ABSTRACT
Janus-faced viscoelastic gelling agents-possessing both elastic and viscous characteristics-provide materials with unique features including strengthening ability under stress and a liquid-like character with lower viscosities under relaxed conditions. The mentioned multifunctional character is manifested in several body fluids such as human tears, synovial liquids, skin tissues and mucins, endowing the fluids with a special physical resistance property that can be analyzed by dynamic oscillatory rheology. Therefore, during the development of pharmaceutical or cosmetical formulations-with the intention of mimicking the physiological conditions-rheological studies on viscoelasticity are strongly recommended and the selection of viscoelastic preparations is highlighted. In our study, we aimed to determine the viscoelasticity of various liposomal dispersions. We intended to evaluate the impact of lipid concentration, the presence of cholesterol or 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and the gelling agents polyvinyl alcohol (PVA) and hydroxyethylcellulose (HEC) on the viscoelasticity of vesicular systems. Furthermore, the effect of two model drugs (phenyl salicylate and caffeine) on the viscoelastic behavior of liposomal systems was studied. Based on our measurements, the oscillation rheological properties of the liposomal formulations were influenced both by the composition and the lamellarity/size of the lipid vesicles.
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.
