Résumé
Objective To explore the effects of dynamic axial compressive strain on the mRNA expression of bone formation related-genes in osteoblasts seeded in 3D silk fibroin scaffolds. Methods In the experimental group, MC3T3-E1 cells were seeded in 3D scaffolds and then subjected to dynamic axial compressive strain (at amplitude of 5% and frequency of 1 Hz, 30 min/day for 20 days), while in the control group, MC3T3-E1 cells were cultured statically without any mechanical stimulation. The gene expression of alkaline phosphatase (ALP), collagenⅠ(COL-Ⅰ), runt-related transcription factor 2 (Runx2), osterix (Osx), osteocalcin (OCN) was detected by real-time PCR. Results Under cyclic axial compressive strain, the Runx2, Osx and COLⅠmRNA levels increased by 280%, 68.9% and 79.6%, respectively, while the ALP and OC mRNA levels also up-regulated by 10.7% and 26.9%, respectively. There were significant differences in mRNA expression of osteogenesis-related genes between the experimental group and control group (P＜0.05). Conclusions Under the stimulation of cyclic axial compressive strain, the osteogenic differentiation of osteoblasts seeded in the silk fibroin scaffolds is promoted, with a significant up-regulation in the mRNA expression of COLⅠ, Runx2, Osx and OCN, which suggests that the stimulation of compressive stress at physiologic magnitude could be one of important mechanisms in promoting fracture healing. This research finding will be important for the clinic application of mechanical stimuli-mediated cell therapy for bone defection.
Résumé
Objective To analyze the clinical feasibility of unilateral transforaminal lumbar interbody fusion (TLIF) for treating lumbar degenerative diseases by finite element method. Methods Based on CT scan data, three-dimensional (3D) finite element models of the normal L3-5 segments under physiological status (intact lumbar model), L4/5 with unilateral pedicle screw fixation plus interbody fusion (unilateral TLIF model) and L4/5 with bilateral pedicle screw fixation plus interbody fusion (bilateral TLIF model) were established by using Mimics, Pro/E, ANSYS software, respectively. Preload of 500 N and load of 10 N•m torque were applied on the superior surface of the L3 segment to simulate 5 physiological activities: body upright, flexion, extension, left lateral bending and right axial rotation. The deformation and stress distributions in vertebral body, vertebral discs, pedicle screw and cage under different loads were then recorded and analyzed to compare mechanical properties of the two fixation methods. Results The deformation of L3-5 segments fixed with unilateral TLIF or bilateral TLIF decreased as compared to the intact lumbar model; the stresses in cage reached the maximum in both unilateral TLIF model and bilateral TLIF model during back extension, meanwhile peak stresses on pedicle screws in unilateral TLIF were significantly higher than those on bilateral TILF model, with the peak stress of 463.39 MPa during back extension. ConclusionsUnilateral TLIF can be selected as a method for treating lumbar degenerative diseases; however, its stability was inferior to bilateral TLIF due to the higher peak stress. Therefore, less stretch exercises may be safe for patients during rehabilitation to avoid surgery failure or pedicle screw fracture.