This master’s thesis investigates development and optimization of alginate hydrogels for entrapment and controlled release of nutrients, using gradual internal gelation with calcium carbonate and glucono-delta-lactone (GDL). The main objective was to create a hydrogel capable of incorporating high concentrations of nutrients and enabling their gradual release into minimal medium over an extended period. Various concentrations of alginate, CaCO3, and GDL, were systematically tested, subsequently determining the optimal formulation (1% alginate, 0.15% CaCO3, 1.1% GDL (w/v)) for suitable gelation times, mechanical stability, and gel homogeneity. We found that up to 15% (w/v) of L- cysteine or MES could be successfully incorporated into the hydrogel, resulting in a homogeneous distribution of the nutrient and controlled release (e.g., an average of 135 mg/h at an initial concentration of 150 g/L of L-cysteine). At higher nutrient concentrations (30% w/v), issues with inhomogeneity and poor solubility were observed. By comparing batch and flow-through systems, we demonstrated that flow- through systems can enable slower and more uniform nutrient release. During an extended experiment in larger volumes, after 35 hours approximately 90% of L-cysteine was released. The remaining nutrient was retained in the hydrogel, what was also confirmed with FT-IR analysis. Results demonstrate great potential of optimized alginate hydrogels for microbial fuel cells as sustainable energy systems, as well as other applications where gradual and long-term nutrient delivery is reqired. Together, these findings offer insight into release behavior from alginate hydrogels and outline considerations that can support further research in the field of biomaterials.
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