Scheme 1.

Photogel preparation and process flow for patterning arrays of microbeads for selective bead retrieval. a) PEG-PS beads are swollen with photogel prepolymer, seeded into PDMS microwells, and transferred to a previously formed 15 µm-thick photogel layer on acrylated glass by µTM. Non-uniform polymerization allows uncrosslinked prepolymer to be washed from bead surfaces. b) Microbead arrays are screened for binding activity and positive beads are isolated by degrading photogel with 365 nm UV light.