Organizational Arrangements Associated with Partial Ion Exchange in Gelation Process ^†

The intention of this work is to use various constituents obtained from bioeconomy side streams, such as brown algae or bacteria, to create a source of biodegradable and environmentally neutral materials for 3D printing.

Sodium alginate is a water-soluble co-polysaccharide that forms a gel when hydrated. It is generally known that sodium alginate has non-Newtonian, pseudoplastic behavior [1]. The challenges in using hydrated sodium alginate hydrogel in 3D printing are reflected in the circumstance that, depending on the degree of hydration, either the viscosity at 0 shear stress is too low and the printed layers cannot be preserved, or the viscosity at high-level shear stress is too high, and large forces are needed to flow the hydrogel through the extrusion nozzle once with the use of special materials (steels) in the manufacture of the extrusion device.

To stabilize the form obtained from the sodium hydrogel, it can be cross-linked by the ionic exchange between sodium ions and calcium ions, resulting in calcium alginate, a water-insoluble gel [2]. To obtain a uniform solution of calcium alginate, it is necessary to introduce a reaction retardant, such as sodium salt, a base, or an acid [3].

The rheology of the partial modified hydrogels and the stability of the compositions were studied (TA Instruments Discovery HR20). The structure of composite and the degree of ionic exchange in the hydrogel were demonstrated and calculated based on the Fourier-transform infrared spectroscopy spectra (Shimadzu IRTracer-100) and X-ray diffraction (Rigaku Smartlab). The morphological changes in the partially calcium ion-modified hydrogel and the mode of organization of the hydrophobic–hydrophilic regions were analyzed using the signals resulting from the interaction of accelerated electrons with the obtained composites (scanning electron microscopy analysis, TM4000plus II, Hitachi, Tokyo, Japan)—Figure 1.