Characterisation of the interactive properties of microcrystalline cellulose-carboxymethyl cellulose hydrogels

Combinations of microcrystalline cellulose (MCC) and sodium carboxymethyl cellulose (Na-CMC) are commonly used as stabilising agents and suspending agents in pharmaceutical formulations. This paper is based on a study of the interactions that take place during the process of hydrogel formation, break down, and recovery. Also considered is the binding that occurs between the MCC and the Na-CMC. Avicel RC 591, a processed mixture of MCC and Na-CMC, is one of the more commonly used commercial suspending agents for aqueous compositions. Avicel RC 591 is used as an effective, blended stabilising agent. In this study, the contributions made by each of the components of Avicel RC 591 have been rationalised by monitoring the behaviour of the individual components in Avicel RC 591 suspensions or solutions. The hydrogels that are formed by Avicel RC 591 and by their laboratory formulated equivalent, which is spray dried (MCC+Na-CMC), have been characterised by confocal microscopy scanning electron microscopy and by dynamic light scattering. A 3D network structure that is formed by the MCC, in Avicel RC 591 is visualised. This network is supported by hydrogen bonding and by ionic interactions among and between the MCC, the Na-CMC and water. The strength of the network determines the physical properties of the hydrogel system, as seen in the rheological behaviour.