Abstract
IntroductionArticular cartilage (AC) is a viscoelastic tissue with a limited regenerative capability because of the lack of vasculature. Mechanical stimulation contributes to the homeostasis of functional AC since it promotes the delivery of nutrients, cytokines and growth factors between the distant chondrocytes. We hypothesized that biomechanical stimulation might enhance mobilization of endogenous mesenchymal stem/stromal cells (MSCs) from neighboring niches as the bone marrow.AimThis study aimed to introduce a bioreactor for inducing mobilization of MSCs from one compartment to another above by mechanical stimulation in vitro.MethodsA novel mechanical system for evaluating mobilization of cells in a 3D context in vitro is presented. The system consists of a compression bioreactor able to induce loading on hydrogel-based scaffolds, custom-made software for settings management and data recording, and image based biological evaluation. Intermittent load was applied under a periodic regime with frequency of 0.3 Hz and unload phases of 10 seconds each 180 cycles over 24 hours. The mechanical stimulation acted on an alginate scaffold and a cell reservoir containing MSCs below it. The dynamic compression exerted amplitude of 200 μm as 10% strain regarding the original height of the scaffold.ResultsThe bioreactor was able to stimulate the scaffolds and the cells for 24.4 (±1.7) hours, exerting compression with vertical displacements of 185.8 (±17.8) μm and a force-amplitude of 1.87 (±1.37; min 0.31, max 4.42) N. Our results suggest that continuous mechanical stimulation hampered the viability of the cells located at the cell reservoir when comparing to intermittent mechanical stimulation (34.4 ± 2.0% vs. 66.8 ± 5.9%, respectively).Functionalizing alginate scaffolds with laminin-521 (LN521) seemed to enhance the mobilization of cells from 48 (±21) to 194 (±39) cells/mm3 after applying intermittent mechanical loading.ConclusionThe bioreactor presented here was able to provide mechanical stimulation that seemed to induce the mobilization of MSCs into LN521-alginate scaffolds under an intermittent loading regime.
Highlights
Articular cartilage (AC) is a viscoelastic tissue with a limited regenerative capability because of the lack of vasculature
Our results suggest that continuous mechanical stimulation hampered the viability of the cells located at the cell reservoir when comparing to intermittent mechanical stimulation (34.4 ± 2.0% vs. 66.8 ± 5.9%, respectively)
This study aimed to introduce a novel bioreactor system in vitro, capable of inducing dynamic mechanical loading on a scaffold; and evaluate whether mesenchymal stem/stromal cells (MSCs) could shift from a compartment beneath to a scaffold after the mechanical stimulation, as cells might move when the subchondral bone is opened
Summary
This study aimed to introduce a bioreactor for inducing mobilization of MSCs from one compartment to another above by mechanical stimulation in vitro. This study aimed to introduce a novel bioreactor system in vitro, capable of inducing dynamic mechanical loading on a scaffold; and evaluate whether MSCs could shift from a compartment beneath to a scaffold after the mechanical stimulation, as cells might move when the subchondral bone is opened. Our aim was to imitate in vitro a situation comparable when there is a defect in the cartilage layer of the tibia plateau of a knee joint by a modified bioreactor [21]
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