Microfluidic fabrication of smart microgels from macromolecular precursors
Written by: Grant England AP225 Fall, 2011
Title: Microfluidic fabrication of smart microgels from macromolecular precursors
Authors: Sebastian Seiffert*, David A. Weitz
Gels can be used as responsive systems for many applications. By using microgels, particles with various functionalities and sensitivities including drastic size change under certain conditions or multiple-functionalities (Janus particles) can be fabricated. By using a microfluidic device along with precursor polymers which consist of multiple polymeric units and contain the desired functionalities, different types of microgels can be fabricated.
Methods and Results
The droplets of different types of gel are formed by creating a laminar flow of three different types of tagged or modified gels which are broken by an orthogonal flow of another fluid. Once the stream is broken into droplets, UV light is used to cure the gels into structures that can be analyzed to verify their properties. Variations of this procedure can be used to create different types of gel and core structures.
In the figure above, part A shows the fabrication set up for generating different numbers of cores for two different fluorescently labelled gels. Different numbers of cores can be created by varying the various flow rates in the system. In part D, the figure is showing that there is relatively little mixing between the different types of gels as exhibited by the amount of fluorescence of the microgel as a function of radius.
By using a temperature-responsive gel which, at its lower critical solution temperature (LCST) undergoes a transition where it expels all of the fluid inside it and therefore undergoes a drastic shrinking--which is reversible upon lowering the temperature below the LCST. In this way the size of the microgels can be tuned to undergo a transition at different temperatures (depending on the functionality of the gels used) .
By using microfludics to fabricate the gel structures which can be UV-cured while still in the microfluidic device, and by using prepolymers which are already comprised of multiple monomer, microgels with various compositions both chemically and morphologically can be generated. This method is very general and could be potentially applied to creating microgels for various applications.