Alginate hydrogels were prepared using four different ionic crosslinking methods: external crosslinking by dripping and spraying, internal crosslinking induced by a change in pH in the presence of a sparingly soluble calcium salt, and pre-crosslinking during 3D bioprinting. The concentration of calcium ions in the prepared hydrogels was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The results showed that the crosslinking method significantly affects the concentration of calcium ions in the hydrogels. Based on the calculated affinity parameters, it was found that the relative fraction of incorporated calcium ions decreases with increasing initial calcium ion concentration, with the highest affinity parameter values obtained for hydrogels prepared by 3D bioprinting with ionic pre-crosslinking. The obtained results contribute to a better understanding of the influence of the crosslinking method on the properties of alginate hydrogels.
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