(T1430-01-01) Alginate Hydrogels: A Tunable Tool for Biotech Applications

Purpose: Alginate is a natural polysaccharide extracted from brown seaweed. Its availability in ultrapure form and capacity to form hydrogels with tunable properties make it ideal for biological applications. Alginate is composed of 1,4 linked β-D-mannuronate (M) and α-L-guluronate (G) – monomers that control its crosslinking with divalent ions. With a growing interest in using alginate gels in cell cultures and bioprocessing, it is important to better understand their formation and mechanical properties. This work explores alginate solutions rheological behavior, the connection between their molecular composition and gelling potential, and an alternative method to produce alginate gels.

Methods: Ultrapure PRONOVA® alginate was provided by NovaMatrix® in multiple forms including sodium alginate, in different G/M ratios and molecular weights (MW), and calcium alginate dispersions. Sodium alginates were used to prepare solutions with different concentrations in water by stirring for 1 hour followed by shaking until full dissolution. Viscosity measurements were performed using a Brookfield viscometer. Shear rate experiments (0.01 – 10,000 s⁻¹ range) were also performed on solutions with different MW and concentrations. Alginate gels were prepared by combining 1% alginate solutions with calcium chloride and letting them set for ~18 hours at 20 ± 1 °C, and their elastic modulus was measured using a KINEXUS rheometer. To test the self-gelling system, 2% PRONOVA® LVG and 2% PRONOVA® calcium alginate were filled separately in two syringes joined by a three-way connector which facilitated gel formation and release.

Results: Alginate solutions exhibited viscosities that increased proportionally with the average MW and concentration but did not seem to be affected by the G/M ratio. Shear-dependent behavior was also driven by concentration and MW in high G/M ratio alginate solutions. However, the elastic modulus of gels formed with sodium alginate showed a stronger correlation with the G-content rather than with the MW of the alginate. An alternative gelling method was also tested where a sodium alginate solution was mixed with a dispersion of calcium alginate; gel formation occurred as the divalent ion was exchanged between the two solutions. This method resulted in successful gel formation which was monitored by measuring the elastic modulus (G’) over ~1 hour. Near-maximum gel elasticity of 4.5 ± 1.5 kPa was reached within around 30 minutes with a half-time in the range of 1.9 ± 0.4 min. An initial delay in gel formation was also noted and was on the order of 0.9 ± 0.2 min.

Conclusion: This study investigated the properties of alginate solutions and gels, and showed connections between their molecular and mechanical properties. Polymer concentration and MW correlated with alginate viscosity and shear-dependent behavior while the guluronic acid content was the main driver of increased elasticity in gels. A self-gelling method was also demonstrated where calcium alginate mixed with sodium alginate resulted in divalent ion exchange between the two solutions. Successful gel formation was shown by the buildup in the gel elastic modulus. The two-component alginate system is a practical tool that can be applied towards the formation of injectable and moldable gels for various applications.