Comparative Evaluation of Commercial Alginate Hydrogels: Effects of Viscosity, Polymer Concentration, and Crosslinking on Structural, Mechanical, and Biological Properties.

Background/Objectives: Alginate hydrogels are widely used in tissue engineering; however, their reported properties vary significantly due to differences in formulations and processing conditions, which limits direct comparison across studies. This study aims to systematically evaluate the relative and combined effects of alginate viscosity grade, polymer concentration, and CaCl2 crosslinking concentration on hydrogel structural, mechanical, and biological behaviour. Methods: Hydrogels were prepared using three commercially available alginates of low, medium, and high viscosity. Polymer concentration (0.5-2% w/v) and CaCl2 concentration (2.5-10% w/v) were systematically varied under controlled fabrication conditions. Morphology was analysed using scanning electron microscopy, swelling and water uptake were quantified, mechanical properties were assessed via dynamic mechanical analysis, and cell viability was evaluated using Chinese hamster ovary (CHO) cells encapsulation over 20 days. Statistical analysis was performed using two-way ANOVA. Results: Hydrogel properties were governed by non-linear interactions between formulation parameters. CaCl2 concentration was identified as the dominant factor influencing structural and biological outcomes, with increasing crosslinking concentration reducing pore size, swelling, and water uptake, and decreasing cell viability by up to ~60%. In contrast, polymer concentration and alginate viscosity grade primarily controlled mechanical behaviour, with increased polymer content and viscosity resulting in higher storage and Young's moduli. Significant interaction effects confirmed that hydrogel properties are not independently tunable but depend on the combined influence of all parameters. Conclusions: Crosslinking concentration dominates structural and biological responses in alginate hydrogels, while polymer parameters modulate mechanical properties within this constraint. These findings establish a formulation-dependent trade-off between mechanical stiffness and cytocompatibility, providing a comparative framework for rational selection of alginate systems based on application-specific requirements.