Changes in the hydrogel structure depending on the crosslinking agent seen by electron microscopy

abstract

English

Hydrogels are materials consisting of crosslinked polymer chains capable of binding substantial amounts of water. Even though several types of hydrogels can be of synthetic origin, there are also hydrogels found in nature. For example, the bacterium Azotobacter vinelandii, belonging to the group of plant growth-promoting bacteria, produces biopolymer alginate to form a polysaccharide capsule, which protects the cell from drying out. Since A. vinelandii can be used as bioinoculants, their production of alginate can be also an advantage in their agricultural utilization. Bacteria encapsulated in hydrogel can be further processed into the final form of bioinoculant and since A. vinelandii produces its own alginate, it is possible to add just the crosslinking agent to the cultures and thus reduce the costs for bioinoculant production. To make the production of hydrogel-encapsulated bioinoculant, it is necessary to choose the most suitable crosslinker since depending on the crosslinking agent the final hydrogel changes its structure. In our study, we have focused on determining the changes in the structure of the alginate-based hydrogel depending on the use of different crosslinkers, namely CaCl2 and glucono-D-lactone together with CaCO3. To observe the structure of hydrogels cryogenic scanning electron microscopy was used. Samples were fixed using a high-pressure freezing method, followed by freeze-fracture and sublimation for 7min at -95°C. Samples were then observed in a scanning electron microscope equipped with a cryo-stage, at −120 °C using a 1–2 keV electron beam. It was possible to distinguish the difference in the hydrogel structure based on the crosslinker used. For 2% CaCl2 solution, the hydrogel formed a polymeric net surrounding the cells where individual fibres could be seen, while samples crosslinked using 1M solution of lactone together with 0,5M CaCO3 formed dense mass. Similar results were also observed in the preliminary STEM study of the same hydrogel-based samples processed using the freeze substitution procedure, supporting our initial findings.

hydrogel; A. vinelandii; cryo-SEM; low voltage STEM;

MRÁZOVÁ, K.; HAVLÍČKOVÁ, A.; ČERNAYOVÁ, D.; HRUBANOVÁ, K.; SEDLÁČEK, P.; KRZYŽÁNEK, V.

20. 5. 2024

Czechoslovak Microscopy Society

Brno

978-80-909216-0-3

Microscopy 2024. Book of abstracts.

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