Naturally occurring anionic polysaccharide Alginate, extracted from brown seaweed, is being widely proposed because of its biocompatibility, gelation character, and viscosity modifier properties. By reading the flow behavior of alginate solutions, it is required that one be able to optimize the use of the solution in different formulations. Rheological tests provide insight into the molecular mechanics and structure of alginate under stress. Whereas rotational rheometers tend to be common, capillary rheometers are especially suited to an artificial processing condition like extrusion or injection.
Instrumentation
Capillary rheometer A capillary rheometer operates under high pressure to determine the flow characteristics of viscous fluids and materials flowing through a narrow die or capillary. It usually comprises a pressure barrel, a type of pressurizing piston, and a die that can be changed and replaced, and has dimensions. The amount of pressure needed to force the material out at different shear rates is measured and used to calculate viscosity, shear stress, and shear rate. It has been shown that stainless steel dies and controlled temperature chambers are more reproducible and accurate (particularly with blue-sensitive biopolymers) in alginate solutions.
Principle and Methodology
Alginate powder may then be dissolved in deionized water (at 1190-5 °C in 1:3-5 (w/v), and this may be magnetically stirred and manually warmed to be fully solubilized. The solution is loaded into the barrel of the rheometer after its degassing. The solution is pumped through the die by the capillary rheometer with the specific piston velocity, translated to the shear rate. Pressure sensor recordings concern the pressure necessary to support flow. Based on this, flow graphs and apparent viscosity are drawn. Corrections to results (removing entrance pressure loss correction, Bagley and non-Newtonian flow correction, and Rabinowitz) are often performed.
Strengths
The advantage of capillary rheometry is also that it is highly operative towards its application in the realm of tissue encapsulation and tissue engineering through alginate by mimicking real-time processing conditions as constituted in the processes of extrusion and injection molding. It has high shear rates and can work with comparatively high-viscosity systems.
Limitations
With samples that have low viscosity or those that are diluted alginate, there is a problem of sample loading. It is even more valid under steady-state flow and would not pick up transient effects or viscoelastic models, which are more effectively measured by rotational rheometry.
Importance
The use of a capillary rheometer in determining rheology is crucial in the prediction of the regime of alginate under the specific manufacturing/application conditions. As an example of bioprinting, the consistency of flow and shear-thinning behavior in a 3D-bioprinting context will have a direct impact on the printability and shape fidelity of alginate-based bioinks. What this means is that capillary rheometry is an invaluable tool that gives critical measurements that connect molecular structure to functional end-use properties and facilitates formulation development and quality control.
