SORPTION BY STRATUM CORNEUM 545 Polymer JR is a quatcrnary nitrogen containing cellulose ether (5). It is available in three grades: JR-125, JR-400, and JR-30 M. Approximate molecu- lar weights for these grades have been estimated from their solution viscosity behavior as compared to that for hydroxyethylcellu]ose (HEC), a closely re- lated but uncharged polymer (6). The estimates are as follows: JR-lg5, tool wt 250,000 JR-400, mol wt 400,- 6'00 JR-30 M, tool wt 600,000. Radio-tagged samples of these various grades were prepared by carrying out the polymer sy•thesis with ethylene oxide tagged with C-14. A tagged sample of HI•_ C equivalent to JR-125 was. also prepared. The uptake of Polymer JR was determined by experiments with these tagged polymers. Samples of stratum corneum of about 2 mg weight were weighed to the nearest tenth of a milligram and placed individually in 1-oz glass vials. Ten ml of a water solution of tagged polymer were pipetted into each vial and left to co•tact the skin for a given time at room temperature after •vhich the solution was poured off. The skin was rinsed with 20 ml of distilled xvater three times. It •vas then removed from the original vial and placed in a new vial. (This eliminated the necessity of correcting for any radioactivity due to polymer adsorbed on the glass walls of the original vial. ) The new vial was placed in a 50øC oven for several hours to drive off moisture. The stratum corneum was dissolved by treatment •vith tissue solu- bilizer, followed by addition of methanol and a scintillation liquid. The vials were counted by the normal liquid scintillation method. Triplicate samples xvere run for each contact time. Because of the small sample size and the relatively large amount of polymer in solution, there was no appreciable change of polymer concentration during a given experiment. In view of the sizable sorption values which were found in the course of this work, some further discussion of the experimental technique seems ap- propriate here. In addition to true sorption, there are two possible mechanisms by xvhich polymer molecules can be "trapped" by the stratum corneum sam- ples and hence, counted in our procedure. First, is simple associaton of vis- cous polymer solution with stratum corneum. If this occurred to any extent, it would bc expected that at equal concentrations, the polymer of highest mo- lecular weight, and hence, most viscous, •vould be trapped in the greatest amount. Exactly the inverse is the case JR-125 shows much higher sorption than does JR-30 M. Also, convincing evidence against this objection is the fact that Polymer JR-125 shows nearly 50 times as much sorption as does a hydroxyethylcellulose of equal solution viscosity (see Figure 3 later on in this paper). A further study of the possibility of viscous entrapment was made by in- vestigating a much more vigorous rinsing procedure, viz. 4 successive rinses

546 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS of 20 ml each, with each rinse conducted for 15 rain on a mechanical shaker. No significant lowering of sorption was noted compared to that observed with the rinsing procedure described above. The second possible mechanism is that some of the polymer is dissolved in the normal water of swelling associated with stratum corneum. This water permeates the entire structure hence, any polymer it contains will probably not be easily removed by a single quick rinse. The amount of this associated water is about three to five times the dry sample weight, estimated from the increase in weight of samples of stratum corneum immersed in water. How- ever, either very little polymer can penetrate with this water of hydration or it is readily rinsed out, as can be inferred from the sorption data for nn- charged hydroxyethylcellulose (see Figure 3 later on in this paper). The measured uptake, after rinsing, for this material is less than 0.5 brg/mg after 24 h contact. This is insignificant compared to the large amounts of Polymer JR sorbed in this period of time. RESV•.TS AND D•scvss•o• Figure 1 shows data obtained for the various types of stratum eorneum ex- posed to 0.1 per cent Polymer JR-125. Typical sorption curves are observed SORPTION OF POLYMER JR-125 BY STRATUM CORNEUM (0.1% Concentration) 80 FETAL PI/ ß 20 ß/ NEONATAL RAT Oo 8 16 24 TIME IN HOURS E •.• 60 mum • 4o o Figure 1. Sorption of Polymer JR-125 by different types of stratum corneum SORPTION OF POLYMER JR-125 BY NEONATAL RAT STRATUM CORNEUM 2O • •5 5 I I i 0 0 8 16 24 TIME IN HOURS Figure 2. Sorption of varying concentra- tions of Polymer JR-125