J. Cosmet. Sci., 68, 74–78 ( January/February 2017) 74 Silicone elastomer blends: A novel topical drug delivery platform HYDER A. ALIYAR, ROBERT O. HUBER, GARY L. LOUBERT, GERALD K. SCHALAU, and BARTLEY D. MAXON, Dow Corning Corporation, Midland, MI. INTRODUCTION Silicone elastomers are well known for their use in skin care for their unique, silky, powdery sensory benefi ts, but are also capable of helping the delivery of active ingredi- ents. The specifi c materials included in this study are cross-linked silicone elastomer (Dimethicone Crosspolymer) and cross-linked polyglycol-modifi ed silicone organic elas- tomer (Dimethicone/Bis-isobutyl PPG 20 Crosspolymer) particles swollen in a carrier fl uid. These are clear to slightly translucent with paste-like consistency and provide smooth, silky, powdery, and nongreasy aesthetics recognized in high-end beauty care applications. The capability of effi ciently delivering a broad range of active ingredients in silicone- based topical formulations including ibuprofen and vitamins C and E has been previously demonstrated (1–3). The purpose of this investigation was to assess the capability of ef- fi cient delivery of the following drugs by silicone-based topical semisolid formulations. Clobetasol propionate (CLP) is a very high potency corticosteroid and is used to treat a variety of skin conditions (e.g., eczema, dermatitis, allergies) and reduces the swelling, itching, and redness that occurs in these conditions (4,5). Diclofenac sodium (DCF) is known as a nonsteroidal anti-infl ammatory drug (NSAID) and is used to relieve pain, swelling, and joint stiffness (6). Lidocaine (LDC) is an anesthetic that works to decrease pain by temporarily numbing the area and is used to treat irritation, soreness, and itchiness from certain skin conditions (e.g., scrapes, minor burns, eczema, insect bites) (7). The capability of silicone elastomer blend–based topical pharmaceutical formulations to deliver CLP, DCF, and LDC effi ciently across human cadaver epidermis was investi- gated using in vitro permeability experiments and compared with commercial benchmark products. Address all correspondence to Bartley Maxon at bart.maxon@dowcorning.com.

SILICONE ELASTOMER BLENDS 75 MATERIALS AND METHODS MATERIALS Excipients. A polyglycol-modifi ed cross-linked silicone elastomer in isododecane (IDD) [INCI: IDD (and) Dimethicone/Bis-isobutyl PPG 20 Crosspolymer (SiE1)] and another cross-linked silicone elastomer in cyclopentasiloxane [INCI: Cyclopentasiloxane (and) Dimethicone Crosspolymer (SiE2)] were used in the formulation preparation. The prod- ucts are dispersions of high molecular weight silicone gels particles swollen in respective carrier solvents with a solids content ranging from 12% to 15.75%. Other excipients used in the formulations include propylene glycol, oleic acid, and isopropyl alcohol. Actives. CLP, DCF, and LDC were used in the experimental formulations at 0.05%, 1%, and 5%, respectively. Benchmarks. Representative commercially available products containing the same drugs and at the same concentration were used in permeability experiments. TEST METHODS In vitro drug permeability. The in vitro permeability of drug through heat-separated human cadaver epidermis was performed at 32°C using a manual Franz diffusion cell console unit. The permeation area of the cell was 0.63 cm2 and the cell volume was 5 ml. The receptor chamber of the cell was initially fi lled with ∼3 ml of phosphate-buffered saline (PBS, pH 7.4) and a small magnetic stir bar was added. A 15.5 ± 0.5 mg of the formula- tion was applied as homogeneously as possible on top of the skin. The experiment was carried out for 8 h for DCF- and LDC-containing formulations and 26 h for CLP-containing formulations. Respective benchmark product was included along with the silicone for- mulations at the same time in the permeability experiment. Samples were collected from the receptor chamber at several intervals throughout the permeability study duration (8 or 26 h) and replaced with fresh PBS solution. All samples were collected in amber high-performance liquid chromatography vials and taken for drug assay. Drug assay. Waters® ultra-performance liquid chromatography (UPLC) coupled with Acquity® UPLC BEH column were utilized to determine the drug concentration in the samples from permeability study. An appropriate assay method for each drug was used accordingly. Formulations. The silicone elastomer–based formulations were prepared and compared versus commercial benchmarks. In a typical formulation preparation, the required amount of drug was weighed into a SpeedMixer™ cup and dissolved by the addition of liquid components of the formulation with mixing. This was followed by weighing the required amount of silicone material and mixing it in the SpeedMixer (Hauschild, AM 501T, Hamm, Germany) at 3000 rpm until a homogeneous formulation was obtained (Table I). RESULTS The in vitro drug delivery profi les obtained from the permeability study for the silicone elastomer blend formulations versus respective commercial benchmark products are