Table 1.

Characteristics of particles and streams for chemistry with spatial control

Class	Typical size utilized	Spatial characteristic	Applications demonstrated
Molecular cages	1 nm–20 nm	Release by bond rupture	Instantaneous chemical gradients, studies with single molecules
Vesicles and liposomes	100 nm–100 μm	High concentration, release by diffusion or rupture	Chemistry within confined spaces, low numbers of molecules, rapid mixing by diffusion
Polyelectrolyte capsules and their assemblies	10 μm–1 mm	3D spherically symmetric diffusion, 1D ejection, confinement	Studies of spatially-confined chemical reactions, 1D chemical delivery
Polymer microspheres	1 μm–100 μm	Spherically-symmetric release by diffusion or degradation	Drug delivery, cell taxis and embryonic studies
Lithographically-structured containers	100 nm–1 cm	Symmetric and asymmetric diffusion and/or degradation	Drug delivery and cell encapsulation therapy
Self-assembled polyhedra	100 nm–1 cm	Arbitrary space curve by diffusion through precisely positioned pores	Bacterial chemotaxis, drug delivery, cell encapsulation therapy
Matrices with immobilized chemicals	1 μm–10 cm	3D bound	Engineering cellular microenvironments for cell and tissue engineering
Arrays	100 nm–1 cm	2D/3D diffusion, 2D/3D bound	Periodic patterns in reaction-diffusion and biological systems
Droplet microfluidics	1 μm–1 mm	Confinement, 3D diffusion	Chemistry within confined spaces, control over reaction rates, cell encapsulation
2D microfluidic networks	10 μm–10 cm	2D flow and diffusion	Cellular chemotaxis, chemistry in laminar flows, substrate patterning
3D microfluidic networks	100 μm–10 cm	3D flow and diffusion	3D gradients in gels