Rheological Considerations of Pharmaceutical Formulations: Focus on Viscoelasticity

Abstract

Controlling rheological properties offers the opportunity to gain insight into the physical characteristics, structure, stability and drug release rate of formulations. To better understand the physical properties of hydrogels, not only rotational but also oscillatory experiments should be performed. Viscoelastic properties, including elastic and viscous properties, are measured using oscillatory rheology. The gel strength and elasticity of hydrogels are of great importance for pharmaceutical development as the application of viscoelastic preparations has considerably expanded in recent decades. Viscosupplementation, ophthalmic surgery and tissue engineering are just a few examples from the wide range of possible applications of viscoelastic hydrogels. Hyaluronic acid, alginate, gellan gum, pectin and chitosan are remarkable representatives of gelling agents that attract great attention applied in biomedical fields. This review provides a brief summary of rheological properties, highlighting the viscoelasticity of hydrogels with great potential in biomedicine.

Keywords: biomedicine; elastic and viscous moduli; oscillatory rheology; viscoelastic gel; viscosity.

Figure 1

Stress-controlled behavior of viscoelastic body fluids: synovial fluid and tear fluid.

Figure 2

Determination of the linear viscoelastic region (LVR). The purple line demonstrates the phase angle (δ).

Figure 3

Frequency sweep measurement.

Figure 4

Oscillational rheology of (A) non-viscoelastic and (B) viscoelastic samples.

Figure 5

Viscous and elastic character of viscoelastic materials.

Figure 6

Behavior of elastic materials under oscillational rheological measurements. The graph shows a relatively small-time lag between the blue sine curve of shear strain and the red sine curve of resulting shear stress.

Figure 7

Behavior of viscous materials under oscillatory rheological measurements. The graph shows a relatively large time lag between the blue sine curve of shear strain and the red sine curve of resulting shear stress.

Figure 8

Oscillatory rheology of viscoelastic liquid and viscoelastic solid.

Figure 9

Possible application forms of viscoelastic hydrogels.

Figure 10

Determination of sol–gel transition temperature using oscillatory rheology.

Figure 11

Timoptic^® XE gellan gum-containing eye drops with sustained drug release.

Figure 12

PecFent^® pectin-containing nasal spray with sustained drug release.