Modification of polymer surfaces to enhance enzyme activity and stability

Publication: ResearchPh.D. thesis – Annual report year: 2017

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Enzyme immobilization is an important concept for the development of improved biocatalytic processes, primarily through facilitated separation procedures. However, enzyme immobilization usually comes at a price of reduced biocatalytic activity. For this reason, different immobilization methods have already been developed, combining the same goal to improve enzyme activity, stability and selectivity. Polymer materials have shown, due to their easy processibility and versatile properties, high potential as enzyme support. However, in order to achieve improved enzyme performance, the combination of different factors, such as the nature of the enzyme, the properties of the support, the type of immobilization and the interaction between enzyme and support, has to be taken into consideration. In this thesis, these factors are pursued and addressed by exploiting various types of polymers with focus on their tailored surface modification in order to obtain improved enzyme-support systems.
Firstly, an off-stoichiometric thiol-ene (OSTE) thermosetting material was used for the development of a screening platform allowing the investigation of micro-environmental effects and their impact on the activity of immobilized enzymes. Micro-environmental changes were generated through the introduction of tailored surface functionalities via thiol-ene chemistry (TEC) and surface chain transfer free radical polymerization (SCT-FRP), which demonstrated a significant influence on the activity of immobilized horseradish peroxidase (HRP). Thereby, this versatile screening substantiated the identification of suitable support surfaces for the immobilization of enzymes.
Secondly, in order to facilitate the application of previously identified enzyme-support combinations, OSTE particles as enzyme carriers were prepared. Here, a novel fabrication process via suspension polymerization in glycerol was applied resulting in microparticles with high control over particle size, which were further surface functionalized through TEC and SCT-FRP. In this case, epoxide functional particles were applied for the covalent immobilization of HRP and thus, demonstrated their potential as enzyme carrier in a continuous biocatalytically active plug-flow reactor.
Thirdly, OSTE particles with different surface functionalities were further used for the immobilization of β-glucosidase. The aim of this study was primarily to improve enzymatic selectivity through tailored changes of the micro-environment between enzyme and surface, which was achieved by introducing different surface chemistries onto the particles. The resulting selectivity between trans-glycosylation and hydrolysis of p-nitrophenyl glucopyranoside (pNPG) catalyzed by immobilized β-glucosidase was significantly improved and showed a direct correlation to the surface chemistry.
Furthermore, enzyme effectiveness is another important factor for the development of biocatalytic processes, which was addressed by immobilizing HRP in microfluidic devices based on OSTE+ materials. In this approach, area selective surface functionalization allowed the immobilization of HRP in various surface patterns and consequently, the effect of spatial enzyme distribution was determined towards the overall reactor performance. Two checkerboard patterns were identified to exploit enzymes more efficiently compared to an even distribution on the surface.
Finally, improvements in enzyme stability was the focus of applying tailored surface functionalization and polymer grafting of polysulfone (PSf) membranes and their subsequent application as biocatalytic membrane reactors (BMRs). Immobilization of alcohol dehydrogenase (ADH) onto poly(1-vinyl imidazole) (pVim) grafted membranes demonstrated increased biocatalytic activity and stability compared to pristine membranes and thus, showed improved enzyme performance through tailored micro-environment by polymer grafting.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark (DTU)
Number of pages155
StatePublished - 2017
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