ABSTRACT
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.
ABSTRACT
Objective To investigate the loading rate-dependent property of different layers for articular cartilage by unconfined compression testing on articular cartilage at different loading rates. Methods The non-contact digital image correlation (DIC) technique was applied to investigate the mechanical properties of different layers for fresh pig articular cartilage at different loading rates. Results At constant loading rate, the compressive strain of superficial layer and deep layer was the largest, while that of middle layer was in between under the same compressive stress. The Poisson’s ratio increased from superficial layer to deep layer along with cartilage depth increasing. The stress-strain curves of cartilage were different at different loading rates, indicating that the mechanical properties of cartilage were dependent on the loading rate. The elastic modulus of cartilage increased with loading rates increasing, and the compressive strains of different layers decreased under the same compressive stress with loading rates increasing. Conclusions The compressive strain decreased while the Poisson’s ratio increased from superficial layer to deep layer along the cartilage depth. The mechanical properties of different layers for cartilage were dependent on the loading rate. This study can provide the basis for clinical cartilage disease prevention and treatment, and is important for mechanical function evaluation of artificial cartilage as well.
ABSTRACT
Objective To design and build a new dynamic load and circulating perfusion bioreactor system and test its performance. Methods The design principle of the bioreactor system was specified and the dynamic strain loading system and 3D perfusion culture system were designed and built accordingly. A special culture chamber for 3D perfusion and compressive loading was also developed. The sterility of the culture chamber and the accuracy and stability of the strain loading were measured, and the result from the culture of tissue engineering bone was preliminarily observed. Results This bioreactor system could provide compressive strains with different magnitudes and frequencies, as well as perfusions under different flow conditions. It could be controlled accurately and operated easily with a steady performance. No germs were grown in the culture medium after 5 days’ running. The preliminary results showed that after the tissue engineering bones were cultured in the bioreactor for 10 days, cell proliferation and ALP activity in this perfusion culture and loading group were significantly higher than those in the static culture group and the simple perfusion culture group. Conclusions The bioreactor could be an ideal dynamic culture and loading device for biomechanical study of tissue engineering bone.