.1), and we hypothesized that gyroid designs would enhance bone regeneration. A total of 72 cylindrical test samples (15 mm outer diameter, 5 mm inner diameter, 10 mm height) were 3D printed. Scaffolds (n=18/group) underwent sterilization and cylindrical cavities were filled with juvenile bovine bone graft collected from proximal tibiae. Constructs were cultured under standard conditions (37°C, 5% CO2) and media was exchanged every 3–4 days. Alamar Blue assays measured metabolic activity at 0, 1, 2, 3, and 4 weeks. Von Kossa staining at 4 weeks assessed calcium deposition. Micro-CT quantified the volume of calcium content at 4 weeks. Compression tests were performed at Day 0 and Week 4 to evaluate scaffold mechanical properties. Alamar Blue assays showed that all constructs were able to maintain a high level of cell viability during the 4-week incubation period. (Fig. 2A). Von Kossa staining showed G40 exhibited greater mineralization (49.60 ± 8.57) compared to H40 (68.42 ± 7.90, p=0.015) (Fig. 2B). Micro-CT analysis showed significantly higher bone volume in gyroid groups (G40: 58.5 ± 5.0 mm 3 ; G60: 58.1 ± 5.4 mm 3 ) versus honeycomb groups (H40: 26.9 ± 2.9 mm 3 ; H60: 26.3 ± 7.4 mm 3 , p<0.0001) (Fig. 2C). Honeycomb samples had higher stiffness and yield force during compression testing compared to gyroid samples. (Fig. 2D). All samples exhibited increased mechanical properties by week 4 due to bone tissue growth. Results confirm our hypothesis that additively manufactured PCL scaffolds with TPMS architecture can create favorable microenvironments that enhance cellular metabolic activity and bone growth. Micro-CT analysis demonstrated that gyroid scaffolds led to double the bone formation compared to honeycomb scaffolds at week 4, highlighting the effectiveness of the gyroid design. However, honeycomb scaffolds provide superior mechanical strength, indicating a tradeoff depending on application requirements. Future research will aim to optimize scaffold designs for clinical applications. This study highlights the potential of TPMS-structured PCL scaffolds for bone defect repair. For any figures or tables, please contact the authors directly.