Elasticity determination of adhesive patches with filler inclusion

Patches can be used for topical and transdermal drug delivery as well as for cosmetic purposes. Their mechanical properties (i.e. strength, brittleness, elasticity, etc.) are important features that can influence their therapeutic success. Most of the drug-in-adhesive (DIA) patches adhere well to the skin or other surfaces. However, their degree of elasticity cannot be accurately determined since during the compression-decompression cycle(s), the patches adhere to the moving plate (and sensor), resulting in under the x-axis forces (and "negative" areas in the stress-strain curves). We overcame this limitation using two different approaches: gluing thin non-adhesive plates to both sides of the patch or applying talc granules to both surfaces. These treatments rendered the patch surfaces non-adhesive, thereby eliminating the "negative" force (and area) and permitting testing of adhesive materials as well as determination of their degree of elasticity. The general level of calculated recoverable work was ∼60-80% of the total work for the patches, i.e., they can be considered elastic entities. When the strain rate was 100 mm/s, the calculated recoverable work "jumped" to ∼92% and changed in a significant manner. Inclusion of fillers (corn or potato starch) in the patch reduced the percent recoverable work and degree of elasticity. For the first compression-decompression cycle, there was an increase in the degree of elasticity of the compressed-decompressed patches; while in the third and fourth cycles, there were no statistical differences in the extents of percent recoverable work. Recoverable work vs cycle number was almost a mirror image of total work.