Development of 3D engineered scaffolds with triply periodic minimal surface (TPMS) structure for bone tissue repair

Abstract

Triply periodic minimal surface (TPMS) structures play crucial roles in natural phenomena such as leaf photosynthesis, coral mineralization, and trabecular bone growth. This thesis introduces the development and creation of high-resolution 3D TPMS structures, which are designed with biomimetic hyperboloidal features and a variety of Gaussian curvatures, aiming to address the considerable difficulties encountered in translating these into practical engineered bone grafts. These scaffolds were composed of body-inherent β-tricalcium phosphate (β-TCP) and were fabricated using stereolithography-based 3D printing followed by post-sintering. The TPMS bone scaffolds exhibited high porosity and interconnectivity, showing improved mechanical strength by reducing stress concentration compared with conventional scaffolds. Furthermore, we investigated the impact of hyperbolic structures with varying Gaussian curvatures on cellular morphology, cellular energy metabolism, and response to physical stimuli, including thermodynamic heat and chemical stimulation involving L-arginine. Our study systematically explored the effectiveness of TPMS structures in biological systems and demonstrated their potential for bone tissue engineering. In the first study, we fabricated TPMS scaffolds with varying Gaussian curvatures (-2 to -6 mm-2) and studied mesenchymal stem cell (MSC) adhesion, proliferation, osteogenesis, and angiogenic paracrine secretion regulation. In our in vitro research, we hypothesize that the hyperboloid architecture stimulates a reorganization of the MSCs’ cytoskeleton, leading to an elongated shape in the direction of convexity and an enhancement of cytoskeletal tension. The TPMS scaffolds facilitated the creation of new bone and neovascularization, as shown by in vivo assessment utilizing mouse subcutaneous implantation and rabbit femur deficiency models. The TPMS scaffolds significantly improved bone regeneration when compared to conventional truss scaffolds by using directional curvatures to drive cell destiny towards osteogenesis. In the second project, we focused on the effects of the porous continuous surface structure of TPMS scaffolds on fluid dynamics and heat exchange. First, we prepared TPMS scaffolds with different concentrations of polydopamine coatings and evaluated how different Gaussian curvatures and dopamine coatings influenced photothermal conversion coefficient. Among the different types of TPMS scaffolds, the Diamond type with a Gaussian curvature of -6 mm-2 exhibited optimal thermal conductivity, reducing heat accumulation and achieving the ideal temperature range (39-41°C) for bone regeneration. Additionally, we explored the interaction between hyperbolic structures and heat on stem cells, revealing that moderate heat facilitated osteogenic differentiation both in vitro and in vivo. Lastly, in the third project, we incorporated L-arginine into the dopamine coating and investigated the combined effects of amino acid metabolism and topological structure on bone metabolism. L-arginine, as a substrate for ATP metabolism, enhanced ATP production in MSCs, RAW267.4 cells, and human umbilical vein endothelial cells (HUVECs). The remodeling of cytoskeleton by hyperbolic surface structures regulated mitochondrial membrane activity, leading to improved ATP utilization efficiency. This efficient production and utilization of ATP played a crucial role in regulating the steady state of osteogenesis, osteoclastogenesis, and angiogenesis, effectively promoting osteogenic regeneration. In conclusion, this thesis provides a comprehensive investigation into the design, fabrication, and biological implications of TPMS scaffolds with hyperboloidal topography and varying Gaussian curvatures for bone tissue engineering. The study highlights the potential of TPMS structures in promoting cellular behavior, enhancing mechanical properties, and regulating bone metabolism. The findings herein will contribute to innovative strategies for bone tissue engineering and provide valuable insights into the role of topological structures in tissue regeneration.