Changes of cell membrane fluidity for mesenchymal stem cell spheroids on biomaterial surfaces

BACKGROUND

The therapeutic potential of mesenchymal stem cells (MSCs) in the form of three-dimensional spheroids has been extensively demonstrated. The underlying mechanisms for the altered cellular behavior of spheroids have also been investigated. Cell membrane fluidity is a critically important physical property for the regulation of cell behavior, but it has not been studied for the spheroid-forming cells to date.

AIM

To explore the association between cell membrane fluidity and the morphological changes of MSC spheroids on the surface of biomaterials to elucidate the role of membrane fluidity during the spheroid-forming process of MSCs.

METHODS

We generated three-dimensional (3D) MSC spheroids on the surface of various culture substrates including chitosan (CS), CS-hyaluronan (CS-HA), and polyvinyl alcohol (PVA) substrates. The cell membrane fluidity and cell morphological change were examined by a time-lapse recording system as well as a high-resolution 3D cellular image explorer. MSCs and normal/cancer cells were pre-stained with fluorescent dyes and co-cultured on the biomaterials to investigate the exchange of cell membrane during the formation of heterogeneous cellular spheroids.

RESULTS

We discovered that vesicle-like bubbles randomly appeared on the outer layer of MSC spheroids cultured on different biomaterial surfaces. The average diameter of the vesicle-like bubbles of MSC spheroids on CS-HA at 37 °C was approximately 10 μm, smaller than that on PVA substrates (approximately 27 μm). Based on time-lapse images, these unique bubbles originated from the dynamic movement of the cell membrane during spheroid formation, which indicated an increment of membrane fluidity for MSCs cultured on these substrates. Moreover, the membrane interaction in two different types of cells with similar membrane fluidity may further induce a higher level of membrane translocation during the formation of heterogeneous spheroids.

CONCLUSION

Changes in cell membrane fluidity may be a novel path to elucidate the complicated physiological alterations in 3D spheroid-forming cells.

Multi-Spheroid-Loaded Human Acellular Dermal Matrix Carrier Preserves Its Spheroid Shape and Improves In Vivo Adipose-Derived Stem Cell Delivery and Engraftment

BACKGROUND

Current in vivo adult stem cell delivery presents limited clinical effects due to poor engraftment and survival. To overcome current challenges in cell delivery and promote surgical cell delivery for soft tissue repair, a multi-spheroid-loaded thin sectioned acellular dermal matrix (tsADM) carrier which preserves loaded spheroids' three-dimensional (3D) structure, was developed.

METHODS

Adipose-derived stem cells (ASCs) were used for spheroid delivery. After generating spheroids in 3D cell culture dishes, spheroid plasticity and survival in-between coverslips were evaluated. Spheroids were loaded onto tsADM, their shape changes were followed up for 14 days, and then imaged. Spheroid adhesion stability to tsADM against shear stress was also evaluated. Finally, cell delivery efficacy was compared with cell-seeded tsADM by in vivo implantation and histological evaluation.

RESULTS

Spheroids withstood cyclic compression stress and maintained their 3D shape without fusion after 48 h of culture in-between coverslips. Cell survival improved when spheroids were cultured on tsADM in-between the coverslips. Spheroid-loaded tsADM with coverslips maintained their spheroid outline for 14 days of culture whereas without coverslips, the group lost their outline due to spreading after 4 days in culture. Spheroids loaded onto tsADMs were more stable after six rather than 3 days in culture. Spheroid-loaded tsADMs showed about a 2.96-fold higher ASCs transplantation efficacy than cell-seeded tsADMs after 2 weeks of in vivo transplantation.

CONCLUSION

These results indicate that transplantation of spheroid-loaded tsADMs significantly improved cell delivery. These findings suggest that a combined approach with other cells, drugs, and nanoparticles may improve cell delivery and therapeutic efficacy.

Synergistic interplay between human MSCs and HUVECs in 3D spheroids laden in collagen/fibrin hydrogels for bone tissue engineering

Stem cell encapsulation in hydrogels has been widely employed in tissue engineering, regenerative medicine, organ-on-a-chip devices and gene delivery; however, fabrication of native-like bone tissue using such a strategy has been a challenge, particularly in vitro, due to the limited cell loading densities resulting in weaker cell-cell interactions and lesser extra-cellular matrix deposition. In particular, scalable bone tissue constructs require vascular network to provide enough oxygen and nutrient supplies to encapsulated cells. To enhance stem cell function and generate pre-vascularized network, we here employed collagen/fibrin hydrogel as an encapsulation matrix for the incorporation of human mesenchymal stem cell/human umbilical vein endothelial cell (MSC/HUVEC) spheroids, and investigated their cellular behavior (including cell viability, morphology, proliferation, and gene expression profile) and compared to that of cell suspension- or MSC spheroids-laden hydrogels. MSC/HUVEC spheroids encapsulated in collagen/fibrin hydrogel showed better cell spreading and proliferation, and up-regulated osteogenic differentiation, and demonstrated pre-vascular network formation. Overall, MSC/HUVEC spheroids-laden hydrogels provided a highly suitable 3D microenvironment for bone tissue formation, which can be utilized in various applications, such as but not limited to tissue engineering, disease modeling and drug screening. STATEMENT OF SIGNIFICANCE: Stem cell encapsulation in hydrogels has been widely used in various areas such as tissue engineering, regenerative medicine, organ-on-a-chip devices and gene delivery; however, fabrication of native-like bone tissue using such an approach has been a challenge, particularly in vitro, due to the limited cell loading densities resulting in weaker cell-cell interactions and lesser extra-cellular matrix deposition. Here in this work, we have encapsulated spheroids of human mesenchymal stems cells (MSCs) in collagen/fibrin hydrogel and evaluated their viability, proliferation, osteogenic differentiation, and bone formation potential in vitro with respect to cell suspension-laden hydrogel samples. We have further incorporated human umbilical vein endothelial cells (HUVECs) into MSC spheroids and demonstrated that the presence of HUVECs in 3D spheroid culture in collagen/fibrin gel induced the formation of pre-vascular network, improved cell viability and proliferation, enhanced the osteogenic differentiation of spheroids, and increased their bone mineral deposition. In sum, MSC/HUVEC spheroids laden hydrogels provided a highly suitable 3D microenvironment for bone tissue formation, which can be utilized in various applications, such as but not limited to tissue engineering and regenerative medicine, disease modeling and drug screening.