Fabrication and modification of functional and enzymatically active hollow fiber membranes

Enzymatic membrane reactors have emerged as powerful tools for process optimization, integrating biocatalysis with membrane separation. The capacity of enzymes to operate under mild conditions (physiological pH and temperature) can significantly lower energy costs while maintaining product quality. However, enzymes degrade under challenging conditions (e.g., high temperatures and organic solvents), limiting their use in industry-relevant processes. To enhance enzyme stability in membrane processes, enzymes are typically immobilized on either the membrane surface or within its matrix. Unfortunately, conventional methods rely on harsh solvents and high temperatures, which degrade enzymes, thus limiting immobilization only after membrane formation. Additionally, most commercial membrane materials lack functional groups for effective enzyme attachment, requiring time-consuming post-modification procedures. This thesis explores innovative techniques for fabricating biocatalytic hollow fiber membranes by directly integrating enzymes and functional materials into the structure, enhancing enzyme stability and introducing new functionalities beneficial to separation processes. Each method improves upon the current state-of-the-art by reducing steps required for enzyme immobilization or by simplifying functionalization. Three methods are discussed: The first method is the fabrication of free-standing, mechanically stable biocatalytic polyelectrolyte complex (PEC) hollow fiber membranes using salt-dilution induced phase separation. Since this method does not involve organic solvents, enzymes can be directly added to the polymer solution, simplifying immobilization. The PEC membranes are characterized by their separation performance in nanofiltration and enzymatic activity. The second method is modifying hollow fiber membranes via single-step PEC coating—a viable alternative to the time-consuming layer-by-layer process—producing membranes with biocatalytic and nanofiltration properties. The third method is fabricating low-fouling and self-cleaning hollow fiber membranes achieved by immobilizing microgels and enzymes on the surface. These methods produced biocatalytic hollow fiber membranes with enhanced enzyme stability and activity and additional beneficial properties such as ion selectivity, reduced fouling propensity, and nanofiltration performance. This work demonstrates that integrating enzymes and functional materials into hollow fiber membranes enhances enzyme stability and introduces new functionalities, advancing the development of biocatalytic membrane reactors for industrial and biomedical applications.