Covalently coated cell stretching devices for osteogenic differentiation of human adipose stem cells

Cells can sense and adapt to the prevailing mechanical environment in vivo. By mimicking such stimulus in vitro, the behaviour and differentiation of stem cells can be guided and modelled. Furthermore, new and more effective differentiation methods are needed for tissue engineering applications to make the process faster, more cost-efficient and to avoid the use of expensive and contradictory growth factors.

In the current study, we aimed to investigate the effect of equiaxial stretching on the attachment and osteogenic differentiation of human adipose stem cells (hASCs) using a polydimethylsiloxane (PDMS) based cell stretching device (Figure 1). As a highly hydrophobic material, pristine PDMS does not support cellular attachment, and physisorbed protein coating does not withstand dynamic loading. Therefore, we developed and characterized a durable covalent coating method for PDMS which supports the attachment and viability of hASCs during mechanical stimulation.

The hASCs were cultured under static and dynamic (cyclic equiaxial strain of 2 to 5 %) conditions on covalently coated PDMS substrate up to 10 days. Based on DNA amount and ALP activity analyses, our results indicated that stretching delayed proliferation and promoted osteogenic differentiation of hASCs. Immunocytochemical vinculin detection and actin staining with phalloidin revealed that stretching also reduced the size of the cells and intensified focal adhesions and actin cytoskeleton.

The developed stretching system can be utilized in the future for studying the effect of different stretching parameters on stem cell behaviour. Furthermore, our results suggest that equiaxial stretching could be used as an additional osteogenic differentiation method for hASCs in bone tissue engineering applications in the future.