Spatial control of cell gene expression by siRNA gradients in biodegradable hydrogels.

The extracellular environment exposes cells to numerous biochemical and physical signals that regulate their behavior. Strategies for generating continuous gradients of signals in biomaterials may allow for spatial control and patterning of cell behavior, and ultimately aid in the engineering of complex tissues. Short interfering RNA (siRNA) can regulate gene expression by silencing specific mRNA molecules post-transcriptionally, which may be valuable when presented in a continuous gradient for regenerative or therapeutic applications. Here, a biodegradable hydrogel system containing a gradient of siRNA is presented, and its capacity to regulate protein expression of encapsulated cells in a spatially continuous manner is demonstrated. Photocross-linkable dextran hydrogels containing a gradient of siRNA have been successfully fabricated using a dual-programmable syringe pump system, and differential gene silencing in incorporated cells that is sustained over time has been shown using green fluorescent protein as a reporter. This platform technology may be applied in tissue engineering to spatially control biologically relevant cellular processes.