Elutable components from catalyst-free Methyl-silicone self-adhesive skin patches
Al-Kaabi, Arshad F. Jassem
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Polymeric patches for skin contact have long been used to deliver medicines and to absorb metabolic products indicative of certain body states. Confounding results have been attributed to the extra barrier layers introduced by skin adhesives, and to the presence of polymerization catalysts that can chemically interact. This investigation addressed the ability of foreign-adhesive-free patches of ultraviolet (UV-C) light-polymerized polydimethylsiloxane (PDMS) skin patches to both deliver and accept physiologically active amounts of the hormone progesterone, and of other compounds ranging from testosterone to fats and dyes. The PDMS (also known as methyl-silicone) patches were made in less than 3 hours by a 2-hour application of UV-C to the base monomer phase of a medical methyl-silicone formulation to fully polymerize one face, and then a 30-minute application of UV-C to the opposite face, providing a reproducibly skin-adhesive layer. In the experiments, the fully polymerized PDMS face served as a skin surrogate with barrier properties similar to those of natural skin stratum corneum. The test compound, mixed into the silicone-base formulation as a dry powder or as a liquid solution prior to UV treatment, was delivered from the less-polymerized adhesive face of each patch. Testing was done, in multiple replicates, by applying the adhesive side of a compound-loaded patch to the fully-polymerized side of another patch for 24 hours, after which the patches were individually extracted in 200-proof ethanol for periods ranging from 4-10 days. Fifty-microliter aliquots of each separate extract solution were analyzed on the surfaces of 10x50x2mm germanium internal reflection prisms by the method of Multiple Attenuated Internal Reflection Infrared (MAIR-IR) spectroscopy, comparing the absorption peak heights of critical compound resonances (bands) to a calibration chart made in advance. When the delivery patches were pre-loaded, by either technique, with progesterone at concentration ratios of compound:silicone from low to high, it was found that the concentration ratios from 1:40 to 1:25 were capable of easily delivering the physiologically therapeutic amounts of 40 micrograms per square centimeter per day to the skin surrogates, the rest remaining in the silicone. In every case, methyl-silicone accompanied the test compound into the elution solution and also into the skin surrogate. Conversely, when applied directly to pig skin (obtained through an IACUC-approved project), the surrogate skin patches further imbibed lipid compounds, as determined again by MAIR-IR spectroscopy. Metabolite absorption into unfilled patches could therefore be expected to be in the same, easily analyzed range. With these findings, further study of the self-adhesive, catalyst-free silicone skin patches is encouraged.