Nanoparticles play a vital role in bone tissue repair engineering, especially iron oxide nanoparticles (IONPs), which have magnetic properties, semiconductor properties, and nontoxicity at the same time, and their applications in biomedicine have received widespread attention. This review summarizes the excellent performance of IONPs in enhancing scaffold functions, promoting stem cell differentiation, and labeling positioning, in order to understand the research progress and future development trends of IONPs in bone tissue repair engineering, as well as the security issues. Firstly, IONPs can affect the expression of genes and proteins to accelerate the process of biomineralization under a magnetic field. Then, the composite of IONPs and polymers can synthesize a scaffold which can promote the attachment, proliferation, and bone differentiation of stem cells. Furthermore, IONPs can also mark the location of drugs in the body to follow up the process of bone repair. Therefore, extensive research on the manufacturing and application range of IONPs is of great significance to bone tissue repair engineering.

There is a high risk of serious injury to the lower extremities during a human drop landing. Prophylactic knee and ankle braces are commonly used to reduce injury by restraining the motion of joints. However, braces that restrain joint range of motion (ROM) may have detrimental effects on the user’s kinematical performance and joint function. The present study aimed to propose a novel set of double-joint braces and to evaluate its protective performance in terms of the ankle and knee. Accordingly, the finite element method was performed to investigate the biomechanical responses of the ankle and knee in braced and unbraced conditions. The results showed that the semi-rigid support at the ankle joint can share the high impact force that would otherwise be inflicted on one’s lower extremity, thereby reducing the peak stress on the inferior articular surface of the tibia, menisci, and articular cartilages, as well as the horizontal force on the talus. Moreover, with knee bending, the elongated spring component at the knee joint can convert the impact kinetic energy into elastic potential energy of the spring; meanwhile, the retractive force generated by the spring also provides a more balanced interaction between the menisci and articular cartilages. This biomechanical analysis can accordingly provide inspiration for new approaches to place human lower extremities at lower risk during landings.

Early onset scoliosis (EOS) is emerging as a serious threat to children’s health and is the third largest threat to their health after myopia and obesity. At present, the growing rod technique (GRT), which allows patients to regain a well-balanced sagittal profile, is commonly considered as an invasive surgical procedure for the treatment of EOS. However, the risk of postoperative complications and instrumentation breakage remains high, which is mainly related to the choice of fixed mode. Several authors have studied primary stability and instrumentation loads, neglecting the mechanical transmission of the spinal long-segment model in different growth phases, which is fundamental to building a complete biomechanical environment. The present study aimed to investigate the kinematic and biomechanical properties that occur after GRT, across the long spinal structure and the posterior instrumentation, which are affected by unilateral or bilateral fixation. Accordingly, spinal segments (C6-S1) were loaded under flexion (Flex), extension (Ext), left lateral bending (LB), right lateral bending (RB), left torsion (LT), and right torsion (RT) using 11 established spinal models, which were from three growth phases. The stress distribution, spinal and intervertebral range of motion (ROM), counter torque of the vertebra, and bracing force on the rods were measured. The results showed that bilateral posterior fixation (BPF) is more stable than unilateral posterior fixation (UPF), at the expense of more compensations for the superior adjacent segment (SAS), especially when the superior fixed segment is closer to the head. Additionally, the bracing force of the instrumentation on the spine increases as the Cobb angle decreases. Accordingly, this biomechanical analysis provides theoretical suggestions for the selection of BPF or UPF and fixed segments in different growing phases.

Aims: Growth rods are the gold standard for treating early-onset scoliosis (EOS), but current treatments often fail to optimally promote spinal growth and require frequent distraction surgeries, leading to complications and significant burdens on patients.Methods: We designed a novel growth rod (NGR) with unidirectional sliding and external regulation capabilities. Using a 3D model, we simulated the implantation of traditional growth rod (TGR) and NGR, applying a 400 N compressive load and a 1 Nm moment to test stiffness. We assessed spinal joint range of motion and growth rod stress distribution, and calculated axial force, moment, and fatigue life.Results: The axial compressive and torsional stiffness of the NGR were higher than those of the TGR and the intact group. The Von Mises stress values of the NGR under all conditions were higher than those of the TGR. Additionally, the fatigue life of the NGR met basic daily living requirements. Overall, the NGR demonstrated superior stiffness and stress distribution, with stress primarily concentrated near the screw fixation points and distributed along the titanium rods.Conclusion: The NGR, based on a distraction implant, includes a unidirectional sliding component and a spring-driven component, providing dynamic correction functionality. Additionally, it features a novel non-invasive lengthening mechanism that reduces the risk of infection. Compared to the current market-leading EOS implants, it offers enhanced stability. The novel device can potentially improve clinical outcomes in the surgical treatment of EOS.Cite this article: Bone Joint Res 2025;14(9):747–759.