TEXTURAL ANALYSIS AND FLOW RHEOMETRY OF NOVEL, BIOADHESIVE ANTIMICROBIAL ORAL GELS

Purpose. This study examined the rheological and textural characterist ics (hardness, compressibilty, adhesiveness and cohesiveness) of bioad hesive oral gels containing the antimicrobial agent chlorhexidine. Met hods. Textural analysis was performed using a Stable Micro Systems tex ture analyser (model TA-XT 2) in texture profile analysis (TPA) mode. In this, an analytical probe was twice compressed into each formulatio n to a defined depth (15 mm) and at defined rates (2, 4, 6, 8, 10 mm s (-1)), allowing a delay period (15 s) between the end of the first and beginning of the second compressions. Flow rheograms were performed u sing a Carri-Med CSL2-100 rheometer with parallel plate geometry under controlled shearing stresses at 20.0 +/- 0.1 degrees C. Results. All formulations exhibited pseudoplastic flow with thixotropy. Increasing concentrations of each polymer significantly increased formulation har dness, compressibility, adhesiveness and zero-rate viscosity. Increase d hardness and compressibility were due to the attendent increased vis cosities of these formulations. Increased adhesiveness was related to the concentrations of the (bioadhesive) polymers employed in these for mulations and, in addition, was dependent on the physical state of pol ycarbophil. Formulation viscosity contributed to product adhesiveness, reflecting the importance of product rheology on this parameter. Decr eased formulation cohesiveness, observed as the concentrations of the PVP, PC and HEC (3-5%w/w) were increased, was due an increase in semi- solid character. Numerical values of hardness, compressibility and adh esiveness were affected by the choice of probe speed, a parameter rela ted to rate of shear in flow rheometry. Statistical interactions were observed and were assigned to the effects of HEC on the physical state of PVP (dissolved or dispersed) and PC (swollen or unswollen). Conclu sions, This study has demonstrated both the applicability of textural analysis for the mechanical characterisation of bioadhesive semi-solid gel systems and, additionally, the direct influence of viscosity on t he parameters defined by textural analysis, namely, hardness, compress ibility and adhesiveness.