Plasticizers in the manufacture of novel skin-bioadhesive patches

The effects of plasticizer inclusion (10%, w/w) on roughness, mechanical and adhesive properties of novel skin-bioadhesive patches produced from polyvinyl alcohol and polyvinyl pyrrolidone were studied. Dry, non-adhesive patches became adhesive upon wetting. Roughness profiles of the patches and a skin model were studied, by measuring average values of Ra (recognized as average roughness in practice) and Rz (average of the vertical distances from the highest peak to the lowest valley within five equal sampling lengths). These values ranged from 2.4 to 3.8 μm and from 10.9 to 12.5 μm, respectively. Plasticizers had no significant effect on them. The average Ra obtained for the skin model was six- to eightfold higher than that obtained for the patches. Plasticizer inclusion caused a reduction in patch tensile strength and an increase in its strain at failure—the lower the plasticizer's molecular weight, the greater its effect. Plasticizer inclusion also caused a significant reduction in peeling force: 1.5 ± 0.11 and 2.8 ± 0.13 g force/cm for patches with and without glycerol, respectively. Patch adhesion to the skin also depended on the time elapsed between application and removal. In summary, plasticizer inclusion widened the range of mechanical and adhesive properties of the patches.