Stress-driven design of intervertebral disc implants and optimization of mechanical and biological performance.

Background: The degeneration of the intervertebral disc (IVD) is a leading cause of low back pain, causing severe pain and spinal motion disorder. While spinal fusion remains the gold-standard treatment of IVD degeneration, it restricts spinal motion and accelerates adjacent segment degeneration. Artificial total disc replacement has emerged as an alternative to preserve mobility, but conventional implants often fail to replicate natural disc mechanics, resulting in high reoperation rates. This study aimed to propose a stress-driven design approach for graded IVD implants that have mechanical properties similar to those of natural discs, with good shock absorption and biocompatibility. Methods: A detailed finite element model of the L1-L2 functional spinal unit (FSU) was developed. Applying axial force of 500 N or 7.5 N⋅m moment, stress distributions of IVD under seven physiological motions (upright standing, flexion, extension, right/left lateral bending, and right/left axial rotation) were obtained. IVD implants were designed using gyroid unit cells (5 × 5 × 5 mm Results: The G65N and G65Y exhibited mechanical performance closest to those of natural IVDs, with G65N showing reduced sensitivity to loading rate, lower irreversible energy dissipation, and enhanced cyclic stability. The L1-L2 FSU implanted with G65N demonstrated stress ranges of 0.00009-26.600 MPa under compression and 0.00067-54.090 MPa under flexion, and it also showed lower endplate contact pressure (2.59 MPa) and axial displacement (1.86 mm), indicating a reduced risk of implant subsidence. In vitro, cells proliferated steadily on both the G65N and G65Y, aligning along the implant struts, with slightly higher proliferation observed on G65N. Furthermore, both implants exhibited high permeability (4.43 × 10 Conclusion: The stress-driven design of G65N reproduced the biomechanical behavior of natural IVDs and improved biocompatibility, offering a promising design strategy to minimize implant failure and promote tissue regeneration. The translational potential of this article: This study presents a stress-driven and patient-specific framework for graded IVD implant design. The optimal implants replicate the biomechanics of natural discs, improve load sharing, and support segmental stability, while demonstrating favorable biological performance. This design approach has significant potential to promote postoperative recovery and reduce the risk of reoperation, thereby supporting precision and patient-specific care in orthopedics. Beyond IVDs, the proposed stress-driven and biomimetic design strategy could be applied to other mechanically adaptive implants, such as femoral stems, knee and hip prostheses, shoulder prostheses, and dental implants, offering a versatile tool for the development of personalized orthopedic devices for various clinical applications.