CHITOSAN BEADS IN COSMETICS 211 Table III Swelling Ratio (w/w) and Mean Diameter (L) (mm) at Time t Values. Bead batches Swelling ratio (W /W 0) I q (mm) at time t A 1.40 ± 0.03 4.24 ± 0.36 A l 1.06 ± 0.01 3.36 ± 0.27 B 1.05 ± 0.02 2.99 ± 0.25 B l 1.03 ± 0.01 2.85 ± 0.19 C 1.87 ± 0.04 3.15 ± 0.22 C l 1.40 ± 0.03 2.67 ± 0.14 ± S.D. on the mean of three measurements. ability of coacervated polymers compared to ionically crosslinked polymers, where the electrostatic interactions between anions and positive chitosan charges increase the me­ chanical strength of the bead structures while reducing their water permeability and therefore also their swelling. All bead batches show good Mentha piperita E.O. encapsulation efficiency in the 65-70% range, with slightly higher values for NaOH beads (A, B, and C). No significant differences in Mentha piperita E.O. encapsulation efficiency were observed when different chitosan dispersions were used. At this point one of the most important objectives was to evaluate the bead disinte­ gration time within the chosen cosmetic formulation (BBF) for the release of Mentha piperita E.O. and also for the stability of the beads during an estimated storage time. Figure 3 shows the results obtained from the bead-breakage assay in BBF. As can be observed, only NaOH-bead batches (A,B, and C) showed positive results to this stress test, and particularly the beads in batch B showed the highest breakage percentage, at Figure 2. Swelling behavior of NaOH beads (sample B) at time t.

212 100 LL. 80 m m C 60 ·- Ill 40 Ill m 20 � a JOURNAL OF COSMETIC SCIENCE / /j ______ ... ·---------····,.····--------· ... ----·· // i A B C Al Bead samples Bl Figure 3. Bead breakage assay in BBF results. �------- ···-------- : Cl about 60-80%. On the other hand, TPP-bead batches (A 1 , B 1 , and C 1 ) did not present marks of breakage, even in conditions of great stress. All bead batches were stable for six months, estimated as storage time. As an example, Figure 4 shows a digital photo of beads in batch A in BBF at six months. Figure 4. Digital photo of beads in batch A in BBF at six months.