Bone transplantation is the primary method to address bone defects, accounting for one-fourth of all procedures related to bone defects and ranking as the second most common human tissue transplant surgery after blood transfusion [1, 2]. Bone defects frequently result from trauma, tumors, infections, metabolic diseases, surgeries, radiation therapy, or functional degeneration, making them a common type of injury in clinical settings. The human skeletal system exhibits a certain degree of recovery and morphological regenerative capability [3, 4], where minor bone defects can typically self-heal without external intervention. However, when bone defects exceed a specific size (greater than 2 cm) or when the bone perimeter around the defect exceeds 50%, the self-healing capacity is significantly impaired. This may lead to complications such as non-union, abnormal healing, or pathological fractures [5, 6], potentially resulting in lifelong disabilities for the patients. Effectively repairing bone defects, alleviating healing burdens on patients, and shortening postoperative recovery periods are currently the primary focuses of orthopedic research.
Bone Tissue Engineering (BTE) was first proposed in 1993 and has since emerged as a rapidly growing research area within tissue engineering. It is regarded as an effective method for addressing the challenges of bone defects [7–9]. Research in BTE has shown that artificial biomimetic bones, which possess characteristics such as bone induction, bone conduction, and bone integration, can effectively promote healing and recovery in the human body [10, 11]. Specifically, the bone-conducting properties of scaffolds prevent fibrous capsule formation and facilitate strong bonding with natural bone [12, 13]. Their sufficient biocompatibility and bioactivity enhance the adhesion of osteogenic cells to surrounding new bone, thereby alleviating postoperative healing burdens on patients. Moreover, these scaffolds need to mimic the structure, shape, and function of the missing bone segment, featuring optimized geometric shapes and porosity to ensure adequate space for bone regeneration and to support bone membrane development, thereby accurately filling the anatomical structure of the bone defect [14, 15]. The interior of bones displays a porous structure, where variations in pore size significantly influence the biological behavior of bone cells. For instance, a pore size of approximately 300 micrometers in trabecular bone is beneficial for bone growth and nutrient exchange within the human tissue environment [18, 19]. Furthermore, scaffolds must exhibit sufficient mechanical strength to satisfy the structural demands of tissue substitutes and possess an elastic modulus akin to that of human bone tissue to prevent stress shielding phenomena [20–22].
In recent years, due to limitations in controlling scaffold geometry, pore size, and inter-connectivity using traditional techniques, Additive Manufacturing (AM) has emerged as the preferred method for creating artificial biomimetic bone scaffolds [13, 23]. AM technology enables precise control over various attributes of bone scaffolds, such as stiffness, biochemical factors, spatial distribution capabilities, as well as complex or irregular pore shapes and surface morphologiess [24–26]. Additionally, this technology facilitates high-density in vivo interactions by using bioinks containing different cell types and extracellular matrix (ECM) for high-density bioprinting, allowing for the fabrication of large-scale alternative structures for damaged bones [27–29]. AM technology also offers several other benefits, including the ability to process multiple materials incorporating drugs and biomolecules, maintaining structural and shape stability, minimizing material wastage, improving mechanical performance, enhancing cell infiltration, and promoting nutrient circulation, making it an ideal choice in bone tissue engineering. Ashby et al. [30] proposed a cubic unit cell model for open-cell foam and closed-cell foam, elucidating the relationship between porosity and overall mechanical properties, thereby providing a more rational theoretical basis for scaffold design. Cheah et al. [31–33], considering the manufacturability and spatial geometric characteristics of specific AM technologies, established a library comprising 11 unit types and investigated scaffolds composed of diamond lattices, cubic lattices, truncated octahedra, rhombic dodecahedra, and rhombicuboctahedra to derive analytical relationships between geometric parameters like porosity, scaffold diameter, pore size, and the scaffold's Young's modulus and Poisson's ratio. G. Bini et al. [34] studied trabecular bone microstructure from a topological perspective, summarizing the concept of topological spatial models for bone tissue microstructure, providing further insights for the design of artificial bone structures. AM technology has become a new trend in preparing artificial biomimetic bone scaffolds in the field of BTE.
Based on the requirements of bone tissue engineering for biomimetic bone scaffolds, this study introduces a novel noise topology-based 3D bone scaffold model. The study establishes a porosity pattern classification based on bone density distribution across different age groups and performs mechanical simulations on the resulting bone structure models using finite element software. AM technology ensures that the porous gradient bone scaffold model closely resembles natural bone in terms of shape, structure, porosity, and stress distribution. The layered structure is also better suited to adapt to the distribution of bone tissue membrane layers, cortical bone layers, and trabecular bone layers, from outer to inner layers. At the medical technology level, this approach helps prevent postoperative bone loss due to stress mismatch after bone grafting, ultimately reducing healing pressures on patients and shortening recovery periods.