Conventional poly(N-isopropylacrylamide) (PNIPAM) microgels prepared via precipitation polymerization have been used in many applications due to their ability to dynamically change their diameter, hydrophobicity, pore size, and surface charge as a function of temperature. However, in the context of practical biomedical use<i> in vivo</i>, the lack of degradability of conventional PNIPAM microgels creates challenges in that conventional microgels cannot be cleared effectively from the body. In response, we have developed a self-assembly method in which well-defined hydrazide and aldehyde functionalized PNIPAM oligomers are used to form microgels linked by hydrolytically degradable hydrazone crosslinks. Hydrazide-functionalized oligomers are pre-heated above their lower critical solution temperature, after which the aldehyde-functionalized oligomer is added to induce crosslinking. Microgels can be fabricated within minutes on the size range of ~180-300 nm and with high monodispersity and degradability (particularly in acidic conditions) while maintaining the same reversible temperature-responsive swelling properties of conventional PNIPAM microgels. Interestingly, while conventional microgels have a dense core/diffuse shell structure due to the faster polymerization rate of the crosslinker used, a combination of surface force measurements, small angle neutron scattering, and ultrasmall angle neutron scattering confirmed that these self-assembled microgels have a homogenously cross-linked internal structure. This somewhat surprising result is attributed to a combination of the dynamic nature of the hydrazone crosslinking chemistry and the assembly conditions used that promote polymer interdiffusion. Coupling the predictable diffusive and refractive properties enabled by the homogeneous internal structure with the degradability enabled by the assembly chemistry, we anticipate that these microgels offer opportunities to address challenges in drug delivery, biosensing, and optics.

Degradable homogeneous microgels via self-assembly of reactive poly(N-isopropylacrylamide) oligomers

255th National Meeting (2018)

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