Synthesis of Monodisperse, Covalently Cross-Linked, Degradable “Smart” Microgels Using Microfluidics

1. Leah R. B. Kesselman¹, 
2. Siawash Shinwary², 
3. P. Ravi Selvaganapathy², 
4. Todd Hoare^1,*

Article first published online: 22 FEB 2012

DOI: 10.1002/smll.201102113

The development of a robust method for the synthesis of highly monodisperse microgels cross-linked with degradable covalent bonds offers the potential for fabricating microgels with the highly controllable porosities, cell interactions, and degradation half-lives required for biomedical applications. A microfluidic chip is designed that enables the on-chip mixing and emulsification of two reactive polymer solutions (hydrazide and aldehyde-functionalized carbohydrates) to form monodisperse, hydrazone cross-linked microgels in the size range of ≈40–100 μm. The device can be run continuously for at least 30 h without a significant drift in particle size. The resulting microgels have a homogeneous bulk composition and can swell and deswell as the solvent conditions change in predictable ways based on the chemistry of the reactive polymers used, thereby enabling improved control over both the chemistry and morphology of the resulting microgels relative to other reported approaches. The in situ gelation chemistry used facilitates rapid microgel formation within the droplets without requiring the use of UV light or heating to initiate polymerization, thus making this approach of particular potential utility in cell encapsulation or drug delivery (as demonstrated).