| BackgroundDegenerative disc disease is an important cause of low back pain,and the affected group is tending to be younger.Discectomy is necessary for patients with severe symptoms and ineffective conservative treatment,but there is no ideal solution for the defect caused by resection.The application of tissue engineering technology to repair defect is a hot research topic,but there is no ideal design of scaffold.ObjectThe advanced triply periodic minimal surfaces(TPMS)concept was used to design the porous intervertebral disc scaffold,and the mechanical,simulation and biological properties were observed to explore the scaffolds suitable for the repair of intervertebral disc defects.MethodsFirstly,the TPMS was used to design three types of scaffolds with different parameters and deform them in the z-axis direction respectively.Polycarbonate urethane(PCU)was adapted to fabricate standard models with 3D printing technology to test the compression performance.The stress-strain curve was drawn,then the elastic modulus,energy dissipation,deformation recovery and fatigue resistance were evaluated.The imaging data were collected for 3D modeling of lumbar spine,and the finite element technology was used to simulate flexion,extension and bending.The stress peak value and the proportion of stress concentration area of each contact surface were compared in the natural state and after loading various types of scaffolds,and the simulation performance of scaffolds under stress was evaluated.Human intervertebral disc nucleus pulposus cells were planted into TPMS-based 3D cultural scaffold to undergo stress culture.The relative expression levels of mRNAs concerning extracellular matrix including COL1A1,MMP-1,MMP-3 and MMP-13,mRNAs associated with inflammation including IL-1β,IL-6,IL-8 and TNF-α were detected at different mechanical stimulation time points.Furthermore,the role of SIRT3,which is closely related to energy metabolism was further studied to explore the biological properties of TPMS porous scaffolds under stress environment.ResultsMechanical tests showed that the P2 model had the lowest energy dissipation rate,the highest recovery rate and the best fatigue resistance.The highest energy dissipation,the lowest deformation recovery,and the worst fatigue resistance were found in P1 model.The finite element analysis showed that the stress peaks of all contact surfaces of P3 model were the lowest and those of DP2 were the highest in the flexion condition,while stress peaks on most of surfaces were the highest in DP2 model in the extension condition.The stress peaks on all surfaces were lowest in P3 model in bending condition.The stress culture showed that the overall level of COL1A1 was stable under different mechanical stimulation time,MMP-1 and MMP-3 decreased briefly in the early stage and then recovered basically,and the level of MMP-13 increased significantly at 24h.Il-1βand IL-8 increased in the early stage and decreased in the middle and late stage,IL-6 remained stable in the early stage and increased significantly in the middle and late stage,while TNF-α decreased significantly in the early stage and increased significantly in the late stage.The expression level of SIRT3 decreased in the early stage and increased in the later stage,and the corresponding protein level showed a similar trend.SIRT3 overexpression promoted the expression of COL1A1,MMP-3,MMP-13 and IL-8,and inhibited the expression of IL-1β and TNF-α.ConclusionsTPMS can be successfully applied to the design of porous disc stents.P2 model has the best mechanical performance,and P3 model has the best simulation performance.When TPMS scaffold was designed for stress culture,MMP-13,IL-6,TNF-α and SIRT3 showed a significant change trend,which could be used as an indicator for evaluating degeneration.SIRT3 may inhibit IL-1β and TNF-α by promoting COL1A1,and thereby delay degeneration.The specific mechanism needs further study. |
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