Characterisation of bioadhesives for periodontal and oral mucosal drug delivery.

Whilst there is keen interest in developing improved drug delivery devices to the periodontal pocket and oral mucosa, there are few reports which have examined the physical properties of gels and semi-solid formulations which favour retention and bioadhesion in situ. Hydration and rheological properties appear to be of prime importance in this context and this study aimed to correlate the measurement of these properties with observed bioadhesion, both in vitro and in vivo. Three candidate bioadhesives were selected from previous experiments which had used in vitro organ culture models. These were chitosan, xanthan gum and poly (ethylene oxide) aqueous formulations. Hydration rates with various media were determined in specially constructed cells. Rheological properties were measured using a controlled stress rheometer under carefully regulated conditions. These findings were also correlated with in vivo assessments in the periodontal pocket and oral mucosa. The results demonstrated that three formulations with differing bioadhesive properties also possessed widely different physical characteristics. Hydration experiments indicated a direct relationship between the rate of hydration and bioadhesion or retention. Rheological studies suggested that possession of a gel structure could be an important determinant of retention where shear displacing forces are present in vivo, e.g. the oral mucosa. Furthermore, these studies indicated that formulations which could demonstrate resistance to changes in rheological properties on hydration would also favour retention in situ. Physical characterisation therefore appears to have an important place in screening polymeric formulations prior to clinical testing in the periodontal pocket and oral mucosa.