Photo- and electropatterning of hydrogel-encapsulated living cell arrays

Living cells have the potential to serve as sensors, naturally integrating the response to stimuli to generate predictions about cell fate (e.g., differentiation, migration, proliferation, apoptosis). Miniaturized arrays of living cells further offer the capability to interrogate many cells in parallel and thereby enable high-throughput and/or combinatorial assays. However, the interface between living cells and synthetic chip platforms is a critical one wherein the cellular phenotype must be preserved to generate useful signals. While some cell types retain tissue-specific features on a flat (2-D) surface, it has become increasingly apparent that a 3-D physical environment will be required for others. In this paper, we present two independent methods for creating living cell arrays that are encapsulated within a poly(ethylene glycol)-based hydrogel to create a local 3-D microenvironment. First, 'photopatterning' selectively crosslinks hydrogel microstructures containing living cells with approximately 100 microm feature size. Second, 'electropatterning' utilizes dielectrophoretic forces to position cells within a prepolymer solution prior to crosslinking, forming cell patterns with micron resolution. We further combine these methods to obtain hierarchical control of cell positioning over length scales ranging from microns to centimeters. This level of microenvironmental control should enable the fabrication of next-generation cellular microarrays in which robust 3-D cultures of cells are presented with appropriate physical and chemical cues and, consequently, report on cellular responses that resemble in vivo behavior.