Fluid shear stress enhanced the infiltration of human mesenchymal stem cell into the electrospun poly(lactic-co-glycolic acid) scaffold

摘要

Introduction: The infiltration of the cells into the scaffolds is important phenomenon to give them good biocompatibility and even biodegradability. Fluid shear stress enhances cell migration in the direction of flow and is called "mechanotaxis". Mechanotaxis could be one of the candidates for the infiltration of cells into scaffolds. Here we investigated the directional migration of human mesenchymal stem cells and infiltration into PLGA scaffold by fluid shear stress. Materials and Methods: Human bone marrow-derived mesenchymal stem cells (hMSCs, Lonza, Basel, Switzerland) were cultured in Mesenchymal Stem Cell Growth Medium (MSCGM, Lonza). We used the parallel plate chamber system to apply shear stress to hMSCs. The parallel plate chamber system was made of incubator system installed with the microscope for observing the live cells and the flow chamber for applying the fluid shear stress to the cells. The PLGA (75:25, Birmingham, USA) scaffold was fabricated by the electrospinning method. The polymer solution (DMF:THF 1:4,20% w/v) was sprayed to the drum collector with 21 gauge syringe tip. The voltage was 20 kV and the distance was 10 cm. The drum was loaded with dry ice which gives low temperatures (-78.5 °C) to the drum surface. PLGA (50:50) nanoparticles were prepared by an improved double- emulsion (water-in-oil-in-water) solvent extraction technique. The peristaltic pump was used to provide the fluid shear stress to the hMSCs seeded PLGA scaffold. Results and Discussion: The application of shear stress for 4 h caused ＞ 80% (8 dyne/cm~2) or ＞ 90% (16 dyne/cm~2) of cells to migrate along the flow direction. After 4 h of shearing (16 dyne/cm~2), the migration speed significantly decreased by 50% above the preshear. According to these results, we determined on 8 dyne/cm~2 of flow shear stress to apply to hMSCs. The diameter of electrospun PLGA fibers was 1.55 ± 0.72 μm and the thickness of the scaffold was 0.98 ±0.14 mm. The cells on the PLGA scaffold under the flow shear stress condition (8 dyne/cm~2) migrated deeper than static conditions. These results suggest that flow shear stress enhances the infiltration of hMSCs into PLGA scaffold, however the reason that infiltration of hMSCs enhanced by flow shear stress still needs to be figured out either cells were pushed by mechanical force of flow shear stress or migrated into the scaffold actively by mechanotaxis. The PLGA (50:50) particles were prepared to prove that the cells infiltrated into the scaffold by mechanotaxis. It was obvious that there was no significant differences of PLGA particle infiltration into PLGA scaffolds between static condition and fluid shear stress applied condition (8 dyne/cm~2). These results support that hMSCs were not just pushed to the inside of scaffolds by physical force of fluid shear stress. Conclusion: In conclusion, cells moved along the direction of flow and they were also infiltrated into the PLGA scaffold by the fluid shear stress. However, the infiltration of PLGA micro particles into PLGA scaffolds was not affected by the fluid shear stress. These results suggest that the cells were infiltrated into the PLGA scaffold by responding to the fluid shear stress through the mechanotransduction.