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To investigate the influence of the hydrophilic polymer, polyvinylpyrrolidone (PVP) on the ex-vivo permeability of the poorly water-soluble photosensitizer, chlorin e6 (Ce6) using the chick chorioallantoic membrane (CAM) model.The CAM was removed from the fertilized chicken egg at embryo age of 15 days. The permeation profiles of Ce6 and PVP complexes (Ce6-PVP) at 1 : 0, 1 : 1, 1 : 10, 1 : 50 and 1 : 100 w/w in different pH conditions were first studied using the CAM model with Franz diffusion cell over 8 h. The solution viscosity of the formulations and apparent solubility of Ce6 were also investigated.The permeability of Ce6 was found to be directly proportional to the amount of PVP used and the apparent solubility of Ce6. Permeability was only marginally affected by the solution viscosity of the formulations. The permeability of Ce6 was lowered in the acidic pH. Ce6-PVP at 1 : 100 w/w gave the highest percentage release of Ce6 across the CAM, with 23% at pH 3 and 55% at pH 7.4, after 8 h, respectively.The present work suggests that PVP had served as penetration enhancer for the poorly water-soluble Ce6 and the CAM can serve as a useful biological membrane model for preclinical permeability study of biological and pharmaceutical substances. The Ce6-PVP formulation at 1 : 100 w/w can be applied for the further clinical investigation.