Problems of in vitro SPF measurements brought about by viscous fingering generated during sunscreen applications.

Up to date, no worldwide standard in vitro method has been established for the determination of the sun protection factor (SPF), since there are many problems in terms of its repeatability and reliability. Here, we have studied the problems on the in vitro SPF measurements brought about by the phenomenon called viscous fingering. A spatially periodic stripe pattern is usually formed spontaneously when a viscous fluid is applied onto a solid substrate. For the in vitro SPF measurements, the recommended amount of sunscreen is applied onto a substrate, and the intensity of the transmitted UV light through the sunscreen layer is evaluated. Our theoretical analysis indicated that the nonuniformity of the thickness of the sunscreen layer varied the net UV absorbance. Pseudo-sunscreen composites having no phase separation structures were prepared and applied on a quartz plate for the measurements of the UV absorbance. Two types of applicators, a block applicator and a 4-sided applicator were used. The flat surface was always obtained when the 4-sided applicator was used, while the spatially periodic stripe pattern was always generated spontaneously when the block applicator was used. The net UV absorbance of the layer on which the stripe pattern was formed was found to be lower than that of the flat layer having the same average thickness. Theoretical simulations quantitatively reproduced the variation of the net UV absorbance led by the change of the geometry of the layer. The results of this study propose the definite necessity of strict regulations on the coating method of sunscreens for the establishment of the in vitro SPF test method.

Iatrogenic paraplegia caused by surgicel used for hemostasis during a thoracotomy: report of a case.

A 46-year-old Japanese woman underwent a right lower lobectomy through a posterolateral incision made in the fifth intercostal space under general and epidural anesthesia on January 23, 1995. During the procedure, oxidized regenerated cellulose (Surgicel) was used to prevent postoperative rebleeding from the dorsal branch of the fifth intercostal artery. The following day it became evident that complete paraplegia had developed below the Th5 level, the cause of which was revealed by an emergency laminectomy, performed within 20 h after the thoracotomy, to be the Surgical treatment. By 50 days after the operation the patient had begun to show improvement, and was able to move her lower extremities against gravity. Her condition is continuing to improve.