Preparation and Properties of Monodisperse Thermo-responsive Microgels
2.6 Summary
up, the inner PNIPAM core shrinks, and the PHEMA shell promptly recovers to the original covering state on the PNIPAM core surface in absence of the expansive force. The as-prepared microspheres with PNIPAM core and PHEMA shell exhibit the thermo-responsive swelling/shrinking and more importantly the “open/close”
switching characteristics during the cooling-down/heating-up processes, and the thermo-responsive function of the proposed microspheres is highly reversible by changing the temperature across the LCST (Fig.2.24).
The thermo-responsive swelling/shrinking behavior of the PNIPAM core and the corresponding opening/closing behavior of the PHEMA shell crack of the microspheres enable such microspheres to be competent to deliver water-soluble drugs in a controllable way. Before delivering, the encapsulated drugs in PNIPAM core are protected by the biocompatible PHEMA shell at temperatures above the LCST, in which case the crack of the PHEMA shell is closed. On request to deliver the encapsulated drugs at specific site or programmed time, the local temperature is decreased below the LCST, so that the PNIPAM core swells and the crack of the PHEMA shell opens to provide unblocked channels for the encapsulated drugs to release.
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