Fabrication of Tailored Microgels in Continuous Processes (Aachener Verfahrenstechnik Series – Process Systems Engineering)

Soft microgels with temperature-responsive behavior are of growing interest in drug delivery, tissue engineering, and chemical engineering. Spherical and anisometric microgels are exciting materials in this variety of possible applications due to their compelling properties. Besides their responsiveness, they can provide softness, bio-compatibility, and an open pore structure. Complex-shaped microgels further present a promising building block for microgel assemblies, for example, in the field of tissue engineering. The numerous possible applications and compelling properties lead to increasing demand for microgels. Yet, the standard microgel fabrication methods do not offer high throughput rates for spherical or anisometric microgels. Therefore, this thesis aims to develop fabrication methods with high throughput for large amounts of spherical and anisometric microgels.
First, a high throughput fabrication method for spherical temperature-responsive microgels is developed by transferring the typical batch precipitation polymerization into a continuous process. In this context, a continuous tubular flow reactor is established and investigated, along with a detailed comparison of the properties of the microgels from standard batch and novel continuous synthesis. Microgels with similar properties are indeed fabricated continuously. The inner structure stays unaltered by the applied fabrication methods.
In a second approach, the fabrication of anisometric microgels is enhanced by adapting the common stop-flow lithography, developing a new temperature-responsive polymerization system, and investigating the process limitations. For the first time, the fabrication of soft temperature-responsive microgels of complex shapes is presented using NIPAmmonomer. It is found that a threshold amount of 10 wt% crosslinker in comparison to the monomer amount is required for the fabrication of stable particles with the stated properties. Above that threshold, the crosslinker amount allows tailoring the stiffness of the responsive microgels from very soft to comparably stiff. Of particular interest is the dynamic swelling behavior of the fabricated NIPAm microgels with complex shapes. A fast contortion during swelling before snapping back into the original shape is evident.
In further investigations of the process limits, it is shown that the process has numerous influencing parameters with complex coherency. Significantly, the diffusion of components needs to be considered in a three-dimensional way to predict particle shapes and process stability precisely. Also, the fluidic parameters are essential for process stability, as automated fabrication shows a start-up behavior.
Finally, the properties of anisometric microgels are broadened by tailoring the porosity of their polymeric network with methanol and adding inorganic nanoparticles for conductivity and magnetic remote control.
Ultimately, this work lays the foundation towards industrial fabrication rates of spherical and anisometric microgels with various properties for multiple applications.