Speaker
Description
"Introduction
Bone is a highly dynamic tissue that undergoes continuous remodeling through lifetime. During this process, two cell types, osteoblasts and osteoclasts, are responsible for bone formation and bone resorption respectively. Mechanical stimuli applied on bone tissue can shift the balance between these two cell populations [1]. Different studies have investigated the impact of the mechanical stimuli on cell proliferation and differentiation [2, 3]. Pre-osteoblastic cells are well established to evaluate in vitro osteogenic responses [4], and they can differentiate into mature osteoblasts under appropriate culture conditions, allowing for the validation of bone tissue formation. In this study, the application of uniaxial compression on pre-osteoblastic cells seeded onto PLLA/PCL/PHBV scaffolds was examined by assessment of cell viability and differentiation markers to determine the effect of the mechanical stimulation on cellular responses.
Methodology
MC3T3-E1 pre-osteoblastic cells (7x104 cells/scaffold) were seeded onto blend scaffolds (5 mm x 5 mm x 1 mm) consisting of PLLA/PCL/PHBV (90/5/5) and cultured under both dynamic and static conditions for 21 days. The scaffolds were subjected to mechanical stimulation for 40 min every day. Three different frequencies of uniaxial compression, 0.5, 1, and 1.5 Hz, with a strain equal to 8% of the scaffold side (400 μm of displacement), were employed to assess their effect on pre-osteoblasts’ differentiation. Cell proliferation and morphology were monitored via a cell viability assay and scanning electron microscopy (SEM). Measurement of alkaline phosphatase (ALP) activity and calcium secretion were conducted to determine the effect of the mechanical stimulation on the osteogenic responses of pre-osteoblasts, and were compared to the static condition.
Results
All dynamic conditions depicted lower cell number than the static equivalent, however comparable at all experimental time periods. These finding are in line with the SEM images showing that the cells adhered strongly to the scaffolds from the early experimental time points.
The ALP activity in all dynamic conditions demonstrated significantly higher values (p<0.0001 for 0.5 Hz, and p<0.001 for 1 and 1.5 Hz) than those of the static one on Day 7. Similarly, the calcium secretion by pre-osteoblasts demonstrated the highest values in all dynamic conditions on Day 7, with the condition at 0.5 Hz indicating the highest level, followed by those at 1 and 1.5 Hz. At Day 14, the calcium concentration decreased, while at Day 21 all conditions displayed similar levels to Day 14.
Conclusions
This study demonstrated that the applied mechanical stimuli affected the cell viability and osteogenic differentiation of the pre-osteoblastic cells leading to their differentiation into mature osteoblasts, revealing that the most efficient applied stimuli condition was at 0.5 Hz.
This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 814410.
References
1. Lang, T. et al., J Bone Miner Res, 19(6), 1006-12 (2004)
2. Zhou, Z. et al., Materials Science and Engineering: C, 93, 975-986 (2018)
3. Lee, J.A. et al., J Biomed Mater Res A, 103(10), 3188-200 (2015)
4. Danilevicius, P. et al., Applied Surface Science, 336, 2-10 (2015)
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