Cryogels Based on Crosslinked Cells as Green Biocatalysts for Biotechnology

Sammanfattning: Popular Abstract in English Popular science Microbial cells are small and difficult to handle in industrial processes, especially if they are to be reused subsequent batches. In order to make them easier to handle, these cells can be attached to a solid support, by so-called immobilization. This provides particles of sizes that are easy to filter and reuse. However, immobilization is associated with two main problems. The first is aggregation of cells with help of polymers, which leads to large clusters, reducing the rate of diffusion. That means that the substrate will not be very accessible to the cells, and the products formed will be enriched around the cells before leaking out into the reaction medium. The second problem is negative effects on the metabolic machinery of the cells, which may lead to cell death during the immobilization procedure. Several mild processes can be used for immobilization, e.g. adsorption of the cells onto a solid surface. However, some cells will leak into the reaction medium, creating the need for an additional separation step. Furthermore, in order to obtain an immobilized preparation with viable cells that have good access to the substrate, and where the products formed are efficiently removed from the neighbourhood of the cells, good mass transfer must be ensured under conditions that are not hazardous to the cells. Cryostructuration offers one such possibility. When an aqueous suspension of small particles is frozen, ice crystals made of pure water are formed and the suspended material collects between the ice crystals. It is possible to cross-link the suspended particles while the ice crystals are still present, and when the ice is melted, a network of interconnected pores with thin filaments of crosslinked cells will be formed. This material has interesting properties for biocatalysis. The work described in this thesis is focused on the preparation of such cryostructured gels with retained metabolic activity, and the evaluation of some of the materials in lab-scale processes. If and when this technology is adapted for large-scale processing, it would provide an important contribution towards a greener society, by facilitating the sustainable conversion of biomass into value-added products.