Differentiation of induced pluripotent stem cells into definitive endoderm on Activin A-functionalized gradient surfaces.

Activin A plays a central role in the differentiation of stem cells into definitive endoderm, the first step in embryonic development and function development in many organ systems. The aims of this study were to induce controlled and fine-tuned cell differentiation using a gradient nanotechnology and compare this with a classic protocol and to investigate how induced pluripotent stem cells differentiated depending on the gradual increase of Activin A. The density difference was tested by attaching Activin A to a gold nanoparticle gradient for high-precision density continuity. Cells expressed the definitive endoderm markers SRY-box transcription factor 17 and transcription factor GATA-4 to different extents along the gradient, indicating a density-dependent cell response to Activin A. In both the gradient and the classic differentiation setups, the protein expression increased from days 1 to 5, but a significant increase already on day 3 was found only in the gradient-based setup. By utilizing the gradient technology to present the right amount of active biomolecules to cells in vitro, we were able to find an optimal setting for differentiation into definitive endoderm. The use of gradient surfaces for differentiation allows for improvements, such as efficiency and faster differentiation, compared with a classic protocol.