Table 2.

On-chip manipulation strategies for hydrogel microcapsules

Purpose	Method	Mechanism	Notes	References
Sorting	Fluorescence activated microcapsule sorting	Apply dielectrophoresis (DEP) or mechanical force on specific microcapsules based on previous detection of fluorescence intensity	With detection and actuation systems; High accuracy; High throughput	129–132
	Acoustic wave - based sorting	Acoustic waves drive microcapsules of different sizes or densities onto different lateral locations	Active sorting without detection system; High throughput	133–135
	Inertial microfluidics	Microcapsules of different sizes would migrate to different equilibrium locations by inertial lift force	Laminar flow with Re > 1; Dean flow can be incorporated; High throughput	136, 137, 139, 142
	Sedimentation-based sorting	Microcapsules of different size or mass would sediment on different locations under gravity or centrifugal force	High throughput; Low accuracy; Has not utilized for cell-laden microcapsules	143, 144
	Deterministic lateral displacement-based sorting	Microcapsules of different sizes would choose different trajectories as they pass through an array of microposts	High throughput; High accuracy	145–147
Extraction from oil into aqueous phase	Spontaneous phase separation	Microcapsules enclosed by a thin layer of oil can transfer into aqueous solution by the spontaneous dewetting of oil phase	The oil shell prevents microcapsule gelation by chemical crosslinking agents	151
	Depletion of carrier oil	The carrier oil of microcapsules is depleted and replaced by aqueous solution via multiple side channels	Complex channel network; Unstable oil-aqueous interface	125, 149
	Mechanical filter gate	Microcapsules can not pass through mechanical filter gates that are smaller than their sizes, and sink into aqueous chamber.	With extra fabrication of aqueous chamber; Potential blockage issue	116
	Interfacial tension-based extraction	Microcapsules in carrier oil would migrate into aqueous solution once they contact oil-aqueous interface by interfacial tension	Require stable oil-aqueous interface; Mechanical stiffness and size constraints	80, 97, 195
	DEP-based extraction	Microcapsules would experience a DEP force towards aqueous solution for extraction under non-uniform electric filed	Combine interfacial tension in extraction; No stiffness or size constraints	152