Scheme 1.

Mimicking 3 types of cell-cell interactions under dynamic flow conditions through engineering the cell surface with aptamers. A) Flowing cell 1 (P-selectin aptamer-MSC) tethers to adherent cell 2 (P-selectin-expressing endothelial cell). B) Flowing cell 2 (L-selectin-expressing leukocyte) tethers to a P-selectin-coated substrate using the native leukocyte-P-selectin interaction and then captures flowing cell 1 (L-selectin aptamer-MSC). C) Cell 1 (L-selectin aptamer-MSC) and cell 2 (L-selectin-expressing leukocyte) first complex in the flowing stream and then tether to a P-selectin-coated substrate.