Evaluation of alginate modification effect on cell-matrix interaction, mechanotransduction and chondrogenesis of encapsulated MSCs.

Mesenchymal stem cells (MSCs) are promising cell candidates for cartilage regeneration. Furthermore, it is important to control the cell-matrix interactions that have a direct influence on cell functions. Providing an appropriate microenvironment for cell differentiation in response to exogenous stimuli is a critical step towards the clinical utilization of MSCs. In this study, hydrogels consisted of different proportions of alginates that were modified using gelatin, collagen type I and arginine-glycine-aspartic acid (RGD) and were evaluated regarding their effects on mesenchymal stem cells. The effect of applying hydrostatic pressure on MSCs encapsulated in collagen-modified alginate with and without chondrogenic medium was evaluated 7, 14 and 21 days after culture, which is a comprehensive evaluation of chondrogenesis in 3D hydrogels with mechanical and chemical stimulants. Alcian blue, safranin O and dimethyl methylene blue (DMMB) staining showed the chondrogenic phenotype of cells seeded in the collagen- and RGD-modified alginate hydrogels with the highest intensity after 21 days of culture. The results of real-time PCR for cartilage-specific extracellular matrix genes indicated the chondrogenic differentiation of MSCs in all hydrogels. Also, the synergic effects of chemical and mechanical stimuli are indicated. The highest expression levels of the studied genes were observed in the cells embedded in collagen-modified alginate by loading after 14 days of exposure to the chondrogenic medium. The effect of using IHP on encapsulated MSCs in modified alginate with collagen type I is equal or even higher than using TGF-beta on encapsulated cells. The results of immunohistochemical assessments also confirmed the real-time PCR data.

A microfabricated platform for the study of chondrogenesis under different compressive loads.

Microfluidic devices are beneficial in miniaturizing and multiplexing various cellular assays in a single platform. Chondrogenesis is known to pertain to chemical, topographical, and mechanical cues in the microenvironment. Mechanical cues themselves have numerous parameters such as strain magnitude, frequency, and stimulation time. Effects of different strain magnitudes on the chondrogenic differentiation of adult stem cells have not been explored thoroughly. Here, a new multilayer microdevice is presented for the unidirectional compressive stimulation of cells in a three-dimensional cell culture. Numerical simulations were performed to evaluate and optimize the design. Results showed a favorable highly uniform axial strain distribution and negligible radial and circumferential strain for the optimized design. Moreover, an experimental study was performed on rabbit adipose-derived stem cells encapsulated in-situ in alginate hydrogel. Strain levels of 20%, 15%, 10%, 5%, and 0% were studied simultaneously on a microfluidic platform. Dynamic mechanical compression positively influenced cellular viability and upregulated collagen II, Sox-9, and aggrecan expression in the absence of exogenous growth factors. The expression of collagen type II as specific marker for articular chondrocytes was further confirmed by immunofluorescence staining of collagen type II. Taking together, 10% strain can be considered as optimal stimulation factor for chondrogenic differentiation of adipose derived stem cells.