On the Rheological Properties and Printability of Sodium Alginate–Carboxymethyl Chitosan Composite Solutions for Tissue Scaffold Printing

Composites of sodium alginate (Alg) and carboxymethyl chitosan (CMCS) are used to 3D print tissue scaffolds, but the rheological properties and printability of these composites remain underreported, resulting in time-consuming trial-and-error printing. This study investigates these properties to rigorously design the 3D printing process. Dynamic shear tests characterize viscoelastic and frequency-dependent properties, while steady shear tests assess the apparent viscosity and temperature-dependent viscosity. A novel approach based on mass flow rate models guides the printing of two-layer scaffolds for printability analysis. Brightfield microscopy and printability indexes quantify the deviations between printed and designed scaffolds, defined as printability. Results show that Alg predominantly directs the rheological properties. At 4% w/v Alg, the addition of < 3% w/v CMCS reduces elasticity, contrary to the trend where increasing CMCS increases elasticity. CMCS improves the thermal resistance of the composites, while Alg reduces it. Of the composites printed, a 4% w/v Alg + 1% w/v CMCS formulation most accurately replicates the designed scaffold, and adding CMCS improves scaffold printing repeatability by at least threefold compared to Alg-only solutions. These findings provide a framework that informs the preparation and performance of Alg-CMCS composites with tunable properties, advancing scaffold bioprinting for tissue engineering.