<p>Transdermal therapeutic systems (TTS) remain adhered to human skin for periods of up to seven days, during which water or vapor continuously diffuses from the skin into the pressure sensitive adhesive (PSA) layer. This water uptake can alter the mechanical and adhesive properties of the PSA, potentially affecting both drug delivery and patient comfort. Despite its clinical relevance, the diffusion behavior of water in silicone-based TTS-PSA has not been systematically characterized to date. Here, we demonstrate that dielectric analysis (DEA) in terms of the ion viscosity enables quantitative characterization of water diffusion in silicone-based PSA. The ion viscosity is linked to polymer chain mobility and free volume, allowing for extraction of diffusion coefficients from time-resolved measurements. Application to six silicone PSA formulations differing in end-group chemistry (nonpolar -CH₃ vs. polar -OH) and resin content, showed that diffusion coefficients increase with decreasing resin content, and are up to 70% higher for PSA with -CH₃ end groups compared to those bearing -OH end groups. Diffusion of 0.9% NaCl solution was consistently slower than that of deionized water across all formulations. Additionally, the DEA method yields parameters that may serve as a quality assurance indicator in TTS-PSA production. These results demonstrate that DEA is a fast, non-destructive, and cost-effective technique with a strong potential as a tool for rational design and quality control of TTS-PSA.</p>

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Diffusion of water and sweat-like aqueous solutions into silicone-based pressure-sensitive adhesives for transdermal therapeutic systems investigated with dielectric analysis

  • Bernhard Möginger,
  • Lucca Retterath,
  • Michael Meurer,
  • Berenika Hausnerova

摘要

Transdermal therapeutic systems (TTS) remain adhered to human skin for periods of up to seven days, during which water or vapor continuously diffuses from the skin into the pressure sensitive adhesive (PSA) layer. This water uptake can alter the mechanical and adhesive properties of the PSA, potentially affecting both drug delivery and patient comfort. Despite its clinical relevance, the diffusion behavior of water in silicone-based TTS-PSA has not been systematically characterized to date. Here, we demonstrate that dielectric analysis (DEA) in terms of the ion viscosity enables quantitative characterization of water diffusion in silicone-based PSA. The ion viscosity is linked to polymer chain mobility and free volume, allowing for extraction of diffusion coefficients from time-resolved measurements. Application to six silicone PSA formulations differing in end-group chemistry (nonpolar -CH₃ vs. polar -OH) and resin content, showed that diffusion coefficients increase with decreasing resin content, and are up to 70% higher for PSA with -CH₃ end groups compared to those bearing -OH end groups. Diffusion of 0.9% NaCl solution was consistently slower than that of deionized water across all formulations. Additionally, the DEA method yields parameters that may serve as a quality assurance indicator in TTS-PSA production. These results demonstrate that DEA is a fast, non-destructive, and cost-effective technique with a strong potential as a tool for rational design and quality control of TTS-PSA.