Rheological characterisation of primary and binary interactive bioadhesive gels composed of cellulose derivatives designed as ophthalmic viscosurgical devices

In this study the formulation and rheological characterisation of novel candidate ophthalmic viscosurgical devices (OVD) based on binary interactive polymer gels is described. Primary systems containing either hydroxyethylcellulose (HEC) or sodium carboxymethylcellulose (NaCMC) or binary interactive gels composed of HEC and NaCMC were manufactured. Rheological characterisation was performed using texture profile analysis and oscillatory rheometry. All formulations exhibited pseudoplastic flow. Systems composed of HEC or HEC and NaCMC behaved as gels (G'>G") over the range of oscillatory frequencies whereas systems composed of NaCMC were primarily elastoviscous, increasing the polymer concentration in all systems increased the compressional rheological properties (hardness, compressibility), zero frequency viscosity (derived from the Cross model) and the viscoelastic properties (G', G" and eta'). Rheological synergy was observed in the binary gels and was indicative of interaction between the parent polymers. Importantly, the range of rheological properties offered by the binary mixtures was greater than those exhibited by the primary systems. The binary systems described in this study possessed viscoelastic properties and steady-state viscosities that were similar to commercially available systems and would therefore be appropriate for the maintenance of the ocular space. The acceptable compressional rheological and pseudoplastic properties of these systems would facilitate administration into the eye using a syringe. Additionally and uniquely, the excellent adhesive properties of the binary interactive gels would suggest an ability to interact with the corneal endothelium that would offer protection during phacoemulsification. Based on the described rheological properties it is suggested that binary gels composed of mass ratios of HEC to NaCMC of either 3.6: 2.4 or 2.4: 3.6 would be acceptable as OVD and would uniquely offer duality of function. (C) 2004 Elsevier Ltd. All rights reserved.