Design of functional microgels for cell encapsulation

Cell encapsulation in multifunctional polymer networks has gained growing interest in the biological and medical field and is considered for many applications such as bio-catalysis, cell protection or remediation. For that reason, in this work functional temperature-responsive microgels are investigated regarding their potential to encapsulate yeast and E. coli cells. Two main approaches are focused on: Simultaneous entrapment of cells while the microgel is formed and encapsulation of cells after microgel synthesis is finished. In the first part, cell entrapment is performed by radical polymerization or coupling of prepolymers in droplets using microfluidic systems. Therefore, two initiating systems are compared regarding their capability to form microgels and perform yeast entrapment. Consequently, thermal initiator ammonium persulfate (APS) and tetramethylenediamine (TEMED) are compared to enzyme-mediated initiation using glucose oxidase (GOx). In a different approach, by combination of free radical and radical ring-opening polymerization, temperature-responsive, epoxy-functionalized terpolymers containing a hydrophobic, degradable ester unit in the polymeric backbone are designed. This is achieved by the polymerization of poly(N-vinycaprolactam) (PVCL) and the cyclic ketene acetal 2-methylene-1,3-dioxepane (MDO). This results in temperature-responsive polymers containing degradable poly(caprolactone) structures and functional epoxy resins for coupling reactions. After successful microgel synthesis in droplets using microfluidic systems, the received microgels are degradable in basic conditions and enzymatically. Furthermore, by adding yeast during microgel formation, cells can be encapsulated. In the second part, cell encapsulation is investigated using previously synthesized PVCL-based functional microgels. As the encapsulation of E. coli is aimed for after synthesis of microgels using precipitation polymerization, this technique is referred to as “post-encapsulation”. Microgels are functionalized and encapsulation of E. coli cells is investigated using different approaches: Covalent binding to the cell surface, electrostatic attraction of pH-independent positively charged microgels to the negative cell surface and lastly, encapsulation by decoration of microgels with surface-binding anchor peptides. The effect of the microgel morphology is investigated. Encapsulation due to electrostatic attraction leads to reduced viability and bacterial survival with increasing positive charges in the shell of the microgels. For covalent as well as anchor peptide-decorated microgels, different crosslinkers are used in the microgel synthesis which results in different microgel morphologies. After encapsulation of E. coli can be noticed, that the more rigid microgels support a single cell encapsulation compared to softer microgels, which form large clusters of microgels and cells.