Anna M. Wokovich

Lack of Significant Dermal Penetration of Titanium Dioxide from Sunscreen Formulations Containing Nano- and Submicron-Size TiO2 Particles

Titanium dioxide (TiO(2)) is included in some sunscreen formulations to physically block ultraviolet radiation. A dermal penetration study was conducted in minipigs with three TiO(2) particles (uncoated submicron sized, uncoated nano-sized, and dimethicone/methicone copolymer-coated nanosized) applied 5% by weight in a sunscreen. These and control formulations were topically applied to minipigs at 2 mg cream/cm(2) skin (4 applications/day, 5 days/week, 4 weeks). Skin (multiple sites), lymph nodes, liver, spleen, and kidneys were removed, and the TiO(2) content was determined (as titanium) using inductively coupled plasma mass spectroscopy. Titanium levels in lymph nodes and liver from treated animals were not increased over the values in control animals. The epidermis from minipigs treated with sunscreens containing TiO(2) showed elevated titanium. Increased titanium was detected in abdominal and neck dermis of minipigs treated with uncoated and coated nanoscale TiO(2). Using electron microscopy-energy dispersive x-ray analysis, all three types of TiO(2) particles were found in the stratum corneum and upper follicular lumens in all treated skin samples (more particles visible with coated nanoscale TiO(2)). Isolated titanium particles were also present at various locations in the dermis of animals treated with all three types of TiO(2)-containing sunscreens; however, there was no pattern of distribution or pathology suggesting the particles could be the result of contamination. At most, the few isolated particles represent a tiny fraction of the total amount of applied TiO(2). These findings indicate that there is no significant penetration of TiO(2) nanoparticles through the intact normal epidermis.

The state of nano‐sized titanium dioxide (TiO2) may affect sunscreen performance

In the past several years, there has been a trend in the sunscreen/cosmetics industry to replace micron‐sized titanium dioxide (TiO2) particles with nanoscale materials. The increased use of nanoscale TiO2 has resulted in questions about these and other nanoproducts. This study examines the effects of using nanoscale TiO2 on ultraviolet (UV) attenuation in simple to complex sunscreen formulations. UV light attenuation, product stability, and potential damage to the skin barrier were examined with both nanoscale and microscale TiO2 particles. Results indicate that none of the formulations decreased the barrier function of the skin and the best UV attenuation occurs when the TiO2 particles are stabilized with a coating and evenly distributed such as with non‐agglomerated coated nanoscale materials. This indicates that nanoscale TiO2 may have better efficacy while lacking toxicity.

Particle size determination of sunscreens formulated with various forms of titanium dioxide

Background: There has been some apprehension expressed in the scientific literature that nanometer-sized titanium dioxide (TiO2) and other nanoparticles, if able to penetrate the skin, may cause cytotoxicity. In light of a lack of data regarding dermal penetration of titanium dioxide from sunscreen formulations, the Food and Drug Administration Center for Drug Evaluation and Research initiated a study in collaboration with the National Center for Toxicology Research using minipigs to determine whether nanoscale TiO2 in sunscreen products can penetrate intact skin. Four sunscreen products were manufactured. Method: The particle size distribution of three TiO2 raw materials, a sunscreen blank (no TiO2) and three sunscreen formulations containing uncoated nanometer-sized TiO2, coated nanometer-sized TiO2 or sub-micron TiO2 were analyzed using scanning electron microscopy (SEM), laser scanning confocal microscopy (LSCM), and X-ray diffraction (XRD) to determine whether the formulation process caused a change in the size distributions (e.g., agglomeration or deagglomeration) of the TiO2. Results: SEM and XRD of the formulated sunscreens containing nanometer TiO2 show the TiO2 particles to have the same size as that observed for the raw materials. This suggests that the formulation process did not affect the size or shape of the TiO2 particles. Conclusion: Because of the resolution limit of optical microscopy, nanoparticles could not be accurately sized using LSCM, which allows for detection but not sizing of the particles. LSCM allows observation of dispersion profiles throughout the sample; therefore, LSCM can be used to verify that results observed from SEM experiments are not solely surface effects.

Evaluation of substrates for 90° peel adhesion—A collaborative study. II. Transdermal drug delivery systems

In a previous study on peel adhesion for medical tapes, it was shown that a stainless steel (SS) substrate better discriminated among medical tapes than a high-density polyethylene (HDPE) substrate. The objective of this study was to determine if a SS substrate would also better distinguish among transdermal drug delivery systems (TDDSs). Five TDDSs (Vivelle Dot, Climara, Catapres-TTS, Duragesic, and Mylan Fentanyl) were evaluated on three different substrates (SS, HDPE, and human cadaver skin). All measurements were made using a dwell time of approximately 3 min, a peel angle of 90 degrees, and a peel speed of 300 mm/min. Differences among TDDSs were greater for SS than for HDPE, using the F statistic for testing for differences among TDDSs means as a measure of heterogeneity, thereby indicating greater discrimination by SS.

Evaluation of substrates for 90° peel adhesion—A collaborative study. I. Medical tapes

As part of a method development for peel testing, an interlaboratory comparison among Food and Drug Administration-Center for Drug Evaluation and Research, Food and Drug Administration-Center for Devices and Radiological Health and Southwest Research Institute was conducted using medical tapes. The aim was to determine which readily available substrate [stainless steel (SS), high density polyethylene (HDPE) or Vitro-Skin(R)] would best distinguish among various medical tapes. Five medical tapes (3M 1523, 3M 1525L, 3M 1776, Mepiform(R) and Mediderm(R) 3505) were evaluated on four different substrates (SS, HDPE, Vitro-Skin, and human cadaver skin) using the following peel parameters: approximately 3 min dwell time, 90 degrees peel angle, and 300 mm/min peel rate. No substrate mimics cadaver skin for all five tapes. SS had the best ability to distinguish among the medical tapes. Overall, for quality control purposes (yielding good discrimination and precision), SS would be the optimal substrate.

Evaluating elevated release liner adhesion of a transdermal drug delivery system (TDDS): A study of Daytrana™ methylphenidate transdermal system

Background: Complaints from healthcare providers that the adhesive on the Daytrana™ methylphenidate transdermal drug delivery system (TDDS) adhered to the release liner to such an extent that the release liner could not be removed prompted this study. Daytrana™ has a packaging system consisting of a moisture-permeable pouch contained within a sealed tray containing a desiccant; the tray is impermeable to ambient moisture. The objective of this project was to determine if the Daytrana™ packaging system influenced the difficulty in removing the release liner. Method: Both a sealed tray and an open tray containing sealed pouches were placed into an environmental chamber at 25°C and 60% relative humidity for 30 days; afterwards, release liner removal testing using a peel angle of 90° and a peel speed of 300 mm/min was performed. Results: TDDS from open chamber trays required less force to remove the release liner than did TDDS from closed chamber trays. For the 10 mg/9 h TDDS and the 15 mg/9 h TDDS (the dosages examined), there were substantial differences in release liner removal force between an old lot and a new lot for closed chamber trays but not for open chamber trays. Conclusion: The results demonstrate that for this particular TDDS, storage conditions such as humidity influence release liner adhesion. This project also demonstrates that, to ensure adequate product quality, adhesion needs to become an important design parameter, and the design of a TDDS should consider the ability to remove the release liner under anticipated storage conditions.

Release liner removal method for transdermal drug delivery systems (TDDS)

A release liner removal test is a valuable test for assessing the quality of a transdermal drug delivery system (i.e., TDDS, patch). This test measures the force required to remove the release liner from a patch. The objective of the present study was to establish sample preparation and instrument parameters for measuring release liner removal adhesion for TDDS. Ten TDDS were evaluated (six drugs for a total of 29 lots). Patches which had a rate-controlling membrane were run as-is, since they could not be cut to a precise width without sacrificing their structural integrity. Patches that were square or rectangular in shape were run as-is, and the width of these patches was determined using a digital caliper. Patches which were not square or rectangular in shape and did not have a rate-controlling membrane were cut to a precise width using a specimen cutter. Double-sided tape was used to adhere the liner side of the transdermal system to a clean stainless steel test panel. A release liner peel adhesion method for TDDS is proposed using a dwell time of approximately 3 min, a peel angle of 90 degrees , and a peel speed of 300 mm/min.