Porcine Ear Skin as a Biological Substrate for in vitro Testing of Sunscreen Performance

Abstract

Purpose: The purpose of the study was to examine the use of skin from porcine ears as a biological substrate for in vitro testing of sunscreens in order to overcome the shortcomings of the presently used polymethylmethacrylate (PMMA) plates that generally fail to yield a satisfactory correlation between sun protection factors (SPF) in vitro and in vivo. Procedures: Trypsin-separated stratum corneum and heat-separated epidermis provided UV-transparent substrates that were laid on quartz or on PMMA plates. These were used to determine surface roughness by chromatic confocal imaging and to measure SPF in vitro of 2 sunscreens by diffuse transmission spectroscopy. Results: The recovered skin layers showed a lower roughness than full-thickness skin but yielded SPF in vitro values that more accurately reflected the SPF determined in vivo by a validated procedure than PMMA plates, although the latter had in part roughness values identical to those of intact skin. Combination of skin tissue with a high roughness PMMA plate also provided accurate SPF in vitro. Conclusions: Besides roughness, the improved affinity of the sunscreen to the skin substrate compared to PMMA plates may explain the better in vitro prediction of SPF achieved with the use of a biological substrate. i 2014 S. Karger AG, Basel

Development of a Synthetic Substrate for the in vitro Performance Testing of Sunscreens

“…The results show that pig ear epidermis yielded SFE values matching the data available for human skin. This suggests that pig ear skin imitates human skin appropriately in terms of adherence characteristics and confirms its suitability as a substrate for the in vitro testing of sunscreens [13]. However, using this substrate as a model requires time-consuming preparation and is not appropriate for routine tests.…”

“…The stratum corneum of the ears of freshly slaughtered pigs was prepared as described previously [13]. Due to its similarity to human skin, skin from pig ears served as the control substrate to set the target range of SFE values for the new proposed synthetic substrate.…”

“…The amount of product applied [7,8], the application procedure [9], the force applied during spreading [10,11], and the type of in vitro substrate have all been shown to impact the in vitro SPF value. Especially careful consideration has been given to the effect of the substrate for SPF measurement, especially its origin, either biological or synthetic [4,12,13,14], its roughness [15], and its surface properties, indicating the affinity of the sunscreen for the in vitro substrate [16]. A substrate made from polymethylmethacrylate (PMMA) is currently favored as it is easy to handle, does not require any preparation, and can be manufactured reproducibly [4].…”

“…Differences in the affinity of the sunscreen formulation for PMMA mold-injected plates compared to human skin is assumed to be the cause of the discrepancies between in vitro and in vivo SPF results. In other words, the currently employed PMMA plates do not simulate human skin properly [13]. Some means of increasing the adherence of the sunscreen product on these plates have been proposed [16,17].…”

Depth-dependent autofluorescence photobleaching using 325, 473, 633, and 785 nm of porcine ear skin ex vivo

“…The experiments were conducted ex vivo on unpigmented, untreated, not preirradiated porcine ears, serving as a skin model, 50 at a maximum of 3 days after slaughter. The hair was carefully removed from the skin without influence on the SC, and the samples were stored at 4°C before the measurements, which were performed at 22°C room temperature.…”