Directed differentiation of size-controlled embryoid bodies towards endothelial and cardiac lineages in RGD-modified poly(ethylene glycol) hydrogels.

Recent advances in stem cell research have demonstrated the importance of microenvironmental cues in directing stem cell fate towards specific cell lineages. For instance, the size of the embryoid body (EB) was shown to play a role in stem cell differentiation. Other studies have used cell adhesive RGD peptides to direct stem cell fate towards endothelial cells. In this study, materials and cell-based approaches are combined by using microwell arrays to produce size-controlled EBs and encapsulating the resulting aggregates in high molecular weight PEG-4 arm acrylate with and without conjugated RGD to study their effect on stem cell differentiation in a 3D microenvironment. Increasing EB size is observed along with a decrease in the total number of EBs in pristine PEG hydrogel, regardless of the initial EB size. In correlation with this aggregation, EBs in PEG show enhanced cardiogenic differentiation compared to RGD-PEG hydrogel. Both aggregation and cardiogenic differentiation are significantly reduced when RGD peptides are introduced to the microenvironment, while endothelial cell differentiation is accelerated by 3 to 5 days, depending on the EB size, and doubled over the course of cell culture for both EB sizes. Presented results indicate that RGD sequence has a dominant effect in driving endothelial cell differentiation in size-controlled EBs, while pristine multi-arm, high molecular weight PEG can induce cardiogenic differentiation, possibly through EB aggregation. The photopatternable nature of the hydrogel used in this study enabled patterning of such domains devoid or abundant of cell attachment sequences. Therefore, these hydrogels can potentially be used for spatially patterned embryonic stem cell differentiation, which may be beneficial for tissue engineering and regenerative medicine applications.